Development of a Dual-Fuel Burner

António Perdigão Duarte Silva

Thesis to obtain the Master of Science Degree in

Mechanical Engineering

Examination Committee

Chairperson: Prof. Luís Rego da Cunha de Eça

Supervisor: Prof. Mário Manuel Gonçalves da Costa

Co-Supervisor: Prof. João Luís Toste de Azevedo

Members of the Committee: Doutora Ana Sofia Oliveira Henriques Moita

October 2013

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Acknowledgments

In first place I would like to thank my supervisors, Professor Mário Costa and Professor João

Toste de Azevedo, for their availability and help throughout the entire course of this work. Their

guidance was key if any success was attained with the present work.

I also want to thank Manuel Pratas for his prompt help and always good mood during the

entire course of the laboratory work, it certainly made the job easier.

I must also show my kind regards to Gongliang Wang who worked with me during all

combustion tests. Without him they would not have gone so swiftly.

To Pedro and Sr. Frade from the workshop of the Mechanical Engineering Department I

express my gratitude for their work with most of the equipment that I needed for the project. Through

their experience and availability I was able to keep moving forward with my experiments.

I owe a special recognition to Tiago Carvalho who was always there to help me during the

entire work and not once refused when asked for.

I must also add the rest of the laboratory colleagues who maintained a good mood during easy

and difficult times and also aided every time they were called for, namely: Francisco Costa, Bruno

Bernardes, João Pina, Isabel Ferreiro, Mafalda Henriques; João Pires and Ricardo Maximino.

To Ana Rita Parreira for her patience and support along this year and all my friends who

accompanied me until this final project I express my deepest gratitude to: António Figueira, João

Sebastião, Nuno Grilo, Diogo Gameiro, Miguel Grencho, Paulo Grão, Alexandre Garcia, Ricardo

Martins and Bruno Coimbra.

I leave my final “thank you” to my parents and sister who were so close to me during all my life

enduring all my ups and downs ultimately giving me the confidence and strength to make this way

through.

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Abstract

The present work focuses on the development of a dual-fuel burner. The developed burner

uses liquid and/or gaseous fuels. Two types of atomizers (pressure and air assisted), were

characterised by a laser diffraction technique to assess the droplet size distribution. On a second part

of the study, combustion tests were carried out with the two types of atomizers. Temperatures and gas

species concentration (O2, CO2, CO, HC and NOx) were measured radially at two different heights

inside the furnace.

The results showed that both atomizers can give good atomization but with the pressure

atomizer flow rates are limited to those close to the nominal value of the nozzle whereas with the air

assisted atomizer lower flow rate values can be used and the atomization quality depends mainly on

the atomizing air flow rate. Although the air assisted atomizer was ultimately chosen as the best one

care must be taken due to flame stabilization. With too much atomizing air the atomizer jet may disrupt

the central recirculation zone while values too low reduce atomization quality affecting combustion.

Keywords

Dual-fuel burner; atomization; Sauter mean diameter; combustion; temperature; gas species.

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Resumo

O presente trabalho tem como objectivo desenvolver um queimador dual-fuel. Este tipo de

queimador usa combustíveis líquidos e/ou gasosos. Para optimizar os parâmetros e configuração

para o queimador foi realizado um estudo com dois tipos diferentes de atomizadores (pressão e

assistidos a ar), utilizando um método de difracção laser para medir a distribuição dos diâmetros das

gotículas para cada atomizador. Numa segunda parte do estudo foi feito o estudo com combustão

para investigar as suas características com os dois tipos de atomizadores estudados previamente.

Este estudo envolveu a medição de temperaturas e concentrações de espécies químicas gasosas

(O2, CO2, CO, HC e NOx) radialmente a diferentes distâncias axiais do queimador.

Os resultados mostraram que ambos os atomizadores geram boa atomização, mas os

atomizadores de pressão estão limitados a uma gama de caudais mássicos perto do valor nominal do

injector, enquanto o atomizador assistido a ar permite a utilização de valores mais baixos. Apesar de

o atomizador assistido a ar ter sido escolhido como o melhor é preciso ter em atenção ao processo de

estabilização de chama. Demasiado ar de atomização pode tornar a chama instável ou demasiado

comprida e valores demasiado baixos reduzem a qualidade de atomização afectando a combustão.

Palavras-chave

Queimador dual-fuel; atomização; diâmetro médio de Sauter; combustão; temperatura;

espécies gasosas.

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Table of Contents

1 – Introduction ........................................................................................................................................ 1

1.1 – Motivation and goals................................................................................................................... 1

1.2 – Previous research ....................................................................................................................... 2

1.2.1 – Dual-fuel burners ................................................................................................................. 2

1.2.2 – Atomization .......................................................................................................................... 3

1.2.3 – Combustion ......................................................................................................................... 4

1.3 – Present contribution.................................................................................................................... 7

2 – Experimental facilities ........................................................................................................................ 9

2.1 – Atomization tests ........................................................................................................................ 9

2.2 – Combustion tests ...................................................................................................................... 12

3 – Experimental techniques and uncertainties .................................................................................... 17

3.1 – Atomization ............................................................................................................................... 17

3.2 – Combustion .............................................................................................................................. 18

4 – Atomization ...................................................................................................................................... 21

4.1 – Test conditions ......................................................................................................................... 21

4.2 – SMD results for pressure atomization ...................................................................................... 23

4.2.1 – Influence of axial position .................................................................................................. 23

4.2.2 – Influence of radial position ................................................................................................. 23

4.2.3 – Influence of injection temperature ..................................................................................... 24

4.2.4 – Influence of injection nozzle .............................................................................................. 25

4.3 – SMD results for air assisted atomization .................................................................................. 25

4.4 – Correlations for SMD prediction ............................................................................................... 26

5 – Combustion ..................................................................................................................................... 31

5.1 – Test conditions ......................................................................................................................... 31

5.2 – Flame stabilization .................................................................................................................... 34

5.3 – Temperature results ................................................................................................................. 35

5.4 – Gas species concentration results ........................................................................................... 39

5.4.1 – Behaviour of HC, CO, CO2 and O2 .................................................................................... 39

5.4.2 – NO formation ...................................................................................................................... 43

5.5 – Energy balances ....................................................................................................................... 45

6 – Closure ............................................................................................................................................ 47

6.1 – Conclusions .............................................................................................................................. 47

6.2 – Future work ............................................................................................................................... 49

References ............................................................................................................................................ 51

Appendix A ............................................................................................................................................ 55

Appendix B ............................................................................................................................................ 57

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ix

List of tables

Table 3.1 - Characteristics of the analysers used in gas analysis. .......................................................19

Table 4.1 - Properties of water and biodiesel (taken from Pereira [8]). ................................................21

Table 4.2 - Tests carried out with pressure atomization. ......................................................................22

Table 4.3 - Tests carried out with air assisted atomization. ..................................................................22

Table 5.1 - Combustion tests conditions. ..............................................................................................32

Table 5.2 - Measurements performed for the combustion tests conditions. .........................................33

Table 5.3 - NG properties (taken from Pereira [8]). ...............................................................................34

Table 5.4 - Energy balances to the cooling water. ................................................................................45

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List of Figures

Fig. 1.1 - DFB used by Colson et al. [7] .................................................................................................. 3

Fig. 2.1 - Experimental set-up used for spray characterization experiments with pressure atomization. 9

Fig. 2.2 - Detailed view of components 4’, 4, 5 and 6. Injection pipe and nozzle (left), biodiesel

preheater (horizontal) and thermostat (right). ........................................................................................ 10

Fig. 2.3 - Danfoss nozzle type OD, used for biodiesel pressure injection. ............................................ 10

Fig. 2.4 - Experimental set-up used for spray characterization experiments with air assisted

atomization. ........................................................................................................................................... 11

Fig. 2.5 - Air assisted atomizer. ............................................................................................................. 11

Fig. 2.6 - Large scale furnace used in combustion tests (numbers in bold identify the rings). ............. 12

Fig. 2.7 - Photograph of the large scale furnace used in combustion tests. ......................................... 13

Fig. 2.8 - Developed burner used for combustion tests using pressure atomization (left); burner

previously built, used for air assisted atomization tests (right). ............................................................. 13

Fig. 2.9 - Furnace top for air assisted atomization (left) and pressure atomization (right). ................... 15

Fig. 2.10 - Schematics of the large scale furnace exhaust system. ...................................................... 15

Fig. 2.11 - Reformer simulator (left) and its model (right). .................................................................... 16

Fig. 2.12 - Reformer simulator side view (left) and actual situation with the tubes (right). ................... 16

Fig. 3.1 - Basic working principle and components of the Malvern particle analyser (Malvern User

Guide). ...................................................................................................................................................17

Fig. 3.2 - Lens particle size range in µm and cut-off distance for all the lenses available (Malvern User

Guide). ...................................................................................................................................................17

Fig. 3.3 - Typical data output window of the Malvern software. ............................................................18

Fig. 3.4 - Schematics of the gas analysis apparatus. ............................................................................19

Fig. 3.5 - Probe used for temperature evaluation. .................................................................................20

Fig. 4.1 - Mass flow rate as a function of the relative pressure for pressure atomization. ....................22

Fig. 4.2 - SMD relation with axial distance from the nozzle (6.08 kg/h S 45º at 62.5% of max flow rate).

...............................................................................................................................................................23

Fig. 4.3 - SMD relation with radial distance from the spray cone axis (6.08 kg/h S 45º). .....................24

Fig. 4.4 - SMD relation with mass flow rate for isothermal and pre-heated situations. .........................24

Fig. 4.5 - SMD relation with flow rate for all the conditions tested at 50 mm. .......................................25

Fig. 4.6 - SMD relation with atomizing air flow rate for five different water flow rates (9 kg/h and 12

kg/h data taken from [8]). .......................................................................................................................26

Fig. 4.7 - SMD relation with biodiesel mass flow rate, theoretical and experimental approaches. .......28

Fig. 4.8 - Comparison between SMD results. ........................................................................................28

Fig. 4.9 - SMD relation with atomizing air mass flow rate, theoretical and experimental approaches. .29

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Fig. 4.10 - Comparison between SMD results.......................................................................................30

Fig. 5.1 - Radial distances of the measurements (mm). ....................................................................... 34

Fig. 5.2 - Recirculation zones inside the furnace according to Ribeirete [33] (left) and for general

burners with swirl from Coelho and Costa [20] (right). .......................................................................... 35

Fig. 5.3 - Temperature variation with radial distance. Tests 1 to 7 (full swirl and pressure atomization,

below the tube tops) (left); impact of excess air (right). ........................................................................ 36

Fig. 5.4 - Temperature variation with radial distance. Tests 8 to 14 (full swirl and pressure atomization,

tests 12 and 13 below the tube tops) (left); variation of biodiesel flow rate (right). ............................... 37

Fig. 5.5 - Temperature variation with radial distance. Tests 15 to 24 (swirler half way and pressure

atomization, tests 16, 18, 19, 22 and 23 below the tube tops) (left); variation of biodiesel flow rate

(right). .................................................................................................................................................... 38

Fig. 5.6 - Temperature variation with radial distance. Tests 25 to 34 (air assisted atomization, tests 26,

27, 30, 31 and 33 below the tube tops) (left); atomizing air influence (right). ....................................... 39

Fig. 5.7 - Test 15: 12.3 m³/h of NG; 0 kg/h of biodiesel; 129.5 kW thermal input and 4.8% of exhaust

O2. .......................................................................................................................................................... 40

Fig. 5.8 - Test 17: 12.3 m³/h of NG; 0 kg/h of biodiesel; 129.5 kW thermal input and 2.5% of exhaust

O2. .......................................................................................................................................................... 40

Fig. 5.9 - Test 21: 6.3 m³/h of NG; 6.0 kg/h of biodiesel; 129.3 kW thermal input and 5.0% of exhaust

O2. .......................................................................................................................................................... 41

Fig. 5.10 - Test 20: 6.3 m³/h of NG; 6.0 kg/h of biodiesel; 129.3 kW thermal input and 3.1% of exhaust

O2. .......................................................................................................................................................... 41

Fig. 5.11 - Test 25: 7.9 m³/h of NG; 0 kg/h of biodiesel; 83.7 kW thermal input, 4.7% of exhaust O2 and

2.6 kg/h of atomizing air. ....................................................................................................................... 42

Fig. 5.12 - Test 28: 7.9 m³/h of NG; 0 kg/h of biodiesel; 83.7 kW thermal input, 4.7% of exhaust O2 and

0 kg/h of atomizing air. .......................................................................................................................... 42

Fig. 5.13 - Test 29: 4.4 m³/h of NG; 3.0 kg/h of biodiesel; 78.2 kW thermal input, 5.3% of exhaust O2

and 6.0 kg/h of atomizing air. ................................................................................................................ 43

Fig. 5.14 - Test 32: 4.4 m³/h of NG; 3.0 kg/h of biodiesel; 78.2 kW thermal input, 3.3% of exhaust O2

and 6.0 kg/h of atomizing air. ................................................................................................................ 43

Fig. 5.15 - Theoretical temperature and reactants distribution in diffusion flames [20]. ....................... 44

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Nomenclature

Abbreviations

AFR Air to Fuel Ratio

DFB Dual-fuel burner

ERZ External Recirculation Zone

FAME Fatty Acid Methyl Esters

HC Unburned Hydrocarbons

IRZ Internal Recirculation Zone

LHV Lower Heating Value

LPG Liquefied Petroleum Gas

NG Natural Gas

PDA Phase Doppler Anemometry

POME Palm Oil Methyl Ester

SMD Sauter Mean Diameter

SOME Soybean Oil Methyl Ester

SRH Steam Reforming of Hydrocarbons

ULO Used Lubrication Oil

List of symbols

D32 Sauter mean diameter

λ Wave length

θ Diffraction angle

ρ Density

σ Surface tension

µ Dynamic viscosity

ν Kinematic viscosity

Liquid’s surface tension in equations (1), (2) and (3)

Liquid’s dynamic viscosity in equations (1), (2) and (3)

Air density in equations (1), (2) and (3)

Pressure differential across the nozzle in equation (1)

Liquid’s density in equations (1), (2) and (3)

Θ Spray cone angle in equation (1)

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Liquid’s mass flow rate in in equations (1), (2) and (3)

Liquid’s discharge orifice diameter in equations (1), (2) and (3)

Air velocity in the mixing zone in equations (2) and (3)

Atomizing air mass flow rate in equations (2) and (3)

c Water specific heat capacity

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1 – Introduction

1.1 – Motivation and goals

The energy market is in constant change. Where the energy is coming from, what is its form,

what is the impact of the production and delivery are important matters nowadays. By a simple life

cycle assessment it is possible to understand that a change is needed to have a sustainable

development. Since the past century there have been increasing concerns regarding pollution, fossil

fuels consumption and improving of renewables.

In terms of renewable energy, hydrogen (if obtained from renewable sources) is one of the

solutions for energy carrier and it is the focus of many studies throughout the world. Its usage in fuel

cells produces no pollution since the product is H2O and in combustion only NO is formed by the

thermal mechanism. The introduction of hydrogen as an energy carrier suffers from the chicken egg

problem since the development of fuel cells and hydrogen production and distribution infrastructure

are running in parallel. There are different ways to produce hydrogen such as water electrolysis, which

requires a high electricity use and others, more efficient, like steam reforming of hydrocarbons (SRH).

SRH is a process that combines the hydrocarbon with water steam to generate synthesis gas

containing mainly hydrogen, carbon monoxide, carbon dioxide and water. This process is strongly

endothermic so it requires a high heat input. For hydrogen application in fuel cells hydrogen has to be

purified separating water for reutilization and the other species such as a low heating value gas that

can be used to supply part of the heat required.

The aim of the present work is to develop a component of a system for hydrogen production

that uses the process specified above, SRH. This system uses biodiesel as the hydrocarbon source in

the reformer. The component to be developed is a dual-fuel burner (DFB) which will be fed with the

same fuel used in the reformer module. The burner will work with biodiesel and off-gas (the gas

separated from hydrogen after the reformer module).

Biodiesel is an ester (generally methyl ester), obtained mainly from vegetable oil through a

process called transesterification. This process consists on a reaction that requires a catalyst such as

sodium hydroxide to split the oil molecules and an alcohol (methanol or ethanol are the most

commonly used) to combine with the separated esters [1]. The biodiesel used in the present

experiments was obtained using methanol reacting with fats/oils producing the so-called Fatty Acid

Methyl Esters (FAME). Due to the lower price of methanol, FAME is the basic composition of most

widely used biodiesels (if ethanol was used instead, Fatty Acid Ethyl Esters would be obtained).

Through transesterification the oil viscosity is highly reduced [2].

Since biodiesel is a renewable and sustainable energy source the whole process can be

regarded as a renewable source of energy. However, since part of the process requires combustion

(for the generation of heat to produce the reforming reaction), pollution is an important factor, thus it is

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important to assess the products of such a reaction, mainly CO, NOx, and unburned hydrocarbons

(HC).

1.2 – Previous research

1.2.1 – Dual-fuel burners

In the past years there has been increasing interest in dual-fuel burners. Their applicability

reaches many different cases, from small engines up to large scale furnaces. Generally they use a

gaseous and a liquid fuel, either at the same time (co-combustion) or separately. In most cases one of

the fuels is used in a non-continuous mode, either for starting the burners or when one of the fuels’ is

not available.

Different configurations have been used on DFB. For instance, Roy et al. [3] built one aiming

to investigate the performance and emissions of a supercharged engine fuelled by hydrogen and

ignited by an initial diesel injection. During the tests they found that a dilution of the mixture with N2

promoted a 100% reduction in NOx emissions.

Yoon and Lee [4] also made tests with a diesel engine to study the emissions using bigoas-

diesel and biogas-biodiesel. The biodiesel used was entirely soybean oil methyl ester (SOME). They

compared the combustion and emission characteristics and concluded that significantly lower

emissions of NOx were obtained when using dual-fuel operation for both pilot fuels. They also noted

that biogas-biodiesel exhibited better performance, reducing soot and SO2 emissions.

Some theoretical works have also been developed. Maghbouli et al. [5] used a 3D-

CFD/chemical kinetics framework. Again, the goal was to study the combustion and emission

characteristics of a DFB. They compared their results with those obtained experimentally in other

similar works. Although they reached higher thermal efficiencies, they also observed an increase in

NOx and CO emissions.

In regard to furnaces, Omari and Abu-Jdayil [6] evaluated the thermal performance of dual-fuel

operating furnaces. For their study they used blends of diesel and used lubrication oil (ULO) co-fired

with liquefied petroleum gas (LPG). They stated that the use of ULO instead of unused fresh oil

enhanced radiation heat transfer due to the presence of small metallic particles. They also observed

that changing the fuel ratio (substituting 30% of LPG mass with a mixture of 20% ULO and 80%

diesel), radiation would again be improved.

Colson et al. [7] used a 15 MW burner to test the effect of the burner head configuration on

flame structure and NO formation. They had independent control over primary and secondary air feed

and also over the swirl generators which allowed them to change the flow pattern both in the burner

and in the furnace. They concluded that the aerodynamic structure of the flame near the burner had a

strong impact on the overall flame structure and formation of NO. So they concluded that the

aerodynamics near the burner controls NOx emissions.

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Fig. 1.1 - DFB used by Colson et al. [7].

1.2.2 – Atomization

Liquid fuels are used in a wide range of applications. In combustion applications the liquid has

to be atomized which is no more than the disintegration of a bulk liquid into small droplets. The major

goal of atomization is to increase the surface to volume ratio to enhance liquid evaporation and

combustion.

To accomplish a good atomization several factors are important such as the flow on the

channels leading up to the atomizer and the growth of small disturbances, for instance, is important as

it might lead to instability promoting disintegration of the liquid into ligaments and then drops.

Important physical properties have to be taken into account when discussing atomization. Viscosity

has an important role on inhibiting the growth of instabilities and thereby delaying disintegration. The

viscosity decreases with an increase in temperature. A fully turbulent jet can break up without external

forces once it is no longer restrained by the orifice walls. When this happens, only surface tension is

responsible for bulk cohesion and when these forces are overcome by shear stresses the liquid

breaks. So, sprays may be produced in different ways. The biggest requisite for good atomization is

the establishment of a high relative velocity between the liquid to be atomized and the surrounding

gas. One way to obtain this is by inserting a relatively slow-moving liquid on a high velocity airstream.

This is generally known as twin-fluid, air assisted or air-blast atomization (see Pereira [8] for a more

detailed discussion on air assisted atomization) and has the advantage of limiting pollutants emission

as it avoids zones with rich mixture as the air used to atomize the liquid promotes good mixing [1] and

better atomization. The problem is that with the extra oxygen content the NO production may increase.

Another option is to inject the liquid at high speed in a relatively slow-moving stream of gas. This is the

case of pressure atomizers. Pressure atomizers work by discharging a liquid at high pressure through

a small orifice into an atmosphere.

A good atomization is important as it promotes a better evaporation and combustion. Prior to

testing the atomizers under combustion conditions it is important to know the spray characteristics and

behaviour as a function of their operating parameters. These can be then controlled to control, up to a

certain extent, the reactions occurring inside the combustion chamber.

4

Xie et al. [10] evaluated the spray flow structure and the droplet Sauter mean diameter (SMD).

Their goal was to describe spray atomization quality on pressure swirl nozzles. Tratnig and Brenn [11]

also worked on pressure swirl atomizers with the aim of investigating the size spectra of the spray.

These authors also used the SMD as the parameter that defines the spray quality. A water-sucrose-

ethanol solution was used with varying compositions thus allowing them to control surface tension and

dynamic viscosity of the liquid independently.

Belhadef et al. [12] made some work with the addition of a modelling approach to predict the

spray behaviour. The fluid selected for the tests was water. Semião et al. [13] encountered

expressions for the SMD using different atomizers. They found a formula that, according to them,

offered distinct advantages when dealing with twin-fluid air blast atomizers.

Biodiesel atomization tests were reported by Kim et al. [14]. They used a common rail system

and tested the injection in a wide range of ambient pressures. They assessed the cone angles and

SMD in a large spectrum of radial and axial distances using both a high-speed camera and Phase

Doppler Anemometry (PDA). Additional biodiesel spray research can be found in [15], [16] and [17].

It is clear that the SMD (also referred to as D32) is the most widely used parameter to

represent the droplet size in a spray. The SMD is defined as the diameter of the drop whose ratio of

volume-to-surface area is equal to that of the spray [9]. The SMD depends significantly on the case

considered, being this the reason why researchers usually end up using a customized formula to

predict it. Although many formulae are suitable for a number of cases, their range of application is

limited thus requiring adaptation when deviating from previously tested situations.

In regard to droplet size measuring techniques, it has already been said that various authors

used PDA that allows for the simultaneous measurement of droplet velocity and diameter. Another

technique that is used (see [8], [18] and [19]) is based on the Fraunhofer principle. This technique,

available in the present laboratory, uses a laser beam and a receiver that detects the light scattered

when it crosses a spray. The information obtained allows for the determination of the droplets’ size

distribution and various mean diameters, including the SMD. Additional information about this

measuring technique is presented in section 3.1.

1.2.3 – Combustion

Combustion is used in a number of engineering applications. It is the main process used in

energy conversion from chemical to thermal and in many cases turned again into mechanical or

electrical. It is said conversion although it is commonly, yet wrongly, referred to as energy production

(“Dans la nature rien ne se crée, rien ne se perd, tout change.” “In nature nothing is created, nothing is

lost, everything changes”; Lavoisier).

Up until 2007, around 90% of the overall energy used in transportation, electric power

generation and thermal energy production resulted from burning of solid, liquid and gaseous fuels [20].

Nowadays combustion still has a huge slice in the fields of application stated previously thus making it

5

still important to develop good combustion systems, better fuel usage and control of the products

resulting from such a reaction.

To achieve a better performance on liquid combustion, a good atomization is required as

previously stated. If the atomization is poor part of the fuel may not burn and more energy is required

to evaporate and burn larger droplets. This case is important, for example, in alcohol working engines

as the latent heat of vaporization of alcohols is high when compared with diesel. Considering this it is

easy to understand that a better atomization promotes better energy efficiency as the combustion will

happen faster allowing for the reactions to consume all the fuel.

One of the major branches of investigation is the use of biodiesel as a substitute of fossil fuel

derived diesel, either as complete suppression of the latter or as a component of a blend mixing

biodiesel with diesel. Many investigations have been carried out regarding this topic mainly concerning

diesel engines. A wide variety of blends obtained with biodiesel from different sources is tested in

many research projects, some of these are referred here.

Özener et al. [21] compared the combustion characteristics of a direct injection diesel engine

with diesel and four different blends of soybean biodiesel-diesel (B10, B20, B50 and B100; in this

nomenclature the number refers to the volume percentage of biodiesel; for instance, B100 is pure

biodiesel). The authors concluded that biodiesel had a shorter ignition delay which had an impact in

pollutants emission. They stated that due to an early start of the reactions the CO formed had more

time to oxidise into CO2. Another reason for a higher CO formation in the diesel rich blends is the

lower fuel oxygen content. From B10 to B100 they noticed a CO emissions decrease as high as 28%,

31%, 38% and 46%, respectively. For HC emissions reduction, values like 20%, 23%, 31% and 44%

were obtained (again from B10 to B100). They associated the presence of oxygen molecules as a

reason for a more complete combustion. Regarding NOx emissions an increase was verified for an

increasing biodiesel percentage. Increasing values, specifically 6.95%, 10.66%, 12.43%, and 17.62%,

were achieved as compared with conventional diesel fuel. These results were in agreement with the

previous literature survey made by them. Recent works with a similar research on biodiesel

combustion in diesel engines, with other biodiesel sources (palm oil, waste oil, rapeseed oil and corn

oil), can be found in [22], [23] and [24]. In all these works the use of biodiesel is recognised as more

environment friendly than regular fossil fuels.

A study comparing the combustion of petrol based diesel with B5, B10, B20, B50, B80 and

B100 using an experimental boiler was conducted by Ghorbani et al. [25]. Their work’s objective was

to assess combustion efficiency and flue gas emissions, namely CO, CO2, NOx and SO2 and the

influence of air flow at two energy levels, 219 kJ/h and 249 kJ/h. Apart from B10, the blends emitted

less CO, CO2 and SO2. At the lower energy level they noticed that NOx had higher values when using

blends in accordance with previous studies although it had a lower value when moving to the higher

energy tests.

Ng and Gan [26] undertook a series of experiments to examine the combustion performance

and emissions from the non-pressurized combustion of palm oil methyl ester (POME) biodiesel

blends. They submitted the biodiesel to a pressure on the range 8-11 bar and used Danfoss oil

nozzles. After the tests they concluded that optimum combustion occurred with an equivalence ratio

6

between 0.75 and 0.85. Beyond this limits the mixture was too rich or too lean to sustain a complete

burning. They also stated that there was a relation between CO and NOx, so the parameters should be

selected considering this trade-off. With increasing pressure the CO and NOx emissions were reduced,

for the same blend.

Tashtoush et al. [27] also made tests with used palm oil (palm oil ethyl ester). Combustion

efficiency, exhaust temperature as well as CO, CO2, SO2 and NOx emissions were tested over a wide

range of air/fuel ratios. In the test they used a water-cooled furnace and defined combustion efficiency

as the ratio of the heat transferred to the water to the amount of thermal heat input. As expected, the

highest values for the efficiency were achieved near stoichiometry. As in other works they verified a

reduction in CO and SO2 formation with biodiesel. For NOx emissions they also noticed a reduction

which was explained by the lower sulphur and nitrogen concentration in the biomass-based fuels

when compared to fossil fuels. NOx depends mainly on oxygen availability and local combustion

temperatures and that is partially why at higher energy levels they obtained higher NOx concentrations

for both fuels.

Szybist et al. [28] focus on biodiesel (four kinds of B20 and one of B100) combustion,

emissions and emission control in a direct injection diesel engine. As in many other studies

undertaken there was a NOx increase with increasing biodiesel concentration. They stated that due to

the higher bulk modulus of compressibility of the biodiesel used the injection would start slightly earlier

when using pump-line-nozzle fuel systems giving more time for combustion. To reduce NOx they

proposed a delay in injection to reduce the time at high temperature and freeze the reactions and/or

additivation with a cetane improver. Soot formation was also reduced when using biodiesel, or other

oxygenated fuels for that matter.

A particularly interesting and very comprehensive work is that of Palash et al. [29] concerning

mainly NOx. They make a description of the most important mechanisms in NO formation and their

weight in combustion, the significant factors affecting NOx emissions and how to reduce these

emissions.

As seen in the above paragraphs there are mixed results for NO formation. In some test

conditions it is seen an increase compared with petroleum based diesel in other studies the opposite.

All data collected is nonetheless explained. Biodiesel present a higher oxygen content promoting

higher hydrocarbon oxidation which yields higher temperatures that promote the reactions that yield

NO, Biodiesel has, however, a reduced amount of nitrogen when compared with fossil diesel so the

NO formation is more dependent on the atmospheric nitrogen.

It is clear that although pollutants such as CO, SO2 and unburned HC are generally reduced

when using biodiesel there are still some uncertainties concerning pollutants emission as its formation

is strongly related to the combustion conditions.

7

1.3 – Present contribution

The main goal of this thesis is to develop a DFB. In a first stage of the study, spray tests under

non-reacting conditions were carried out to select the best injection parameters and atomizer type to

be used in the DFB. This part of the study involved the detailed characterization of a number of sprays

(determination of the droplet size distribution) using a laser diffraction technique.

In the second stage of the study, the combustion performance of the DFB, equipped with the

atomizers studied earlier, was assessed in the test furnace available. Combustion tests were

performed using NG and/or biodiesel. In the tests, temperature and gas species concentration

distributions along the radius of the furnace were carried out at two axial distances for the temperature

and one distance for gas species concentration. It should be noted that the furnace was equipped with

a reformer simulator.

8

9

2 – Experimental facilities

2.1 – Atomization tests

Pressure atomization:

Fig. 2.1 presents the experimental set-up used for the spray characterization experiments. The

fuel tank (1) uses nitrogen (2) to pressurize the liquid. The flow rate is measured and regulated by a

valve in a calibrated rotameter (3). A preheater, (4) and (4’), heats the liquid up to 70 ºC. The pattern

of the spray depends on the nozzle selected. The nozzles have three independent parameters:

nominal flow rate; spray pattern (full spray (S), hollow cone spray (H) and semi-solid (SS)) and spray

cone angle.

To evaluate the droplets’ size distribution the Malvern Particle Sizer 2600 (7, 7’) was used. An

extraction fan (8) is used to increase the quality of the results. To reutilize the biodiesel a reservoir (9)

is used. Fig. 2.2 shows in greater detail components (4), (5) and (6).The pipe to attach the injectors (6)

is adapted to use Danfoss injectors type OD (Fig. 2.3).

Fig. 2.1 - Experimental set-up used for spray characterization experiments with pressure atomization.

10

Fig. 2.2 - Detailed view of components 4’, 4, 5 and 6. Injection pipe and nozzle (left), biodiesel preheater (horizontal) and thermostat (right).

Fig. 2.3 - Danfoss nozzle type OD, used for biodiesel pressure injection (courtesy of Danfoss).

11

Air assisted atomization:

Fig. 2.4 presents the experimental set-up used for the spray characterization experiments

using the air assisted atomization and Fig. 2.5 shows the atomizer with the relevant dimensions. For

this type of atomization water was used and taken directly from the tap flowing through a rotameter to

control the flow rate. The atomising air was supplied from a compressor available in the laboratory and

controlled by a calibrated rotameter. All the remaining equipment is the same used in pressure

atomization tests.

Fig. 2.4 - Experimental set-up used for spray characterization experiments with air assisted atomization.

Fig. 2.5 - Air assisted atomizer.

12

2.2 – Combustion tests

Test furnace:

Fig. 2.6 schematically shows the large-scale furnace and Fig. 2.7 presents a photograph of the

furnace. A major advantage of the present furnace is that it is large enough to ensure that the

essential physics of full-scale combustors are simulated. It is large enough to ensure fully turbulent

flow combined with significant thermal radiation transfer, but small enough to enable the collection of

detailed reliable data [8]. The liquid fuel, NG, primary air and secondary air feeding systems can also

be seen in the scheme.

Combustion chamber:

The combustion chamber consists of a top disc and eight cylindrical sections, all water cooled.

The burner is placed on the top of the furnace to facilitate the removal of the particles arising from the

combustion process. Its axis is vertical to minimize asymmetry due to natural convection. Each section

has an inner diameter of 600 mm and a height of 300 mm. The top of the furnace, as well as the four

upper sections have an internal refractory coating with a thickness of 130 mm, capable of withstanding

temperatures up to 1500 ºC. A ceramic fibre is placed between the refractory material and the water

cooled jackets. The remaining four lower segments are water cooled only. Each segment has a pair of

diametrically opposed 215 mm diameter ports for probing and viewing that are closed with castable

refractory inserts in the upper sections and steel inserts in the lower sections. The top four segments

are equipped with type R thermocouples that allow the user to monitor the temperatures of the internal

walls. Probes are also installed in the top four segments to register the static pressure inside the

combustion chamber. The water cooling system is independent for each one of the eight segments,

which are equipped with type J thermocouples to control the water inlet and outlet temperature. The

cooling water mass flow rate is controlled by a valve and adjusted in a rotameter.

Fig. 2.6 - Large scale furnace used in combustion tests (numbers in bold identify the rings).

13

Fig. 2.7 - Photograph of the large scale furnace used in combustion tests.

Burner guns:

The burner geometry is typical of that used in power stations for wall-fired boilers and consists

of a burner gun and a secondary air supply in a conventional double-concentric configuration,

terminating in an interchangeable refractory quarl which ends with an angle of 30º with the vertical

direction. Swirl is imparted to the secondary air stream using vanes inclined at 30º (with a plane

normal to the burner axis) when using air assisted atomizers and by a swirl generator when using

pressure atomizers. The burners, presented in Fig. 2.8, are mounted on the top of the combustion

chamber of the furnace (additional images of the burners are shown in appendix A). The burner with

air assisted atomization consists of two different parts. The first one constitutes the atomizer used in

air assisted spray evaluation, where the central orifice is used for the introduction of the liquid fuel and

the annular section for the atomizing air. The second component is a tube used for the secondary

(gaseous) fuel feeding in the co-combustion tests. Finally, a last annular section, limited by the exterior

tube of the burner gun and the quarl, is used for the introduction of secondary air.

Fig. 2.8 - Developed burner used for combustion tests using pressure atomization (left); burner previously built, used for air assisted atomization tests (right).

14

For pressure atomization testing the burner is composed by two concentric tubes where the

outer tube has a diameter of 30 mm to fit in the swirl generator and the inner tube has 17 mm to attach

the nozzles. The NG, supplied around the 17 mm tube, passes through a contraction to increase the

gas speed so it can be in the acceptable range for the tests. The top disc of the furnace, where the

burners are mounted, can be seen in greater detail in Fig. 2.9 (left) for air assisted atomization and

Fig. 2.9 (right) for pressure atomization.

On the top of the furnace it is possible to mount a wind box, swirler, to generate secondary air

swirl, Fig. 2.9. This box has four air inlets connected to a fan of adjustable speed to change the

amount of air going in.

Fuels and air feeding systems:

The fuel injection set-up is the same described in 2.1. The pressure inside the tank is

measured by a gauge and the fluid mass flow rate is monitored in a calibrated rotameter. The NG is

supplied independently to the burner and ignition system (see below). The NG is fed continuously from

the IST grid at a pressure of 22 mbar and a maximum flow rate of 40 m³/h. The atomizing air is

supplied by an air compressor (10 bar) and its flow rate is measured using a calibrated rotameter. The

secondary air is supplied by a fan of variable speed and its flow rate is adjusted measuring the oxygen

concentration at the exit of the combustion chamber, allowing to determine the excess air coefficient

and therefore to know the secondary air mass flow rate.

Ignition system of the furnace:

A small NG burner placed on the top of the furnace provides a pilot flame to ignite the main

flame. The combustion air is supplied by a fan used only for this purpose. The ignition of the pilot

flame is attained by the means of a high voltage electrical discharge. Once established the main flame

the pilot flame is turned off.

Exhaust system of the furnace:

The exhaust system is schematically represented in Fig. 2.10. It was designed to minimize the

emission of particles and to decrease the temperature of the exhaust gases.

On the first part of the system, inside the combustion chamber, a central shower is placed

inside a convergent tube which is followed by a constant section tube, with two plain water jets

situated in its interior. Finally, a separator is located at the tube’s exit. The exhaustion is performed

tangentially in such a way that the centrifugal force projects the larger particles towards the separator.

These particles end up being dragged by the water coming from the showers to the container’s

interior. During the tests, the water level in the container is kept constant to avoid flow disturbances in

the combustion chamber’s interior.

The second part of the exhaust system connects the separator to the chimney. The latter is

equipped with an adjustable opening to regulate the pressure inside the combustion chamber. A bag

filter for gas treatment and a cyclone for particle removal also integrate this part of the exhaust

15

system, which is intended to capture the particles that may have escaped from the separator. The bag

filter has a capacity of 800 m³/h, a filtering area of 11 m² and a filtering velocity of 73 m³/m²/h that

assures a particle emission under 10 mg/m³.

Fig. 2.9 - Furnace top for air assisted atomization (left) and pressure atomization (right).

Fig. 2.10 - Schematics of the large scale furnace exhaust system.

Reformer simulator:

To simulate the flow conditions a reformer simulator was built and mounted inside the furnace.

This reformer simulator consists of a structure made of stainless steel. The discs on the top have a

16

hemispherical cap made of refractory cement that can withstand temperatures up to 1600 ºC. Both

photographs and model images can be seen in Fig. 2.11.

Fig. 2.11 - Reformer simulator (left) and its model (right).

The aerodynamics of the chamber due to the presence of the reformer simulator is important.

The component consists of a bank of discs directly above a large drilled disc (Fig. 2.12, left) that

simulate the head loss for the flue gas exit. The space in-between is empty and a good mixture of the

gases is promoted due to the presence of the discs that work as a bluff body. With the tubes present

(Fig. 2.12, right) in this empty space the flow may not have the same mixture and will be more

restrained to the axial direction.

Fig. 2.12 - Reformer simulator side view (left) and actual situation with the tubes (right (courtesy of HyGear)).

Liquid fuel:

In the case of the present work the biodiesel available was aged and was kept at atmospheric

pressure in contact with air (in a closed tank but with no inert atmosphere). This increases the

oxidation and may cause properties alteration. The biodiesel should not be stored for more than 12

months even in the best storage conditions. After some time the acid values start to change, the

oxidation stability may go out of specification and some deposits may form [30].

17

3 – Experimental techniques and uncertainties

3.1 – Atomization

To obtain the data to assess the SMD the Malvern instruments System 2600 was used. This

equipment uses the Fraunhofer principle which is based on light diffraction. The Malvern works by

generating a 10 mW He-Ne laser beam with a wave length (λ) equal to 0.6328 µm and a diameter of 9

mm. The beam then crosses the spray and undergoes the diffraction phenomenon mentioned earlier.

Depending on the droplet size, different diffraction angles are obtained (θ in Fig. 3.1) being the larger

angles associated with smaller droplets (Fig. 3.1, right). After changing direction the Fourier lens on

the detector redirects the scattered light to the 31 diodes circular array and the intensity on each diode

is processed. Regardless of the distance to the lens, same angle of diffraction is redirected to the

same diode so the distance from the spray control volume to the receptor is not important as long as it

doesn’t exceed the maximum distance allowed for the diffracted light to enter the lens (cut-off

distance, A). If this happens the droplets crossing the beam outside the lens range will not be

accounted for and part of the light emitted will be scattered out. In Fig. 3.2 the cut-off distance for each

available lens is presented along with the diameter range that it is sensible to. For the present study

the lens with a focal range of 300 mm was selected.

Fig. 3.1 - Basic working principle and components of the Malvern particle analyser (Malvern User Guide).

Fig. 3.2 - Lens particle size range in µm and cut-off distance for all the lenses available (Malvern User Guide).

18

After acquiring the data the Malvern software treats all the values to create the droplet’s size

distribution of the spray and calculate the SMD. To do this four functions are available: normal, log

normal, Rosin-Rammler and the independent model. Pereira [8] and Queirós [1] both used the same

equipment. The first used the independent model while the second chose the Rosin-Rammler. Since

the Rosin-Rammler model adapts the spectrum to a standard distribution some mistakes are made

(Malvern user guide; Queirós [1] estimated 5%). The independent model makes no assumptions

regarding the size distribution providing more realistic values. For these reasons the independent

model was chosen.

An important parameter to take into account is the obscuration. Obscuration is defined as the

fraction of light that is not detected after crossing the control volume. The light is lost either by being

absorbed by the particles crossing the beam or by being scattered out. This means that obscuration is

equal to zero if no sample is present and equal to one if no light reaches the detector. To have reliable

data the obscuration values must not be higher than 0.5. If the value is higher it means that multiple

diffraction phenomena are present and the results become dubious. Multiple diffraction is what

happens when the light beam is deviated by more than one droplet reaching the detector at higher

angles thus reducing the diameter values. The higher the density of the spray the more difficult it is for

the beam to cross the particle volume which means that the obscuration will have higher values. Near

the top of the spray (on the outlet orifice) this is noticeable and reliable measurements are not

possible. In the next figure there is a typical output window of the Malvern software. The SMD (D32),

the percentage of volume below the lens minimum, the model selected and the obscuration level are

highlighted.

Fig. 3.3 - Typical data output window of the Malvern software.

3.2 – Combustion

In the combustion analysis two properties are to be assessed: gas temperature and gas

species concentration. Measurements were made above the tube caps and in the section below

19

(temperature only). To make these measurements the two top windows of the furnace are used. The

holes for probe insertion are 150 mm away from the top of the reformer simulator (above and below).

A third probe is used to measure exhaust gas properties that allow for characterization of the

combustion regime knowing the excess air and the fuel flow rate. After collecting a gas sample the gas

is analysed over a set of analysers (schematics in Fig. 3.4). This sampling system consists of the

stainless steel probe, condenser, drier, filter, a pump and a rotameter. The connections along the

system are made with a non-reacting material, teflon. Any water present in the sample is removed on

the condenser being the remaining water removed in the drier placed ahead. The filter removes any

solid particles present in the gas thus obtaining a clean and dry sample. The analysers must be

calibrated prior to each testing session. In Table 3.1 are shown the brand and model of the analyser,

the gas it analyses, its working principle and the range.

Fig. 3.4 - Schematics of the gas analysis apparatus.

In [31] are reported the main factors that influence the measurements which are: the

disturbances in the flow due to the presence of the probe and the errors related with a non-isokinetic

sampling; the effectiveness of the chemical reactions freezing at the entrance of the probe to assure

the gas species in that zone of the flame suffer no alterations until they reach the analysers; and

Analyser Gas Method Range

Horiba, model CMA-331 A

O2 Paramagnetism 0-25%

Horiba, model CMA-331 A and

VIA-510 CO

Non-dispersive infrared

0-1000/5000 ppm and

0-2/5/10/20 %

Horiba, model CMA-331 A

CO2 Non-dispersive

infrared 0-50 %

Horiba, model CLA-510 SS

NOX Chemiluminescence 0-100/250ppm

Amluk, model FID E 2020

HC Flame ionization

detection 0-10/100ppm

Table 3.1 - Characteristics of the analysers used in gas analysis.

20

dissolutions of species in the water. The aerodynamic effects are the most important since the

changes that occur in the flow on the near-probe region may change the species concentration. In the

same work tests were made changing the flow rate inside the probe and it was found that no changes

were encountered in the gas species rendering them independent of this parameter. These results

together with the work of Heitor [32] confirm the statement regarding aerodynamics and prove that a

good chemical reaction halt is verified. Ribeirete [33] made a series of radial tests with the exhaust

gas probe and noticed no differences on the gas species concentrations related with the probe

position thus confirming that the aerodynamic disturbances are not important in this region of the

furnace.

For temperature analysis a probe, schematically presented in Fig. 3.5, has been used. For

every measurement an average of the values obtained during 30 seconds was made, after the

temperature stabilized. The probe uses a Platinum-Rhodium type R thermocouple (pure Platinum in

one conductor and a Rhodium/Platinum alloy containing 13% Rhodium on the other) that can measure

temperatures up to 1800 ºC. These are the most commonly used types in combustion applications

[34]. This probe can be moved radially inside the furnace at the predefined heights. According to [34],

for a thermocouple junction diameter of 80 µm the error in the measurements is approximately

constant and lower than 5.5% above 1200 ºC.

Fig. 3.5 - Probe used for temperature evaluation.

21

4 – Atomization

In this chapter all the results about atomization are presented. There is a description of the

liquids studied and test conditions and then the results obtained are presented. A first set of tests was

made at different axial distances to decide the location of the following measurements based on the

SMD obtained for a given regime. After deciding the axial distance, different conditions were tested at

the defined distance. For all the conditions three measurements were made and then averaged to

ensure repeatability. The difference on the calculated SMD between every measurement was never

higher than 5%.

4.1 – Test conditions

Different liquids were used to make the non-reacting study of the sprays. With pressure

atomization the liquid used was biodiesel. For the second part, with air assisted atomization, water

was used. There are two reasons for this: first, the previous tests with air assisted atomization

obtained by Pereira [8] were also made using water; second, the mist obtained using biodiesel with air

assisted atomization is very dense and it’s extraction is extremely difficult. In Table 4.1 the properties

of both liquids are presented. The biodiesel used is 40% SOME and 60% POME.

Table 4.1 - Properties of water and biodiesel (taken from [8]).

Property Value

WATER

Density (kg/m³) at 25ºC 997

Surface tension (N/m) at 25 ºC 0.0717

Dynamic viscosity (Ns/m²) at 25 ºC 0.000855

BIODIESEL

Chemical formula C18.3H34.8O2

C (wt%) 76.68

H (wt%) 12.15

O (wt%) 11.17

Density at 15ºC (kg/m³) 875

LHV (MJ/kg) 37.79

FAME (vol%) 99.4

The tests were performed by releasing the liquid into atmospheric pressure and temperature.

Tests were made isothermally and with biodiesel preheating. The biodiesel was heated to a

temperature around 70 ºC for these tests. At 50 mm from the nozzle a radial analysis was made with

10 mm spacing. At the end of the first tests it was concluded that preheating was not important so,

tests with different nozzles were carried out in isothermal conditions. All the nozzles tested are a 6.08

kg/h nominal flow rate nozzle (nozzle specifications on section 2.1). To define the curve that relates

mass flow rate with pressure the manometers in the circuit were used and their values compared with

those obtained by the rotameter calibration. These values were then compared with the theoretical

22

values obtained by the data sheet provided by the nozzles’ manufacturer. This comparison is shown in

Fig. 4.1 (both pressure values correspond to relative pressure). The flow rate values used in Table 4.2

are from the experimental tests. In the next table all the test conditions regarding pressure atomization

are presented. The test conditions for air assisted atomization are presented in Table 4.3.

Table 4.2 - Tests carried out with pressure atomization.

Type of test Nozzle Range in mm (Direction) Flow rate

(kg/h) Tinj (ºC)

SMD (Axial) 6.08 S 45º 15-80 (Axial) 3.8 70

SMD (Radial) 6.08 S 45º 0-30 (Radial) at 50 mm 6.04 70

SMD (pre-heated, nozzle 1) 6.08 S 45º 50 (Axial); 0 (Radial) 3.8-6.4 70

SMD (isothermal, nozzle 1) 6.08 S 45º 50 (Axial); 0 (Radial) 3.8-6.4 21

SMD (isothermal, nozzle 2) 6.08 H 45º 50 (Axial); 0 (Radial) 3.8-6.4 21

SMD (isothermal, nozzle 3) 6.08 S 60º 50 (Axial); 0 (Radial) 3.8-6.4 21

Table 4.3 - Tests carried out with air assisted atomization.

Air flow rate (kg/h) 3 4 6 7.4

Water flow rate (kg/h) 2 4 6 2 4 6 2 4 6 2 4 6

To calibrate the rotameter a measuring tube was filled without using the nozzle. The tube was

filled with a specific volume and the time measured. After knowing the volumetric flow rate for each

rotameters’ percentage and comparing these values with the pressure the experimental data is

obtained.

Fig. 4.1 - Mass flow rate as a function of the relative pressure for pressure atomization.

2

2.5

3

3.5

4

4.5

5

5.5

6

6.5

0 1 2 3 4 5 6 7 8 9 10 11 12

Mass f

low

rate

(kg/h

)

Pressure (bar)

Experimental

Theoretical

23

4.2 – SMD results for pressure atomization

4.2.1 – Influence of axial position

Fig. 4.2 shows the results obtained at different distances from the nozzle. The erratic

behaviour is due to the fact that the tests were made with a relatively low flow rate (62.5% of the

nominal flow rate). The effect of low flow rates is noticeable visually. The spray assumes an

intermittent behaviour and if the flow rate is too low the droplets are even perceptible with no visual

aid. Still, a trend is recognisable showing that the lower values are obtained somewhere in the range

of 30 to 55 mm. This behaviour is related with film breakup near the nozzle and droplets’ coalescence

and evaporation farther from it.

The distance selected based on the lower SMD values is in accordance with results found in

similar studies like [35], [36] and [37]. Pereira [8] used 40 mm. For the present study, considering the

works mentioned and the experimental results the 50 mm distance was selected.

Fig. 4.2 - SMD relation with axial distance from the nozzle (6.08 kg/h S 45º at 62.5% of max flow rate).

4.2.2 – Influence of radial position

Fig. 4.3 shows the SMD relation with radial distance from the spray cone axis obtained 50 mm

away from the nozzle. With the data obtained it can be seen that the smaller droplets are concentrated

near the centre of the spray cone. Although there is an increase with increasing distance from the

spray cone axis, the maximum values obtained for the SMD are still below 40 µm which is a value

considered acceptable for a good combustion.

50

52

54

56

58

60

62

64

66

68

70

0 10 20 30 40 50 60 70 80 90

SM

D (

µm

)

Axial distance from the nozzle (mm)

24

Fig. 4.3 - SMD relation with radial distance from the spray cone axis (6.08 kg/h S 45º).

4.2.3 – Influence of injection temperature

Viscosity decreases with increasing temperature in liquids. Pressure, too, has influence on

viscosity although it is a much less important factor. The viscosity has a decrease roughly exponential

with temperature [38]. In the work by Moradi et al. [39] is an analysis of the viscosity and density of

several biodiesels with different compositions, including SOME, at various temperatures. The

kinematic viscosity at 70 ºC (2.659 mm²/s) is 60% of that at 40 ºC (4.404 mm²/s). Using the remaining

values from the same work to make an appropriate regression it yields ν=6.104 mm²/s at 21 ºC.

Fig. 4.4 presents the SMD values at 70 ºC which are lower than those at 21 ºC, as expected.

These are, in average, 73% of those at 21 ºC. There is some gain in atomization, thus in combustion,

by preheating the biodiesel. The heat required from the surroundings is lower and the droplets are

smaller. Since even with preheating the results are only good with flow rates above 4.5 kg/h its use

can be discarded since lower values are desired for some conditions.

Fig. 4.4 - SMD relation with mass flow rate for isothermal and pre-heated situations.

15

18

20

23

25

28

30

33

35

38

40

0 5 10 15 20 25 30 35

SM

D (

µm

)

Radial position (mm)

20

30

40

50

60

70

80

3 3.5 4 4.5 5 5.5 6 6.5 7

SM

D (

µm

)

Biodiesel flow rate (kg/h)

21ºC

70ºC

25

4.2.4 – Influence of injection nozzle

According to the manufacturer, no differences should be noticed when using the same nozzle

type with the same nominal flow rate. This is true especially at higher values close to the nominal

operating conditions. Fig. 4.5 shows that the differences are indeed small and all the curves tend to a

value somewhere between 25 and 30 µm. Although the trend is asymptotical the actual value wasn’t

reached due to the high pressures required, as suggested by the results from Fig. 4.1, where the flow

rates higher than 6.08 kg/h were obtained with lower pressure than the theoretical. With these results

present the decision for the nozzle to be used was made. Considering the distance from the burner to

the reformer equivalent, the 6.08 kg/h 80º S nozzle was selected (even though it wasn’t tested in spray

evaluation).

Fig. 4.5 - SMD relation with flow rate for all the conditions tested at 50 mm.

4.3 – SMD results for air assisted atomization

On air assisted atomization only a few regimes were tested to complement the previous study

from Pereira [8]. For a more complete set of results refer to the mentioned work. In this work SMD

assessment was made for water mass flow rates of 9.2 and 12.7 kg/h and the results were plotted as

a function of air to fuel ratio (AFR) as happens in many studies of this subject. By plotting them as

function of atomizing air flow rate instead, it is clear that the SMD behaviour is fairly independent of

the liquid flow rate with air flow rates above 4kg/h, for the conditions tested. Fig. 4.6 presents these

results. After 6 kg/h the changes become minimal for these test conditions. With too much air the

flame may become too long and cross the tube caps section and in some cases blowout may occur.

For air flow rates too low the air loses its relative importance due to the low velocities and the changes

in SMD become important with AFR. This is seen looking at the deviation in the results for lower water

flow rates.

20

25

30

35

40

45

50

55

60

65

70

75

80

3 3.5 4 4.5 5 5.5 6 6.5 7

SM

D (

µm

)

Biodiesel flow rate (kg/h)

45º S pre-heated

45º S isothermal

45º H isothermal

60º S isothermal

26

Fig. 4.6 - SMD relation with atomizing air flow rate for five different water flow rates (9 kg/h and 12 kg/h data taken from [8]).

4.4 – Correlations for SMD prediction

Most of the correlations available in the literature [8] have a wide range of application

considering the type of atomization and different properties of the fluids involved while others are

stricter. For pressure atomization Wang and Lefebvre [40] present correlations that take into account

primary and secondary breakup, defined as SMD1 and SMD2, respectively. SMD1 depends partly on

the Reynolds number (

) which provides a measure of the disruptive forces present within the

liquid sheet. It also depends on the Weber number (

) which governs the growth rate of

perturbations. SMD2 represents the last stage of atomization. Here, the high relative velocity induced

at the liquid/air interface causes the surface protuberances generated in the first stage to become

detached and break down into ligaments and then drops. Although the correlation has been useful in a

variety of situations, it is not the case for the atomizers studied. After making the tests with pressure

atomization an error is verified but it can be reduced by changing the exponent related with the last

factor of SMD2, C. Changing this, a slightly different correlation that works well with the nozzles tested

can be found and has the form (SMD (m)):

(

)

(

)

(

)

(

)

Eq. (1)

0

20

40

60

80

100

120

140

160

180

200

220

240

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

SM

D (

µm

)

Atomizing air flow rate (kg/h)

Water flow rate:

2 kg/h

4 kg/h

6 kg/h

9 kg/h

12 kg/h

27

where (N/m) is the liquids surface tension, (Ns/m²) its dynamic viscosity, (kg/m³) is the air

density, (Pa) the injection pressure differential across the nozzle, (kg/m³) is the liquids

density, θ (º) is the spray cone angle. A and B are constants that depend on the geometrical

characteristics of the atomizer and according to [13] are given by:

[ (

)]

(

)

Eq. (1.A)

[ (

)]

(

)

Eq. (1.B)

C (equal to 0.7 in the original correlation by Wang and Lefebvre [40]) is an exponent changed to fit the

theoretical curve to the experimental data:

Eq. (1.C)

where (kg/s) is the liquids mass flow rate. t (m) is the film thickness given by:

[

( ) ]

Eq. (1.D)

where (m) (equal to 0.5 mm for the present atomizers) is the discharge orifice diameter and FN is

the nozzle flow number given by:

√ Eq. (1.E)

In the work of Freitas et al. [41] there is a wide range of biodiesels studied including one with

the same composition of that used in this work. From their results it can be found that = 0.0313

(N/m) at 30 ºC and using the remaining results the value for 21 ºC can be estimated as 0.0322 (N/m).

With all the results obtained previously and using Eq. (1), Figs. 4.7 and 4.8 are obtained.

28

Fig. 4.7 - SMD relation with biodiesel mass flow rate, theoretical and experimental approaches.

Fig. 4.8 - Comparison between SMD results.

For the air assisted atomization two correlations are used as base. Both expressions are

dependent on AFR but in this case they are presented with both flow rates separated (air and liquid).

The first is an expression based on that presented in [13] for plain-jet air blast atomizers and has the

form (SMD (m)):

[

]

[

]

(

)

[

]

[

]

[

]

(

)

[

]

Eq. (2)

0

10

20

30

40

50

60

70

80

90

3 3.5 4 4.5 5 5.5 6 6.5 7

SM

D (

µm

)

Biodiesel mass flow rate (kg/h)

Eq. (1)

SMD experimental 60S

SMD experimental 45H

SMD experimental 45S

0

10

20

30

40

50

60

70

80

0 10 20 30 40 50 60 70 80

Calc

ula

ted S

MD

(µ

m)

Measured SMD (µm)

60S

45H

45S

29

where (m/s) is the air velocity in the mixing zone, (kg/s) is the atomizing air mass flow rate

and (m) is the liquids discharge orifice diameter. All the other parameters have the same meaning

of those used for pressure atomization. For the expression used by Pereira [8] we have (SMD (m)):

[

]

[

]

[

] [

] Eq. (3)

Both expressions work fine for an air flow rate above 6.0 kg/h. For lower values of atomizing

air flow rate (higher SMDs) the correlations tend to deviate from the experimental results. Fig. 4.9 and

Fig. 4.10 present the results of both correlations. In Fig. 4.10 the calculated SMDs are compared with

the experimental results obtained. The results for higher values of SMD are not presented in Fig. 4.10

for the reason stated above. The values of SMD chosen for comparison in Fig. 10 were those obtained

by Pereira [8] with a water flow rate of 12.7 kg/h.

The weight of SMD2 in both expressions is negligible which can be verified making the

calculations. Eq. (2) is less sensitive to variations in which can be seen in both figures for the

limits presented (2 kg/h and 9 kg/h). Comparing the results a fixed value for may be selected in

order to make a better prediction of the SMD with lower values of atomizing air flow rate.

Fig. 4.9 - SMD relation with atomizing air mass flow rate, theoretical and experimental approaches.

0

20

40

60

80

100

120

140

160

180

200

220

240

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

SM

D (

µm

)

Atomizing air flow rate (kg/h)

Water flow rate:

2 kg/h

4 kg/h

6 kg/h

9 kg/h

12 kg/h

SMD Eq. (2) 2 kg/h

SMD Eq. (2) 9 kg/h

SMD Eq. (3) 2 kg/h

SMD Eq. (3) 9 kg/h

30

Fig. 4.10 - Comparison between SMD results.

0

5

10

15

20

25

30

35

40

0 5 10 15 20 25 30 35 40

Calc

ula

ted S

MD

(µ

m)

Measured SMD (µm)

Experimental vs Eq. (2) 2 kg/h

Experimental vs Eq. (2) 9 kg/h

Experimental vs Eq. (3) 2 kg/h

Experimental vs Eq. (3) 9 kg/h

31

5 – Combustion

The following chapter presents all the information regarding combustion. There is a description

of all the test conditions, a section regarding flame stabilization and then the results for temperature,

gas species and cooling water energy balances.

5.1 – Test conditions

The criteria to define the conditions are dependent on the project demands. A certain power

input is desired, 130kW, such as the temperatures of the gas entering the reformer unit where a

minimum of 950 ºC is required. For these specifications of power input the temperature is controlled by

the excess air. The first 24 tests were made with pressure atomization and the remaining 10 with air

assisted atomization. As it was described in chapter 2.2, for pressure atomization the swirl generator

was used. Two regimes were tested: swirler in the maximum swirl position and half way,

corresponding to swirl numbers estimated as 1 and 0.7, although no calibration of the block swirler is

available. When the blades are in the position to generate the maximum swirl the overall head loss is

too high, rendering it impossible, with the current equipment, to achieve the desired values of 3% and

5% of O2 in the exhaust with 130 kW thermal input. For these reason only values up to 86 kW were

tested. Changing the swirler to the middle position this problem was overcome and the conditions with

130 kW were tested. With air assisted atomization the pressure drop was also high so the thermal

input, with the desired O2 values, was limited to 84 kW.

In-flame gas species concentrations were assessed in a number of tests. These tests were

made with specific conditions from the 130 kW input, because it was the one closer to the real

conditions when using pressure atomization and with air assisted atomization. Data were obtained for

different relations NG/Biodiesel and different O2 values.

Table 5.1 presents the test conditions for all the combustion tests carried out and table 5.2 the

measurements made for each combustion test. In Fig. 5.1 the distances relative to the reformer

simulator, where the measurements took place (red dotted line), are shown. It should be noted that the

reformer simulator was slightly rotated. Regarding energy balances, values were only registered for a

limited number of tests because the losses were only related with the power input and the inner

temperature of the walls of the furnace.

32

Table 5.1 - Combustion tests conditions.

Atomization type

Swirl

NG Flow rate

(m³/h)

Biodiesel Flow rate

(kg/h)

Total Power Input

(kW)

Exhaust O2 Dry volume

(%)

Atomizing Air Flow

rate/Theoretical Secondary Air

Flow rate (kg/h)

Test Number

Pressure Atomization

Full Swirl

8.1 0 85.3 5.0 - / 135.0 1

1.8 6.3 85.1 5.4 - / 135.3 2

3.7 4.1 82.0 5.3 - / 130.6 3

6.1 0 64.2 5.4 - / 104.0 4

0 6.6 70.0 7.8 - / 128.3 5

0 6.7 71.2 5.1 - / 110.3 6

0 6.8 71.4 3.0 - / 99.4 7

7.6 0 80.0 5.0 - / 127.0 8

5.6 2.0 79.9 5.4 - / 129.1 9

3.6 4.0 79.9 5.1 - / 125.9 10

1.8 6.1 83.2 5.0 - / 129.0 11

1.8 6.1 83.2 5.0 - / 129.0 12

1.8 6.0 82.1 2.9 - / 113.4 13

1.8 6.0 82.1 2.9 - / 113.4 14

Swirler Half Way

12.3 0 129.5 5.0 - / 204.8 15

12.3 0 129.5 4.8 - / 202.5 16

12.3 0 129.5 2.5 - / 179.1 17

12.3 0 129.5 2.5 - / 179.1 18

6.3 6.0 129.3 3.1 - / 181.9 19

6.3 6.0 129.3 3.1 - / 181.9 20

6.3 6.0 129.3 5.0 - / 202.1 21

6.3 6.0 129.3 5.0 - / 202.1 22

9.3 3.0 129.4 5.1 - / 206.2 23

9.3 3.0 129.4 5.1 - / 206.2 24

Air Assisted

Atomization

30º Fixed Vanes

7.9 0 83.7 4.7 2.6 / 129.5 25

7.9 0 83.7 5.0 2.6 / 131.8 26

7.9 0 83.7 4.8 0.0 / 130.3 27

7.9 0 83.7 4.7 0.0 / 129.5 28

4.4 3.0 78.2 5.3 6.0 / 124.7 29

4.4 3.0 78.2 5.3 6.0 / 124.7 30

4.4 3.0 78.2 3.3 6.0 / 111.4 31

4.4 3.0 78.2 3.3 6.0 / 111.4 32

3.9 3.0 72.3 3.3 4.0 / 104.2 33

3.9 3.0 72.3 3.3 4.0 / 104.2 34

33

Table 5.2 - Measurements performed for the combustion tests conditions.

Atomization type

Swirl Temperature Measurement

Location

Gas Species

Energy Balance

Test Number

Pressure Atomization

Full Swirl

Below No No 1

Below No No 2

Below No No 3

Below No No 4

Below No No 5

Below No No 6

Below No No 7

Above No No 8

Above No No 9

Above No Yes 10

Above No No 11

Below No Yes 12

Below No No 13

Above No No 14

Swirler Half Way

Above Yes No 15

Below No Yes 16

Above Yes No 17

Below No No 18

Below No Yes 19

Above Yes No 20

Above Yes Yes 21

Below No No 22

Below No Yes 23

Above No Yes 24

Air Assisted Atomization

30º Fixed Vanes

Above Yes Yes 25

Below No No 26

Below No No 27

Above Yes Yes 28

Above Yes Yes 29

Below No No 30

Below No No 31

Above Yes No 32

Below No No 33

Above No No 34

34

Fig. 5.1 - Radial distances of the measurements (mm).

Biodiesel composition can be seen in table 4.1 and NG composition in table 5.3.

Table 5.3 - NG properties (taken from Pereira [8]).

CH4 (vol%) 92.40

C2H6 (vol%) 4.95

N2 (vol%) 0.10

C3H8 (vol%) 1.96

C4H10 (vol%) 0.52

C5H14 (vol%) 0.01

CO2 (vol%) 0.05

LHV (MJ/Nm³) 38.78

5.2 – Flame stabilization

The present section poses a small approach on flame behaviour and stabilization based on

the work of Queirós [1], Ribeirete [34] and Coelho and Costa [20]. Due to the position of the burner

and the geometry of the top of the combustion chamber two recirculation zones appear. An internal

recirculation zone (IRZ) generated by the air swirl and an external recirculation zone (ERZ) originated

by the separation in the flow at the quarl’s exit due to the sudden expansion. In the ERZ the gases

concentrations are similar to those of the exhaust further downstream. The IRZ stability increases with

increasing swirl speed. It also promotes a better mixture of the reactants which reduces the flame

length. Since the liquid fuel is injected directly into the IRZ it is important to keep it stable to maintain

35

the reaction. The hot gases in the IRZ play an important role helping the evaporation and burning of

the fuel. The momentum of the injected fuel is important as it may destroy the IRZ if its value is too

high. This breakup is particularly important when using air assisted atomization because of the

atomizing air jet. If the secondary air swirl isn’t enough to stabilize the flame it may blow out or

become too long. The next figures were taken and adapted from the mentioned works. Ribeireite [34]

discussed three possible trajectories (A, B and C) for the injected particles depending on their injection

speed for pulverized coal. An additional trajectory, D, was added for the atomizers with higher injection

angles.

Fig. 5.2 - Recirculation zones inside the furnace according to Ribeirete [33] (left) and for general burners with swirl from Coelho and Costa [20] (right).

5.3 – Temperature results

This section presents and evaluates the temperature profiles. There is a similar behaviour in

each section, above and below the tube caps. The tests are numbered in their chronological order so,

as a first remark, it is important to say that the very first test has no reliable results since it is the one

with more fluctuations and no other tests had such unstable results. This is possibly due to fluctuations

in operating conditions that were carefully checked for the later tests during the measurements.

Fig. 5.3 presents the results for test 1 to 7. In tests 2, 3, 4 and 6 the temperature distribution is

fairly the same with tests 5, 6 and 7 showing slightly lower temperatures near the furnace walls due to

the fact that only biodiesel was used and it was injected in an inner diameter relatively to the NG, also

the power was lower. In test 5 the overall lower temperatures result from the higher combustion air

flow rate (7.8% of exhaust O2) whereas the exact opposite is verified in test 7 where there is 3.0% of

O2. It is also important to notice that tests 5, 6 and 7 were conducted with lower power because only

biodiesel was used and the maximum flow rate was limited due to pressure requisites.

36

Fig. 5.3 - Temperature variation with radial distance. Tests 1 to 7 (full swirl and pressure atomization, below the tube tops) (left); impact of excess air (right).

From these results it can be seen that the co-combustion of NG with biodiesel has not a big

impact on temperature distribution below the tube caps by changing the relation NG/Biodiesel, with

these thermal inputs. Also there are no big changes in temperature because a good mixture of the

gases is obtained below the tube caps. Still, in all the measurements made below using pressure

atomization the temperature values are a little higher from 50 to 150 mm because of the small

aperture due to the position of the reformer simulator as can be seen in Fig. 5.1 and the temperature

distributions in the upper section.

Fig. 5.4 presents the results from tests 8 to 14. The total power for each test is close to 80 kW.

There is a clear distinction between the temperature distribution above (dashed lines) and below the

tube caps, obviously due to the presence of the flame and the recirculation zones. In tests 8, 9, 10 and

11 only the NG/Biodiesel relation was altered (decreased) maintaining the excess air. For test 9, with

a biodiesel flow rate of 2 kg/h, which means 34% of the nozzle’s nominal flow rate, the temperatures

observed were much lower than for other cases although with a comparable profile shape. This

situation was already mentioned in the previous chapter and was confirmed in combustion tests: due

to the low flow rate the droplet sizes increase considerably and these are not burned within the short

residence time. This also has great impact on CO concentration in the exhaust gas which changed

from an average of 25 ppm (in the previous tests also with 5.0% O2) to 550 ppm. Furthermore, with

this test condition, flames randomly appeared on the cement caps, this was the unburned biodiesel

burning in contact with the tube caps at high temperatures. Regarding the remaining tests it can be

noted that test 12 has conditions similar to those of test 2 but with less power. The fact that it has a

higher temperature is due to the lower oxygen in the exhaust (5.0% vs 5.4%) and the higher

temperature of the inner walls of segment 2 (841 ºC vs 807 ºC). For test 13, the increase in

temperature comes from the oxygen decrease, 2.9%, and finally the same happens with test 14. So, it

can be said that the comparable conditions are 11/12 with 14/13 (only the excess air was decreased)

and 8, 9, 10 and 11 where there is an increase in biodiesel proportion with fixed value of

approximately 5% in the exhaust O2.

800

900

1000

1100

1200

1300

1400

1500

1600

-50 0 50 100 150 200 250

Tem

pera

ture

(ºC

)

Radial distance (mm)

Test number 1234567

800

900

1000

1100

1200

1300

1400

1500

1600

-50 0 50 100 150 200 250Radial distance (mm)

5 - NG=0; BD=6.6; O2=7.8

6 - NG=0; BD=6.7; O2=5.1

7 - NG=0; BD=6.8; O2=3.0

37

Fig. 5.4 - Temperature variation with radial distance. Tests 8 to 14 (full swirl and pressure atomization, tests 12 and 13 below the tube tops) (left); variation of biodiesel flow rate (right).

Fig. 5.5 presents the results for tests 15 to 24. The tests were carried out with the lower swirl

number and higher thermal input. It can be seen that the temperature peak is radially displaced

outwards, possibly due to the less intense swirl and the values are in general higher due to the higher

thermal input. For this thermal input and the lower biodiesel flow rates (3 kg/h) in tests 23 and 24,

despite the worst atomization, the larger temperature ensures a complete combustion. As in previous

tests, the greater increase with O2 differences is noticeable farther from the centre. This is evidenced

comparing test 15 (5.0%) with 17 (2.5%) and test 21 (5.0%) with 20 (3.1%). The impact of the

NG/Biodiesel relation above the tube caps is clear when comparing tests 15, 21 and 24, all with a

fixed value of approximately 5% in the exhaust O2 (Fig. 5.5 (right)). With decreasing NG/Biodiesel

(increase of biodiesel proportion) values (15, 24, 21) there is an increase in temperature near the

centre due to centralized injection of the biodiesel. This has to do with the fact that higher biodiesel

flow rates yield smaller droplets improving combustion. For test 20, compared to 21, the temperatures

follow the expected relation with exhaust O2, a general increase although at the centre the values

observed in test 21 are higher possibly due to a small modification in the velocity field.

Even though there was not a pronounced change bellow the tube caps with the NG/Biodiesel

relation for lower powers a trend similar to that which happens above is also seen below in these

tests. This is clear evaluating tests 16, 23 and 22, a general increase of temperature with a decrease

in NG/Biodiesel fraction. In tests 18 and 19 this also happens. Their even higher temperatures are due

to the decrease in the excess air. The temperature below the tube caps is higher with 130 kW and

may have to be limited for the final application increasing excess air.

800

900

1000

1100

1200

1300

1400

1500

1600

-50 0 50 100 150 200 250

Tem

pera

ture

(ºC

)

Radial distance (mm)

Test number 891011121314

800

900

1000

1100

1200

1300

1400

1500

1600

-50 0 50 100 150 200 250Radial distance (mm)

8 - NG=7.6; BD=0; O2=5.0

9 - NG=5.6; BD=2.0; O2=5.4

10 - NG=3.6; BD=4.0; O2=5.1

11 - NG=1.8; BD=6.1; O2=5.0

38

Fig. 5.5 - Temperature variation with radial distance. Tests 15 to 24 (swirler half way and pressure atomization, tests 16, 18, 19, 22 and 23 below the tube tops) (left); variation of biodiesel flow rate

(right).

Fig. 5.6 presents the results for tests 25 to 34. These tests were carried out with air assisted

atomization. It is important to refer that it was extremely difficult (ultimately impossible) to exactly

centre the flame using this burner. The main problem is related with the fact that the guide vanes that

promote the air swirl have some space between them and the quarl thus generating an unbalanced

secondary air distribution. Regardless of this problem it was possible to see that the flame behaviour

was good enough to make a similar analysis as that of the previous tests. The main differences are

obvious below the tube caps where the decentralization is more noticeable. Instead of having the

temperature peak in the 50 to 150 mm range as before, it is seen from tests 26, 27, 30, 31 and 33

(tests below the tube caps) that the higher temperatures are between 150 and 225 mm. The only

differences are on tests 30 and 31 where the highest temperatures are in the centre because of the

high atomizing air flow rate (6.0 kg/h) with biodiesel injection. The atomizing air jet is perfectly centred

as it is independent from the swirl blades thus its influence in the furnaces axis. The atomizing air jet in

tests 30 and 31 has a greater importance as it causes the reaction to go below the tube caps. The

temperature distributions in the upper section near the furnace’s walls show the effects of excess air

with values of tests 32 and 34 being larger due to the lower excess air. The lower values are obtained

for the case of NG combustion tests, 25 and 28. Looking at test 29 the highest temperatures are

obtained near the middle. This is due to the fact that there is biodiesel and 6.0 kg/h of atomizing air.

The lower temperatures in the outside result from the higher O2 percentage of 5.3%. Comparing this

situation with that of test 32, where there is a reduction of exhaust O2 from 5.3% to 3.3%, the

temperatures in the ERZ increase whereas in the IRZ they decrease, possibly due to lower intensity of

the IRZ that results from the lower velocities of the secondary air.

An option for the nominal operating conditions of the final burner would be to keep the

atomizing air flow rate even without biodiesel being injected, situation verified in tests 25 and 28 which

differ only in atomizing air flow rate (2.6 kg/h vs 0 kg/h). The atomizing air also promotes the reaction

occurring in the IRZ by providing more oxygen. It can be seen that in the only case where no

atomizing air was used (test 28) a strong recirculation should be present with high temperature at a

950

1050

1150

1250

1350

1450

1550

1650

1750

1850

-50 0 50 100 150 200 250

Tem

pera

ture

(ºC

)

Radial distance (mm)

Test number 15161718192021222324

950

1050

1150

1250

1350

1450

1550

1650

1750

1850

-50 0 50 100 150 200 250Radial distance (mm)

15 - NG=12.3; BD=0; O2=5.01621 - NG=6.3; BD=6.0; O2=5.0222324 - NG=9.3; BD=3.0; O2=5.1

39

distance close to 100 mm. When atomizing air is used the combustion reaction is more distributed.

The impact of the atomizing air can be seen in Fig. 5.6 (right). With increasing atomizing air flow rate

(28, 25, 34 and 32) there is also an increase in the temperatures near the centre and a similar,

although less intense, behaviour near the wall. It should be noted that for tests 32 and 34 there is also

biodiesel being injected although the importance of atomizing air can be seen when there isn’t.

The secondary air flow rate has more impact on the exhaust O2 than the atomizing air because

of its high relative flow rate, typically more than 10 times higher (in test 29, for instance, there is a

secondary air flow rate of 124.7 kg/h.

Fig. 5.6 - Temperature variation with radial distance. Tests 25 to 34 (air assisted atomization, tests 26, 27, 30, 31 and 33 below the tube tops) (left); atomizing air influence (right).

5.4 – Gas species concentration results

5.4.1 – Behaviour of HC, CO, CO2 and O2

This section is dedicated to the gas species study that was performed measuring radial

profiles above the tube caps. The discussion regarding NOx is presented afterwards. It starts by

describing the typical distribution verified in this type of flames having in mind the shape of the flame

shown in Fig. 5.2. In the IRZ it is typical to have low O2 values and eventually higher values of HC and

CO due to recirculation and fuel ignition. In the ERZ the gas concentration values are fairly

homogeneous and similar to those of the exhaust which is verified due to the recirculation of the gases

outside the main combustion zone.

Figs. 5.7, 5.8, 5.9 and 5.10 present the results for tests 15, 17, 21 and 20, respectively. These

tests were conducted with pressure atomization and 129.5 kW.

800

900

1000

1100

1200

1300

1400

1500

1600

0 50 100 150 200 250

Tem

pera

ture

(ºC

)

Radial distance (mm)

Test number 25262728293031323334

800

900

1000

1100

1200

1300

1400

1500

1600

0 50 100 150 200 250Radial distance (mm)

25 - NG=7.9; BD=0; AA=2.6

28 - NG=7.9; BD=0; AA=032 - NG=4.4; BD=3.0; AA=6.034 - NG=3.9; BD=3.0; AA=4.0

40

Figures 5.7 and 5.8 present the results for tests 15 and 17 that were carried out with NG only

and 4.8% and 2.5% of exhaust O2, respectively. For these cases, the measured profiles enter the IRZ,

which is longer with the lower swirl number, showing large values of HC and CO with higher values in

test 17 as the global excess air is lower. However, in the IRZ, the O2 levels, in test 17 compared to 15,

are higher like those of HC and CO. This may be a consequence of poor mixture when compared with

test 15 which has a bigger recirculation zone due to higher inlet velocities of the secondary air [20].

Near 150 mm we enter the ERZ where the mixture composition is similar to that of the exhaust

(appendix B).

Fig. 5.7 - Test 15: 12.3 m³/h of NG; 0 kg/h of biodiesel; 129.5 kW thermal input and 4.8% of exhaust O2.

Fig. 5.8 - Test 17: 12.3 m³/h of NG; 0 kg/h of biodiesel; 129.5 kW thermal input and 2.5% of exhaust O2.

Figs. 5.9 and 5.10 present the results for tests 21 and 20, respectively. In these tests there is

also biodiesel injection. Again, reducing the excess air, results in an overall O2 decrease. For this

reason the values of HC and CO increase in the IRZ. This is also complemented by an increase in

CO2 and temperature confirming that there is a better combustion in the IRZ, also promoted by the

oxygen content of the biodiesel.

1358 1398

1053

0102030405060708090100

0123456789

10111213

0 25 50 75 100 125 150 175 200

HC

and N

Ox (

dry

volu

me

ppm

)

O2, C

O2 a

nd C

O (

dry

volu

me %

)

Radial distance (mm)

O2 (%)

CO2 (%)

CO (%)

HC/10 (ppm)

NOx (ppm)

T ºC

1336 1365

1095

0102030405060708090100

0123456789

10111213

0 25 50 75 100 125 150 175 200

HC

and N

Ox

(dry

volu

me

ppm

)

O2, C

O2 a

nd C

O (

dry

volu

me %

)

Radial distance (mm)

O2 (%)

CO2 (%)

CO (%)

HC/100(ppm)

NOx (ppm)

T ºC

41

Fig. 5.9 - Test 21: 6.3 m³/h of NG; 6.0 kg/h of biodiesel; 129.3 kW thermal input and 5.0% of exhaust O2.

Fig. 5.10 - Test 20: 6.3 m³/h of NG; 6.0 kg/h of biodiesel; 129.3 kW thermal input and 3.1% of exhaust O2.

Figs. 5.11, 5.12 present the results obtained with air assisted atomization for tests 25 and 28,

respectively. The same trends of HC and CO of test 15 are verified in test 25 farther from the furnace’s

axis confirming the fact that the flame is not exactly centred. The higher O2 values in the centre of the

furnace, for test 25, are influenced by the atomizing air and the asymmetry of the flame while in test 28

they depend only on the second. In test 28 there was problem with the HC analyser rendering it

useless during this test, hence the value 0. The test was not repeated due to the availability of

biodiesel in the reservoir for the other test conditions and the logistics required to refill it, however, the

other results are discussed. As it has been said in the previous section, the lack of atomizing air in the

centre promotes a higher temperature peak, at 100 mm, this higher temperature may promote the

conversion of CO into CO2 yielding the peaks noticeable in the CO2 and O2 curves.

1427 1459

1081

0102030405060708090100

0123456789

10111213

0 25 50 75 100 125 150 175 200

HC

and N

Ox (

dry

volu

me

ppm

)

O2, C

O2 a

nd C

O (

dry

volu

me %

)

Radial distance (mm)

O2 (%)

CO2 (%)

CO (%)

HC (ppm)

NOx (ppm)

T ºC

1408 1446

1129

0

10

20

30

40

50

60

70

80

90

100

0123456789

10111213

0 25 50 75 100 125 150 175 200

HC

and N

Ox (

dry

volu

me

ppm

)

O2, C

O2 a

nd C

O (

dry

volu

me %

)

Radial distance (mm)

O2 (%)

CO2 (%)

CO (%)

HC/10 (ppm)

NOx (ppm)

T ºC

42

Fig. 5.11 - Test 25: 7.9 m³/h of NG; 0 kg/h of biodiesel; 83.7 kW thermal input, 4.7% of exhaust O2 and 2.6 kg/h of atomizing air.

Fig. 5.12 - Test 28: 7.9 m³/h of NG; 0 kg/h of biodiesel; 83.7 kW thermal input, 4.7% of exhaust O2 and 0 kg/h of atomizing air.

Figs. 5.13 and 5.14 present the results obtained with air assisted atomization for tests 29 and

32, respectively. These tests were carried out with 5.3% and 3.3% of exhaust O2, respectively. The

influence of excess air is clear and the fact that this time there is biodiesel, a reduction of the O2 value

near the furnace’s axis is noticeable. The more intense peak in the O2 curves results from the

secondary air flow paths and the more pronounced changes near the outer wall suggest a reduction of

the ERZ. As it has already been seen in temperature profiles the flow structure is modified. The

increased atomizing air flow rate may lead to a jet type flame that is longer than the previous ones.

This is the reason why the peaks in HC curves and CO, for test 32, are close to the centre where there

is a richer mixture.

1116 1230

921

0102030405060708090100

0123456789

10111213

0 25 50 75 100 125 150 175 200

HC

and N

Ox (

dry

volu

me

ppm

)

O2, C

O2 a

nd C

O (

dry

volu

me %

)

Radial distance (mm)

O2 (%)

CO2 (%)

CO (%)

HC/100(ppm)

NOx (ppm)

T ºC

1053

1376

924

0102030405060708090100

0123456789

10111213

0 25 50 75 100 125 150 175 200

HC

and N

Ox (

dry

volu

me

ppm

)

O2,

CO

2 a

nd C

O (

dry

volu

me %

)

Radial distance (mm)

O2 (%)

CO2 (%)

CO (%)

HC (ppm)

NOx (ppm)

T ºC

43

Fig. 5.13 - Test 29: 4.4 m³/h of NG; 3.0 kg/h of biodiesel; 78.2 kW thermal input, 5.3% of exhaust O2 and 6.0 kg/h of atomizing air.

Fig. 5.14 - Test 32: 4.4 m³/h of NG; 3.0 kg/h of biodiesel; 78.2 kW thermal input, 3.3% of exhaust O2 and 6.0 kg/h of atomizing air.

5.4.2 – NO formation

The NOx curves follow the same trend along all tests and have this shape due to the

mechanisms of NO formation. In [20] these mechanisms are explained. It is important to say that there

are no definite rules to define the relative importance of each mechanism in a given combustion

system as they depend on many parameters such as the geometry of the burner and combustion

chamber, the fuels used, type of flame (pre-mixed or diffusion) and operating conditions of the

equipment, among others [20]. Nevertheless, due to each mechanism’s requisites a fair assumption

can be made to which are the important ones.

The fuel mechanism can be ignored since there is no bond nitrogen in the fuels’ composition

so that the potential sources of NO in the present conditions are the prompt and thermal mechanism.

Owing to the temperatures measured and considering the precision of the measurements it is likely

that the NO extracted was formed on a position closer to the furnace top with higher temperatures

evidencing the thermal mechanism. The prompt mechanism involves HC reactions with molecular

1322

972

0

10

20

30

40

50

60

70

80

90

100

0123456789

10111213

0 25 50 75 100 125 150 175 200

HC

and N

Ox (

dry

volu

me

ppm

)

O2, C

O2 a

nd C

O (

dry

volu

me %

)

Radial distance (mm)

O2 (%)

CO2 (%)

CO (%)

HC/10 (ppm)

NOx (ppm)

T ºC

1187 1220

1022

0

10

20

30

40

50

60

70

80

90

100

0123456789

10111213

0 25 50 75 100 125 150 175 200

HC

and N

Ox (

dry

volu

me

ppm

)

O2, C

O2 a

nd C

O (

dry

volu

me %

)

Radial distance (mm)

O2 (%)

CO2 (%)

CO (%)

HC/10 (ppm)

NOx (ppm)

T ºC

44

nitrogen (N2, available from the combustion air) that generate cyanide compounds which in turn are

converted into intermediate compounds that potentiate the formation of NO. This is the dominant

mechanism in turbulent diffusion flames [20]. With these principles present the prompt mechanism

may be important looking at the results: the higher values of NOx are in general accompanied by a

higher HC concentration close by.

Comparing tests 15 and 17 (Figs. 5.7 and 5.8, respectively) with 21 and 20 (Figs. 5.9 and

5.10) the higher values of NOx in the latter may result from the increased availability of HC and O (fuel

bond) in the centre as there is biodiesel being injected and the higher temperatures. In test 25 (Fig.

5.11) a similar trend to that of test 15 (Fig. 5.7) is verified but when compared with test 28 (Fig. 5.12)

the NOx curve has a peak at 100 mm. There is also a temperature peak leading to the thermal

mechanism.

Comparing the values of pressure atomization with those of air assisted atomization there is a

difference in the absolute values of NOx (higher with pressure atomization). This difference may be

due to the higher thermal power (130 kW vs 80 kW) which yields higher temperatures increasing the

importance of the thermal mechanism in those tests.

By looking at Fig. 5.15, it can be seen that the results obtained with air assisted atomization

with high atomizing air flow rate are in accordance with the predicted distributions for gas species

concentration in jet type flames suggesting that the IRZ is destroyed with high values of atomizing air.

Although this is an idealized situation and this particular image refers to laminar diffusion flames, the

trends of the curves from the results are not that different. Tests 17, 29 and 32 have a similar

behaviour looking at the gas species concentrations at X. The same happens in general for the

temperature distributions above the tube caps.

Fig. 5.15 - Theoretical temperature and reactants distribution in diffusion flames [20].

45

5.5 – Energy balances

This section presents the last results of the combustion tests. There is no relation between the

heat loss for the outside and what happens inside the furnace besides the thermal input as long as the

flames are similar. To obtain these results an energy balance was made to the cooling water using for

inlet temperature 20 ºC. For water specific heat, c, an averaged value of 4180 J/kgK was used. The

“Top top” refers to the furnaces top section sealing whereas the “top side” refers to the lateral walls of

the same section. The higher value in ring 5 (see figure 2.7 for rings numbering) is due to the fact that

this is the first ring with no refractory cement in the inner wall. Tests 16, 19, 21, 23 and 24 correspond

to the, approximately, 130 kW thermal input. The reason the heat loss increases until test 21 is

because the conditions weren’t yet at their nominal stage, the inner walls were still heating up.

Table 5.4 - Energy balances to the cooling water.

Test 10

Test 12

Test 16

Test 19

Test 21

Ring Q

(kW)

Ring Q

(kW)

Ring Q

(kW)

Ring Q

(kW)

Ring Q

(kW)

Top top 1.6

Top top 1.6

Top top 1.7

Top top 1.6

Top top 2.2

top side 1.8

top side 1.8

top side 1.9

top side 1.8

top side 2.3

1 3.7

1 3.7

1 4.1

1 5.7

1 5.9

2 4.9

2 5.5

2 4.9

2 6.4

2 7.0

3 3.4

3 3.4

3 4.7

3 5.0

3 5.3

4 3.3

4 3.3

4 4.3

4 3.2

4 3.5

5 9.0

5 9.0

5 12.6

5 17.3

5 18.7

6 2.6

6 2.6

6 3.0

6 4.4

6 5.2

7 3.9

7 3.9

7 4.6

7 5.3

7 5.3

8 2.6

8 2.6

8 3.7

8 4.1

8 4.6

TOTAL 36.9

TOTAL 37.5

TOTAL 45.6

TOTAL 54.8

TOTAL 59.9

Test 23

Test 24

Test 25

Test 28

Test 29

Ring Q

(kW)

Ring Q

(kW)

Ring Q

(kW)

Ring Q

(kW)

Ring Q

(kW)

Top top 2.2

Top top 2.2

Top top 1.1

Top top 1.6

Top top 1.4

top side 2.3

top side 2.3

top side 1.4

top side 1.9

top side 2.2

1 5.9

1 5.9

1 3.7

1 4.2

1 4.5

2 7.0

2 7.0

2 4.3

2 5.0

2 5.3

3 5.3

3 5.3

3 4.8

3 5.5

3 6.1

4 3.5

4 3.5

4 3.9

4 4.6

4 4.7

5 18.7

5 18.7

5 9.1

5 9.5

5 10.2

6 5.0

6 5.0

6 2.3

6 2.6

6 11.5

7 5.3

7 5.3

7 3.1

7 3.7

7 3.8

8 4.6

8 4.6

8 2.5

8 2.6

8 2.6

TOTAL 59.7

TOTAL 59.7

TOTAL 36.1

TOTAL 41.1

TOTAL 52.1

46

47

6 – Closure

6.1 – Conclusions

The main objective of this work was the development of a dual-fuel burner to work with liquid

and gaseous fuels either alone or in co-combustion. The study was divided in two main investigations:

non-reactive spray characterization with two different types of atomization, pressure and air assisted,

and combustion performance with both kinds of atomization mentioned.

The main conclusions that can be drawn about pressure atomization are as follows:

1 - The variation of mass flow rate with injection pressure is approximately linear so, either

mass flow rate or pressure differential, can be used as the governing parameter.

2 - The main breakup of the bulk liquid into a spray occurs before 20 mm even for low flow

rate sprays having the lowest results been obtained 50 mm away from the nozzle.

3 - Increasing the liquids temperature decreases its viscosity. This fact is fairly important in this

kind of atomization as it promotes lower SMD values for the same pressures. Still the gain is not good

enough to use low flow rates where the spray deteriorates regardless of the temperature.

4 - There is no intense variation of SMD values across the radial position although there is a

small increase in particles diameter when moving outwards.

5 - By changing the geometrical parameters of the nozzles (angle and spray pattern) no great

differences are noticeable in the SMD behaviour.

6 - The apparatus to use this kind of atomization is relatively simple as only a small pump is

needed to feed the fuel.

7 - The main drawback is the limitation to a narrower range of flow rates near the nozzle’s

nominal value (at least 75% of the mass flow rate is required to achieve recommended values of SMD,

below 40 µm). In fact, if the values are too low, there is a huge impact in combustion: flames appear

randomly around the combustion chamber, temperature decreases and the CO levels go up in the

exhaust.

Regarding air assisted atomization:

1 - The main parameter controlling the SMD is the atomizing air mass flow rate for the range

of liquid flow rates used. The SMD behaviour is only dependent on the liquids flow rate when these

values are too low and the atomizing air flow rate is lower than 4.0 kg/h.

2 - After 6.0 kg/h the changes in SMD values are marginal discarding the need to use flow

rates above this value.

For the studied atomizers empirical correlations were found for SMD prediction (Equations (1),

(2) and (3)). These correlations are based on already existing correlations that account for the liquids’

properties. They work well with the present data in the range desired (atomizing air with flow rates

above 4 kg/h).

About combustion using the burner with pressure atomization it can be said that:

48

1 - The temperature distribution below the tube caps suffers no big fluctuations having a

somewhat homogeneous profile decreasing a little near the outer rims.

2 - Above the tube caps the temperatures are significantly higher in the flame zone and similar

to those below out of it, in the ERZ.

3 - Poor atomization yields lower temperatures and high CO formation.

4 - Decreasing the NG/Biodiesel relation maintaining the power yields slightly higher

temperatures.

5 - For a decrease in secondary air flow rate there is an increase in CO and HC formation

either injecting biodiesel or not, though with biodiesel these values are greatly reduced but an increase

in NO is verified.

6 - The mechanisms responsible for NO formation are most likely the thermal mechanism and

the prompt mechanism which depends mostly on unburned HC and molecular nitrogen present in

combustion air.

Using the burner with air assisted atomization:

1 - For the temperature profiles there is a strong dependence on the atomizing air flow rate.

Even without biodiesel, increasing the availability of air in the centre also promotes a temperature

increase as the reactions get favoured. Adding biodiesel increases the temperature even further.

2 - The gas species profiles are similar to those obtained with pressure atomization with more

O2 in the centre when using atomizing air without biodiesel. Adding the biodiesel the HC and CO

values increase in the centre of the furnace.

3 - Values of O2 too low and high atomizing air flow rates make the flame longer enabling it to

go beneath the tube tops which is unacceptable for this work.

Finally, as general remarks applicable to basically all cases, the higher the power input and/or

the lower the values of exhaust O2 the higher the temperatures. With both temperature and gas

species profiles the position of the flame can be identified.

With the energy balances made to the cooling water, the knowledge of where and how much

power is lost is obtained. The heat losses that occur in the furnace trough the walls are comparable

with those required for the reforming reaction.

Dual-fuel burner

With all the data collected in this work the decisions regarding the final burner can be made.

Due to the fact that a wide range of biodiesel flow rates will be required the air assisted atomization

should be used as it allows for a wider range of liquid flow rates. The atomizing air should have a fixed

value between 4.0 and 6.0 kg/h as lower values will reduce the quality of atomization thus reducing

combustion efficiency and increasing pollutants emissions, and values above 6.0 kg/h may be too high

as they “push” the flame downwards making the reactions occur until bellow the tube caps destroying

the IRZ. To avoid this problem higher swirl numbers must be attained for lower air velocities. There

49

are no special remarks concerning the NG/Biodiesel ratio as the temperatures suffer no major

variation radially, bellow the tube caps.

6.2 – Future work

To obtain more detailed values regarding biodiesel atomization with the air assisted technique

tests should be carried out with a proper extraction system as the current available apparatus makes

this analysis impossible.

Creating a hybrid atomizer with both pressure and air assisted atomization would be

interesting. Such an atomizer would probably promote better atomization with low liquid flow rates and

avoid the problem of narrow angles [8] inherent to air assisted atomization.

Testing liquids with different properties would be interesting to assess the SMD and study the

validity of the correlations presented.

For combustion, tests with a swirler in the middle of the burner tube should have an outer tube

protection to guide the air and avoid bypass effects between the swirler and the outlet tube.

Tests with a reformer simulator like that of the reformer module should be tried to assess the

importance of the aerodynamics of the chamber in the temperature distribution below the tube caps.

A broader range of temperature and gas assessment locations should be analysed to better

understand which the most important mechanisms in pollutants formation are.

50

51

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54

55

Appendix A

56

Pressure atomization burner, nozzle detail

Air assisted burner, swirler detail

57

Appendix B

Test 1

Test 2

Test 4

Test 5

O2 (%) 5

O2 (%) 5.4

O2 (%) 5.4

O2 (%) 7.8

CO2 (%) 8.1

CO2 (%) 9.6

CO2 (%) 8.5

CO2 (%) 8.9

CO (ppm) 20

CO (ppm) 20

CO (ppm) 25

CO (ppm) 21

1st Ring Temp. (ºC) 720

1st Ring Temp. (ºC) 760

2nd Ring Temp. (ºC) 807

2nd Ring Temp. (ºC) 814

3rd Ring Temp. (ºC) 522

3rd Ring Temp. (ºC) 542

4th Ring Temp. (ºC) 396

4th Ring Temp. (ºC) 416

Test 8

Test 9

Test 10

O2 (%) 5

O2 (%) 5.4

O2 (%) 5.1

CO2 (%) 8.8

CO2 (%)

CO2 (%) 10.1

CO (ppm) 3.3

CO (ppm) 550

CO (ppm) 25

NOx (ppm) 43

NOx (ppm) 5

NOx (ppm) 52

1st Ring Temp. (ºC) 690

1st Ring Temp. (ºC) 701

1st Ring Temp. (ºC) 719

2nd Ring Temp. (ºC) 779

2nd Ring Temp. (ºC) 784

2nd Ring Temp. (ºC) 798

3rd Ring Temp. (ºC) 491

3rd Ring Temp. (ºC) 507

3rd Ring Temp. (ºC) 517

4th Ring Temp. (ºC) 253

4th Ring Temp. (ºC) 252

4th Ring Temp. (ºC) 250

Test 11

Test 12

Test 13

O2 (%) 5

O2 (%) 5

O2 (%) 2.9

CO2 (%) 11

CO2 (%) 11

CO2 (%) 12.3

CO (ppm) 24

CO (ppm) 22

CO (ppm) 39

NOx (ppm) 64

NOx (ppm) 64

NOx (ppm) 67

1st Ring Temp. (ºC) 756

1st Ring Temp. (ºC) 767

1st Ring Temp. (ºC) 796

2nd Ring Temp. (ºC) 832

2nd Ring Temp. (ºC) 841

2nd Ring Temp. (ºC) 863

3rd Ring Temp. (ºC) 535

3rd Ring Temp. (ºC) 540

3rd Ring Temp. (ºC) 550

4th Ring Temp. (ºC) 241

4th Ring Temp. (ºC) 239

4th Ring Temp. (ºC) 234

Test 14

Test 15

Test 16

O2 (%) 3

O2 (%) 5

O2 (%) 4.8

CO2 (%) 12

CO2 (%) 9.1

CO2 (%) 8.9

CO (ppm) 22

CO (ppm) 16

CO (ppm) 35

NOx (ppm) 78

NOx (ppm) 48

NOx (ppm) 48

1st Ring Temp. (ºC) 801

1st Ring Temp. (ºC) 820

1st Ring Temp. (ºC) 833

2nd Ring Temp. (ºC) 867

2nd Ring Temp. (ºC) 862

2nd Ring Temp. (ºC) 875

3rd Ring Temp. (ºC) 552

3rd Ring Temp. (ºC) 529

3rd Ring Temp. (ºC) 544

4th Ring Temp. (ºC) 234

4th Ring Temp. (ºC) 235

4th Ring Temp. (ºC) 254

58

Test 17

Test 18

Test 19

O2 (%) 2.5

O2 (%) 2.5

O2 (%) 3.1

CO2 (%) 11

CO2 (%) 11

CO2 (%) 11.7

CO (ppm) 43

CO (ppm) 43

CO (ppm) 33

NOx (ppm) 52

NOx (ppm) 52

NOx (ppm) 72

1st Ring Temp. (ºC) 893

1st Ring Temp. (ºC) 911

1st Ring Temp. (ºC) 961

2nd Ring Temp. (ºC) 935

2nd Ring Temp. (ºC) 947

2nd Ring Temp. (ºC) 954

3rd Ring Temp. (ºC) 617

3rd Ring Temp. (ºC) 631

3rd Ring Temp. (ºC) 658

4th Ring Temp. (ºC) 407

4th Ring Temp. (ºC) 438

4th Ring Temp. (ºC) 521

Test 20

Test 21

Test 22

O2 (%) 3.1

O2 (%) 5

O2 (%) 5

CO2 (%) 11

CO2 (%) 10

CO2 (%) 10.1

CO (ppm) 35

CO (ppm) 29

CO (ppm) 29

NOx (ppm) 72

NOx (ppm) 64

NOx (ppm) 64

1st Ring Temp. (ºC) 973

1st Ring Temp. (ºC) 968

1st Ring Temp. (ºC) 968

2nd Ring Temp. (ºC) 966

2nd Ring Temp. (ºC) 968

2nd Ring Temp. (ºC) 968

3rd Ring Temp. (ºC) 677

3rd Ring Temp. (ºC) 701

3rd Ring Temp. (ºC) 701

4th Ring Temp. (ºC) 549

4th Ring Temp. (ºC) 589

4th Ring Temp. (ºC) 589

Test 23

Test 24

Test 25

O2 (%) 5.1

O2 (%) 5.1

O2 (%) 4.7

CO2 (%) 9

CO2 (%) 9

CO2 (%) 9.5

CO (ppm) 28

CO (ppm) 28

CO (ppm) 19

NOx (ppm) 56

NOx (ppm) 56

NOx (ppm) 28

1st Ring Temp. (ºC) 975

1st Ring Temp. (ºC) 975

1st Ring Temp. (ºC) 779

2nd Ring Temp. (ºC) 966

2nd Ring Temp. (ºC) 966

2nd Ring Temp. (ºC) 804

3rd Ring Temp. (ºC) 716

3rd Ring Temp. (ºC) 716

3rd Ring Temp. (ºC) 418

4th Ring Temp. (ºC) 612

4th Ring Temp. (ºC) 612

4th Ring Temp. (ºC) 147

Test 26

Test 27

Test 28

O2 (%) 5

O2 (%) 4.8

O2 (%) 4.7

CO2 (%) 9.5

CO2 (%) 9.5

CO2 (%) 9.5

CO (ppm) 19

CO (ppm) 19

CO (ppm) 19

NOx (ppm) 28

NOx (ppm) 28

NOx (ppm) 28

1st Ring Temp. (ºC) 813

1st Ring Temp. (ºC) 813

1st Ring Temp. (ºC) 826

2nd Ring Temp. (ºC) 837

2nd Ring Temp. (ºC) 837

2nd Ring Temp. (ºC) 848

3rd Ring Temp. (ºC) 444

3rd Ring Temp. (ºC) 444

3rd Ring Temp. (ºC) 451

4th Ring Temp. (ºC) 159

4th Ring Temp. (ºC) 159

4th Ring Temp. (ºC) 161

59

Test 29

Test 30

Test 31

O2 (%) 5.3

O2 (%) 5.3

O2 (%) 3.3

CO2 (%) 11

CO2 (%) 11

CO2 (%) 11.6

CO (ppm) 17

CO (ppm) 17

CO (ppm) 22

NOx (ppm) 28

NOx (ppm) 28

NOx (ppm) 28

1st Ring Temp. (ºC) 845

1st Ring Temp. (ºC) 845

1st Ring Temp. (ºC) 865

2nd Ring Temp. (ºC) 862

2nd Ring Temp. (ºC) 862

2nd Ring Temp. (ºC) 871

3rd Ring Temp. (ºC) 465

3rd Ring Temp. (ºC) 465

3rd Ring Temp. (ºC) 467

4th Ring Temp. (ºC) 166

4th Ring Temp. (ºC) 166

4th Ring Temp. (ºC) 164

Test 32

Test 33

Test 34

O2 (%) 3.3

O2 (%) 3.3

O2 (%) 3.3

CO2 (%) 12

CO2 (%) 9.5

CO2 (%) 9.5

CO (ppm) 22

CO (ppm) 19

CO (ppm) 19

NOx (ppm) 28

NOx (ppm) 5

NOx (ppm) 5

1st Ring Temp. (ºC) 885

1st Ring Temp. (ºC) 775

1st Ring Temp. (ºC) 778

2nd Ring Temp. (ºC) 890

2nd Ring Temp. (ºC) 772

2nd Ring Temp. (ºC) 774

3rd Ring Temp. (ºC) 477

3rd Ring Temp. (ºC) 340

3rd Ring Temp. (ºC) 341

4th Ring Temp. (ºC) 174

4th Ring Temp. (ºC) 136

4th Ring Temp. (ºC) 138