iii

PULSE COMBUSTION STUDIES OF PROPANE AND NATURAL GAS

MIXTURES

MOHD HAFFIS BIN UJIR

A thesis submitted in fulfillment of the

requirements for the award of the degree of

Master of Engineering (Mechanical)

Faculty of Mechanical Engineering

Universiti Teknologi Malaysia

JULY 2009

v

To mak, abah, my siblings,

my nephews and niece, pikah, yaya, ami

Thanks for your support

vi

ACKNOWLEDGMENT

Alhamdulillah, thank to Allah S.W.T and our prophet Muhammad S.A.W.

I would like to express my deepest gratitude to my supervisor, Dr, Mazlan

Abdul Wahid for his invaluable supervision, advise, guidance, encouragement and

assistance.

Many thanks to all technicians at Combustion Laboratory, Thermodynamic

Laboratory, lathe and milling workshop, Vibration Laboratory and metal fabrication

workshop for their assistance, guidance and kindness.

The discussion with, perspectives, suggestions and opinions of Mr Mohsin

Mohd Sies, Mr Mohd Shukri Ramli, Mr Abdul Halim Abdul Rahman, Mr Rosli

Ismail, Mr Khalid Saqr, Mr Mohammad Akmal Bahrain and Dr Henry Nasution have

enlightened my insight throughtout the duration of this research. I am deeply

thankful to all of them.

My sincere appreciation also goes to my family, my friends and those who

have devoted every precious hour and their leisure time, either directly or indirectly

for their support and cooperation during the course of this project.

vii

ABSTRACT

The phenomenon of pulse combustion of hydrocarbon-oxygen mixtures was

investigated experimentally. An experimental rig that consists of a stainless steel

tube with inner diameter of 100mm and length of 1700mm, data acquisition system,

ignition control unit and filling system was built in order to measure the

characteristics of pulse combustion such as, pressure, velocity and impulse. Three

equivalence ratios of fuel-oxidizer; 0.75, 1 and 1.25 were chosen to investigate the

effect of fuel concentration on the pulse combustion wave propagation. It was found

that combustion of high fuel concentration mixture propagates as a detonation wave

while for low fuel concentration mixture; the combustion wave propagates as

deflagration wave. Two types of hydrocarbon fuels were used, i.e, propane and

natural gas with 92.7% methane. Results showed that natural gas is not sensitive to

detonation propagation compared to propane. It was found that in smooth inner wall

tube, combustion wave propagates as a detonation wave if the percent of dilution gas

is not more than 35% and it is a function of the equivalence ratio. In order to

accelerate the combustion wave into detonation wave within 0.5m of the tube, array

of obstacles with identical blockage ratio was placed inside the tube, near to the

ignition source. It was observed that the obstacle enhances the transition process

within the given length. The ignition source was set at three energy levels, i.e., 25mJ,

5J and 100J. The chosen level of ignition energy did not affect the combustion wave

propagation in a smooth inner wall tube but in a rough inner wall tube, it improved

the generated impulse force. Impulse measurement using an accelerometer was made

to measure the impulse produced by the combustion wave. Generally, the detonation

wave produces larger impulse force as compared to deflagration wave.

viii

ABSTRAK

Fenomena pembakaran denyut telah diselidik secara ujikaji. Rig ujikaji yang

terdiri daripada tiub besi tahan karat dengan garis pusat dalam 100mm dan 1700mm

panjang, sistem pengumpulan data, unit kawalan nyalaan dan sistem pengisian telah

dibina untuk tujuan mengukur ciri pembakaran denyut seperti tekanan, halaju

rambatan dan denyut dorongan. Tiga nisbah campuran bahan api-pengoksida, 075, 1

dan 1,25, telah dipilih untuk menkaji kesan kepekatan bahan api terhadap rambatan

gelombang pembakaran denyut. Didapati bahawa pembakaran bagi campuran bahan

api berkepekatan tinggi merambat secara detonasi manakala campuran bahan api

berkepekatan rendah merambat secara deflagrasi. Dua jenis bahan api fosil telah

digunakan iaitu propana dan gas asli yang mengandungi 92.7% metana. Keputusan

menunjukkan bahawa gas asli tidak sensitif terhadap rambatan detonasi berbanding

propana. Didapati, di dalam tiub tanpa halangan, gelombang pembakaran terambat

secara detonasi jika peratusan gas pencair tidak melebihi 35% dan bergantung

kepada nisbah campuran bahan api. Untuk memecutkan gelombang pembakaran

dalam jarak 0.5 m tiub tersebut, susunan halangan dengan nisbah halangan yang

sama telah ditempatkan di dalamnya berhampiran dengan sumber nyalaan. Ia telah

diperhatikan bahawa halangan tersebut membantu proses pertukaran dalam jarak

yang diberikan. Sumber nyalaan telah ditetapkan pada tiga peringkat tenaga iaitu

25mJ, 5J dan 100J. Nyalaan dengan tahap yang telah dipilih tidak memberi kesan

yang nyata terhadap gelombang pembakaran di dalam tiub tanpa halangan tetapi

membantu dalam tiub berhalangan dengan menambahbaik denyut dorongan yang

terjana. Pengukuran denyut dorongan menggunakan pengukur pecutan telah

dilakukan untuk mengukur denyut dorongan yang dihasilkan oleh gelombang

pembakaran. Secara amnya, gelombang detonasi menghasilkan denyut dorongan

yang besar berbanding gelombang deflagrasi.

ix

TABLE OF CONTENTS

CHAPTER TOPICS PAGE

DECLARATION ii

TITLE PAGE iii

DECLARATION OF ORIGINALITY AND

EXCLUSIVENESS iv

DEDICATION v

ACKNOWLEDGEMENT vi

ABSTRACT vii

ABSTRAK viii

TABLE OF CONTENTS ix-xi

LIST OF TABLES xii

LIST OF FIGURES xiii – xv

LIST OF SYMBOLS xvi-xvii

LIST OF APPENDIXES xviii

CHAPTER 1 INTRODUCTION

1.1 Introduction 1-2

1.2 Combustion 2 - 6

1.3 Problem statement 6 - 8

1.4 Research Objectives 9

1.5 Research Scopes 9

CHAPTER 2 LITERATURE REVIEW

2.1 Pulse combustion 10 - 11

x

2.2 Steady 1-D Inviscid Flow Analysis 11 – 15

2.2.1 Rayleigh Relation 15 – 16

2.2.2 Hugoniot Relation 16 – 19

2.3 Chapman-Jouguet Detonation Condition 19

2.3.1 Chapman-Jouguet Detonation

Velocity 20 – 22

2.4 Detonation Front Structure 22 – 23

2.4.1 Detonation front transverse wave 23 – 25

2.5 Detonation Initiation 26

2.5.1 Direct Initiation 26

2.5.2 Flame Acceleration and Deflagration

to Detonation Transition (DDT) Phenomenon 27 – 29

2.6 Impulse of Pulse Detonation 29 – 32

2.7 Literature Review Summary 32 – 33

CHAPTER 3 EXPERIMENTAL APPARATUS AND

PROCEDURE

3.1 Overview of Experimental Setup 34

3.2 Single Pulse Detonation Tube 35

3.3 Filing Apparatus 35 – 36

3.3.1 Vacuum Service 37

3.4 Ignition System 37 - 39

3.5 Data Acquisition Setup 39 - 42

3.5.1 Post Processing Signal 42 – 43

3.5.2 Velocity Measurement 44

3.6 Impulse Measurement 44 – 45

3.7 Cell Width Measurement 46

3.8 Obstacle Configuration 47 - 48

3.9 Experimental Mixtures and Condition of

Initial Set Up 49

CHAPTER 4 RESULT AND DISCUSSION

4.1 Experimental Mixture 50

xi

4.2 Pulse Combustion Wave Propagation 51 – 55

4.2.1 DDT between PT1 and PT2 56 – 60

4.2.2 Effect of Ignition Energy on Pulse

Combustion Wave 60 – 62

4.3 Effect of Obstacle on Pulse Combustion

Wave Propagation 63 – 68

4.4 Cell Width (λ) Criterion of Pulse

Combustion Wave 69 – 71

4.5 Impulse Measurement 72

4.5.1 Impulse Determination from

Acceleration Measurement 72 – 74

4.5.2 Resultant Impulse Force by the Pulse

Combustion Wave 74 - 76

CHAPTER 5 CONCLUSION AND RECOMMENDATION

5.1 Conclusion 77 – 78

5.2 Recommendation 78

REFERENCES 79 – 83

APPENDICES 84 – 111

xii

LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 Properties of normal shock, detonation and deflagration 11

3.1 Sensitivity of transducers 42

3.2 Experimental configuration 49

4.1 Comparison value of pendulum and acceleration impulse 74

xiii

LIST OF FIGURES

Num. TITLE PAGE

1.1 Fossil fuel reserves-to-production (R/P) ratios at end 2006 2

1.2 Steady state combustion 3

1.3 Rankine-Hugoniot curve with limiting Rayleigh lines 3

1.4 Valved pulse combustor 4

1.5 Temperature versus entropy for brayton, humprey and

detonation cycle

5

1.6 Specific Impulse versus Mach number for propulsion engines 6

2.1 Detonation wave front 12

2.2 Control-volume for detonation analysis 13

2.3 Rayleigh line 16

2.4 The Hugoniot curve 17

2.5 Interaction of Rayleigh line and Hugoniot curve 18

2.6 Development of detonation mach stem cell 24

2.7 Soot trace of mach stem cell structure of 2H2

+ 02 + 3Ar at Po = 7.7kPa

24

2.8 Cell width 25

2.9 Geometries definition of obstacle-filled tube 28

2.10 Impulse measurement using pendulum arrangement 30

2.11 Typical pressure history diagram on the trust wall 30

xiv

2.12 Space-time diagram for detonation wave propagation 32

3.1 Detonation tube 34

3.2 Plumbing schematic 36

3.3 Capacitors arrangement 38

3.4 Spark ignition circuit diagram 39

3.5 Sensors and DAQ connection 40

3.6 LabView data acquisition platform 41

3.7 Post processing Labview Platform 43

3.8 Pendulum tube arrangement 45

3.9 Soot film arrangement 46

3.10 Array of obstacles 48

4.1 Pressure signal for deflagration, detonation and DDT cases 52

4.2 Pulse combustion wave velocity of propane /natural gas +

oxygen at various percentage of nitrogen dilution in an

unobstructed channel

53

4.3 Pressure of combustion wave at PT1 and PT2, Configuration

T1, 25mJ ignition energy

55

4.4 Pressure signals for the location of occurrence of DDT 56

4.5 Multiple pressure spikes at the combustion wave front 57

4.6 Illustration of developing and developed detonation fronts 57

4.7 Closed wall pressure trace for detonation, deflagration and

DDT cases, Configuration T1

58

4.8 Distance (x)- time (t) diagram of propagating combustion wave 59

4.9 Combustion wave velocity for 3 level of ignition energy;

Configuration T1

61

4.10 Combustion wave velocity for 3 level of igntion energy for

propane and natural gas mixture at 35 and 50% of nitrogen

dilution

62

4.11 Velocity of combustion wave for 3 length of obstacles for

propane and natural gas at 35 and 50% of nitrogen dilution

64

4.12 Propagation velocity of pulse combustion wave in obstructed

channel

65

4.13 Combustion wave propagation pressure in an obstructed 66

xv

channel

4.14 Pressure profile of deflagration wave in obstructed channel;

C3H8 + 5O2 + 9.28N2, Configuration T4

67

4.15 Time of arrival at PT1and PT3 after ignition, (Ø=1, N2 = 35%) 68

4.16 Cell width of detonation wave 69

4.17 Cell width of successfully detonated mixtures 70

4.18 Transition to detonation trace on soot foil for natural gas-

oxygen with 10% nitrogen dilution, Configuration T1

71

4.19 Peak acceleration measured by the accelerometer 72

4.20 Time profile of the magnitude of a typical impact force 73

4.21 Specific impulse of combustion wave propagate in unobstructed

channel

75

4.22 Specific impulse of combustion propagation within obstructed

channel at 3 level ignition energy, 65% N2,Ø =1

76

xvi

LIST OF SYMBOLS

Ø - Equivalence ratio

D - Tube’s internal diameter (m)

d - blocakge passable diameter (m)

νx,i - Velocity (m/s)

Xi - Species’ mole fraction

Yi - Species’ mass fraction

P - Pressure (Pa)

ρ - Density (kg/m3)

MW - Molecular weight (kg/kmol)

m - Mass flow rate (kg/s)

m - Mass flux (kg/s-m2)

Ma - Mach number

MCJ - Chapman-Jouguet Mach number

c - speed of sound (m/s)

q - Heat addition (J/kg)

R - Specific gas constant (J/kg-K)

Ru - Universal gas constant (J/kmol-K)

ref - Reference state

νD - Detonation velocity (m/s)

CJ - Chapman-Jouguet point

Cv - Constant-volume specific heat (J/kmol)

Cp - Constant-pressure specific heat (J/kmol)

γ - Specific heat ratio (Cp / Cv)

υ - Specific volume (m3/kg)

atm - Atmospheric pressure

xvii

h - enthalpy (J/kg)

λ - Detonation cell width (mm)

Ec - Direct ignition energy (J)

S - Obstacle spacing (m)

I - Impulse (Ns)

Isp - Specific impulse (s)

m - tube weight

Scw - Closed wall area

A - Tube cross section area (m2)

g - Gravititional acceleration (m/s2)

∆x - Horizontal deflection

V - Tube volume (m3)

CNG - Compressed natural gas

AC - Alternating current

DC - Direct current

MS/s - Megasample per second

xviii

LIST OF APPENDIXES

APPENDIX TITLE PAGE

A Tube strength calculation 84

B Partial pressure filling technique 85 – 89

C Experimental and calculation data 89 – 94

D Soot-film trace of detonation transverse

wave

95 – 100

E List of equipments 101

F Image of experimental rig 102– 107

G Experimental procedure 108 - 111

1

CHAPTER 1

INTRODUCTION

1.1 Introduction

Combustion is a process where fuel and oxidizer will chemically react upon the

presence of ignition to produce heat and sometimes light that is useful for mankind.

The use of combustion in heat generation process started since the first time man

discovered fire. From a simple wood stove to a complex turbine engine, men have

discovered a wide range of combustion application but where fuel and oxidizer are

always required. Between the two, the amount of fuel available is finite and its

supply is decreasing by time. As shown in Figure 1.1, British Petroleum predicted

based on their survey that the fossil fuel reserve to production ratio for the world is

less than 100 years where 41.6 years for oil, 60.3 years for natural gas and 133 years

for coal [1]. In the survey, Malaysia energy production in 2007 was 60.2 billion of

cubic meters of natural gas and 33.8 million tones of oil [1]. The survey also shows

that hydrocarbon reserved in Malaysia at the end of 2007 was 0.7 billion tonnes of

oil and 2.48 trillion cubic meters of natural gas. By keeping this trend, the source of

hydrocarbon in Malaysia will exhaust in 19.4 years for oil and 40.9 years for natural

gas. Therefore concerted efforts are very much required not only to search for

alternative energy but also to find method that able to combust and convert these

fuels efficiently and effectively.

2

Figure 1.1: Fossil fuel reserves-to-production (R/P) ratios at end of 2007 [1]

1.2 Combustion

Combustion process can occur either in steady or unsteady (pulsating) manner.

In steady state combustion, combustion zone or called flame is stationary and fuel-

oxidizer is flowing toward the reaction zone either premixed or nonpremixed

(diffusion) such as shown in Figure 1.2. In steady state mode, the combustion

process is controlled by the flowrate of fuel and air (oxidizer). In pulsating

combustion, reaction process occurs at an interval of time either the fuel-oxidizer is

flowing toward the flame or stationary just before the reaction take place. In most of

pulse combustion device, fuel is premixed with oxidizer.

OECD Former Soviet Union EMEs excl. Former Soviet Union World

Oil

Natural gas Coal

500

400

300

200

100

0

3

a) Premixed flame b) Diffusion flame

Figure 1.2: Steady state combustion [2]

Combustion wave propagate either at low speed (deflagration) or high speed

(detonation) propagation velocity. The general property that differentiates between

deflagration and detonation is its propagation velocity. In deflagration mode of

propagation, the combustion wave propagates at subsonic speed whereas in

detonation mode of propagation, the combustion wave propagates at supersonic

speed. Figure 1.3 shows the region of deflagration and detonation in Rankine-

Hugoniot curve.

Figure 1.3: Rankine-Hugoniot curve with limiting Rayleigh lines. [5]

Flame

4

Deflagration mode of pulsating combustion occurs in pulse combustor. Figure

1.4 shows the example of pulse combustor. The nature of this device is depending on

its geometry. The important aspect that needs to be considered in developing a pulse

combustor is to identify its proper geometry so it can be self-sustained. A pulse

combustor operates based on one of the three principles; 1) Schmidt tube, 2)

Helmholtz resonator and 3) Rijke tube. Most of the pulse combustors today were

designed based on the principle of Helmholtz resonator [6]. The pulse combustor can

be divided into 2 categories; valved and valveless. The valved pulse combustor is

easy to design but it cannot be operated continuously over a long period of time due

to fatigue failure of the valve cause by ram pressure. On the other hand, valveless

pulse combustor can be operated over a long period of time since it does not depend

on the movement of the valve but it is difficult to be designed since one need to

understand the pulsating flow of gas. The interest of pulse combustor (deflagration)

as a propulsion system declined in late 50’s due to the emergence of gas turbine

engines. Nowadays, the interest of pulse combustor is more for on-land applications

such as boiler, dryer and heat generator [7].

Figure 1.4: Pulse combustor [6]

The advantage of pulsating combustion is that the reaction occurs either self-

sustaining or controlled and consumes just enough amount of fuel to react and

pulsate. A study on pulse combustion by Mazlan et. al [3] shows that in an operating

helmholtz pulse combustor with operating frequency equal to 125Hz, the air-fuel

equivalence ratio was below 1. Therefore, in pulsating combustion, there is less or no

excess fuel. Since the resident time of each cycle of the pulse combustion is short,

NOx production during the combustion process is low. It was reported by Sonodyne

Inc. [4] that a pulse combustor produce only 20-70mg/m3 nitrogen concentration

compared to a steady state burner that produce 100-7000 mg/m3 nitrogen

5

concentration with the same amount of fuel consumption. Furthermore, the burning

efficiency of their combustor was about 90-99% while for the steady state was about

80-86%.

Device that applies detonation combustion process is still being investigated

and most of the researches are aiming for a detonation-based propulsion system

[5,8,9,11-14,33,42-44]. Detonation process offer several advantages for a propulsion

system such as more compact system and highly efficient combustion process due to

rapid energy conversion [8]. Although the studies on detonation phenomenon started

earlier than that of gas turbine, the interest of applying detonation in propulsion

system was started only in the early 90’s [9]. Before this, the studies on detonation

were performed mainly on the hazardous prevention purpose. Due to its high energy

conversion process, detonation has been recently considered for propulsion. In fact,

according to Wildon et. al.[10], 20 m2 square detonation may produce power that

equal to the power the earth receives from the sun [10]. Compared to a conventional

propulsion system that applies constant pressure combustion process (Brayton cycle),

detonation process is closer to constant-volume process (Humprey cycle) which offer

more efficient energy conversion process [11]. Figure 1.5 shows the comparison

among Brayton, Humprey and detonation cycle.

Figure 1.5: Temperature versus entropy for brayton, humprey and detonation

cycle [11]

6

By applying constant-volume process, a propulsion system could save up to 7%

of fuel consumption compared to conventional gas turbine [12]. In addition, since

compression of air is not required, pulse detonation engine has fewer components

thus allows it to produce higher specific impulse at all Mach number compare to

other propulsion engines [13]. The comparison of pulse detonation engine to other

types of propulsion system is shown in Figure 1.6.

Figure 1.6: Specific Impulse versus Mach number for propulsion engines [13]

1.3 Problem Statement

In combustion process where hydrocarbon fuel reacts with air as the oxidizer,

the flame may propagate at a few meters per second depending on the type of fuel.

Air is known as the common oxidizer in combustion process. In the combustion

process, air is known to comprise of 21% oxygen and 79% nitrogen. Even though the

7

nitrogen may react with the oxygen during the combustion process and produce NOx,

it is considered as diluent species in the process. By decreasing the amount of

nitrogen, the combustion rate can be increased due to shorter route of combustion

process thus increasing the released energy. At some point where the percent of

oxygen is high enough and the characteristics of geometry meet the required

specification, detonation mode of combustion wave propagation can be produced.

In a fuel-oxidizer mixture where the oxidizer contains 100% oxygen,

detonation propagation can be initiated with a small amount of ignition energy.

Increasing diluent gas such as nitrogen in the mixture will decrease the possibility of

detonation to be initiated. In a fuel-air mixture, the method of direct ignition energy

that is required to initiate detonation is more than 1kJ which is not practical to be

used in a transportation system [14]. Multiple point spark ignition had been proven

to assist combustion wave to propagate as detonation wave [29-31]. The detail study

on the effect of variable single point spark ignition energy on pulse combustion is

still lacking. Not only via high ignition energy, detonation propagation also can be

generated using a deflagration to detonation transition technique. This technique

requires some set up of internal configuration within the flame propagation channel.

Different types of fuel require different type of configuration. Some fuel requires a

few meters of obstacle set up to create DDT. To apply this kind of pulse combustion

in a propulsion system, the length of DDT should be shortened. This research is

focused on the possibility of shortening the length of DDT in pulse combustion

process of hydrocarbon fuel in low amount of oxygen addition via combination of

configuration of obstacle assisted by high ignition energy (below critical detonation

ignition energy).

This work is an experimental study aimed at understanding the single pulse

combustion phenomenon especially the case for detonation propagation of

combustion wave. The experiments are conducted using detonation tube that is

closed at one end, open at the other and are filled with reactive mixture that is

combusted by means of spark generated by a system with variable ignition energy.

Since a pulse detonation engine applies intermittent combustion process, impulse

generation from single pulse detonation tube is an important aspect to determine the

efficiency of the PDE. The conventional method to measure the impulse is to use

8

pendulum arrangement of pulse detonation experimental rig. Using this method, one

requires a larger space of experimental area to allow the tube to swing due to the

generated detonation wave. Even though the pendulum arrangement is the cheapest

method to measure the impulse, it only measure the maximum impulse force based

on the maximum deflection of the tube. The use of accelerometer to determine the

impulse generated from the combustor is an interesting method to be explored. There

has been no existing study in the literature that applies accelerometer to measure

impulse. By using an accelerometer, analysis on impulse generated by pulse

detonation wave can be done in detail. Since the propagation of detonation wave

produces several reflected wave (wave that travel back to the thrust wall) that is the

source of impulse force, the use of accelerometer allow researchers to differentiate

the impulse force generated by the reflected wave due to transmitted detonation wave

into atmosphere with the generated impulse force cause by the other reflected wave.

Along with the aim to study the potential of applying detonation in a propulsion

system, the result from this research also can be used to prevent hazardous accident

from occurring. As the use of gas-type fuel in transportation is increasing, study on

combustion propagation of gas fuel is required. One of the hydrocarbon fuel used in

this research is natural gas which is being used a gas fuel in transportation ad power

generation. Since the natural gas is delivered through a link of pipeline, accidentally

combusted natural gas may propagate along the pipeline. The combustion wave of

natural gas may transit to detonation due to the presence of valve gate that act as

obstacle. Since detonation wave propagate at supersonic speed and produce high

propagation pressure, the accident could cause damage in several places that are

connected with the link of pipeline. Even though there was no specific incident

reported in Malaysia, accidents that occur in other countries should be a lesson to

prevent hazardous accident. For example, Ukraine gas pipe line that transporting

Russian gas to Europe had hit by a explosion in May 2007 [58]. The blast damaged

30m of pipe line. Even though the explosion did not cause any casualties, it cause

uneasy situation between Ukraine and Russia. Another example of explosion of fuel

pipe line was in Nigeria [59]. The accident that occurred in May 2006 cause

casualties between 150 and 200 people. Thus, investigation on how the combustion

wave of natural gas can be transited to detonation is required so that prevention of

the transition can be done.

9

1.4 Research Objectives

This study is about propagation of single pulse combustion wave in an

obstructed channel. The objective of this study is mainly:

1) To investigate the effect of diluent composition and elevated ignition

energy on the pulse combustion process of hydrocarbon-oxygen mixture

toward detonation propagation.

2) To measure the generated impulse using an accelerometer.

1.5 Research Scope

This work involves primarily experiments on single pulse detonation

combustion and will concentrate only on gaseous hydrocarbon fuel which is propane

and natural gas of 97.2% methane. The reactive mixtures of hydrocarbon-oxygen

will be diluted with nitrogen gas at various proportions. In order to conduct series of

experiments, a complete experimental rig will be constructed. The study comprise of

the development of single pulse detonation experimental rig which comprise of:

a. Combustor section with various types of obstacles

b. Partial pressure filling system

c. Ignition system with variable ignition energy