st

tiondiesto thh isas be futanriodimu

ergy eumptiowithel. Biosuch ae throerin is

and low volatility cause durability problems in fuel systems [2,3,5].Various processes convert biomass to diesel fuels. Among these

is transesterication of triglycerides, which produces esters. Theresulting fuel ts into the denition of biodiesel. Other processesinclude hydrothermal processing, hydroprocessing, and indirectliquefaction. These processes yield distillates that are not esters.

rst published as a fuel in shock tube experiments [12], followedby another article about diesel engine burning this fuel [11] andit has been then used in a dual fuel engine [10]. Another articlehas been also published from the same laboratory [13]. Jojoba oilcomes from very promising plant that lives for more than one hun-dred and fty years and has unique properties. This is due to manyfactors [13] such as its high contents of oil per seed, its moleculescontains a carbon chain of 2022 carbon atoms and its chemicalstability. The plant itself is very promising for cultivation in hotweather as it resists salinity and dryness. It gives acceptable

* Tel.: +971 504494723; fax: +971 37623158.

Energy Conversion and Management 50 (2009) 17811788

Contents lists availab

n

lseE-mail address: mohamed.selim@uaeu.ac.aeesters derived from the fat or oil. The methyl ester product is whatis known as biodiesel and must meet the standards set forth by theAmerican Society of Testing and Materials (ASTM) for fuel gradebiodiesel, specically ASTM D6751 (or EN14214 in Europe) [2].

Technically, any hydrocarbon distillate material derived frombiomass that meets the appropriate ASTM specication can be de-ned as diesel, or as biodiesel. Feedstocks for diesel fuels derivedfrom biomass include soybean [3], rape seed [46], and wastecooking oils, along with animal fats [7]. Vegetable oils can be useddirectly as diesel fuels, but their properties such as high viscosity

is a byproduct.Use of biodiesel can also result in some reduction in fuel econ-

omy depending on the blend due to biodiesels slightly lower en-ergy content. The primary concern is one of quality assurance.While many people can produce biodiesel, the production of bio-diesel that meets the ASTM standard is more difcult. As the per-centage of biodiesel in the blend increases, the sensitivity toquality of the biodiesel increases proportionately [8,9].

Of the several biodeisel sources that started to appear in the lit-erature by the current author is Jojoba oils [1012]. It appears to be1. Introduction

In addition to diesels inherent enable fuels can reduce petroleum conssel drivers have the option to ll updomestically produced renewable fufrom a variety of biomass sourcesfat, and cooking oil. Biodiesel is madcalled transesterication, where glyc0196-8904/$ - see front matter 2009 Elsevier Ltd. Adoi:10.1016/j.enconman.2009.03.012fciency, use of renew-n even further [1]. Die-blends of biodiesel adiesel fuels are deriveds vegetable oil, animalugh a chemical processseparated from methyl

Biodiesel is dened as the mono alkyl esters of long-carbon-chain fatty acids derived from renewable lipid feedstocks. It is pro-duced by transesterication of triglycerides (fatty acids) containedin oil-rich biomass and animal fats. The triglycerides can be con-verted to esters that have properties more compatible with petro-leum diesel fuel. In the base-catalyzed transesterication process,the triglycerides are reacted with an alcohol, either methanol orethanol, in the presence of an alkaline catalyst, normally potassiumhydroxide. This reaction forms methyl or ethyl esters, and glycerinViscosityPerformance both approaches are scrutinized.

2009 Elsevier Ltd. All rights reserved.Reducing the viscosity of Jojoba Methyl Eengine performance and roughness

Mohamed Y.E. Selim *

Mech. Eng. Dept., UAE University, Al-Ain, Abu Dhabi 17555, United Arab Emirates

a r t i c l e i n f o

Article history:Received 23 October 2007Received in revised form 8 August 2008Accepted 14 March 2009Available online 16 April 2009

Keywords:Jojoba Methyl Ester (JME)Diesel engine

a b s t r a c t

An experimental investigaJojoba Methyl Ester (JME)50 and 70 C as comparedadding one chemical whicEther (DEE). The viscosity ha diesel engine using thoswith the engine speed consature, the ignition delay peeffective pressure and max

Energy Conversio

journal homepage: www.ell rights reserved.er diesel fuel and effects on diesel

has been carried out to test two approaches to reduce the viscosity of theel fuel. The rst approach is the heating of the fuel to two temperatures ofe base ambient temperature and to diesel fuel too. The second approach isconsidered by its own as alternative and renewable fuel which is Diethyleen reduced by both methods to close to diesel values. The performance ofels has been tested in a variable compression research engine Ricardo E6t at 1200 rpm. The measured parameters included the exhaust gas temper-, the maximum pressure rise rate, maximum pressure, and indicated meanm heat release rate. The engine performance is presented and the effects of

le at ScienceDirect

and Management

vier .com/ locate /enconman

production per acre and is currently used for cosmetics applica-tions. The properties of Jojoba Methyl Ester (JME) are unique aswill be shown later. However, so far only the viscosity needs tobe reduced so that it will be accepted by fuel properties standards,hence it should be reduced from more than 19 cSt. to lower than7 cSt. All previous publications about this fuel were for high viscos-ity version and no work has been reported about the long term ef-fects of the high fuel viscosity. The current high viscosity affectsnegatively the injection, atomization and mixing process of the fuel

System. Two data acquisition systems are used to collect theimportant data and store it in a personal computer for ofine anal-ysis. The following parameters are fed into the computer: cylinderpressure, crank angle degrees, liquid fuel ow rate data, enginespeed and torque, and air/oil/coolant/oil/exhaust temperatures. Acomputer program in lMACBASIC language is written to collectthe data and manage the system and a workstation operating sys-tem has been used to run the program.

The pressure signal is fed into a charge amplier then to a dataacquisition card linked to the personal computer and the crank an-gle signal is fed into a degree marker shape channel and the outputis fed into the acquisition card. The acquisition card could collectdata at the rate of 250 kHz. The pressure and crank angle dataare stored in the computer disk for further analysis. A MS Excelcomputer program is written to nd the pressure rise rate, com-bustion maximum pressure of the cycle, ignition delay, the heat re-lease and the indicated mean effective pressure data at all cyclepoints from mid compression stroke to mid expansion stroke.The maximum value of pressure rise rate is obtained and recorded.This value will be used to represent the combustion noise level at

1782 M.Y.E. Selim / Energy Conversion and Management 50 (2009) 17811788with air.Atomization is the breakup of bulk liquid jets into small drop-

lets by using an atomizer. Adequate atomization enhances mixingand complete combustion in a direct injection (DI) engine andtherefore is an important factor in engine emission and efciency.According to Lefebvre [14], the physical properties of a liquid fuelthat affect its atomization in a diesel engine are viscosity, density,and surface tension. For a DI diesel injector at xed operating con-dition, use of fuel with higher viscosity delays atomization by sup-pressing the instabilities required for the fuel jet to breakup. Anincrease in fuel density adversely affects atomization, whereashigher fuel surface tension opposes the formation of droplets fromthe liquid fuel [14]. Hence a suitable diesel fuel in a DI engine re-quires balanced values of viscosity, density, and surface tension,for a given atomizer to function properly.

Therefore the objectives of the present work are to reduce theviscosity of the Jojoba Methyl Ester so that its properties will beacceptable by fuel properties standards and it is acceptable as agood fuel for diesel engines. The reduction of viscosity will be car-ried out by different approaches to match the required viscositiesfor diesel fuels. Two approaches are used here of heating the JMEfuel to different temperatures and the second is by adding verylow viscosity renewable fuel to the JME. The effect of using thenew reduced-viscosity fuel on a real diesel engine will also bepresented.

2. Experimental engine test RIG

The research engine used in the present study is the Ricardo E6single cylinder variable compression indirect injection diesel en-gine. The specications of the engine are listed in Table 1. The en-gine cylinder head has a Ricardo Comet Mk V compression swirlcombustion chamber. This type of combustion system consists oftwo parts. The swirl chamber in the head has a top half of sphericalform and the lower half is a truncated cone, which communicateswith the cylinder by means of a narrow passage or throat. The sec-ond part consists of special cavities cut into the crown of thepiston.

The engine is loaded by an electrical dynamometer rated at22 kW and 420 V. The engine is fully equipped for measurementsof all operating parameters and noise data. The pressure time his-tory is measured by a water-cooled piezo-electric pressure trans-ducer and crankshaft degree angle sensor connected to therelevant ampliers. The liquid fuel ow rate is measured digitallyby a multi-function microprocessor-based fuel system, Compuow

Table 1Engine specications.

Model Ricardo E6

Type IDI with the pre-combustion chamberBore stroke (mm) 76.2 111.1 1 cylinderCycle 4-strokeCompression ratio Variable, max. 22Maximum power (kW) 9, naturally aspirated

Maximum speed (rpm) 3000Injection timing Variable, 20 to 45 BTDCthat operating condition. The typical combustion pressure historymay be seen in Fig. 1 with the corresponding pressure rise rate.The maximum combustion pressure has also been calculated forthe all operating conditions. Another program has been writtento calculate the heat release rate [1517] during the combustionprocess and the maximum value only has been presented here.The ignition delay period has been also calculated from the startof injection to the onset of pressure deviation from the motoringpressure values; Fig. 2. Experiments have been carried out afterrunning the engine for some time until it reaches steady stateand oil temperature is at 60 5 C, and cooling water temperatureis at 60 5 C.

Data are presented as exhaust gas temperature, ignition delayperiod, maximum pressure rise rate (dP/dh)max, maximum pressure(Pmax), maximum heat release rate (HRRmax), and indicated meaneffective pressure (imep) for the following operating parameters:

a. The brake mean effective pressure (bmep) and it is variedfrom 50 to 450 kPa.

b. The liquid fuel inlet temperature to the pump and it is variedat 25, 50 and 70 C.

c. The DEE concentration (viscosity reduction additive) and itis varied at 5%, 10%, and 15% of the JME mass used.

-40 -20 0 20 400

20

40

60

Pres

sure

, bar

-4

-2

0

2

4

(dP/

d)m

ax, b

ar/d

eg.

JME + 15% DEELoad=16.7 Nm

Combustion pressurePressure rise rateCrank angle, degrees ATDC

Fig. 1. Typical pressure and pressure rise rate for the diesel engine.

has been placed inside the fuel injection pump to measure the tem-perature of liquid fuel inside the pump tray. Three temperatureshave been tested here which are the atmospheric temperature of25 C, 50 C, and 70 C. The temperatures of 50 and 70 C are easilyachieved by the water cooling system in the vehicle. The fuel isheated here by passing it through an electric heater compartmentconnected to the fuel line.

The second method of reducing the viscosity of the JME is bymixing it with a very low viscosity renewable fuel which is theDiethyl Ether (DEE). The viscosity of DEE is about 0.23 cSt at40 C compared to 19.2 cSt for JME. The DEE has been selectedon purpose for its favorable features. It has a renewable origin, out-standing cetane number, reasonable energy density, very low vis-cosity [18,19]. It is also a liquid at ambient conditions. Table 2shows the properties of DEE as compared to JME fuel. Three differ-ent blends have been tested here which are: 5%, 10%, and 15% DEEwith JME. The results of both approaches are illustrated in Fig. 3.

3. Results and discussion

3.1. Viscosity reduction

The effects of adding DEE to JME as well as heating up the JMEto reduce its viscosity are shown in Fig. 3. The viscosity of the useddiesel oil is given also for reference. The JME has been heated from25 C (atmospheric conditions) to 40 C, 55 C, and 70 C, and thedynamic viscosity has been measured. It may be seen from the g-ure that heating the JME from 25 to 70 C decreased its viscosityfrom about 16.6 cP to about 4.59 cP. It has been then become with-in the acceptable range for diesel engine fuels. The highest temper-

d Management 50 (2009) 17811788 1783During the experiments the following parameters have beenkept constant:

the engine speed and it is kept at 1200 rpm. the fuel injection timing and it is kept at 35 BTDC. the engine compression ratio and it is kept constant at 22.

The diesel fuel has been used also as another base for the exper-iments and it is used for comparison with the JME case at ambienttemperature.

The maximum uncertainties in the measured quantities were2% in the engine speed, 4% in the engine torque, 6% in the massof fuel, 3% in the pressure rise rate, and 0.6% in the exhausttemperature.

2.1. The viscosity of the Jojoba Methyl Ester

-40 -20 0 20 40Crank angle, degrees ATDC

0

10

20

30

40

50

60Pr

essu

re, b

arDiesel, Load=14.6 Nm

MotoringCombustion

TDCInjection

Fig. 2. Typical combustion pressure and motoring pressure for ID calculation.

M.Y.E. Selim / Energy Conversion anThe main objective of the present work is to examine differentapproaches to reduce the viscosity of the Jojoba Methyl Ester to be-come within the acceptable range for diesel engine fuels. The JMEfuel has excellent physical and chemical properties e.g. high cetanenumber (63.5), relatively high heating value (47.38 MJ/kg), accept-able pour point (4.4 C), higher than diesel ash point (61 C), low-er than diesel C/H ratio and zero sulfur content. However, the onlyproperty that needs reduction is viscosity of the oil. This oil is vis-cous by nature as the product of it is actually a wax not liquid.Therefore, its viscosity is very high relative to other oils and thisproperty is attractive to its use in cosmetics applications e.g. bodyoils etc. The transesterication process has been optimized to pro-duce the highest yield of the oil, best properties of the oil and low-est viscosity of the oil. The viscosity of the oil (JME) is now 19.2 cSt.at 40 C (16.6 cP), which is far away from the recommended valuesfor diesel engine fuels (1.67 cSt.). All methods applied here are toreduce it to the allowable range for alternative fuel suitable for die-sel engines. If the viscosity has been reduced, then it would be suit-able for diesel engines fuels.

2.2. Viscosity reduction approaches

Two methods have been tested here in the current work to re-duce the viscosity of the JME from over 19 to lower than 7 cSt.

The rst method is by direct heating of the liquid fuel just be-fore it goes to the fuel injection pump [3,5]. One thermocoupleature used (70 C) is easily achievable from the vehicle systems,e.g. the water heating system or exhaust system, etc.

Table 2Fuels properties.

Test JME DEE

Density (15 C), kg/l 0.866 0.713Kinematic viscosity at 40 C, cSt. 19.2 0.23Caloric value, MJ/kg 47.38 33.9Cetane no. 63.5 >125Carbon content % by weight 87 C2H5OC2H5Hydrogen content % by weight 13Final boiling point, C 383 34.4Auto-ignition temperature, C NA 160

0

2

4

6

8

10

12

14

16

18

Diese

l

ME@

25 oC

ME @

40 oC

ME@

55 oC

ME @

70 oC

100%

DEE

E+5%

DEE

E+10

%DEE

E+15

% DE

E

Visc

osity

, cPJ J J J JM JM JM

Fig. 3. Viscosity of JME under heating and adding DEE.

Also the effect of adding the DEE to the JME may be shown inFig. 3. The selection of the DEE is made because of its very low vis-cosity and its renewable sources. It viscosity is about 0.18 cP and itis mixed with JME at 5%, 10%, and 15%. The viscosity of the blend isshown as compared to the heating process and diesel fuel too. Itmay be seen that adding 5% DEE caused the viscosity to drop from16.6 cP to 11.3 cP. Adding 10% of DEE reduced it to 7.7 cP and 15%of DEE decreased it to 5.3 cP. Both 10% and 15% of DEE can then re-duce the viscosity of the JME to the acceptable range.

The tested methods of changing the viscosity have proven to besuccessful and reduced the viscosity of JME to acceptable range fordiesel fuels. It has been decided then that those fuels with reduced-viscosity must be tested in a real diesel engine and the effect of thedesign and operating parameters on the performance must bemade clear.

3.2. Effects on exhaust temperature

The effect of adding DEE and heating JME on the exhaust gastemperature of the diesel engine may be seen in Figs. 4 and 5

respectively. Fig. 4 shows the effect of adding DEE to the JojobaMethyl Ester at the rate of 5%, 10%, and 15% as compared to pureJME as well as diesel fuel on the exhaust gas temperature. It maybe seen from the gure that increasing the brake mean effectivepressure generally increases the exhaust temperature as the loadis increased and the amount of fuel used is increased. It may beseen also that the exhaust gas temperature is almost the samefor diesel engine using diesel fuel, JME, or using JME with 5% or10% or 15% DEE. This is at the low and high load range. Althoughthe heating value of the DEE is lower than for diesel and for JME,it is at low mixing ratio (up to 15%) and it did not change muchthe exhaust gas temperature or other cycle temperature.

Fig. 5 illustrates the effect of the load and heating the JME onthe exhaust gas temperature of the diesel engine. It may be seenfrom the gure that the exhaust gas temperatures for diesel andJME at ambient temperature of 25 C are almost the same at allloads as the JME has similar caloric value and did not changethe cycle temperatures. However, it is noticed that when JME isheated to 50 or 70 C the gas temperature is reduced slightly. Heat-ing the JME appears to cause the cycle temperatures near the end

0 100 200 300 400 500Brake mean effective pressure, kPa

100

200

300

400

500

Exha

ust t

empe

ratu

re, o

C

Effect of adding DEE on TexDiesel fuelJME - 25oCJME + 5% DEEJME + 10% DEEJME + 15% DEE

Fig. 4. Effect of adding DEE to JME exhaust gas temperature.

1784 M.Y.E. Selim / Energy Conversion and Management 50 (2009) 178117880 100 200 300 400 500100

200

300

400

500

Exha

ust t

empe

ratu

re, o

C

Effect of heating on TexDiesel fuelJME - 25oCJME - 50oCJME - 70oCBrake mean effective pressure, kPa

Fig. 5. Effect of heating the JME on exhaust gas temperature.of the expansion stroke to reduce due to the early self-ignition ofJME when heated as discussed below.

3.3. Effects on ignition delay period

The effects of adding DEE to JME and heating the JME may beseen in Figs. 6 and 7, respectively. Fig. 6 depicts the effects of add-ing DEE to JME at 5%, 10%, and 15%. It may be seen that as the loadis increased the ignition delay period is decreased for all cases. Thisis due to the higher amount of fuel injected and higher cycle tem-peratures that reduces the ignition delay period, i.e. the fuel be-comes easier to self-ignite. It may be also noticed from Fig. 6 thatthe JME has lower ignition delay period than diesel fuel as it hashigher cetane number or it is easier to self-ignite. Adding moreDEE to JME causes the ignition delay period to reduce more asthe DEE has much higher cetane number than JME and dieseland it is much easier to self-ignite so adding up to 15% of it helpsburning the JME to ignite faster once injected in the compressionstroke. Also adding more DEE caused the viscosity of JME to reduceand the JME fuel becomes more readily mixed with hot air andachieve the self-ignition temperature faster.

Fig. 7 shows the effect of heating the JME to 50 and 70 C ascompared to JME at room temperature and diesel fuel. it may be

0 100 200 300 400 5000

10

20

30

40

50

Igni

tion

Del

ay, C

A d

egre

es

Effect of adding DEE on IDDiesel fuelJMEJME + 5% DEEJME + 10% DEEJME + 15% DEEBrake mean effective pressure, kPa

Fig. 6. Effect of adding DEE to JME ignition delay period.

seen from the gure that heating the JME to 50 then 70 C causedthe ignition delay period to reduce as the viscosity becomes smal-ler and the JME fuel mixes faster and better with hot air to achievethe self-ignition temperature and self-ignite faster. The ignition de-lay period is then decreased. Therefore it is advantageous to heat itas the delay period is reduced.

3.4. Effects on maximum pressure rise rate and maximum pressure

The effects of adding DEE to JME and heating it are shown inFigs. 8 and 9, respectively. Fig. 8 depicts the effect of adding DEEat the level of 5%, 10%, and 15% to JME to the maximum pressurerise rate. The maximum pressure rise rate presents the combustionnoise which is the main source of the diesel engine noise. It may beseen from the gure that the maximum pressure rise rate generallydecreases slightly with increasing the engine load output. This maybe due to the reduction of the ignition delay period shown above.However, adding more DEE to the JME caused the maximumpressure rise rate to slightly decrease as the delay period is alsodecreased. Decreasing the ignition delay period causes the com-bustion to start faster and smoother for a smaller amount of the

0 100 200 300 400 500Brake mean effective pressure, kPa

52

56

60

64

68

Max

imum

pre

ssur

e, b

ar

Effect of heating on PmaxDiesel fuelJME - 25CJME - 50CJME - 70C

0 100 200 300 400 500Brake mean effective pressure, kPa

0

2

4

6

8

dP/d

, bar

/deg

.

Effect of heating on (dP/d )maxDiesel fuelJME - 25oCJME - 50oCJME - 70oC

Fig. 9. Effect of heating the JME on the maximum pressure rise rate.

0 100 200 300 400 500Brake mean effective pressure, kPa

0

10

20

30

40

50Ig

nitio

n D

elay

, CA

Deg

rees

Effect of heating on IDDiesel fuelJME - 25oCJME - 50oCJME - 70oC

Fig. 7. Effect of heating the JME on ignition delay period.

0 100 200 300 400 500Brake mean effective pressure, kPa

0

2

4

6

8

dP/d,

bar

/deg

.

Effect of adding DEE on (dP/d)maxDiesel fuelJME - 25CJME + 5% DEEJME + 10% DEEJME + 15% DEE

Fig. 8. Effect of adding DEE to JME the maximum pressure rise rate.

M.Y.E. Selim / Energy Conversion and Management 50 (2009) 17811788 1785Fig. 10. Effect of heating the JME on the maximum pressure.

0 100 200 300 400 500

52

56

60

64

68

Max

imum

pre

ssur

e, b

ar

Effect of adding DEE on TexDiesel fuelJME - 25CJME + 5% DEEJME + 10% DEEJME + 15% DEEBrake mean effective pressure, kPa

Fig. 11. Effect of adding DEE to JME on the maximum pressure.

injected fuel with less pressure rise rates. The effects of heating theJME to 50 and 70 C on the maximum pressure rise rate may beseen in Fig. 9. It ma y noticed that the maximum pressure for theengine using JME at 25 C is less than that for diesel fuel. However,heating the JME to higher temperatures did not change much themaximum pressure rise rate. This is considered as good enough re-sult as heating the JME already decreased the viscosity and heredid not change the combustion noise.

Figs. 10 and 11 show the effects of heating JME and adding DEEon the maximum combustion pressure of the cycle. It may be no-ticed from Fig. 10 that heating the JME to higher temperatures of50 and 70 C did not change the maximum pressure as the pressurerise rate (above) did not change. The pressure rise rate did notchange so the maximum pressure would occur at similar crank an-gles around the top dead center with the same values. Adding 5%,10% or 15% DEE to JME did not change also the maximum pressure

(a)

(b)

(c)

(e)

(d) (f)

-40 -20 0 20 40Crank angle, degrees ATDC

0

10

20

30

40

50

60

P, b

ar

DieselTorque=16.4 Nm

-40 -20 0 20 40Crank angle, degrees ATDC

0

10

20

30

40

50

60

P, b

ar

JME, ambientTorque=16.5 Nm

-40 -20 0 20 40Crank angle, degrees ATDC

0

20

40

60

P, b

ar

JME - 50oCTorque=18 Nm

-40 -20 0 20 40Crank angle, degrees ATDC

0

20

40

60

P, b

arJME - 70oCTorque=17.2 Nm

-40 -20 0 20 40Crank angle, degrees ATDC

0

20

40

60

P, b

ar

JME + 5% DEETorque=17.3 Nm

-40 -20 0 20 400

20

40

60

P, b

ar

JME + 10% DEETorque=15.7 Nm

0 de

0

0

40

60

P, b

ar

1786 M.Y.E. Selim / Energy Conversion and Management 50 (2009) 17811788-40 -20Crank angle,

2

Fig. 12. Typical pressurecrank angl20 40grees ATDC

JME + 15% DEETorque=16.7 Nm(g) e diagram for all cases studied.

as may be seen in Fig. 11 due to similar pressure rise rate shownabove.

Individual pressure-crank angle cycles are illustrated in Fig. 12for different cases of fuel temperatures and DEE concentrations atalmost similar loads. It may be noticed that all cases were almostthe same with regard to the maximum pressure, the pressure riserate, the location of the maximum pressure, and the pressure timehistory in general.

3.5. Effects on the maximum heat release rate

Figs. 13 and 14 show the effect of heating JME and adding DEEto the JME respectively. The effect of heating the Jojoba Methyl Es-ter to 50 and 70 C as compared to ambient fuel temperature of25 C may be seen in Fig. 13. It may seen that the heat release ascalculated from the pressure history in the pre-chamber decreasesas the load output increases for all cases studied. As the load is in-creased the amount of fuel and total heat release should increase,however it decreases here. It has been shown by other researchers[15] that at low loads, the overall conditions in the pre-chamberare stoichiometric, considering its relative size. At much lower

loads, combustion in the pre-chamber would proceed as usual,ignorant of what would follow in the main chamber. On the con-trary, at higher loads than this, the pre-chamber basically cannotoffer anymore heat release with duel regard to its limited availabil-ity of air but now the heat release in the main chamber increaseswith load, extending progressively deeper into the expansionphase. As the heat release rate calculated here is based only onthe measurements of the pressure history in the pre-chamber, itwould be then expected that the heat release would decrease asthe load is increased.

It can be seen also from the same gure that heating the JME tohigher temperatures if 50 and 70 C generally increases the maxi-mum value of the heat release rate as the JME fuel becomes easierto mix and react with the available oxygen in the pre-chamber. It isevident that reducing the viscosity of the JME affected positivelythe injection, atomization, and mixing processes of the fuel airmixture as more heat is released.

Fig. 14 shows the effect of adding DEE to the JME fuel on themaximum value of heat release rate. It may be noticed from the g-

0 100 200 300 400 500Brake mean effective pressure, kPa

0

20

40

60

(HR

R) m

ax, J

/deg

.

Effect of heating on (HRR)maxDiesel fuelJME, 25CJME, 50CJME, 70C

M.Y.E. Selim / Energy Conversion and Management 50 (2009) 17811788 1787Fig. 13. Effect of heating the JME on the maximum heat release rate.

0 100 200 300 400 5000

20

40

60

(HR

R) m

ax, J

/deg

.

Effect of adding DEE on HRRmaxDiesel fuelJME - 25CJME + 5% DEEJME + 10% DEEJME + 15% DEEBrake mean effective pressure,kPa

Fig. 14. Effect of adding DEE to JME on the maximum heat release rate.ure that adding the DEE to the JME has two effects. The rst effectis at low loads, which is noticeable reduction in the heat releaserate than diesel and pure JME. Adding more DEE with lower heat-ing value would then decreases the amount of heat released at lowloads than that of diesel and JME. While at the higher loads theaddition of more DEE seems to have increased the maximum valueof the heat release rate. This may be postulated to the fact that theDEE has higher cetane number than diesel or JME, then it is easierto self-ignite with its own oxygen content and gives more heat inthe pre-chamber than the diesel or JME which results in the highamount of (HRR)max.

3.6. Effects on indicated mean effective pressure

The indicated mean effective (imep) has been calculated fromthe pressure history of the whole cycle and it gives indication tothe net work produced inside the engine cylinder. Figs. 15 and16 depict the effect of heating the JME and adding DEE on the imeprespectively. Fig. 15 shows the effect of heating JME to 50 and 70 Cas compared to ambient fuel temperature of 25 C and base dieselfuel. It may be seen from the gure that the load increases is nec-essarily accompanied by an increase in the imep for all cases stud-ied as more fuel is burned and more heat is released, then more network is produced. It may be also seen from the same gure thatheating the JME generally increased the imep as more heat is

0 100 200 300 400 500440

480

520

560

600

Indi

cate

d m

ean

effe

ctiv

e pr

essu

re, k

Pa

Effect of heating on " imep"Diesel fuelJME - 25CJME - 50CJME - 70CBrake mean effective pressure,kPa

Fig. 15. Effect of heating the JME on the indicated mean effective pressure.

efciency is lower. This means more friction losses occur for

5. Adding DEE to the JME caused the maximum pressure rise rateto decrease slightly than pure JME or pure diesel fuel.

6. Heating the JME did not change much the maximum pressurerise rate.

7. The maximum combustion pressure slightly increased forheated JME or when DEE is added to JME.

8. Heating the JME increased the maximum HRR at all load rangestested while adding DEE affected the (HRR)max in different waysaccording to the load output.520

560

600 e

ffect

ive

pres

sure

, kPa

Effect of adding DEE imepDiesel fuelJME - 25CJME + 5% DEEJME + 10% DEEJME + 15% DEE

1788 M.Y.E. Selim / Energy Conversion and Management 50 (2009) 17811788heated fuel than for relatively cold viscous fuel. It has been shownalso by Nwafor [3] that friction power was also increased when thediesel engine burned heated Rapeseed oil and the mechanical ef-ciency was decreased. It was obvious that the high viscosity of thevegetable oil can play favorable roles in combustion process de-spite its adverse effect on droplet sizes, distribution, and possibleover penetration.

Similar trend is noticed when comparing JME to the diesel fuelcase, as it produced higher imep or lower mechanical efciency isproduced. Adding more DEE with its low viscosity caused similartrend as shown in Fig. 16. It shows higher imep for the same bmep,i.e. less mechanical efciency.

4. Conclusionsreleased; as discussed above, and then more work is produced. Forthe same bmep, the imep is higher for heated JME or the mechanical

0 100 200 300 400 500Brakemean effective pressure, kPa

440

480

Indi

cate

d m

ean

Fig. 16. Effect of adding DEE to JME on the indicated mean effective pressure.From the experimental study carried out here, the followingconclusions may be summarized:

1. Heating the Jojoba Methyl Ester fuel with its high viscosity helped to reduce the viscosity to its acceptable range for dieselfuel.

2. Adding very low viscosity renewable oil such Diethyl Etherhelped the JME to reduce its viscosity to the acceptable range.

3. Heating the JME or adding DEE did not change the exhaust gastemperature or other cycle temperatures.

4. Heating the JME or adding DEE reduced the ignition delay per-iod for the JME.9. Adding DEE to the Jojoba Methyl Ester or heating it resulted inan increase in the indicated mean effective pressure or reducingthe mechanical efciency.

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Reducing the viscosity of Jojoba Methyl Ester diesel fuel and effects on diesel engine performance and roughnessIntroductionExperimental engine test RIGThe viscosity of the Jojoba Methyl EsterViscosity reduction approaches

Results and discussionViscosity reductionEffects on exhaust temperatureEffects on ignition delay periodEffects on maximum pressure rise rate and maximum pressureEffects on the maximum heat release rateEffects on indicated mean effective pressure

ConclusionsReferences