-
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: [email protected] 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