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Experimental evaluation of Diesel engine performance and emission using blends of jojoba oil and Diesel fuel
Energy Conversion and Management 45 (2004) 2093–2112 www.elsevier.com/locate/enconman
Experimental evaluation of Diesel engine performance and emission using blends of jojoba oil and Diesel fuel A.S. Huzayyin a, A.H. Bawady b, M.A. Rady b
a,*
, A. Dawood
a
a Department of Mechanical Engineering Technology, Benha High Institute of Technology, Benha 13 512, Egypt Department of Automotive Engineering, Faculty of Engineering, University of Ain Shams, Abbassia 11566, Cairo, Egypt
Received 22 July 2003; accepted 26 October 2003
Abstract An experimental evaluation of using jojoba oil as an alternate Diesel engine fuel has been conducted in the present work. Measurements of jojoba oil chemical and physical properties have indicated a good potential of using jojoba oil as an alternative Diesel engine fuel. Blending of jojoba oil with gas oil has been shown to be an effective method to reduce engine problems associated with the high viscosity of jojoba oil. Experimental measurements of different performance parameters of a single cylinder, naturally aspirated, direct injection, Diesel engine have been performed using gas oil and blends of gas oil with jojoba oil. Measurements of engine performance parameters at different load conditions over the engine speed range have generally indicated a negligible loss of engine power, a slight increase in brake specific fuel consumption and a reduction in engine NOx and soot emission using blends of jojoba oil with gas oil as compared to gas oil. The reduction in engine soot emission has been observed to increase with the increase of jojoba oil percentage in the fuel blend. Ó 2003 Elsevier Ltd. All rights reserved. Keywords: Jojoba; Alternative fuel; Diesel engine; Performance; Direct injection; Vegetable oils
1. Introduction Over the years, since of invention of internal combustion engines, the development of internal combustion engines has been based on the availability of petroleum derived fuel, which, in turn, has been tailored to meet the needs of current engines. In recent years, the issues of steadily
*
Corresponding author. Present address: MASTER-ENSCPB, 16 Avenue Pey Berland, Pessac Cedex 33607, France. Tel.: +33-540002703; fax: +33-540006668. E-mail address: [email protected] (M.A. Rady). 0196-8904/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.enconman.2003.10.017
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increasing fuel cost, decreasing petroleum reserves, air pollution and market competitiveness have motivated the search for alternative engine fuels. Successful alternative fuels should fulfill environmental and energy security needs without sacrificing operating performance. For Diesel engines, a great deal of research effort has been oriented towards using vegetable oils and their derivatives as alternative fuels. Often, the vegetable oils investigated for their suitability as Diesel engine fuels are those that occur abundantly in the country of the testing. Therefore, soybean oil is of primary interest in the United States, while many European countries are concerned with rapeseed oil and countries with a tropical climate prefer to utilize coconut oil or palm oil. Other vegetable oils, such as sunflower oil, safflower oil etc. have also been investigated. Short term engine performance tests have indicated good potential for most vegetable oil fuels [1–5]. However, long term endurance tests [6–9] show that there are some problems, such as injector coking, ring sticking, gum formation and lubricating oil thickening. These problems have been related to the high viscosity and non-volatility of neat vegetable oils [10]. Poor atomisation patterns associated with high fuel viscosity results in decreasing the combustion quality. This may result in an increase in combustion chamber deposits and the introduction of unburned fuel into the lubricating oil. Methods being investigated for reducing vegetable oils viscosity include dilution with Diesel oil, heating of fuel supply lines and transesterification of vegetable oils using methanol or ethanol. Jojoba (pronounced ho-ho-ba) is a name that is becoming increasingly common as an industrial crop in some countries. At present, growers are producing this obscure desert shrub in the USA, Latin America, South Africa and many other countries. In recent years, jojoba oil has become one of the most genuinely Egyptian products [11]. Jojoba oil makes up to half the weight of the seeds. The characteristics of jojoba oil differ fundamentally from other common vegetable oils [12–14]. Its chemical structure is that of a long straight chain ester, while other common vegetable oils are triglycerides (branched esters based on the molecule glycerol). Conventional oil seed crops produce glyceride oils in which fatty acids are connected to a glycerol molecule. Jojoba oil, on the other hand, contains no glycerides [15]. It is composed of fatty acids connected directly to fatty alcohols. No other plant is known to produce liquids of this type. Jojoba oil and its derivatives find applications in the fields of cosmetics, pharmaceuticals and lubricants. Research studies on the utilization of jojoba oil as an alternate Diesel engine fuel are very little. Recent studies conducted by Radwan et al. [16] and Osayed [17] have highlighted the suitability of such a promising fuel for Diesel engines. Radwan et al. [16] carried out an experimental study for measuring the thermal ignition delay of jojoba methyl ester and its blend with gas oil and methanol. The results have shown that jojoba methyl ester has superior ignition characteristics to gas oil and methanol and the blends with them. Osayed [17] studied the laminar burning velocity of two grades of jojoba methyl ester under variable conditions using a constant volume bomb test rig and compared the results to the values of gas oil and iso-octane. The laminar burning velocities of jojoba methyl esters were comparable yet lower than those of gas oil or iso-octane under all test conditions of equivalence ratio, initial temperature and initial pressure of the unburned mixture. More research work on both short and long term engine performance is required for complete evaluation of using jojoba oil as an alternative Diesel engine fuel. The foregoing introduction summarizes the potential of using vegetable oils as alternate Diesel engine fuels. The distinctive characteristics of jojoba oil [12–15], apart from other vegetable oils,
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and the encouraging preliminary experimental evaluation of its combustion characteristics [16,17] have provided the main motivations to the present work. The present study is an experimental evaluation of Diesel engine performance and emissions using jojoba oil blends with gas oil. Experimental measurements of different performance parameters for a single cylinder, direct injection, naturally aspirated, Diesel engine have been performed using gas oil and blends of gas oil with jojoba oil. The engine performance parameters obtained using 100% gas oil at different engine load conditions, over the engine speed range, have been compared with those of other fuel blends.
2. Fuel preparation and specifications A commercially available No. 2 Diesel fuel, referred to as gas oil, has been selected as the basic engine fuel as recommended by the engine manufacturer. Fine quality jojoba oil extracted from jojoba seeds grown in the Egyptian desert has been utilized in the present study with no additional chemical treatments. The jojoba oil has been filtered and kept in a storage tank inside the laboratory. Blends of jojoba oil with gas oil have been prepared in the laboratory for the purpose of engine operation and experimental measurements. Different blend ratios have been selected for measurements and evaluation. These blend ratios include 0, 20, 40 and 60 percent by volume of jojoba oil in a mixture of jojoba oil and gas oil. They are referred to as gas oil, 20%J–80%G, 40%J– 60%G, and 60%J–40%G, respectively. These abbreviations are adopted throughout the present study. Specimens of the different fuel blends, open to the atmosphere, have been observed to be totally free from any signs of mixture separation, deposits or surface reactions after several weeks of monitoring. Experimental measurements of the different chemical and physical properties of the gas oil and blends of the gas oil with jojoba oil have been performed. Table 1 shows the measured properties for gas oil, jojoba oil and different blend ratios of jojoba oil and gas oil. The standard test methods adopted for each measurement are also included in Table 1. It has been observed that the values of fuel density and carbon and hydrogen content of neat jojoba oil are approximately equal to the corresponding values of gas oil. Jojoba oil contains a smaller percentage of ash than gas oil. The pour point of neat jojoba oil is relatively higher than that of gas oil. The pour point is the lowest temperature at which the fuel is observed to flow and, thus, is important for cold weather operation. Blending of jojoba oil with gas oil reduces the value of the pour point to acceptable levels. Blend ratios as high as 60% jojoba oil result in a pour point temperature of )3 °C as compared to a value of )6 °C for 100% gas oil. The observed values of flash point for jojoba oil and gas oil are 292 and 69 °C, respectively. The flash point temperature is critical from a safety viewpoint. The flash point must be as high as practical. Blending of jojoba oil with gas oil reduces the value of the flash point of the blend. However, the flash point of the different blend ratios is relatively higher than that of gas oil. The measured calorific value of jojoba oil is 12% lower than that of gas oil. As expected, the viscosity of jojoba oil is much higher than that of gas oil. The measured value of the kinematic viscosity of jojoba oil at 40 °C is 25.484 cSt as compared to only 3.294 cSt for gas oil at the same temperature. However, the difference in viscosity decreases with the increase in fuel
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Table 1 Physical and chemical specifications of jojoba–gas oil blends Property
Test method
100%Gas oil
20%J– 80%G
40%J– 60%G
60%J– 40%G
100% jojoba oil
Flash point (°C) Pour point (°C) Ash content (% by weight) Kinematic viscosity at 40 °C (cSt) Kinematic viscosity at 100 °C (cSt) Density at 23 °C (g/cm3 ) Specific density at 15 °C Carbon content (% by mass) Hydrogen content (% by mass) Calorific value (MJ/kg)
ASTM D-93 ASTM D-97 ASTM D-482
69 )6 0.017
75 )3 –
78 )3 –
83 )3 –
292 6 0.014
Modified ASTM D-445
3.294
5.03
7.606
11.375
25.484
Modified ASTM D-445
1.269
1.799
2.498
3.443
6.459
PAAR
0.8316
0.8337
0.841
0.8483
0.8631
0.8323
0.8377
0.847
0.8543
0.864
Heraeus device
81.7
–
–
–
81.8
Heraeus device
5.4
–
–
–
5.2
46.506
44.081
43.52
48.61
42.761
temperature. This can be inferred by comparing the values of the fuel viscosities at 100 °C for gas oil and jojoba oil. It should be mentioned here that heating of fuel lines is sometimes proposed as one of the solutions to overcome the problems related to the high fuel viscosity of vegetable oils. The kinematic viscosity decreases with the decrease of jojoba oil percentage in the mixture. The rate of decrease of viscosity is higher at lower temperatures. For the 20% blend ratio of jojoba oil, the value of the viscosity of the blend is very close to the corresponding value of gas oil. Blending of jojoba oil with gas oil seems to be an effective tool to overcome engine problems associated with the high viscosity of neat jojoba oil. The above observations indicate a good potential of using jojoba oil as an alternative Diesel engine fuel and encourage continuation of the present experimental program.
3. Experimental set up and instrumentation An air cooled, single cylinder, four stroke, DEUTZ F1L511, direct injection Diesel engine has been employed as a test engine in the present study. The engine has 100 mm bore, 105 mm stroke, compression ratio of 17 and a rated brake power of 5.775 kW at 1500 rpm. Fuel injection starts at 24° before TDC. A schematic layout of the experimental set up is shown in Fig. 1. A simple mechanism has been attached to the engine rack to allow variation of the engine speed by controlling the rack position. Facilities for engine operation using different test fuels have been
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Fig. 1. Schematic layout of the experimental set up.
designed and attached to the engine. The fuel piping system allows two separate paths for Diesel fuel and the tested alternative fuel in order to avoid mixing between the tested fuels. A DC electric generator (MEZ-BURNO) with maximum electric power output of 10.5 kW has been directly coupled to the engine output shaft. An external excitation electric circuit is used to generate the generator magnetic field. This circuit consists of an AC autotransformer and a rectifier bridge. The DC generator excitation voltage is controlled and adjusted by the autotransformer. The value of excitation voltage is measured using a digital AC voltammeter (RADIO-SHACK) of 750 V measurement range and 1 V resolution. The electric power output from the DC electric generator is consumed in heating water flowing through a water tank. The present system provides a facility to conduct engine performance tests at different values of engine load. The load values are chosen and defined by selecting the generator excitation voltage values. The value of the Diesel engine rated power of 5.775 kW at 1500 rpm rated engine speed has been selected as a reference point to define the load ratio applied on the engine shaft. For example, the engine is said to be working at full load when the generator excitation field intensity voltage is adjusted to produce an output power of 5.775 kW at 1500 rpm rated engine speed. Similarly, the engine is said to be working at a certain load ratio when the excitation field voltage applied on the DC generator is adjusted to produce a ratio of engine output power to full load power at the rated engine speed that is equal to the prescribed load ratio. The values of the excitation field voltage corresponding to the prescribed engine load have been maintained constant over the entire engine speed range during a single experiment. A generator water cooling system has been installed to maintain a constant generator temperature of 25 °C during all the experiments. This cooling system has been found essential to avoid the effect of generator internal losses on the accuracy of engine power measurements. The differences between the values of the measured generator electric power output and the expected value of engine brake power, which equals the load percentage multiplied by the engine rated power of 5.775 kW, are less than 1%, 2% and 5% for the 1/3, 2/3 load and full load values, respectively. Instrumentation for measuring engine power, fuel consumption, intake air flow rate, speed, temperature at selected points and emission analysis are included in the test rig. Measurements of the engine brake power have been performed by measuring the output DC voltage and current of
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the DC generator using an analogue voltammeter (0–300 V range and 1 V resolution) and ammeter (0–30 A range and 0.1 A resolution). Fuel consumption measurements have been performed by using a graduated glass jar (100 ml capacity and 1 ml division) and a stop watch of 1 s accuracy. The intake air flow rate measurement system consists of a damping box of 0.45 m3 volume and a MERIAM-50MC2 laminar flow element. The damping box volume is about 500 times the swept volume of the engine and is fitted downstream of the laminar flow element. Pressure drop through the laminar flow element is measured using a digital differential pressure manometer with a measurement range of 1–5000 and 1 Pa resolution. A digital (AMETEX 1726) optical tachometer with a measurement range up to 99,999 rpm and 1 rpm resolution has been used for engine speed measurements. Measurements of ambient air temperature, intake air temperature inside the intake air manifold, exhaust temperature inside the exhaust manifold, and exhaust sample temperature have been performed using calibrated type (K) thermocouple probes. A National SCXI data acquisition system connected to a PC, Pentium III 750 MHZ has been utilized to process the output signals from the thermocouples. The emission measurement system consists of a water cooled exhaust gas sampler and an ANAPOLE EU200 self calibration exhaust gas analyzer. The exhaust gas sample is sucked by a membrane pump and distributed to different built in electrochemical sensing cells through a water separator. The outgoing signals of the cells are manipulated and digitized by a built in A/D converter. Soot measurement is effectuated using a filter paper method. The filter paper is inserted in the sampling probe and 1.63 l is sucked by the analyzer pump. The soot stain is compared to a reference soot scale that is divided into 10 different soot numbers ranging from 0 to 9. A high soot number indicates a high level of soot density in the exhaust gasses. Digital readouts of O2 , CO2 , CO, and NOx are available through the analyzer screen. A print out report containing the same information can be obtained by using a built in printer. A quantitative evaluation of the expected uncertainty in the present measurements has been performed following the procedure of Kline [18]. The maximum uncertainty in the measurements of output brake power, brake specific fuel consumption, brake mean effective pressure and engine torque are 1.825%, 2.85%, 1.829% and 1.829%, respectively. The experimental test procedure adopted in the present work starts by warming up the engine using gas oil from the main tank. Then, using control valves, the engine is operated using the test fuel. The required engine load percentage is adjusted by using the generator external excitation field voltage. The rack position controls the value of the required engine speed. Instrument readings for a particular test case are recorded after a sufficiently long time that ensures steady state engine operation. These procedures are repeated to cover the engine speed range at the specified load percentage. At the end of a specified load test, the engine is allowed to operate using gas oil for half an hour under no load and at 1000 rpm to avoid thermal cracking and make sure that the engine fuel system is clean from any residual test fuels.
4. Results and discussion Experimental measurements of different performance parameters of a single cylinder, naturally aspirated, direct injection Diesel engine have been performed using gas oil and blends of gas oil
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with jojoba oil. The engine performance parameters obtained using 100% gas oil at no load, 1/3, 2/3 and full engine load over the engine speed range represent a base line for comparison with the other fuel blends. 4.1. Engine performance using blend of 20% jojoba–80% gas oil Experimental investigations of engine performance and emissions using 20%J–80%G have been conducted. The results have been compared with the basic engine performance using 100% gas oil at different load conditions over the engine speed range. The variations of engine power, brake mean effective pressure (b.m.e.p.), and brake specific fuel consumption (b.s.f.c.) with engine speed at the different load conditions are shown in Fig. 2. It can be observed that the engine power and b.m.e.p. increase with increase of engine speed. The rate of increase in engine power and b.m.e.p. with engine speed decreases with decrease of applied engine load. At full load conditions, the b.s.f.c. exhibits a local minimum at about 1300 rpm engine speed. At part loads, the engine b.s.f.c. decreases gradually with the increase in engine speed. Using 20%J–80%G, for most of the engine load and speed conditions, the engine power and b.m.e.p. are generally slightly lower than the corresponding values using 100% gas oil. The engine b.s.f.c. is observed to be slightly higher. However, the slightly higher values of engine power and b.m.e.p. and lower values of b.s.f.c. using 20%J–80%G oil are observed at full engine load and high speed conditions and at 1/3 engine load and low speed conditions. It should also be mentioned that no remarkable difference has been observed in the exhaust temperature using 20%J–80%G as compared to gas oil. Since the calorific value of 20%J–80%G is relatively lower than that of gas oil, this negligible difference in the exhaust gas temperature and engine power, may be an indication of a relatively more complete combustion of 20%J–80%G. Fig. 3 shows the variations of mass of fuel injected, air/fuel ratio and fuel conversion efficiency with engine speed at different engine load conditions. It can be observed that the fuel conversion efficiency exhibits a local maximum at about 1300 rpm at the full engine load conditions. This local maximum corresponds to the local minimum of engine b.s.f.c. at the same conditions. At the part loads, the fuel conversion efficiency increases with the increase in engine speed. The mass of fuel injected per cycle increases and the air/fuel ratio decreases with the increase of engine speed. In general, the variations of mass of fuel injected, air/fuel ratio and fuel conversion efficiency with engine speed using 100% gas oil and 20%J–80%G exhibit similar trends and comparable values. The slight increase in the mass of fuel injected using 20%J–80%G as compared to 100% gas oil can be attributed to the relatively high viscosity of 20%J–80%G. Higher fluid viscosity decreases the fuel leakage in the injection pump. Analysis of the variations of engine emissions with engine speed at different load conditions using 20%J–80%G as compared to 100% gas oil is presented in the following paragraphs. The results have been compared on the basis of the absolute values of NOx , CO, CO2 and O2 in the exhaust. This presentation may be useful in analysing different trends and formation mechanisms of the engine exhaust gases, an issue that requires further detailed experimental work that focuses on the engine combustion characteristics. From the point of view of evaluating jojoba oil as an alternate engine fuel, one may accept a small percentage loss in engine power in favour of a reduction in the absolute emission of a certain exhaust gas component. However, proper
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Fig. 2. Comparison of variation of engine power, b.m.e.p. and b.s.f.c. with engine speed at different load conditions using 100% gas oil and 20%J–80%G.
evaluation of the viability of using jojoba oil as an alternate engine fuel should consider these two engine performance parameters, for which a convenient comparison method should relate the engine developed power with the engine emissions. Therefore, it has been deemed useful also to present the engine emissions in terms of specific units, per unit power output. Fig. 4 shows the variations of the absolute values of the engine emissions with engine speed at different engine load conditions. It can be observed that for both 20%J–80%G and 100% gas oil, the amount of NOx and CO2 in the exhaust increases with the increase in engine load. The increase of NOx and CO2 in the exhaust is accompanied by a decrease in the absolute values of CO
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Fig. 3. Comparison of variation of fuel conversion efficiency, A=F ratio and mass of fuel injected with engine speed at different load conditions using 100% gas oil and 20%J–80%G.
and O2 . This may be attributed to the increase in engine temperature and oxidization rates with increasing engine load. It should be mentioned here that the formation of CO2 is an exothermic reaction. Therefore, more CO2 in the exhaust indicates a relatively higher engine temperature. Also, the observed increase in mass of fuel injected per cycle and decrease in A=F ratio with increasing engine load, shown in Fig. 3, may result in more regions inside the combustion chamber that are close to stoichiometric. These two factors provide a favourable environment for high NOx formation rates with increasing load value.
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Fig. 4. Comparison of variation of absolute values of engine emission (NOx , O2 , CO2 , CO) with engine speed at different load conditions using 100% gas oil and 20%J–80%G.
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Using 20%J–80%G, different trends of the variations of NOx emission with engine speed have been observed at 1/3 load and full load conditions as compared to 100% gas oil. At 1/3 engine load, the NOx emission values using 20%J–80%G are relatively lower at intermediate values of engine speed. At full load conditions, the absolute values of NOx emission using 20%J–80%G increase with the increase in engine speed. In general, for most of the engine speed and load conditions, the absolute values of NOx emission using 20%J–80%G are relatively lower than those using 100% gas oil. At part load conditions (no load, 1/3 load), the absolute values of NOx and CO2 in the exhaust are relatively lower, while the O2 and CO values are relatively higher using 20%J–80%G as compared to 100% gas oil. At 2/3 and full load conditions, in spite of the observation that the absolute values of CO using 20%J–80%G are relatively higher and O2 values are relatively lower, the CO2 values are relatively higher as compared to those of 100% gas oil. This may indicate higher oxidization rates of unburned hydrocarbons using 20%J–80%G as will be verified by the soot measurements. The absolute values of NOx using 20%J–80%G are relatively higher than those of 100% gas oil only at high engine speed and full load conditions. Fig. 5 shows the variations of the specific values of engine emission with engine speed using 20%J–80%G as compared to those using 100% gas oil under different load conditions. In general, it has been observed that the specific values of NOx emission using 20%J–80%G are relatively lower than those using 100% gas oil. The specific values of CO in the exhaust using 20%J–80%G are slightly higher than those using 100% gas oil, except at 1/3 load and low engine speed. The specific values of O2 and CO2 using 20%J–80%G are lower than those using 100% gas oil at 1/3 engine load, while they have been observed to be slightly higher at 2/3 load and full engine load conditions. The differences in the specific values of engine emissions using 20%J–80%G and 100% gas oil decrease with the increase in engine speed. From the above discussion, it can be concluded that the adoption of 20%J–80%G as an alternate Diesel engine fuel seems to be promising in terms of engine performance and emissions. The loss in engine power is insignificant and the improvement in engine NOx emission is remarkable. The apparent increase in CO emission using 20%J–80%G can be easily controlled by adoption of catalytic reactors. This performance can be further enhanced by using minor modifications in the engine operating conditions (injection timing, pressure etc) that can be tailored to suit this new fuel.
4.2. Effect of jojoba–gas oil blend ratio on engine performance The effect of the jojoba–gas oil blend ratio on the engine performance and emissions has been studied by using blends of 20%, 40% and 60% jojoba oil with gas oil as engine fuels. Engine performance parameters using these fuel blends have been measured and compared with the basic engine performance using 100% gas oil at 2/3 engine load over the engine speed range. Moreover, measurements and comparisons have been performed at all values of engine load at rated engine speed and under the condition of full load at 1300 rpm, the speed corresponding to minimum brake specific fuel consumption. The variations of engine power, b.m.e.p. and b.s.f.c. with engine speed at 2/3 engine load using blends of 20%, 40% and 60% jojoba oil with gas oil as compared to 100% gas oil are shown in
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Fig. 5. Comparison of variation of specific values of engine emission (NOx , O2 , CO2 , CO) with engine speed at different load conditions using 100% gas oil and 20%J–80%G.
Fig. 6. The engine power and b.m.e.p. slightly decrease and the b.s.f.c. slightly increases with the increase of jojoba oil percentage in the fuel blend. Fig. 7 shows the variations of the amount of fuel injected per cycle, A=F ratio and fuel conversion efficiency with engine speed at 2/3 load using 0%, 20%, 40% and 60% jojoba–gas oil blend ratios. The amount of fuel injected per cycle and A=F ratio slightly change with the jojoba–gas oil
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Fig. 6. Comparison of variation of engine power, b.m.e.p. and b.s.f.c. with engine speed at 2/3 engine load using different values of jojoba–gas oil blend ratio.
blend ratio. In general, the fuel conversion efficiency using 40% and 60% jojoba–gas oils fuel blend is relatively higher than that obtained using 100% gas oil. At high values of engine speed, the fuel conversion efficiency increases with the increase of jojoba oil percentage in the fuel blend. However, at low values of engine speed, the fuel conversion efficiency using 20% jojoba oil blend ratio is lower than that using 100% gas oil. The trends of the variations of engine power, b.m.e.p. and b.s.f.c. with jojoba–gas oil blend ratio have been verified by comparisons of these values at different load conditions and rated engine speed as shown in Fig. 8. The engine power output and b.m.e.p. slightly decrease with the increase of jojoba–gas oil blend ratio at 1/3 and 2/3 load, while they remain practically constant at full engine load. On the other hand, the b.s.f.c. slightly increases with the increase of jojoba–gas
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Fig. 7. Comparison of variation of fuel conversion efficiency, A=F ratio and mass of fuel injected with engine speed at 2/3 engine load using different values of jojoba–gas oil blend ratio.
oil blend ratio. This may be attributed to the decrease in the calorific value of the blended fuel with the increase of jojoba oil percentage in the blend. Similar trends in the variation of engine power, b.m.e.p. and b.s.f.c. have been observed at 1300 rpm and full load, as also shown in Fig. 8. The variations of the absolute values of the engine emissions with engine speed at 2/3 load using different fuel blends is shown in Fig. 9. The NOx emission values using jojoba–gas oil blends are generally lower than those using 100% gas oil. The maximum reduction in NOx emission has been observed using 40%J–60%G and occurs at about the rated engine speed. Using 60%J–40%G fuel
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Fig. 8. Comparison of variation of engine power, b.m.e.p. and b.s.f.c. with jojoba oil percentage in the fuel blend at 1500 and 1300 rpm engine speed and different load conditions.
blend the absolute values of NOx emission increase with the increase of engine speed. The absolute emission values of CO increase with the increase of jojoba oil percentage in the fuel blend. It has also been observed that the variations of the absolute values of CO2 and O2 in the exhaust exhibit no specific trend as a function of the fuel blend ratio. Fig. 10 shows the variations of the specific values of the engine emissions with engine speed at 2/3 engine load. The reduction in specific engine NOx emission and the increase of engine specific CO emission with the increase of jojoba–gas oil blend ratio can be observed. The differences in the specific engine emissions using different fuel blends decrease with the increase of engine speed. This may be attributed to the increase in engine power and the enhancement of mixing with the increase of engine speed.
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Fig. 9. Comparison of variation of absolute values of engine emission (NOx , O2 , CO2 , CO) with engine speed at 2/3 engine load using different values of jojoba–gas oil blend ratio.
Fig. 11 shows the variations of the specific values of the engine emissions with jojoba–gas oil blend ratio at 1500 rpm rated engine speed for different load conditions. Specific NOx , CO and CO2 emissions slightly increase and O2 remains practically constant with the increase of jojoba percentage in the fuel blend. At 1/3 load, the NOx and CO2 emission are minimum using 20%J– 80%G fuel blend. Similar trends in the variations of specific engine emissions with blend ratio have been observed at 1300 rpm and full load, as also shown in Fig. 11.
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Fig. 10. Comparison of variation of specific values of engine emission (NOx , O2 , CO2 , CO) with engine speed at 2/3 engine load using different values of jojoba–gas oil blend ratio.
It can be concluded from the above discussion that adoption of jojoba–gas oil fuel blend ratio as high as 60% results in an insignificant loss in engine power and a reduction in NOx emission. The observed differences in the behaviour of the variations of engine emissions using different fuel blends indicate the need to adjust the engine operating parameters to suit a particular jojoba–gas oil blend. 4.3. Comparison of engine soot emission using jojoba–gas oil blends Comparisons of engine soot emission using different values of jojoba–gas oil blend ratio have been performed at 1300 and 1500 rpm engine speed for different load conditions. Table 2 shows
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Fig. 11. Comparison of variation of specific values of engine emission (NOx , O2 , CO2 , CO) with jojoba oil percentage in the fuel blend at 1500 and 1300 rpm engine speed and different load conditions.
the values of soot number at different conditions of engine speed and load using 0%, 20%, 40% and 60% jojoba–gas oil blend ratios. It can be observed that at the rated engine speed of 1500 rpm, the soot number increases with the increase of engine load. For a given engine load, the soot number decreases with the increase of jojoba oil percentage in the fuel blend. This decrease in soot number with increasing jojoba oil percentage in the blend may explain the increase in CO and CO2 emissions using jojoba–gas oil fuel blends, as compared to those using 100% gas oil. This may be attributed to relatively more oxidization of unburned hydrocarbons. On the other hand, oxidization of hydrocarbons may compensate for the relatively lower calorific
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Table 2 Soot number using different blend ratios of jojoba–gas oil at different engine load and speed conditions Fuel type
Engine load No load
1/3 load
2/3 load
1500 rpm 100% Gas oil 20%J–80%G 40%J–60%G 60%J–40%G
2 1–2 1 1
6 5–6 4–5 4
8 7–8 7 6–7
Full load 1500 rpm
1300 rpm
Over 9 Over 9 9 8–9
7 7 6–7 6
value of the jojoba oil blends as compared to that of gas oil. Thus, resulting in producing comparable values of engine power output using the jojoba–gas oil blends and 100% gas oil. These results are encouraging and prompt the feasibility to achieve further enhancement in engine performance and emission using jojoba–gas oil blends by adjustment of the engine operating parameters. A detailed study on engine combustion characteristics using different blends is a useful tool to optimise the engine performance for a particular fuel blend ratio.
5. Summary and conclusion An experimental evaluation of using jojoba oil as an alternate Diesel engine fuel has been conducted in the present work. Measurements of jojoba oil chemical and physical properties have indicated a good potential of using jojoba oil as an alternative Diesel engine fuel. Blending of jojoba oil with gas oil has been shown to be an effective method to reduce engine problems associated with the high viscosity of jojoba oil. Reasonable viscosity values have been obtained using blend ratios as high as 60%J–40%G oil. Other fuel properties, such as the flash point, pour point and calorific value are comparable. In addition, apart from other vegetable oils, jojoba oil contains no glycerides and has a straight chain chemical structure. Therefore, long term engine performance difficulties encountered using other vegetable oils may not be expected while using jojoba oil. Experimental measurements of different performance parameters of a single cylinder, naturally aspirated, direct injection Diesel engine have been performed using gas oil and blends of gas oil with jojoba oil. Measurements of engine performance parameters at different load conditions over the engine speed range have generally indicated a negligible loss of engine power, a slight increase in brake specific fuel consumption and a reduction in engine NOx and soot emission using blends of jojoba oil with gas oil as compared to those using gas oil. The reduction in engine soot emission has been observed to increase with the increase of jojoba oil percentage in the fuel blend. The results reported in this study should be viewed in the light of the fact that the engine used was unaltered and was designed to run on Diesel fuel. The observed differences, and sometimes inconveniences, in the behaviour of the variations of the engine emissions using different fuel blends calls for the need to adjust the engine parameters to suit a particular fuel blend. Further enhancement in the engine performance parameters are expected using minor modifications in the engine operating conditions, such as injection timing and pressure that can be optimized as a
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function of the jojoba–gas oil blend ratio. In general, the present results are encouraging and open a large scope for additional research work related to the evaluation and utilization of jojoba oil as an alternate Diesel engine fuel.
References [1] Wagner GL, Peterson CL. Performance of winter rape (Brassica napus) based fuel mixture in diesel engines. In: Proceedings of the International Conference on Plant and Vegetable Oils as Fuels, 1982. p. 329. [2] Varde KS. Some correlation of diesel engine performance with injection characteristics using vegetable oil as fuels. In: Proceeding of the International Conference on Plant and Vegetable Oils as Fuels, 1982. p. 303. [3] Schlautman NJ, Schinstock JL, Hanna MA. Unrefined expelled soybean oil performance in a diesel engine. Trans ASAE 1986;29(1):70–3. [4] Schmidt K, Van Gerpen JH. The effect of biodiesel fuel composition on diesel combustion and emissions. SAE 961086, 1996. [5] Zhang Y, Van Gerpen JH. Combustion analysis of esters of soybean oil in a diesel engine. SAE 960765, 1996. [6] Baranescu RA, Lusco JJ. Performance, durability and low temperature evaluation of sunflower oil as a diesel fuel. In: Proceeding of the International Conference on Plant and Vegetable Oils as Fuels, 1982. p. 312. [7] Borgelt SC, Harris FD. Endurance tests using soybean oil–diesel fuel mixture to fuel small pre-combustion chamber engines. In: Proceedings of the International Conference on Plant and Vegetable Oils as Fuels, 1982. p. 364. [8] Goodrum JW, Patel VC, McClendon RW. Diesel injector carbonization by three alternative fuels. Trans ASAE 1996;39(3):817–21. [9] Peterson CL, Thompson JC, Taberski JS. One thousand hour engine durability test with HYSEE and using a 5X-EMA test cycle. Trans ASAE 1999;42(1):23–30. [10] Pryde EH.Vegetable oil fuel standards. In: Proceedings of the International Conference on Plant and Vegetable Oils as Fuels, 1982. p. 101. [11] Salem AE. Synthesis of extreme pressure petroleum additive from local jojoba oil. In: The 12th International Seminar, New Trends in Engine and Industrial Lubricants, Fuels, Chemicals and Additives, Cairo, 2000. [12] Wisniak J. Chemistry and technology of jojoba oil: state of the art. In: Proceedings of the Sixth International Conference on Jojoba and its Uses, 1984. p. 311. [13] Wisniak J. Recent advances in the chemistry and properties of jojoba oil. In: Proceedings of the Seventh International Conference on Jojoba and its Uses, 1988. p. 222. [14] Spencer GF, List GR. Specifications, physical properties and methods of analysis for jojoba oil. In: Proceeding of the Seventh International Conference on Jojoba and its Uses, 1988. p. 173. [15] Wisniak J. Jojoba oil and derivatives. Prog Chem Fats Lipids 1977;15:176–218. [16] Radwan MS, Dandoush SK, Selim MYE, Kader AMA. Ignition delay period of jojoba diesel engine fuel. SAE 972975, 1997. [17] Osayed SMA. Measurement of laminar burning velocity of jojoba methyl ester. MSc Thesis, Faculty of Engineering, Mataria, Helwan University, Cairo 2001. [18] Kline SJ. The purposes of uncertainty analysis. Trans ASME 1985;107:153.
Experimental evaluation of Diesel engine performance and emission using blends of jojoba oil and Diesel fuel A.S. Huzayyin a, A.H. Bawady b, M.A. Rady b
a,*
, A. Dawood
a
a Department of Mechanical Engineering Technology, Benha High Institute of Technology, Benha 13 512, Egypt Department of Automotive Engineering, Faculty of Engineering, University of Ain Shams, Abbassia 11566, Cairo, Egypt
Received 22 July 2003; accepted 26 October 2003
Abstract An experimental evaluation of using jojoba oil as an alternate Diesel engine fuel has been conducted in the present work. Measurements of jojoba oil chemical and physical properties have indicated a good potential of using jojoba oil as an alternative Diesel engine fuel. Blending of jojoba oil with gas oil has been shown to be an effective method to reduce engine problems associated with the high viscosity of jojoba oil. Experimental measurements of different performance parameters of a single cylinder, naturally aspirated, direct injection, Diesel engine have been performed using gas oil and blends of gas oil with jojoba oil. Measurements of engine performance parameters at different load conditions over the engine speed range have generally indicated a negligible loss of engine power, a slight increase in brake specific fuel consumption and a reduction in engine NOx and soot emission using blends of jojoba oil with gas oil as compared to gas oil. The reduction in engine soot emission has been observed to increase with the increase of jojoba oil percentage in the fuel blend. Ó 2003 Elsevier Ltd. All rights reserved. Keywords: Jojoba; Alternative fuel; Diesel engine; Performance; Direct injection; Vegetable oils
1. Introduction Over the years, since of invention of internal combustion engines, the development of internal combustion engines has been based on the availability of petroleum derived fuel, which, in turn, has been tailored to meet the needs of current engines. In recent years, the issues of steadily
*
Corresponding author. Present address: MASTER-ENSCPB, 16 Avenue Pey Berland, Pessac Cedex 33607, France. Tel.: +33-540002703; fax: +33-540006668. E-mail address: [email protected] (M.A. Rady). 0196-8904/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.enconman.2003.10.017
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increasing fuel cost, decreasing petroleum reserves, air pollution and market competitiveness have motivated the search for alternative engine fuels. Successful alternative fuels should fulfill environmental and energy security needs without sacrificing operating performance. For Diesel engines, a great deal of research effort has been oriented towards using vegetable oils and their derivatives as alternative fuels. Often, the vegetable oils investigated for their suitability as Diesel engine fuels are those that occur abundantly in the country of the testing. Therefore, soybean oil is of primary interest in the United States, while many European countries are concerned with rapeseed oil and countries with a tropical climate prefer to utilize coconut oil or palm oil. Other vegetable oils, such as sunflower oil, safflower oil etc. have also been investigated. Short term engine performance tests have indicated good potential for most vegetable oil fuels [1–5]. However, long term endurance tests [6–9] show that there are some problems, such as injector coking, ring sticking, gum formation and lubricating oil thickening. These problems have been related to the high viscosity and non-volatility of neat vegetable oils [10]. Poor atomisation patterns associated with high fuel viscosity results in decreasing the combustion quality. This may result in an increase in combustion chamber deposits and the introduction of unburned fuel into the lubricating oil. Methods being investigated for reducing vegetable oils viscosity include dilution with Diesel oil, heating of fuel supply lines and transesterification of vegetable oils using methanol or ethanol. Jojoba (pronounced ho-ho-ba) is a name that is becoming increasingly common as an industrial crop in some countries. At present, growers are producing this obscure desert shrub in the USA, Latin America, South Africa and many other countries. In recent years, jojoba oil has become one of the most genuinely Egyptian products [11]. Jojoba oil makes up to half the weight of the seeds. The characteristics of jojoba oil differ fundamentally from other common vegetable oils [12–14]. Its chemical structure is that of a long straight chain ester, while other common vegetable oils are triglycerides (branched esters based on the molecule glycerol). Conventional oil seed crops produce glyceride oils in which fatty acids are connected to a glycerol molecule. Jojoba oil, on the other hand, contains no glycerides [15]. It is composed of fatty acids connected directly to fatty alcohols. No other plant is known to produce liquids of this type. Jojoba oil and its derivatives find applications in the fields of cosmetics, pharmaceuticals and lubricants. Research studies on the utilization of jojoba oil as an alternate Diesel engine fuel are very little. Recent studies conducted by Radwan et al. [16] and Osayed [17] have highlighted the suitability of such a promising fuel for Diesel engines. Radwan et al. [16] carried out an experimental study for measuring the thermal ignition delay of jojoba methyl ester and its blend with gas oil and methanol. The results have shown that jojoba methyl ester has superior ignition characteristics to gas oil and methanol and the blends with them. Osayed [17] studied the laminar burning velocity of two grades of jojoba methyl ester under variable conditions using a constant volume bomb test rig and compared the results to the values of gas oil and iso-octane. The laminar burning velocities of jojoba methyl esters were comparable yet lower than those of gas oil or iso-octane under all test conditions of equivalence ratio, initial temperature and initial pressure of the unburned mixture. More research work on both short and long term engine performance is required for complete evaluation of using jojoba oil as an alternative Diesel engine fuel. The foregoing introduction summarizes the potential of using vegetable oils as alternate Diesel engine fuels. The distinctive characteristics of jojoba oil [12–15], apart from other vegetable oils,
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and the encouraging preliminary experimental evaluation of its combustion characteristics [16,17] have provided the main motivations to the present work. The present study is an experimental evaluation of Diesel engine performance and emissions using jojoba oil blends with gas oil. Experimental measurements of different performance parameters for a single cylinder, direct injection, naturally aspirated, Diesel engine have been performed using gas oil and blends of gas oil with jojoba oil. The engine performance parameters obtained using 100% gas oil at different engine load conditions, over the engine speed range, have been compared with those of other fuel blends.
2. Fuel preparation and specifications A commercially available No. 2 Diesel fuel, referred to as gas oil, has been selected as the basic engine fuel as recommended by the engine manufacturer. Fine quality jojoba oil extracted from jojoba seeds grown in the Egyptian desert has been utilized in the present study with no additional chemical treatments. The jojoba oil has been filtered and kept in a storage tank inside the laboratory. Blends of jojoba oil with gas oil have been prepared in the laboratory for the purpose of engine operation and experimental measurements. Different blend ratios have been selected for measurements and evaluation. These blend ratios include 0, 20, 40 and 60 percent by volume of jojoba oil in a mixture of jojoba oil and gas oil. They are referred to as gas oil, 20%J–80%G, 40%J– 60%G, and 60%J–40%G, respectively. These abbreviations are adopted throughout the present study. Specimens of the different fuel blends, open to the atmosphere, have been observed to be totally free from any signs of mixture separation, deposits or surface reactions after several weeks of monitoring. Experimental measurements of the different chemical and physical properties of the gas oil and blends of the gas oil with jojoba oil have been performed. Table 1 shows the measured properties for gas oil, jojoba oil and different blend ratios of jojoba oil and gas oil. The standard test methods adopted for each measurement are also included in Table 1. It has been observed that the values of fuel density and carbon and hydrogen content of neat jojoba oil are approximately equal to the corresponding values of gas oil. Jojoba oil contains a smaller percentage of ash than gas oil. The pour point of neat jojoba oil is relatively higher than that of gas oil. The pour point is the lowest temperature at which the fuel is observed to flow and, thus, is important for cold weather operation. Blending of jojoba oil with gas oil reduces the value of the pour point to acceptable levels. Blend ratios as high as 60% jojoba oil result in a pour point temperature of )3 °C as compared to a value of )6 °C for 100% gas oil. The observed values of flash point for jojoba oil and gas oil are 292 and 69 °C, respectively. The flash point temperature is critical from a safety viewpoint. The flash point must be as high as practical. Blending of jojoba oil with gas oil reduces the value of the flash point of the blend. However, the flash point of the different blend ratios is relatively higher than that of gas oil. The measured calorific value of jojoba oil is 12% lower than that of gas oil. As expected, the viscosity of jojoba oil is much higher than that of gas oil. The measured value of the kinematic viscosity of jojoba oil at 40 °C is 25.484 cSt as compared to only 3.294 cSt for gas oil at the same temperature. However, the difference in viscosity decreases with the increase in fuel
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Table 1 Physical and chemical specifications of jojoba–gas oil blends Property
Test method
100%Gas oil
20%J– 80%G
40%J– 60%G
60%J– 40%G
100% jojoba oil
Flash point (°C) Pour point (°C) Ash content (% by weight) Kinematic viscosity at 40 °C (cSt) Kinematic viscosity at 100 °C (cSt) Density at 23 °C (g/cm3 ) Specific density at 15 °C Carbon content (% by mass) Hydrogen content (% by mass) Calorific value (MJ/kg)
ASTM D-93 ASTM D-97 ASTM D-482
69 )6 0.017
75 )3 –
78 )3 –
83 )3 –
292 6 0.014
Modified ASTM D-445
3.294
5.03
7.606
11.375
25.484
Modified ASTM D-445
1.269
1.799
2.498
3.443
6.459
PAAR
0.8316
0.8337
0.841
0.8483
0.8631
0.8323
0.8377
0.847
0.8543
0.864
Heraeus device
81.7
–
–
–
81.8
Heraeus device
5.4
–
–
–
5.2
46.506
44.081
43.52
48.61
42.761
temperature. This can be inferred by comparing the values of the fuel viscosities at 100 °C for gas oil and jojoba oil. It should be mentioned here that heating of fuel lines is sometimes proposed as one of the solutions to overcome the problems related to the high fuel viscosity of vegetable oils. The kinematic viscosity decreases with the decrease of jojoba oil percentage in the mixture. The rate of decrease of viscosity is higher at lower temperatures. For the 20% blend ratio of jojoba oil, the value of the viscosity of the blend is very close to the corresponding value of gas oil. Blending of jojoba oil with gas oil seems to be an effective tool to overcome engine problems associated with the high viscosity of neat jojoba oil. The above observations indicate a good potential of using jojoba oil as an alternative Diesel engine fuel and encourage continuation of the present experimental program.
3. Experimental set up and instrumentation An air cooled, single cylinder, four stroke, DEUTZ F1L511, direct injection Diesel engine has been employed as a test engine in the present study. The engine has 100 mm bore, 105 mm stroke, compression ratio of 17 and a rated brake power of 5.775 kW at 1500 rpm. Fuel injection starts at 24° before TDC. A schematic layout of the experimental set up is shown in Fig. 1. A simple mechanism has been attached to the engine rack to allow variation of the engine speed by controlling the rack position. Facilities for engine operation using different test fuels have been
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Fig. 1. Schematic layout of the experimental set up.
designed and attached to the engine. The fuel piping system allows two separate paths for Diesel fuel and the tested alternative fuel in order to avoid mixing between the tested fuels. A DC electric generator (MEZ-BURNO) with maximum electric power output of 10.5 kW has been directly coupled to the engine output shaft. An external excitation electric circuit is used to generate the generator magnetic field. This circuit consists of an AC autotransformer and a rectifier bridge. The DC generator excitation voltage is controlled and adjusted by the autotransformer. The value of excitation voltage is measured using a digital AC voltammeter (RADIO-SHACK) of 750 V measurement range and 1 V resolution. The electric power output from the DC electric generator is consumed in heating water flowing through a water tank. The present system provides a facility to conduct engine performance tests at different values of engine load. The load values are chosen and defined by selecting the generator excitation voltage values. The value of the Diesel engine rated power of 5.775 kW at 1500 rpm rated engine speed has been selected as a reference point to define the load ratio applied on the engine shaft. For example, the engine is said to be working at full load when the generator excitation field intensity voltage is adjusted to produce an output power of 5.775 kW at 1500 rpm rated engine speed. Similarly, the engine is said to be working at a certain load ratio when the excitation field voltage applied on the DC generator is adjusted to produce a ratio of engine output power to full load power at the rated engine speed that is equal to the prescribed load ratio. The values of the excitation field voltage corresponding to the prescribed engine load have been maintained constant over the entire engine speed range during a single experiment. A generator water cooling system has been installed to maintain a constant generator temperature of 25 °C during all the experiments. This cooling system has been found essential to avoid the effect of generator internal losses on the accuracy of engine power measurements. The differences between the values of the measured generator electric power output and the expected value of engine brake power, which equals the load percentage multiplied by the engine rated power of 5.775 kW, are less than 1%, 2% and 5% for the 1/3, 2/3 load and full load values, respectively. Instrumentation for measuring engine power, fuel consumption, intake air flow rate, speed, temperature at selected points and emission analysis are included in the test rig. Measurements of the engine brake power have been performed by measuring the output DC voltage and current of
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the DC generator using an analogue voltammeter (0–300 V range and 1 V resolution) and ammeter (0–30 A range and 0.1 A resolution). Fuel consumption measurements have been performed by using a graduated glass jar (100 ml capacity and 1 ml division) and a stop watch of 1 s accuracy. The intake air flow rate measurement system consists of a damping box of 0.45 m3 volume and a MERIAM-50MC2 laminar flow element. The damping box volume is about 500 times the swept volume of the engine and is fitted downstream of the laminar flow element. Pressure drop through the laminar flow element is measured using a digital differential pressure manometer with a measurement range of 1–5000 and 1 Pa resolution. A digital (AMETEX 1726) optical tachometer with a measurement range up to 99,999 rpm and 1 rpm resolution has been used for engine speed measurements. Measurements of ambient air temperature, intake air temperature inside the intake air manifold, exhaust temperature inside the exhaust manifold, and exhaust sample temperature have been performed using calibrated type (K) thermocouple probes. A National SCXI data acquisition system connected to a PC, Pentium III 750 MHZ has been utilized to process the output signals from the thermocouples. The emission measurement system consists of a water cooled exhaust gas sampler and an ANAPOLE EU200 self calibration exhaust gas analyzer. The exhaust gas sample is sucked by a membrane pump and distributed to different built in electrochemical sensing cells through a water separator. The outgoing signals of the cells are manipulated and digitized by a built in A/D converter. Soot measurement is effectuated using a filter paper method. The filter paper is inserted in the sampling probe and 1.63 l is sucked by the analyzer pump. The soot stain is compared to a reference soot scale that is divided into 10 different soot numbers ranging from 0 to 9. A high soot number indicates a high level of soot density in the exhaust gasses. Digital readouts of O2 , CO2 , CO, and NOx are available through the analyzer screen. A print out report containing the same information can be obtained by using a built in printer. A quantitative evaluation of the expected uncertainty in the present measurements has been performed following the procedure of Kline [18]. The maximum uncertainty in the measurements of output brake power, brake specific fuel consumption, brake mean effective pressure and engine torque are 1.825%, 2.85%, 1.829% and 1.829%, respectively. The experimental test procedure adopted in the present work starts by warming up the engine using gas oil from the main tank. Then, using control valves, the engine is operated using the test fuel. The required engine load percentage is adjusted by using the generator external excitation field voltage. The rack position controls the value of the required engine speed. Instrument readings for a particular test case are recorded after a sufficiently long time that ensures steady state engine operation. These procedures are repeated to cover the engine speed range at the specified load percentage. At the end of a specified load test, the engine is allowed to operate using gas oil for half an hour under no load and at 1000 rpm to avoid thermal cracking and make sure that the engine fuel system is clean from any residual test fuels.
4. Results and discussion Experimental measurements of different performance parameters of a single cylinder, naturally aspirated, direct injection Diesel engine have been performed using gas oil and blends of gas oil
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with jojoba oil. The engine performance parameters obtained using 100% gas oil at no load, 1/3, 2/3 and full engine load over the engine speed range represent a base line for comparison with the other fuel blends. 4.1. Engine performance using blend of 20% jojoba–80% gas oil Experimental investigations of engine performance and emissions using 20%J–80%G have been conducted. The results have been compared with the basic engine performance using 100% gas oil at different load conditions over the engine speed range. The variations of engine power, brake mean effective pressure (b.m.e.p.), and brake specific fuel consumption (b.s.f.c.) with engine speed at the different load conditions are shown in Fig. 2. It can be observed that the engine power and b.m.e.p. increase with increase of engine speed. The rate of increase in engine power and b.m.e.p. with engine speed decreases with decrease of applied engine load. At full load conditions, the b.s.f.c. exhibits a local minimum at about 1300 rpm engine speed. At part loads, the engine b.s.f.c. decreases gradually with the increase in engine speed. Using 20%J–80%G, for most of the engine load and speed conditions, the engine power and b.m.e.p. are generally slightly lower than the corresponding values using 100% gas oil. The engine b.s.f.c. is observed to be slightly higher. However, the slightly higher values of engine power and b.m.e.p. and lower values of b.s.f.c. using 20%J–80%G oil are observed at full engine load and high speed conditions and at 1/3 engine load and low speed conditions. It should also be mentioned that no remarkable difference has been observed in the exhaust temperature using 20%J–80%G as compared to gas oil. Since the calorific value of 20%J–80%G is relatively lower than that of gas oil, this negligible difference in the exhaust gas temperature and engine power, may be an indication of a relatively more complete combustion of 20%J–80%G. Fig. 3 shows the variations of mass of fuel injected, air/fuel ratio and fuel conversion efficiency with engine speed at different engine load conditions. It can be observed that the fuel conversion efficiency exhibits a local maximum at about 1300 rpm at the full engine load conditions. This local maximum corresponds to the local minimum of engine b.s.f.c. at the same conditions. At the part loads, the fuel conversion efficiency increases with the increase in engine speed. The mass of fuel injected per cycle increases and the air/fuel ratio decreases with the increase of engine speed. In general, the variations of mass of fuel injected, air/fuel ratio and fuel conversion efficiency with engine speed using 100% gas oil and 20%J–80%G exhibit similar trends and comparable values. The slight increase in the mass of fuel injected using 20%J–80%G as compared to 100% gas oil can be attributed to the relatively high viscosity of 20%J–80%G. Higher fluid viscosity decreases the fuel leakage in the injection pump. Analysis of the variations of engine emissions with engine speed at different load conditions using 20%J–80%G as compared to 100% gas oil is presented in the following paragraphs. The results have been compared on the basis of the absolute values of NOx , CO, CO2 and O2 in the exhaust. This presentation may be useful in analysing different trends and formation mechanisms of the engine exhaust gases, an issue that requires further detailed experimental work that focuses on the engine combustion characteristics. From the point of view of evaluating jojoba oil as an alternate engine fuel, one may accept a small percentage loss in engine power in favour of a reduction in the absolute emission of a certain exhaust gas component. However, proper
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Fig. 2. Comparison of variation of engine power, b.m.e.p. and b.s.f.c. with engine speed at different load conditions using 100% gas oil and 20%J–80%G.
evaluation of the viability of using jojoba oil as an alternate engine fuel should consider these two engine performance parameters, for which a convenient comparison method should relate the engine developed power with the engine emissions. Therefore, it has been deemed useful also to present the engine emissions in terms of specific units, per unit power output. Fig. 4 shows the variations of the absolute values of the engine emissions with engine speed at different engine load conditions. It can be observed that for both 20%J–80%G and 100% gas oil, the amount of NOx and CO2 in the exhaust increases with the increase in engine load. The increase of NOx and CO2 in the exhaust is accompanied by a decrease in the absolute values of CO
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Fig. 3. Comparison of variation of fuel conversion efficiency, A=F ratio and mass of fuel injected with engine speed at different load conditions using 100% gas oil and 20%J–80%G.
and O2 . This may be attributed to the increase in engine temperature and oxidization rates with increasing engine load. It should be mentioned here that the formation of CO2 is an exothermic reaction. Therefore, more CO2 in the exhaust indicates a relatively higher engine temperature. Also, the observed increase in mass of fuel injected per cycle and decrease in A=F ratio with increasing engine load, shown in Fig. 3, may result in more regions inside the combustion chamber that are close to stoichiometric. These two factors provide a favourable environment for high NOx formation rates with increasing load value.
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Fig. 4. Comparison of variation of absolute values of engine emission (NOx , O2 , CO2 , CO) with engine speed at different load conditions using 100% gas oil and 20%J–80%G.
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Using 20%J–80%G, different trends of the variations of NOx emission with engine speed have been observed at 1/3 load and full load conditions as compared to 100% gas oil. At 1/3 engine load, the NOx emission values using 20%J–80%G are relatively lower at intermediate values of engine speed. At full load conditions, the absolute values of NOx emission using 20%J–80%G increase with the increase in engine speed. In general, for most of the engine speed and load conditions, the absolute values of NOx emission using 20%J–80%G are relatively lower than those using 100% gas oil. At part load conditions (no load, 1/3 load), the absolute values of NOx and CO2 in the exhaust are relatively lower, while the O2 and CO values are relatively higher using 20%J–80%G as compared to 100% gas oil. At 2/3 and full load conditions, in spite of the observation that the absolute values of CO using 20%J–80%G are relatively higher and O2 values are relatively lower, the CO2 values are relatively higher as compared to those of 100% gas oil. This may indicate higher oxidization rates of unburned hydrocarbons using 20%J–80%G as will be verified by the soot measurements. The absolute values of NOx using 20%J–80%G are relatively higher than those of 100% gas oil only at high engine speed and full load conditions. Fig. 5 shows the variations of the specific values of engine emission with engine speed using 20%J–80%G as compared to those using 100% gas oil under different load conditions. In general, it has been observed that the specific values of NOx emission using 20%J–80%G are relatively lower than those using 100% gas oil. The specific values of CO in the exhaust using 20%J–80%G are slightly higher than those using 100% gas oil, except at 1/3 load and low engine speed. The specific values of O2 and CO2 using 20%J–80%G are lower than those using 100% gas oil at 1/3 engine load, while they have been observed to be slightly higher at 2/3 load and full engine load conditions. The differences in the specific values of engine emissions using 20%J–80%G and 100% gas oil decrease with the increase in engine speed. From the above discussion, it can be concluded that the adoption of 20%J–80%G as an alternate Diesel engine fuel seems to be promising in terms of engine performance and emissions. The loss in engine power is insignificant and the improvement in engine NOx emission is remarkable. The apparent increase in CO emission using 20%J–80%G can be easily controlled by adoption of catalytic reactors. This performance can be further enhanced by using minor modifications in the engine operating conditions (injection timing, pressure etc) that can be tailored to suit this new fuel.
4.2. Effect of jojoba–gas oil blend ratio on engine performance The effect of the jojoba–gas oil blend ratio on the engine performance and emissions has been studied by using blends of 20%, 40% and 60% jojoba oil with gas oil as engine fuels. Engine performance parameters using these fuel blends have been measured and compared with the basic engine performance using 100% gas oil at 2/3 engine load over the engine speed range. Moreover, measurements and comparisons have been performed at all values of engine load at rated engine speed and under the condition of full load at 1300 rpm, the speed corresponding to minimum brake specific fuel consumption. The variations of engine power, b.m.e.p. and b.s.f.c. with engine speed at 2/3 engine load using blends of 20%, 40% and 60% jojoba oil with gas oil as compared to 100% gas oil are shown in
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Fig. 5. Comparison of variation of specific values of engine emission (NOx , O2 , CO2 , CO) with engine speed at different load conditions using 100% gas oil and 20%J–80%G.
Fig. 6. The engine power and b.m.e.p. slightly decrease and the b.s.f.c. slightly increases with the increase of jojoba oil percentage in the fuel blend. Fig. 7 shows the variations of the amount of fuel injected per cycle, A=F ratio and fuel conversion efficiency with engine speed at 2/3 load using 0%, 20%, 40% and 60% jojoba–gas oil blend ratios. The amount of fuel injected per cycle and A=F ratio slightly change with the jojoba–gas oil
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Fig. 6. Comparison of variation of engine power, b.m.e.p. and b.s.f.c. with engine speed at 2/3 engine load using different values of jojoba–gas oil blend ratio.
blend ratio. In general, the fuel conversion efficiency using 40% and 60% jojoba–gas oils fuel blend is relatively higher than that obtained using 100% gas oil. At high values of engine speed, the fuel conversion efficiency increases with the increase of jojoba oil percentage in the fuel blend. However, at low values of engine speed, the fuel conversion efficiency using 20% jojoba oil blend ratio is lower than that using 100% gas oil. The trends of the variations of engine power, b.m.e.p. and b.s.f.c. with jojoba–gas oil blend ratio have been verified by comparisons of these values at different load conditions and rated engine speed as shown in Fig. 8. The engine power output and b.m.e.p. slightly decrease with the increase of jojoba–gas oil blend ratio at 1/3 and 2/3 load, while they remain practically constant at full engine load. On the other hand, the b.s.f.c. slightly increases with the increase of jojoba–gas
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Fig. 7. Comparison of variation of fuel conversion efficiency, A=F ratio and mass of fuel injected with engine speed at 2/3 engine load using different values of jojoba–gas oil blend ratio.
oil blend ratio. This may be attributed to the decrease in the calorific value of the blended fuel with the increase of jojoba oil percentage in the blend. Similar trends in the variation of engine power, b.m.e.p. and b.s.f.c. have been observed at 1300 rpm and full load, as also shown in Fig. 8. The variations of the absolute values of the engine emissions with engine speed at 2/3 load using different fuel blends is shown in Fig. 9. The NOx emission values using jojoba–gas oil blends are generally lower than those using 100% gas oil. The maximum reduction in NOx emission has been observed using 40%J–60%G and occurs at about the rated engine speed. Using 60%J–40%G fuel
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Fig. 8. Comparison of variation of engine power, b.m.e.p. and b.s.f.c. with jojoba oil percentage in the fuel blend at 1500 and 1300 rpm engine speed and different load conditions.
blend the absolute values of NOx emission increase with the increase of engine speed. The absolute emission values of CO increase with the increase of jojoba oil percentage in the fuel blend. It has also been observed that the variations of the absolute values of CO2 and O2 in the exhaust exhibit no specific trend as a function of the fuel blend ratio. Fig. 10 shows the variations of the specific values of the engine emissions with engine speed at 2/3 engine load. The reduction in specific engine NOx emission and the increase of engine specific CO emission with the increase of jojoba–gas oil blend ratio can be observed. The differences in the specific engine emissions using different fuel blends decrease with the increase of engine speed. This may be attributed to the increase in engine power and the enhancement of mixing with the increase of engine speed.
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Fig. 9. Comparison of variation of absolute values of engine emission (NOx , O2 , CO2 , CO) with engine speed at 2/3 engine load using different values of jojoba–gas oil blend ratio.
Fig. 11 shows the variations of the specific values of the engine emissions with jojoba–gas oil blend ratio at 1500 rpm rated engine speed for different load conditions. Specific NOx , CO and CO2 emissions slightly increase and O2 remains practically constant with the increase of jojoba percentage in the fuel blend. At 1/3 load, the NOx and CO2 emission are minimum using 20%J– 80%G fuel blend. Similar trends in the variations of specific engine emissions with blend ratio have been observed at 1300 rpm and full load, as also shown in Fig. 11.
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Fig. 10. Comparison of variation of specific values of engine emission (NOx , O2 , CO2 , CO) with engine speed at 2/3 engine load using different values of jojoba–gas oil blend ratio.
It can be concluded from the above discussion that adoption of jojoba–gas oil fuel blend ratio as high as 60% results in an insignificant loss in engine power and a reduction in NOx emission. The observed differences in the behaviour of the variations of engine emissions using different fuel blends indicate the need to adjust the engine operating parameters to suit a particular jojoba–gas oil blend. 4.3. Comparison of engine soot emission using jojoba–gas oil blends Comparisons of engine soot emission using different values of jojoba–gas oil blend ratio have been performed at 1300 and 1500 rpm engine speed for different load conditions. Table 2 shows
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Fig. 11. Comparison of variation of specific values of engine emission (NOx , O2 , CO2 , CO) with jojoba oil percentage in the fuel blend at 1500 and 1300 rpm engine speed and different load conditions.
the values of soot number at different conditions of engine speed and load using 0%, 20%, 40% and 60% jojoba–gas oil blend ratios. It can be observed that at the rated engine speed of 1500 rpm, the soot number increases with the increase of engine load. For a given engine load, the soot number decreases with the increase of jojoba oil percentage in the fuel blend. This decrease in soot number with increasing jojoba oil percentage in the blend may explain the increase in CO and CO2 emissions using jojoba–gas oil fuel blends, as compared to those using 100% gas oil. This may be attributed to relatively more oxidization of unburned hydrocarbons. On the other hand, oxidization of hydrocarbons may compensate for the relatively lower calorific
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Table 2 Soot number using different blend ratios of jojoba–gas oil at different engine load and speed conditions Fuel type
Engine load No load
1/3 load
2/3 load
1500 rpm 100% Gas oil 20%J–80%G 40%J–60%G 60%J–40%G
2 1–2 1 1
6 5–6 4–5 4
8 7–8 7 6–7
Full load 1500 rpm
1300 rpm
Over 9 Over 9 9 8–9
7 7 6–7 6
value of the jojoba oil blends as compared to that of gas oil. Thus, resulting in producing comparable values of engine power output using the jojoba–gas oil blends and 100% gas oil. These results are encouraging and prompt the feasibility to achieve further enhancement in engine performance and emission using jojoba–gas oil blends by adjustment of the engine operating parameters. A detailed study on engine combustion characteristics using different blends is a useful tool to optimise the engine performance for a particular fuel blend ratio.
5. Summary and conclusion An experimental evaluation of using jojoba oil as an alternate Diesel engine fuel has been conducted in the present work. Measurements of jojoba oil chemical and physical properties have indicated a good potential of using jojoba oil as an alternative Diesel engine fuel. Blending of jojoba oil with gas oil has been shown to be an effective method to reduce engine problems associated with the high viscosity of jojoba oil. Reasonable viscosity values have been obtained using blend ratios as high as 60%J–40%G oil. Other fuel properties, such as the flash point, pour point and calorific value are comparable. In addition, apart from other vegetable oils, jojoba oil contains no glycerides and has a straight chain chemical structure. Therefore, long term engine performance difficulties encountered using other vegetable oils may not be expected while using jojoba oil. Experimental measurements of different performance parameters of a single cylinder, naturally aspirated, direct injection Diesel engine have been performed using gas oil and blends of gas oil with jojoba oil. Measurements of engine performance parameters at different load conditions over the engine speed range have generally indicated a negligible loss of engine power, a slight increase in brake specific fuel consumption and a reduction in engine NOx and soot emission using blends of jojoba oil with gas oil as compared to those using gas oil. The reduction in engine soot emission has been observed to increase with the increase of jojoba oil percentage in the fuel blend. The results reported in this study should be viewed in the light of the fact that the engine used was unaltered and was designed to run on Diesel fuel. The observed differences, and sometimes inconveniences, in the behaviour of the variations of the engine emissions using different fuel blends calls for the need to adjust the engine parameters to suit a particular fuel blend. Further enhancement in the engine performance parameters are expected using minor modifications in the engine operating conditions, such as injection timing and pressure that can be optimized as a
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function of the jojoba–gas oil blend ratio. In general, the present results are encouraging and open a large scope for additional research work related to the evaluation and utilization of jojoba oil as an alternate Diesel engine fuel.
References [1] Wagner GL, Peterson CL. Performance of winter rape (Brassica napus) based fuel mixture in diesel engines. In: Proceedings of the International Conference on Plant and Vegetable Oils as Fuels, 1982. p. 329. [2] Varde KS. Some correlation of diesel engine performance with injection characteristics using vegetable oil as fuels. In: Proceeding of the International Conference on Plant and Vegetable Oils as Fuels, 1982. p. 303. [3] Schlautman NJ, Schinstock JL, Hanna MA. Unrefined expelled soybean oil performance in a diesel engine. Trans ASAE 1986;29(1):70–3. [4] Schmidt K, Van Gerpen JH. The effect of biodiesel fuel composition on diesel combustion and emissions. SAE 961086, 1996. [5] Zhang Y, Van Gerpen JH. Combustion analysis of esters of soybean oil in a diesel engine. SAE 960765, 1996. [6] Baranescu RA, Lusco JJ. Performance, durability and low temperature evaluation of sunflower oil as a diesel fuel. In: Proceeding of the International Conference on Plant and Vegetable Oils as Fuels, 1982. p. 312. [7] Borgelt SC, Harris FD. Endurance tests using soybean oil–diesel fuel mixture to fuel small pre-combustion chamber engines. In: Proceedings of the International Conference on Plant and Vegetable Oils as Fuels, 1982. p. 364. [8] Goodrum JW, Patel VC, McClendon RW. Diesel injector carbonization by three alternative fuels. Trans ASAE 1996;39(3):817–21. [9] Peterson CL, Thompson JC, Taberski JS. One thousand hour engine durability test with HYSEE and using a 5X-EMA test cycle. Trans ASAE 1999;42(1):23–30. [10] Pryde EH.Vegetable oil fuel standards. In: Proceedings of the International Conference on Plant and Vegetable Oils as Fuels, 1982. p. 101. [11] Salem AE. Synthesis of extreme pressure petroleum additive from local jojoba oil. In: The 12th International Seminar, New Trends in Engine and Industrial Lubricants, Fuels, Chemicals and Additives, Cairo, 2000. [12] Wisniak J. Chemistry and technology of jojoba oil: state of the art. In: Proceedings of the Sixth International Conference on Jojoba and its Uses, 1984. p. 311. [13] Wisniak J. Recent advances in the chemistry and properties of jojoba oil. In: Proceedings of the Seventh International Conference on Jojoba and its Uses, 1988. p. 222. [14] Spencer GF, List GR. Specifications, physical properties and methods of analysis for jojoba oil. In: Proceeding of the Seventh International Conference on Jojoba and its Uses, 1988. p. 173. [15] Wisniak J. Jojoba oil and derivatives. Prog Chem Fats Lipids 1977;15:176–218. [16] Radwan MS, Dandoush SK, Selim MYE, Kader AMA. Ignition delay period of jojoba diesel engine fuel. SAE 972975, 1997. [17] Osayed SMA. Measurement of laminar burning velocity of jojoba methyl ester. MSc Thesis, Faculty of Engineering, Mataria, Helwan University, Cairo 2001. [18] Kline SJ. The purposes of uncertainty analysis. Trans ASME 1985;107:153.