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characteristics of rapeseed oil and its blends with diesel fuel in amulti-cylinder direct injection diesel engine. The results showeda significant reduction in NOxand relatively higher amount of sootfor rapeseed oil compared to diesel fuel. Huzayyin et al. [20] exper-imentally evaluated the jojoba oil as an alternative fuel in a singlecylinder, diesel engine. The results indicated that there was anegligible loss of engine power, a slight increase in BSFC and areduction in NO

xand soot emission using blends of jojoba oil with

diesel fuel. Golimowski et al.[21]studied the performance of rawrapeseed oil in a common rail diesel engine and concluded that thepower was reduced 1214% compared to that of diesel fuel.Fontaras et al. [22] measured the regulated and non-regulatedpollutants of three different vegetable oils (cottonseed, sunflower,and rapeseed) blended with diesel fuel, on a 1090% v/v ratio eachby using chassis dynamometer according to the legislated proce-dure and the Artemis driving cycles. The results indicated that allblends have limited effects on gaseous pollutants and vehicleperformance.

Engine performance and its emission characteristics alsodepend on the quality of the air-to-fuel mixture, actual start ofinjection, ignition delay and heat release process, therefore, thetest results obtained from different types of engines may varysubstantially. The objective of the present work is to evaluate theperformance of rapeseed oil blended with diesel fuel in a twocylinder agricultural direct injection diesel engine. The experimen-tal results of the engine combustionand emission characteristics ofthe diesel engine operated on the blends were analyzed and com-pared with the baseline data of diesel fuel in an unmodified dieselengine.

2. Rapeseed oil and its properties

Rapeseed is the second most important oilseed crop in theworld after soybean. Every year, about 31 million hectares of rape-seed are cultivated and 60 million tons of oilseed rape is produced.In China, the planting area of the rapeseed is about 6.7 millionhectares, and the total yield is about 12 million tons, accountingfor 20% of the worlds supply. Rapeseed oil contains low levels ofsaturated fatty acids (510%), high amounts of monounsaturatedfatty acids (4475%), some linoleic acid (1822%) and alpha-linole-nic acid (913%)[23]. Velasco and Becker[24]evaluated the fattyacid composition of rapeseed oil by near infrared reflectancespectroscopy (NIRS) and found average percentages of individualacids to be: palmitic, 4.0; stearic, 1.4; oleic, 46.8; linoleic, 19.5;linolenic, 8.7; eicosenoic, 6.2 and erucic, 11.4.

The diesel fuel and RSO used in this study was obtainedcommercially from a local company.Table 1reports the fuel prop-erties of diesel fuel and RSO. Without engine modification, the fuelproperties of the blends will affect the engine combustion andemissions. The density was measured following the ASTM D1298.The measurements were carried out at 20 C by using a calibratedglass gravity hydrometer, conducted three times for each sampleand the results were averaged. Viscosity is a physical phenomenoncaused by the resistance of a liquid to flow. A glass capillary kine-matic viscometer was used to measure viscosity at 40 C accordingto ASTM D445. The lower heating values (LHV) were measured byan automated bomb calorimeter. Other main properties were citedfrom other literatures [25,26]. In this study, the test engine wasoperated with diesel fuel and two different blends: 20% rapeseedoil80% diesel fuel (RSO20) and 50% rapeseed oil50% diesel fuel(RSO50). Main properties of RSO and its blends (RSO20 andRSO50) were measured and compared with those of diesel fuel.The results are shown inTable 2.

3. Experimental procedure

The engine used was a two-cylinder, naturally aspirated, fourstroke, water-cool, and direct injection diesel engine with a bowlin piston combustion chamber. The basic data of the engine usedare given inTable 3. With the liquid fuel injection, a high pressurefuel pump was used, having a plunger diameter of 8 mm connectedto a four-hole injector nozzle. The injector nozzle was located inthe center of the combustion chamber and had an opening pres-sure of 18 MPa. A high precision flow meter was used to measurethe fuel flow per 30 s. A Kistler piezoelectric transducer wasinstalled for monitoring the cylinder pressure (average for 100working cycles) coupled with Kistler charge amplifier. Indimeterwas used to record the measured data. Gaseous emissions weremeasured by a gas analyzer (AVL Digas 4000). Smoke was mea-sured by a part-flow smoke opacimeter (AVL Dismoke 4000). The

test installation is shown inFig. 1. To insure that the accuracy ofthe measured values was high, the gas analyzer was calibratedbefore each measurement using reference gases. The smoke den-sity was indicated by Kvalue.Table 4 shows the main specificationand the resolution of the measurement devices.

To prevent problems of high fuel viscosity and cold start, the en-gine was always started using diesel fuel and then switched to theblends. The engine was allowed to run for approximately4550 min to make sure that all diesel fuel was flushed out bythe blends before the start of measurements. Similarly, while shut-ting down, the engine was switched back from the blends to dieselfuel and run for another 45 min to ensure that only diesel fuel wasleft inside the fuel system to avoid problems associated with coldstart. The experiments were carried out under different engine

loads at engine speed of 1500 r/min. The cylinder pressure, fuelconsumption and exhaust emissions such as NOx, HC, CO andsmoke were measured. Significant engine performance parameterssuch as BSFC, BSEC and brake mean effective pressure (BMEP) werecalculated. In addition, the heat release rate was calculated toevaluate the combustion characteristics of the test fuels.

Due to the pulsed characteristics of the engine, we always took3 measurements to average the data for each operating condition.To estimate the repeatability of measurements and the accuracy ofthe procedure, the coefficient of variance (COV) for each measuredparameter was determined. It represented the standard deviationof each magnitude as a percentage of its mean value. The COVfor each main measured parameter is presented in Table 5. Consid-ering these values, it revealed that the measurements were quite

repeatable especially for engine performance. As far as pollutantemissions were concerned, the COV was less than 3.5% for gaseous

Table 1

Main properties of diesel and rapeseed oil.

Properties Diesel Rapeseed oil

Chemical formula C13H14 C57H105O6Average molecular weight 180192 885Density at 20 C (g/ml) 0.829 0.912Kinematic viscosity at 40 C (mm2 s1) 2.68 23.91Flash point (C) 78 244Self-ignition temperature (C) 250 320Cold filter plugging point (C) 5 15Pour point (C) 0 20Cetane number 51.6 4448Sulfur (mg/kg) 33 2Contamination (mg/kg) 0.2 25Iodine number (J2g/100 g) 6 111Acid value (mg KOH/g) 0.06 2.0Oxygen content (wt%) 0.4 10.8Carbon to hydrogen ratio 6.9 6.5Lower heating value (kJ/kg) 42,636 36,995Stoichiotric airfuel ratio (kg/kg) 14.45 12.56Ash content (mass %) 0.01 0.01

Water content (mg/kg) 28 75

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pollutants and 3.7% for smoke. Using the measured data, we canderive sound conclusions for the effects of rapeseed oil operationon engine performance and emissions.

4. Results and discussion

4.1. Combustion characteristics

The cylinder pressures variation of the test fuels under differentengine loads at engine speed of 1500 r/min is shown inFig. 2. It isclear that the cylinder pressure is increased with increase of engineload. The test fuels follow the similar cylinder pressure patternunder different engine loads, but the peak cylinder pressure andits corresponding crank angle vary significantly with the volumefraction of RSO in the blends. It can be seen that RSO50 showsthe highest peak cylinder pressure at low engine load, and almostsimilar value to that of RSO20 and diesel fuel at high engine load.The corresponding crank angles are retarded with the increase ofRSO volume fraction in the blends at low engine load, but advancedat high engine load.

Ignition delay is one of the important combustion parameter asit affects the start of combustion, cylinder pressure and heat

release rate. The ignition delay is a period between start of injec-tion into the combustion chamber and start of combustion. In thisstudy, the ignition delay period was not measured, but, the start ofcombustion may reflect the variation of the ignition delay becausethe fuel pump and injector setting were kept identical for the testfuels. FromFig. 2, it can be seen that the combustion of the testfuels starts almost at the same crank angle at low engine load,and the start of combustion is advanced with the increase of RSOvolume fraction in the blends at high engine load. Because of ahigher bulk modulus and higher viscosity of RSO, the injection tim-ing of the blends would be earlier than that of diesel fuel, whichindicates longer ignition delay of the blends at low engine load[27].When the ignition delay period increases, more fuel will bephysically prepared for chemical reaction which increases theamount of air-fuel mixture burned and the heat release rate inthe premixed combustion phase. This leads to the rise in peakcylinder pressure. As the engine load is increased, the ignitiondelay period decreases because the gas temperature in the cylinderis increased, which result in the earlier start of combustion for theblends. The peak cylinder pressures of the test fuels are almostidentical due to the almost same ignition delay and different startof combustion.

The heat release rate variation of the test fuels under differentengine loads at engine speed of 1500 r/min is shown in Fig. 3. Itcan be seen that the combustion process of the blends is similar,consisting of premixed combustion phase following by diffusioncombustion phase. It also shows that the peak heat release rate in-

creases with the growth of engine load. There is a little differenceamong the traces of the test fuels. At low engine load, the peak heatrelease rate of RSO50 is the highest and that of diesel fuel is lowest.As mentioned above, when the ignition delay increases, more fuelwould be physically prepare, which increases the amount of fuelburned and the heat release rate in the premixed combustionphase. At high engine loads, the peak heat release rate is almostidentical, but the combustion process of RSO50 is advanced. Theadded RSO slightly affected spray tip penetration and spray cone

Table 2

Main properties of the test fuels.

Properties Diesel Rapeseed oil RSO20 RSO50 Test methods

Density at 20 C (g/ml) 0.829 0.912 0.848 0.873 ASTM D1298Kinematic viscosity at 40 C (mm2 s1) 2.68 23.91 4.46 9.64 ASTM D445Lower calorific value (kJ kg1) 42,636 36,995 41,420 39,680 ASTM D2015Flash point (C) 68 234 86 122 ASTM D93

Table 3

Specification of test diesel engine.

Engine type Two cylinder, 4-stroke, DI

Bore (mm) 100Stroke (mm) 105Connecting rod (mm) 164Compression ratio 17:1Displacement (ml) 1650Rated power (kW) 13.7Rated speed (r/min) 2500Fuel injection timing (deg. BTDC) 19 (Static)Injector holes (mm) 4 0.32Injector opening pressure (MPa) 18

Fig. 1. Schematiclayout of the testinstallation. 1. CI Engine2. Eddy current dynamometer 3. Injector 4. Fuel pump 5. Fuel filter 6. Fuel tank7. Airstabilizing tank8. Airfilter 9.AVL smoke meter 10. AVL Di-gas analyzer 11. Pressure transducer 12. TDC encoder 13. Charge amplifier 14. Indimeter 15. Monitor 16. Exhaust silencer.

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angle, whereas the droplet size of the blends increased with an in-crease of the RSO volume fraction because of the high viscosity.Although the beginning of heat release is advanced with theincrease of RSO volume fraction, the end of heat release remainsat almost the same crank angle for the blends, which leads to theextension in the combustion duration.

4.2. Performance and emissions

Fig. 4 shows the BSFC variation of the diesel and the blends withrespect to BMEP at engine speed of 1500 r/min. It can be seen thatunder almost all engine loads, BSFC of RSO20 is almost similar tothose of diesel fuel, but those of RSO50 are evidently higher. Thedifference of BSFC between them is reduced with the increase ofengine load. The BSFC of diesel engine depends on the relationship

among volumetric fuel injection system, fuel density, viscosity andlower heating value (LHV). More blends are needed to produce thesame amount of power due to its lower LHV in comparison withdiesel fuel, especially for RSO50. Brake specific energy consump-tion (BSEC) is an ideal parameter for comparing engine perfor-mance of fuels having different LHV.Fig. 5shows the comparisonof BSEC of the test fuels under different engine loads. The figure

Table 4

The main specification and the resolution of the measurement devices.

Instrumentation Measuring range Resolution Operating Temperature (C)

AVL Digas 4000 HC (ppm) 020,000 1 535, max.40CO (%) 010 0.01NOx(ppm) 04000 1CO2(%) 020 0.1

AVL Dismoke 4000 Kvalue (m1) 099.99 0.01 545

Opacity (%) 0100 0.1Kistler 6051B1 transducer for cylinder pressure Pressure (bar) 0250 1 10-4 -50-350, max.400Fuel Flow Meter Flow (ml) 0100 0.01 545Oxygen bomb calorimeter Heat capacity (JK1) 14,00015,000 1528

T(C) 1035 0.001

Table 5

Coefficient of variance for measured magnitudes.

Measured magnitude Coefficient of variance

Cylinder pressure 1.4BSFC 2.3Nitrogen oxide 3.5Hydrocarbon 3.4Carbon monoxide 2.8Kvalue 3.7

Fig. 2. Variation of cylinder pressure with respect to crank angle. Fig. 3. Variation of heat release rate with respect to crank angle.



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shows that the BSEC of RSO20 is almost similar to that of diesel fuelunder all range of engine load. At low engine loads (less than0.32 MPa), BSEC of RSO50 is higher than that of diesel fuel, but isalmost identical at high engine loads (more than 0.4 MPa).

Fig. 6shows the variations of NOxemissions with respected toengine loads at engine speed of 1500 r/min. Generally speaking,there are three primary sources of NOx in combustion processes:thermal NOx, fuel NOx and prompt NOx. Thermal NOx formation,which is highly temperature dependent, is recognized as the mostrelevant source from engine combustion. The formation rate of NOxis primarily a function of combustion (flame) temperature, the res-idence time of nitrogen at that temperature, and the contents ofoxygen in the reaction regions in the combustion chamber [28].It can be seen fromFig. 6that the NOxemission is increased withthe rising of engine load. This is due to more fuel is injected andcombusted in the cylinder when engine load increases, whichcauses higher gas temperature.

It also can be seen that the emission of NOxis slightly lower forthe blends at low engine load. As the engine load is increased, thegap of the emissions between he blends and diesel fuel gets nar-rowed. The main reason is that RSO have higher viscosity thereforethe fuel droplet size in the cylinder is expected to be larger thanthat of diesel fuel. Larger droplets have longer combustion dura-tion and significant energy release during the late burning phase.This suggests that the peak combustion chamber temperature ispossibly lower for the blends compared to diesel fuel, leading tolower formation of NOx. With the increase of engine load, due tomore fuel injections and then higher combustion temperature,the effect of viscosity may not be a dominating factor, and the con-tents of oxygen in the reaction regions has an increased effect onthe NOxformation. So the NOxemissions of the blends are almostsimilar to that of diesel fuel. It has been shown fromthe multi-zonemodeling studies that the temperature distribution for the plant oil

sprays was lower compared to diesel fuel, which resulted in lowerNOxemissions for plant oils[29].

Fig. 7shows the variation of the light absorption coefficient ofsmoke (Kvalue) with respect to BMEP at engine speed of 1500 r/min. With the increase of engine loads, smoke emission is

increased. It can be seen that RSO50 gives higher smoke even atlower engine loads. Higher smoke opacity may be due to pooratomization of RSO. Bulky fuel molecules and higher viscosity ofRSO result in poor atomization of the blends. In addition, thesmoke emissions are higher due to faster chemical decompositionand cracking at low temperatures. This leads to formation of a ser-ies of hydrocarbons, which tend to act as soot precursors leading tohigher amount of soot formation[30].

Figs. 8 and 9show the variations of the CO and HC emissionswith respect to BMEP at engine speed of 1500 r/min. Within themost experimental range, CO and HC emissions from the blendsare higher than those from diesel fuel. This is possible because ofthe high viscosity of RSO, which made it the more difficult toatomize for the blends. This resulted in locally rich mixtures in

the engine. In consequence it caused more CO and HC generatedduring the combustion, due to the lack of oxygen locally. Only at

Fig. 4. Variation of BSFC with respect to engine loads.

Fig. 5. Variation of BSEC with respect to engine loads.

Fig. 6. Variation of NOxemission with respect to engine loads.

Fig. 7. Variation of smoke emission with respect to engine loads.

Fig. 8. Variation of CO emission with respect to engine loads.

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high engine load (0.61 MPa), the CO emission of the blends is lowerthan that of diesel fuel. The findings and trends were supported byliterature available data[31,32]. This is possibly due to two factorsthat the temperature in the cylinder is higher at the high engineload, which makes the blends easier to atomize, a better airfuelmixture and then a better combustion can be achieved. In addition,

the oxygen contents in RSO make it easier to be burnt at highertemperature in the cylinder, which also results in the lower COemission for the blends.

5. Conclusions

The objective of this study was to characterize the rapeseedoildiesel blends on the combustion, performance and exhaustemissions of a diesel engine. Based on the experimental results,the following conclusions can be drawn:

(1) Blending rapeseed oil with diesel fuel was an effectivemethod to reduce the viscosity of the fuel and can be usedin diesel engine without any modification.

(2) The BSFC of rapeseed oildiesel blends was higher than thatof diesel fuel under all range of engine loads, but the BSECwas improved at high engine loads.

(3) At different engine load, rapeseed oildiesel blends showedvarious combustion characteristics compared to that of die-sel fuel. The peak cylinder pressure and heat release ratewere higher at low engine loads, but almost identical at highengine loads.

(4) The smoke, CO and HC emissions of the blends were higherthan that of diesel fuel under almost all engine loads, but thedifferences of NOx emissions among the test fuels were notevident.

Acknowledgements

The authors wish to express their deep thanks to the scientificresearch foundation for the returned overseas of China and thecolleagues in the center for combustion energy at TsinghuaUniversity.

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Fig. 9. Variation of HC emission with respect to engine loads.

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