| Diesel engines have the advantage of high thermal efficiency and stable work,which is widely used in the industrial field and transportation industry.At the same time,the extensive use of diesel engines have caused energy and environmental problems.Because vegetable oil is renewable and environmentally friendly,applying vegetable oil to diesel engines can solve these problems.Palm oil is the most productive vegetable oil in the world,but it has a high viscosity and cannot be used directly in engines.The micro-emulsified technology is a method of reducing viscosity.In order to investigative the influences of EGR rate(0% to 40%)and injection strategy(PIT 5°CA to 13°CA and PIQ 1.6mg/Stroke to 2.4mg/Stroke)on a high-pressure common rail four-cylinder diesel engine,this paper formulated four different ratios of diesel/palm oil/ethanol micro-emulsified fuel,including D70P30E10 D70P30E30D50P50E10 and D50P50E30.Research shows that:(1)Compared with D100,the theoretical air-fuel ratio of the four micro-emulsified fuels has been reduced.As the proportion of ethanol in micro-emulsified fuels increases,the density and kinematic viscosity of the fuel decrease,but as the proportion of palm oil in micro-emulsified fuels increases,the density and kinematic viscosity of the fuel increase.Among them,D50P50E10 has the highest density and kinematic viscosity.However,increasing the proportion of ethanol and palm oil in the micro-emulsified fuel has little effect on the surface tension of the fuel.(2)The ignition delay(ID)of D70P30E10 and D50P50E10 fuels is shorter,and the ID of D70P30E30 and D50P50E30 fuels is longer.After the introduction to EGR,the ID of the five fuels has been extended,but with the increase PIQ,the ID of the five fuels has a tendency to shorten.Under the same load,the in-cylinder pressure on fuel D50P50E30 is the largest,and the in-cylinder pressure on D100 is the smallest.This trend is the same as the change trend of the heat releases rate(HRR).After the introduction to EGR,there is a decreasing trend.However,with the advancement of PIT and the increase PIQ,the in-cylinder pressure and the HRR tend to increase.In the test,the COVIMEP varies from 0.98% to 4.87%,and the COVPmax varies from 0.51% to 1.08%.As the average effective pressure increases,COVIMEP tends to decrease.(3)Compared with D100,the brake specific fuel consumption(BSFC)and the brake thermal efficiency(BTE)of the four micro-emulsified fuels are more increased,which the fuel of the highest BSFC is D50P50E30.After the introduction to EGR,the BTE has decreased,however the BSFC has increased.With the advancement of the pilot injection timing(PIT)and the expand pilot injection quantity(PIQ)the change law of the BSFC and the BTE is the same as the change trend of the introduced EGR rates.(4)The NOx emissions of all the tested fuels were almost the same and decreased as the EGR rate increased.As the content of ethanol and palm oil in the micro-emulsified fuel increases,HC emissions decrease slightly,However,with the increase of EGR rate,there is a slight increase in HC emissions.Meanwhile,the pre-injection advances and the PIQ increases will lead to a decrease in HC emissions,but an increase in NOx emissions,Respectively.After ethanol and palm oil are added to the micro-emulsified fuel,the soot emissions are significantly reduced.The PIT and PIQ have little effect on the particulate matter emissions,but after the introduction of EGR,the soot emissions has a slight upward trend. |
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