| Faced with the dual pressure of environment and energy brought by the vigorous development of automobile industry,the development of internal combustion engine is facing enormous challenges.In this severe situation,it is particularly important to find new renewable clean energy to alleviate oil pressure and improve vehicle emissions.Palm oil is the main raw material for biodiesel production.As the largest vegetable oil in the world,palm oil can be used as an alternative fuel for diesel engines because of its high cetane number and oxygen content.However,the viscosity of palm oil is very high,and it is solid at room temperature,so it can not be directly used in diesel engines.The kinematic viscosity of gasoline and the temperature of distillation are low.Adding gasoline to diesel/palm oil base fuel can make the physical and chemical properties of the blend reach the level of diesel oil.It can not only effectively replace fossil diesel oil,but also improve the evaporation and atomization effect of fuel,and form a more uniform combustible mixture.It has high expectations for improving engine emissions.In this paper,a four-cylinder high pressure common rail diesel engine was tested.The diesel/palm oil blend(D70Z30)with a volume ratio of 7:3 was used as the basic fuel.Choosing gasoline as blending fuel,adding 20% and 40% volume ratio into the base fuel to prepare diesel/palm oil/gasoline blends,expressed in D70Z30G20 and D70Z30G40 respectively.Firstly,the effects of diesel/palm oil/gasoline blends with different blending ratios on engine combustion performance and emission performance were studied.Secondly,EGR was introduced to study the effects of different EGR rates on engine combustion performance and emission performance.The results show that:(1)With the increase of gasoline blending ratio,the cetane number,kinematic viscosity,cold filter point,condensation point and calorific value of D70Z30G20 and D70Z30G40 blends decreased,and the 50% distillation temperature of D70Z30G40 blends was the lowest.(2)With the increase of engine load,the ignition delay of D100,D70Z30G20 and D70Z30G40 is shortened,the combustion pressure in cylinder increases,the instantaneous heat release rate increases,and the average temperature in cylinder increases.With theincrease of gasoline blending ratio,the ignition delay and peak combustion temperature of blended fuel increase.(3)With the increase of engine load,NOx emissions of D100,D70Z30G20 and D70Z30G40 fuels increase,and the peak concentration of ultrafine particles gradually shifts from small particle size to large particle size.With the increase of gasoline blending ratio,the NOx emission of blended fuel increases and the peak concentration of particulate matter gradually shifts to the direction of small particle size.(4)With the increase of EGR rate,the ignition delay of D100,D70Z30G20 and D70Z30G40 fuels prolongs,the peak combustion pressure and peak heat release rate decrease,and the combustion temperature decreases.(5)With the increase of EGR rate,NOx emissions of D100,D70Z30G20 and D70Z30G40 fuels decreased and the peak values of particle concentration and volume concentration gradually shifted from small particle size to large particle size. |
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