Simulation Study On Performanceof Diesel Engine Fueled Oxygenatedblend Fuel At Different Altitudes

Since fossil fuels were non-renewable,energy crisis has became more and more serious nowadays and a lot of attention has been paid to the research of alternative fuels for diesel engine.Biodiesel and ethanol,with its oxygenated and renewable property,can improve the physicochemical properties of the fuel after mixing with diesel fuel,thus meeting the requirements of diesel engine combustion.Therefore,the application of biodiesel-ethanol-diesel(BED)blends in diesel engines has been widely studied.Firstly,the miscibility of BED blends was tested,and the physical and chemical properties were calculated,which verified the feasibility of taking BED blends as diesel alternative fuels.Based on the simulation model,the effects of BED blends with different mixing ratios on diesel engine performance were analyzed.Based on the result,B15E5D blends were selected as the research fuel for further study on the effects of altitude on the external characteristics of diesel engine,as well as operating conditions of 1800r/min partial load and transient operating condition.Finally,the dynamic performance of diesel engine at high altitude is restored by oxygen-enriched intake,and its influence on the performance of diesel engine is further studied.The results show that:(1)BED blends can be completely soluble at 20℃,and the physical and chemical properties can meet the working requirements of diesel engines.(2)Compared with 0#diesel fuel,with the increase of BED blending ratio,the external characteristic torque decreases,the brake specific fuel consumption increases,the NO_x emission increases,and the Soot emission decreases.At 1000r/min,when B15E5D mixed fuel is used,the torque is reduced by 34.97%and the fuel consumption is increased by9.95%compared with 0km above sea level and 4km above sea level.(3)When the altitude rises,the maximum pressure in the cylinder of the diesel engine decreases,the maximum temperature in the cylinder rises,theNO_x emission decreases,the Soot emission increases,the torque decreases,the effective fuel consumption increases,and the lower the speed,the greater the impact.(4)The simulation result on operating conditions of 1800r/min partial load(25%full load,50%full load,75%full load)shows that with the increase of altitude,the maximum temperature in cylinder rises,the maximum cylinder pressure decreases,the Soot emission increases,and the combustion duration increases.At 25%of full load,the brake specific fuel consumption is firstly reduced and then increased with the increase of altitude,at other loads the brake specific fuel consumption increased with the increase of altitude,while theNO_x emissions has ups and downs.(5)Under transient operating condition of constant speed and increasing torque,the influence of elevation on the transient and steady-state process of diesel engine is similar,but there is turbine hysteresis in the transient process.And with the increase of altitude,the fluctuation of diesel engine performance parameters caused by the change of fuel injection rate is greater.(6)It is found that with the increase of oxygen concentration in intake air,the torque of diesel engine increases,the brake specific fuel consumption decreases,the combustion improves,and the Soot emission decreases sharply,while theNO_x emission increases.At the altitude of 3km and the intake oxygen concentration of 26%,compared with the torque at 0km altitude,it recovered to92.14%at 1200R/min and 97.78%at 1800r/min.