Study On Combustion And Emission Characteristics Of P50/Methanol Dual Fuel Engine

Diesel engines have the characteristics of high thermal efficiency,good power performance,and low HC and CO emissions.They are widely used in passenger cars,commercial vehicles,special vehicles,construction machinery,agricultural machinery,and ships,but their nitrogen oxides(NOx)and particulate matter(PM)emissions are high.In the face of increasingly strict diesel engine emission regulations,in order to achieve the goal of diesel engine energy conservation and emission reduction,the development and use of diesel alternative fuels has become an important research direction to solve the problem.Polymethoxy dimethyl ether(PODE)is often used as an alternative fuel for diesel.It is mainly prepared from production materials such as methanol,methylal and dimethyl ether.The physical properties of PODE are similar to that of diesel oil.They can be miscible with diesel oil and have high oxygen content and cetane number.China’s methanol fuel is mainly prepared from coal,and its production process is mature.It is currently a clean alternative fuel with great application prospects.Methanol has the characteristics of high latent heat of vaporization,low boiling point,and high octane number.At the same time,the oxygen content of methanol is as high as 50%,which can effectively suppress the formation of diesel particulate matter.However,methanol is highly polar and difficult to dissolve with diesel.Therefore,compact engines are generally used.The dual fuel combustion mode is used to study methanol and diesel fuel.The exhaust gas recirculation system can significantly reduce the combustion temperature in the cylinder,which can reduce the NOx emissions of the diesel engine.In order to further reduce diesel particulate emissions,this article chooses to add a highly miscible fuel with high oxygen content PODE to the pilot diesel.As the PODE kinematic viscosity is too low,direct use as a pilot fuel will exacerbate the wear of the high-pressure oil pump,and even cause damage to the high-pressure oil pump plunger components.Therefore,the PODE/diesel fuel is prepared by blending PODE with 0~#diesel according to 50%volume fraction,which is P50 fuel.In this test,P50 and methanol are used as test fuels.In the dual fuel mode,methanol is injected into the intake port to form a methanol-air premix,and then ignited by P50directly injected in the cylinder.This article is based on an in-line four-cylinder electronically controlled high-pressure common rail diesel engine.At an engine speed of1800 r/min,when BMEP is 0.42 MPa,0.70 MPa,and 0.98 MPa,different methanol substitution ratios(10%,20%,30%and 40%)and EGR valve opening(10%,20%,30%and 40%)on the combustion and emission performance of P50/methanol dual fuel engines.The results showed that:(1)Under all test conditions,the engine’s injection strategy includes pilot injection and main injection;under the same load,the ignition delay increases with the increase of the methanol replacement rate;as the EGR valve opening increases,the ignition delay slightly increased at different methanol replacement ratios.(2)Under the same load and EGR valve opening,as the methanol substitution ratio increases,the peak fuel heat release rate increases.When the load is 0.42 MPa,the peak combustion pressure and in-cylinder combustion temperature show a slight decrease trend,and the combustion starting point is shifted backward.Under the loading conditions of0.70 MPa and 0.98 MPa,the peak combustion pressure and peak combustion temperature increase with the increase of the methanol substitution ratio,but the average temperature in the cylinder gradually decreases during the afterburning period.At the same load and methanol replacement rate,as EGR valve opening increases,the peak in-cylinder pressure,peak heat release rate,and peak in-cylinder combustion temperature decrease slightly.(3)Under the same methanol replacement rate,as the load increases,the engine NOx emissions increase;when the load and EGR valve opening are the same,NOx emissions decrease as the methanol substitution ratio increases;and at the same load and At the methanol substitution ratio,NOx emissions decrease as the EGR valve opening increases.(4)When the engine low load is 0.42 MPa,when the EGR valve opening is less than30%,the methanol replacement rate has little effect on the ultrafine particle quantity concentration and volume concentration in the dual fuel combustion mode.When the load is 0.70 MPa,in the dual fuel combustion mode,when the EGR valve opening is constant,the number and volume concentration of ultrafine particles will gradually decrease with the increase of the methanol substitution ratio.The geometric average particle diameter shifts to a small particle diameter direction.When the load is 0.98 MPa,compared with the original machine using P50,with the increase of the methanol substitution ratio,the number and volume concentration of ultrafine particles increase in the dual fuel mode,and the geometric average particle size of the ultrafine particles increases.At the same load and methanol substitution ratio,as the EGR valve opening increases,the number and volume concentration of ultrafine particles increase.