The Study Of Gasoline-ethanol Dual Fuel Injection On Engine Combustion And Emission Performance

Ethanol is considered as a promising alternative fuel in terms of addressing future energy and environmental problems.However,the existing method of blending gasoline and ethanol does not fully exploit ethanol's advantages.A new methods,dual fuel compound injection strategy,namely ethanol direct injection plus gasoline port injection(EDI+GPI),provides a new way to make more efficient use of ethanol fuel properties.An ethanol direct injection(EDI)system was installed to a single-cylinder four-stroke SI engine,originally equipped with gasoline port-fuel injection(GPI)system,making it possible for dual-injection.The influence of ethanol/gasoline energy ratio(EER)on engine emission performance was first experimental studied,and then engine computational fluid dynamics(CFD)model was established to visually analyze the characteristics of in-cylinder temperature and composition distribution,which may add for better understanding the experimental results,the formation mechanism of pollutants in the cylinder.By analysing of test data and simulation results,it is shown that:(1)According to the experimental data,after adding ethanol into the gasoline engine,with the increase of EER,the faster flame propagation speed of ethanol accelerated the combustion heat release,the overall combustion phase in the cylinder advanced,and the maximum burst pressure Pmax increased.The combustion duration,both of CA50(the Angle at which the crankshaft rotates when the fuel burns50%)and CA90(the Angle at which the crankshaft rotates when the fuel burns 90%)are gradually shortened,which indicates an increase in thermal efficiency;The volume efficiency of the engine increases and the IMEP increases too.As the low heat value of ethanol is lower than that of gasoline,the indicated specific fuel consumption rate(ISFC)increases,while the indicated specific energy consumption(ISEC)decreases.Direct injection of ethanol reduced the number of C atoms in the cylinder and increased the oxygen content,and improved the combustion quality.The emission of CO and soot were significantly lower than that of pure gasoline.The charge cooling effect of direct injection of ethanol reduced the temperature in the cylinder and NO_x emissions.As can be seen from the simulation results,under the condition of pure gasoline,CO and soot are distributed in the whole cylinder space,while at the condition of compound injection,CO and soot are mainly generated in the area belowthe air inlet valve.NO_x is generated in the area with high combustion temperature in the center of the cylinder.HC mainly exists near the side wall of the inlet valve.(2)With the increase of fuel injection pressure,the break up and evaporation of ethanol spray jet is more sufficient,and the improvement of in-cylinder mixing period,which improves the combustion efficiency.Finally IMEP increases,while ISFC and ISEC decrease.The full combustion in the cylinder reduces the ISCO and the ISHC rises due to the enhanced fuel film and gap action on the wall.(3)When the injection pressure is fixed,with the advance of the injection time,the ethanol has more adequate time for heat absorption and evaporation,the quality of the mixture in the cylinder is improved,and the combustion efficiency is improved.The ISFC and ISEC of the engine are reduced,but the IMEP is increased.Ethanol evaporation and heat absorption reduces the temperature in the cylinder,and ISNO_x decreases.The variation of ISCO and ISHC are generally small.Influenced by the opening time of the inlet valve,when the EDI injection time is 130 CAD BTDC,the emissions of ISCO and ISHC are at high level.(4)Advancing ignition timing makes the overall combustion pressure and temperature in the cylinder rise,and NO_x emissions increase;Insufficient mixing timing leads to increased CO and HC emissions;Soot is oxidized adequately,and the emission decreased.