Study On The Method Of Improving Ethanol Substitution Rate Of Diesel Engine Under High Load

At present,diesel engines using ethanol fuel can achieve good energy saving and emission reduction effects,but high ethanol substitution rate under high load will sharply increase the maximum pressure rise rate of the engine,making the engine work rough.In order to explore the performance of high ethanol substitution rate under high load of diesel engine and the method of improving ethanol substitution rate,this study adopts GT-Power software,introduces the numerical calculation theory of each model,establishes numerical simulation model of diesel engine and conducts experimental verification,and simulates different ethanol The influence of the substitution rate on the combustion characteristics of diesel engines was selected as the optimal basic operating condition when rough combustion occurs with high ethanol substitution rate.)on the combustion performance of diesel engines.By changing the boundary conditions,the rough combustion conditions under high ethanol substitution rate are optimized,and the combustion characteristics and performance parameters of the ethanol-diesel dual-fuel engine before and after optimization are compared.The main research content with the result as follows:(1)The effects of different ethanol substitution rates on engine combustion and performance parameters were studied by simulation.It can be seen that with the increase of ethanol substitution rate,the maximum burst pressure in the cylinder decreases,and the maximum heat release rate increases gradually.The average temperature in the cylinder first increased and then decreased,and the ignition delay period gradually became longer with the increase of ethanol blending ratio,and reached the maximum at E50,and the combustion duration was the shortest.The effective power,torque and effective indicated pressure rise to varying degrees.The effective thermal efficiency of the engine increases and the equivalent fuel consumption decreases.(2)The ethanol substitution rate of 30% was selected as the optimal operating point for rough combustion,and the comprehensive effects of fuel injection timing,intake air temperature,EGR rate and ethanol water content on the combustion and performance parameters of the diesel engine were simulated and studied,and it was known that the fuel injection timing The increase is beneficial to the mixing of oil and gas,which makes the combustion rapid and concentrated,and the peak values of cylinder pressure and heat release rate increase.At-14°CA ATDC,the power and economy reach the best;However,the combustion speed slows down at the same time,so the combustion duration increases,the peak value of cylinder pressure and heat release rate decreases,and the power and economy decrease;the increase of EGR rate is affected by the heat capacity effect of the introduced exhaust gas,which reduces the combustion temperature in the cylinder.The combustion reaction rate decreases,the combustion phase is delayed,and the economy and power are reduced;the increase of the ethanol water content increases the latent heat of vaporization of water molecules,which can reduce the in-cylinder combustion temperature,combustion rate and cylinder pressure peak,and the power and economy are improved.Due to the influence of the increase of water content on the calorific value of fuel,the thermal efficiency is the largest at 10% water content.(3)Comparing the combustion and performance parameters before and after the optimization of the high ethanol substitution rate condition,it can be seen that the cylinder pressure,heat release rate,maximum combustion temperature,power,and torque of the optimized engine decrease to varying degrees;the change in the maximum pressure increase rate In order to reduce from 6.25 bar/deg to 4.96 bar/deg,the reduction rate is 20.64%,which can effectively alleviate rough combustion.The equivalent fuel consumption increased during this process,and the thermal efficiency decreased,but it had a good consistency with the working conditions before optimization.Therefore,through the study of different boundary conditions for high load and high ethanol substitution rate,it can provide a feasible scheme and theoretical basis for improving the ethanol substitution rate under high load.