Research On The Effect Of Percentage Of Energy Substitution Of Diesel-piloted Direct-injection Natural Gas Engine

Natural gas has the characteristics of high reserves,high octane number,relatively clean combustion products,and wide ignition limit,which determine that natural gas is a reliable alternative fuel with great potential,relatively low cost,and suitable for today’s market.In order to better meet the popular National VI emission regulations and the"dual carbon"target,natural gas engines have occupied a certain share in the market,but traditional port injection natural gas engines have problems such as throttling loss,which lead to Compared with the original engine,the power of the engine has a power loss of about 15%.Therefore,in order to ensure the power of the engine,the diesel pilot direct injection natural gas engine has become an excellent choice for today’s internal combustion engine research.For a dual-fuel engine,the injection of diesel and natural gas in different proportions has a greater impact on the engine.In order to explore the specific impact of the substitution rate on the engine,this paper modifies the natural gas direct injection system on the basis of the Changfa CF-18M single-cylinder diesel engine.And use the d SPACE platform to develop a rapid control prototype,through its complete software and hardware environment to carry out the open control of high-pressure natural gas injection,and build a diesel pilot direct injection natural gas engine test platform.This paper chooses to conduct experimental research by controlling the diesel throttle opening and the natural gas injection pulse width under the premise of ensuring that other boundary conditions such as intake air temperature,intake flow rate,diesel and natural gas injection advance angles remain unchanged.Due to the after-combustion phenomenon caused by the low flow rate of the natural gas nozzle and the limiting factors such as the in-cylinder temperature,the 3-10ms natural gas injection pulse width and the 25%,30%,35%,40%diesel throttle opening,3-8ms natural gas injection pulse width test scheme to explore the effect of substitution rate on engine power,economy,combustion process and emission performance.In the test process,it was first found that for the direct injection of natural gas,due to the high injection pressure,the in-cylinder turbulence intensity is large,and the ordinary spark plug or low diesel fuel injection volume is not enough to fully burn the natural gas,which will cause the engine to work.Extremely unstable phenomenon,after testing,the test platform built in this paper can work stably and reliably when the throttle opening is higher than 8%,that is,when the diesel flow is 0.4kg/h.The main research results show that:from the perspective of power,the change of the substitution rate has no obvious effect on the peak torque that the engine can achieve.From the perspective of combustion,the main reason is that the peak cylinder pressure does not change significantly,which fully proves that the direct injection The huge potential of natural gas engine power;the increase of diesel fuel injection amount and natural gas injection amount will speed up the combustion rate and make the combustion phase move forward.The combustion duration is greatly shortened,and the combustion end point is greatly advanced;the increase of the natural gas replacement rate will lead to a"double-peak trend"in the heat release rate curve,and the peak of the second heat release rate will increase accordingly.The heat release rate peak phase shifts forward,and the single heat release rate peak can be recovered under the condition of large throttle opening and high natural gas replacement rate;affected by the mixing degree of natural gas and air and the mixing degree of diesel and natural gas,with the amount of diesel and The increase of the natural gas substitution rate will make the effective thermal efficiency increase and then decrease,and there is an optimal economic operating point at low throttle opening and high natural gas substitution rate;CO,THC,NO_Xemissions will all increase with the natural gas substitution rate.The emission performance can be improved by increasing the throttle opening,but it will be accompanied by a slight increase in the exhaust temperature.