高压缩比点燃式发动机甲醇/PODE燃烧特征研究

Study on Combustion of Methanol/PODE in High Compression Ratio Spark-Ignition Engines

在甲醇发动机中,通过提高压缩比和火花点火,并采用聚甲氧基二甲醚(PODE)作为活性改进燃料,可实现混合气压燃,突破火焰传播速度对热效率的限制。研究了双燃料火花辅助压燃(SACI)模式与单燃料甲醇点燃在不同负荷和转速下的燃烧特征、热效率和排放特性。结果表明,双燃料SACI对热效率的作用效果与负荷区间相关,BMEP为0.8 MPa时,热效率可达到41.9%,相比甲醇点燃提高1.9%,BMEP小于0.4 MPa时,循环变动较高,热效率低于甲醇点燃;双燃料SACI有利于降低NO_(x)排放,在BMEP为0.8 MPa时,NO_(x)排放比甲醇点燃减少79%;转速提高可加速PODE扩散,有助于初期可燃混合气形成,燃烧中压燃比例降低,火焰传播引燃比例提高;低负荷时HC排放随转速增加而降低;高转速会导致压燃比例降低,NO_(x)排放增加;低速大负荷对效率和排放较有利。

In methanol engines,mixed-gas compression ignition can be achieved by increasing the compression ratio,using spark ignition,and adopting polyoxymethylene dimethyl ethers(PODE)as the active improved fuel.This approach overcomes the limitations imposed by flame propagation speed on thermal efficiency.Experiments were conducted to investigate and compare the combustion characteristics,thermal efficiency and emission properties of dual-fuel spark-assisted compression ignition(SACI)mode and single-fuel methanol ignition at different loads and engine speeds.The main conclusions are as follows:the effect of dual-fuel SACI on thermal efficiency varies with the load range.At a BMEP of 0.8 MPa,the thermal efficiency reaches 41.9%,an increase of 1.9%compared to methanol ignition.However,at BMEP levels below 0.4 MPa,the cyclic variability is higher and the thermal efficiency is lower than that of methanol ignition.Dual-fuel SACI reduces NO_(x) emissions,achieving a 79%reduction compared to methanol ignition at a BMEP of 0.8 MPa.Increasing RPM accelerates PODE diffusion,aiding the formation of the initial combustible mixture,decreasing the proportion of compression ignition in combustion,and enhancing the proportion of flame propagation ignition.At low loads,HC emissions decrease with higher RPM.However,high RPM reduces the compression ignition ratio and increases NO_(x) emissions.Low RPM and high load conditions are more favorable for efficiency and emissions.These findings provide valuable support for the application of methanol engines.