直喷米勒循环汽油机燃用甲醇/汽油燃料燃烧及排放特性分析

Analysis of Combustion and Emission Characteristics of Methanol/Gasoline Fuels in a Direct Injection Miller Cycle Gasoline Engine

围绕高压缩比米勒循环发动机的热效率潜力及甲醇及甲醇/汽油混合燃料对燃烧过程和排放特性的影响进行了深入分析。通过试验对比分析,研究了不同压缩比下米勒循环与传统奥托循环的热效率,探究了甲醇燃料对发动机燃烧性能和排放影响的机理。结果表明,米勒循环在高速高负荷工况下相比奥托循环展现出更高的热效率潜力,同时能够提高对高压缩比的耐受性。试验所选2000 r/min、总平均指示压力(global indicated mean effective pressure,GIMEP)为0.66 MPa工况下,采用米勒循环后在压缩比分别为11.5和14.5时,指示热效率可相对于奥托循环提升约0.6和0.8个百分点。燃用甲醇/汽油燃料能够在保持负荷不变的情况下使燃烧相位提前,有助于进一步提升发动机指示热效率水平。当燃用纯甲醇时,高负荷工况下可显著改善燃烧过程,相比于汽油燃料,缸内最大压力增加约30%,指示热效率增加7.2个百分点,NOx排放明显升高,增幅达80%。此外,燃用甲醇燃料时核模态颗粒物数量显著升高,同时积聚模态微粒数量减少,不同模态微粒峰值均向小粒径方向迁移。

The thermal efficiency potential of high compression ratio Miller cycle engines and the effects of methanol and methanol/gasoline blended fuels on combustion processes and emission characteristics were studied.Through comparative experimental analysis,the thermal efficiencies of the Miller cycle versus the conventional Otto cycle under different compression ratios were investigated,along with the mechanisms by which methanol fuel affects engine combustion performance and emissions.Results indicate that,under high-speed and high-load conditions,the Miller cycle exhibits a higher thermal efficiency potential compared to the Otto cycle,also improving tolerance to higher compression ratios.In conditions selected for the experiments at 2000 r/min,global indicated mean effective pressure(GIMEP)at 0.66 MPa,employing the Miller cycle at compression ratios of 11.5 and 14.5 respectively,it was found that the indicated thermal efficiency increased by approximately 0.6 and 0.8 percentage points relative to the Otto cycle.Utilizing methanol/gasoline fuel could advance the combustion phase without altering the load,aiding in further enhancing the engine’s indicated thermal efficiency level.When burning pure methanol,under heavy load conditions,the combustion process is significantly improved.Compared to gasoline fuel,the in-cylinder maximum pressure increased by about 30%,the indicated thermal efficiency increased by 7.2 percentage points,and NOx emissions rose significantly,with an increase of 80%.Moreover,when using methanol fuel,the number of nucleation mode particles significantly increased,while the number of accumulation mode particles decreased,with the peak values of different mode particles shifting towards smaller diameters.