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OA北大核心CSTPCD

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 2 000 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.