直喷汽油机预混和分层稀薄燃烧特性对比研究

摘要

以多孔喷油器中间布置的热力学单缸直喷汽油机为平台,研究了预混和分层2种喷雾模式在发动机不同负荷的燃烧与排放特性,以及分层稀薄燃烧对发动机最大指示热效率的影响.研究结果表明:在燃烧循环变动系数(COV)不超过3的情况下,分层稀薄燃烧能够显著提高发动机部分负荷的过量空气系数极限,并且能在增压全负荷稀薄燃烧工况提高发动机的燃烧稳定性.在部分负荷(转速为1 500 r/min,平均指示压力(IMEP)为0.2 MPa)过量空气系数λ从1.0提高到1.5,泵气损失降低了26.30％,在2 000 r/min自然吸气全负荷工况,单缸机的最大指示热效率达到44.25％.提高λ,CO排放降低,NOx排放先升高后降低,HC排放先降低后升高.%Combustion and emission characteristics at different loads of pre-mixed and stratified lean spay modes were experimentally studied on a direct injection gasoline engine with center-mounted injector. The influence of stratified lean combustion on the maximum indicated thermal efficiency of engine was also researched. The results show that the stratified lean combustion can significantly increase the limit of excess air coefficient of the engine in partial load, and improve the combustion stability of the engine at the supercharged full load lean combustion condition in the case of no more than 3 of the coefficient of variation (COV). When the excess air coefficient of part load (rotational speed is 1 500 r/min, IMEP is 0.2 MPa) increases from 1.0 to 1.5, the pump air loss is reduced by 26.30％. The maximum indicated thermal efficiency of the single cylinder engine reaches 44.25％ under the 2 000 r/min natural suction full load condition. With the increase of excess air coefficient, CO emissions decrease, NOx emissions first increase and then decrease, HC emissions first decrease and then increase.