进排气压力对气门式二冲程柴油机扫气过程的影响

Effects of intake and exhaust pressures on the scavenging process in a poppet-valved two-stroke diesel engine

为深入理解气门式二冲程发动机的扫气过程,以顶端入口进气道气门式二冲程柴油机为研究对象,在1 500 r/min转速下采用三维仿真研究了扫气过程中进排气压差和排气背压对缸内气体流动的影响机理。结果表明:由左侧进气道流入气缸的新鲜充量形成逆滚流,其前锋面抵达排气门之前经右侧进气道流入气缸的新鲜充量主要影响排气纯度,而在之后排气纯度明显增加;压差从30 kPa增加至210 kPa时左侧排气道排气纯度增加,在中低压差下右侧排气道排气纯度较高,扫气品质系数先从0.61降低至0.52,之后增加至0.56且保持不变;定压差和背压从100 kPa增加至190 kPa时排气纯度接近,而扫气效率增加较慢,扫气品质系数从0.55降低至0.53。

To further investigate the scavenging process of poppet-valved two-stroke engines, the effects of pressure difference in intake and exhaust ports and exhaust gas back pressure on fresh charge flow during the scavenging process of a poppet-valved two-stroke diesel engine with top-entry intake port were investigated through establishing three-dimensional model of the engine at 1 500 r/min engine speed. The results show that the fresh charge flowing into the cylinder from the left side of intake port forms a reverse tumble. The exhaust gas purity is mainly affected by the fresh charge flowing into the cylinder from the right side of intake port before the reverse tumble front closing to exhaust valve, while it obviously increases after the reverse tumble front reaching exhaust valve. With the pressure difference increasing from 30 to 210 kPa, the exhaust gas purity of the exhaust gas in the left side of exhaust port increases, and that in the right side of exhaust port becomes relatively high at medium-low pressure difference, resulting in that the scavenging quality coefficient is firstly decreased from 0.61 to 0.52 and then increased to 0.56, and finally slightly changed. At fixed pressure difference and higher back pressure ranged from 100 to 190 kPa, exhaust gas purity is close, while scavenging efficiency increases slower, leading to the gradual reduction of scavenging quality coefficient from 0.55 to 0.53.