缸内流动对对置活塞二冲程发动机换气效果的影响

The effect of in-cylinder flow and residual distribution on gas exchange of opposed-piston 2-stroke （OP2S） engines is yet to be thoroughly studied. The effects of scavenge port angle，scavenge port structure and engine speed on scavenge efficiency by directing scavenge flow in OP2S engine were investigated by modeling and CFD simulation with CONVERGE software. Result showed that scavenge port angle had significant and non-monotonic effect on in-cylinder flow. For scavenge port angle α≤5°，scavenge flow was collected around cylinder axis and a border residual area appeared next to liner; for scavenge port angle α>5°，scavenging flow formed a circular downward flow around cylinder axis at the early stage of scavenging. A low-pressure area was induced by this circular flow at its center and drew nearby gas upwards，forming a column of central residual area along cylinder axis. As scavenge port angle increased，the border residual area declined and disappeared while central residual area came into being and got strengthened. The combined effects of both residual areas resulted in the non-monotonic trend in residual ratio. Composite scavenge port produced drastically lower residual ratio than simple port at relatively larger scavenge port angle， since uniform scavenge flow suppressed the low-pressure area，weakening central residual area. This effect was less prominent for reversed composite scavenge port，rendering it less effective than composite scavenge port.