Abstract:

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.

Key words: poppet-valved two-stroke diesel engine, reverse tumble, pressure difference in intake and exhaust ports, exhaust gas back pressure, scavenging process