The Effects of Pressure Difference on Opposed Piston Two Stroke Diesel Engine Scavenging Process

Opposed Piston Two Stroke (OP2S) engines are widely used for its high power density and high thermal efficiency. For OP2S diesel engines, the scavenging process is accomplished by the pressure difference between intake chamber and exhaust chamber. 1-D model of OP2S diesel engine is built and the accuracy of the model is validated by tracer gas method. Based on the 1-D model, the influence of pressure difference to OP2S diesel engine scavenging process is studied. The results illustrated that: (1) in order to obtain higher pressure difference, the pressure in exhaust chamber should also be higher; (2) pressure difference has vital influence in gas exchange process. With the incensement of pressure difference, the delivery ratio increases but the trapping ratio decreases; (3) under the condition of the same pressure difference, the delivery ratio decreases and the trapping ratio increases in higher engine speed; (4) the scavenging efficiency range of OP2S diesel engine is 0.7-0.96. (5) the increment of pressure difference or back pressure is beneficial in improving engine thermal efficiency.