Experimental Study of Combustion Characteristics on an Opposed-Piston Two-Stroke Gasoline Engine

Combustion characteristics of an opposed-piston two-stroke(OP2S)gasoline direct injection(GDI)engine was investigated through experiment. Effects of opposed-piston motion phase difference, scavenging pressure, ignition timing and ignition scheme on the combustion process and engine performances were discussed. Results show that the heat release rate of the OP2S-GDI engine is in accordance with the conventional gasoline engine, which is also divided into the flame developing period, the rapid burning period and the post burning period. With the increase of piston motion phase difference, the scavenging efficiency decreases and more residual gas is trapped in the cylinder, not beneficial to the combustion process. Meanwhile, the faster relative velocity of the two opposed pistons near the inner dead center enhances the change rate of the swept volume, leading to the rapid decline of the cylinder pressure and temperature. The 15°, CA of opposed-piston motion phase difference improves the scavenging and combustion process effectively. When the engine speed increases, higher scavenging pressure is required in order to improve the scavenging efficiency. As a consequence, the air/fuel mixing process and the combustion process are accelerated. When scavenging pressure is 0.12, MPa, both the scavenging efficiency and the combustion process are improved at medium-high speeds. It is noted that a flat piston structure of the OP2S-GDI engine needs dual spark plugs with an ignition advance angle of 20°, CA. Thus, the maximum of indicated thermal efficiency is achieved at mediumhigh load conditions. © 2019, Editorial Office of the Transaction of CSICE. All right reserved.