Combustion cycle-to-cycle variations of opposed-piston two-stroke gasoline direct injection engine

Abstract

The combustion characteristics and cycle-to-cycle variations of opposed-piston two-stroke (OP2S) gasoline direct injection (GDI) engine are investigated with experiment. The effects of engine speed on the combustion process and cycle-to-cycle variations are discussed. This paper chooses the indicated mean effective pressure, the maximum cylinder pressure and the maximum pressure rising rate to characterize the combustion cycle-to-cycle variations. The heat release rate of OP2S-GDI engine is in accordance with the conventional gasoline engine, which is divided into flame developing period, rapid burning period and after burning period. With the increase of engine speed, the maximum combustion pressure and maximum pressure rise rate decrease, and the time corresponding to the maximum in-cylinder pressure is delayed. The pressure rise rate associated with different engine speeds all show an increasing trend, with maximum values less than 0.2 MPa/°CA. The peak value of instantaneous heat release rate in the combustion process decreases and the combustion amount in the post-combustion period increases as the engine speed increases. The cycle-to-cycle variation rate of indicated mean effective pressure (IMEP) increases as the engine speed increases. The maximum IMEP cycle-to-cycle variation rate is 6.101% at 4000 rpm, which is less than the traditional gasoline engine cycle-to-cycle variation rate (10%). The cycle-to-cycle variation rate of the maximum cylinder pressure ( pmax) increases as the engine speed increases. The pmax cycle-to-cycle variation rate is 1.083% at 4000 rpm, which is less than traditional gasoline engine cycle-to-cycle variation rate (2%). The R ( pmax, pi) is weakly correlated at 2000 rpm and uncorrelated at 3000 rpm and 4000 rpm. The R( θ( pmax), pi) is strongly correlated at 3000 rpm and uncorrelated at 2000 rpm and 4000 rpm. The cycle-to-cycle variation rate of the maximum pressure rise rate (d p/d φ) is 7.406%%, 7.919% and 7.667% respectively at 2000 rpm, 3000 rpm and 4000 rpm. The R ((d p/d φ) max, pi) is weakly correlated at different engine speed, the R( θ(d p/d φ) max, pi) is moderately correlated at 2000 rpm and positive correlation at 3000 rpm and 4000 rpm.