Direct start of a gasoline direct-injection engine without a starter

When start–stop system technology is employed, the direct-start method without requiring a starter is considered to be a viable and low-cost solution for a gasoline direct-injection engine in a good thermal state to guarantee that the engine starts frequently and quickly. In this experimental work, the effects of the initial start conditions on successful realization of the direct-start method were investigated by using a four-cylinder gasoline direct-injection engine without considering the effect of the residual gas. Moreover, the changes in the combustion pressure and the rotational speed of the engine with different control parameters of the cylinders which were stopped on the compression and expansion strokes were examined, and the reliability and the stability of the direct-start method were analysed. Some control parameters have significant influences on the combustion pressure and the rotational characteristics of the crankshaft. The initial position of the piston stopped on the compression stroke and located between 60° crank angle before top dead centre and 70° crank angle before top dead centre is optimal to the direct-start method. The raised fuel pressure is beneficial for accomplishing a direct start, resulting in a lower fuel consumption and a shorter response time during the start. When the initial position of the piston is between 50° crank angle before top dead centre and 85° crank angle before top dead centre, the direct start method can still be realized successfully at an injection pressure of 0.5–2.3 MPa. From 50 tests, it was demonstrated that the direct-start method has a better reliability and a better stability at the initial piston position of 50°–85° crank angle before top dead centre, which acquired a nearly 100% probability that the gasoline direct-injection engine is successfully started with a variation in the rotational speed of less than 7%. The engine can almost reach the idle speed after the initial five working cycles. In comparison with the conventional start mode with a starter, the direct-start mode also has a better start response.