Abstract: To promote the realization of direct-start mode without using starter, the influences of active and passive factors on the first-cycle ignition and engine rotation characteristics were investigated on a four-cylinder GDI engine. Under different passive factors, the control ranges of the active factors, which assure the reliable first-cycle ignition, and optimized control making engine to gain higher speak speed are analyzed. Experimental results indicate that the reasonable control of ignition timing and excess air coefficient can obtain higher combustion pressure and consistency for the first-cycle. Under different passive factors including coolant temperature, initial piston position and fuel pressure in oil rail, certain differences exist in the ranges of ignition timing and excess air coefficient that assure the reliable first-cycle ignition. Meanwhile, the excess air coefficient and ignition timing should be selected separately to get better rotation characteristics and promote the realization of direct-start mode for different passive factors.

Key words: engineering of power and machinery, GDI engine, direct-start mode, first cycle, ignition and rotation characteristics