Abstract: The effects of idle speed and throttle opening on the engine shutdown characteristics and the realization of direct start mode were studied on a 4G15 gasoline direct injection engine. Results show that the average number of rotations during the shutdown process significantly increases with the idle speed. However, when the throttle opening is small, simply raising the idle speed before shutdown, the effect for cylinder exhaust scavenging is limited, and the final stop phase of the expansion cylinder piston has great randomness, which was difficult to the realization of direct start mode. With the increase in the throttle opening, the number of rotations of the crankshaft increases, the final stop phase range of the piston in the expansion cylinder decreases, and the stop probability in the middle position of the cylinder significantly decreases. At the same time, increasing the throttle opening is also a very effective method to remove the residual gas inside the cylinder, which can significantly increase the success probability of the first cycle ignition and the direct starting.

Key words: power machinery and engineering, direct injection gasoline engine, idle speed, throttle opening, engine shutdown characteristics, realization of direct start mode