The frequent starting of gasoline engines for hybrid vehicles, the high starting speed, and the high transient nature of the starting process and the rapid changes in intake tract pressure make it difficult to precisely control the air-fuel ratio of gasoline engines around the theoretical air-fuel ratio, resulting in deterioration of combustion and emissions during starting. The use of an over-injection strategy when starting a gasoline engine results in a significant increase in fuel consumption. Gasoline direct injection (GDI) engine has the characteristics of fast transient response, short starting time and low THC emission during starting, which is suitable for the operating conditions of hybrid electric vehicles with frequent starting and stopping. At present, the study of the starting conditions of gasoline engines for hybrid vehicles is mainly focused on the port fuel injection (PFI) engine, and the study of the starting conditions of GDI engines for hybrid vehicles is relatively small. Based on the gasoline engine fast start test bench system and the in-cylinder sampling system, this paper conducts experimental research on a 1.5L turbocharged GDI engine. In this paper, different ignition angle, injection angle, lambda, drag speed, water temperature and other parameters are designed to test and study starting emission characteristics of hybrid gasoline engine. By optimizing parameters of starting process of hybrid gasoline engine, pollutant emission during starting process can be reduced and engine starting power performance can be increased. The test results show that the hybrid gasoline engine starting with lean mixture, large ignition advance angle and high water temperature strategy can significantly reduce the fuel injection and THC emissions. With a lean mixture starting strategy, engine dynamics are reduced, but this power can be compensated by the electric motor. Higher starting water temperatures reduce THC emissions, but also increase NOx emissions. This paper is an important reference for energy saving and emission reduction in the starting process of hybrid gasoline engines.

Mr. Guokang Lou, PhD students, Tongji University