Gasoline-direct-injection (GDI) engines have been adopted increasingly by the automotive industry in the recent years due to their performance, effects on the environment, and customers' demand on advanced technology. However, the knowledge of detailed combustion process in such engines is still not thoroughly analyzed and understood. With optically accessible engines (OAE) and advanced measuring techniques, such as high-speed digital imaging, the in-cylinder combustion process is made available directly to researchers. The present study primarily focuses on the effects of different parameters of engine control on the combustion process, such as fuel types, valve deactivation, ignition timing, spark energy, injection timing, air-fuel ratio, and exhaust gas recirculation. Three engine heads of a 2.0L GDI engine are used with modification to acquire different optical access. Pure (E0) and ethanol-blended (E85) gasoline are used, and the engine speed and coolant temperature are kept low to imitate start-up situations in the normal driving condition. The visualization study is realized with two high-speed digital cameras, a color one and a monochrome one with an intensifier, to capture the combustion images.
The results indicate that the engine could start up in the first cycle by injecting E85 even for coolant at room temperature. Valve deactivation operation, which usually enhances the air-fuel mixing under low load conditions, may have a negative impact due to the convection effects on spark and spray plume at starting conditions. Optimal ignition timing and higher spark energy could also improve the combustion process to reduce misfire and cycle-to-cycle variation at the low speed conditions.