Combustion phenomena affecting particle emission under boosting conditions in a turbocharged gasoline direct injection engine

•Boosting makes particle size decrease rather than preventing generation.•Flame direction causes knocking, and soot as injection differed.•Oxidation contribute to decrease PN emission rather than atomization under boosting.•Effect of SOI on mixture stratification becomes larger with more boosted condition. As emission regulations for vehicles have become stricter, the survival of direct injection technologies has been threatened due to increased particle emissions. By many researchers, there has been the effort to reduce the particle emissions. Nonetheless, the sources of particle emissions from turbocharged gasoline direct injection engines (T-GDI) were still not investigated enough. In this research, the particle emission from a modern turbocharged gasoline direct injection engine was investigated through combustion analysis accompanying simultaneous flame visualization. The experiments were conducted under three load conditions from naturally-aspirated to highly boosted conditions. The start of injection was swept to identify the effect of fuel mixing processes and differed combustion phenomena by the fuel injections and the boosting on engines. As results, the boosting changed the influence of heterogeneity and flow interaction by sprays, resulting differences in heat release from combustion and particle generation. The boosting on engines suppressed the agglomeration of particles into large aggregate in half, but promoted the nucleation of particles become double compared to natural aspiration. With optimized injection systems, the most impacting factors are the control of spray interaction with in-cylinder flow and oxidation processes of particles. In the boosted conditions, the uncertain particle sources could occur, such as spontaneous ignitions by mixture stratification and biased flame propagation by flow interaction. Through optimization of injection strategies, the combustion phenomena can be controlled to reduce the particle emissions in the moderate boosted conditions. The results of combustion analysis affecting the particle generation can provide the clues to reduce particle emission from T-GDI engines.