Investigation of the Swirl Effect on Diffusion Flame in a Direct-Injection (DI) Diesel Engine Using Image Processing Technology

Swirl flow in a diesel engine can promote combustion efficiency and help suppress emissions. Optimal efficiency can also be achieved with optimized injection timing. The characteristics of the swirl flow generated by swirl control valves (SCVs) were investigated as well as the effects of swirl flow on combustion and flame characteristics in terms of various injection timings and air/fuel ratios. Flame visualizations and an imaging process were performed to examine the influence of swirl flow on the flame in a single-cylinder visualization diesel engine. It was found that swirl flow helped fuel to be distributed more uniformly in the combustion chamber, thereby decreasing ignition delay and promoting combustion efficiency. The flame was noticed to be distributed and exist for a long time in the center area of the combustion chamber by the swirl flow. Furthermore, the swirl interacting with squish flow near TDC was observed to give rise to quenching and shifting of the flame center during combustion in the chamber.