Effects of engine operating conditions on flame propagation processes in a compression ignition optical engine

[Display omitted] •Coupled investigation using an optical single cylinder and KIVA code was performed.•Flame intensities are dependent on the combustion timing and diffusion combustion.•Wall heat transfer was calculated based on the KIVA code. This paper describes the effects of swirl flow in a diesel optical single-cylinder engine with experimental results and simulation results obtained using KIVA code. Experiments were conducted with an optical single-cylinder engine for various operating conditions such as injection timing, exhaust gas recirculation (EGR), and swirl ratio, and a numerical study was also conducted to analyze the effects of swirl flow and combustion characteristics in detail. Correlations between in-cylinder flow from numerical simulations and the flame propagation process from experiments were conducted. The optical experimental and simulation results demonstrated that retarded injection timing and high EGR rate reduced the luminosity of flame and the wall heat transfer. However, a high EGR rate simultaneously reduced the combustion efficiency. The average luminosity of the optical image was determined by the flame in the high-temperature region above 2400 K. The luminosity and volume fraction of the temperature region above 2400 K showed the same trends. Correlation results between the experiment and simulation showed that swirl flow affects the propagation process. The flame region was generated in the center of the combustion chamber due to swirl flow based on visualization and analysis results. That is, swirl flow caused separation of the flame by disrupting the continuity of the spray.