Experimental study on diesel spray combustion and heat transfer characteristics with multiple injection strategies by means of rapid compression and expansion machine

A comprehensive investigation was carried out to understand diesel spray combustion processes and heat transfer by applying multiple injection strategies. Experiments were conducted under different injection pressure con-ditions ranging from 30 MPa to 180 MPa, and the results clarified the capability of high injection pressure to facilitate spray evaporation and distribution in detail. It also demonstrated that the local heat flux at the piston lip started to increase earlier, followed by the upper lip and lower lip resulting from the spray/wall interaction and mixture development. In addition, the heat flux at the chamber head showed the highest value and longest duration, which was primarily related to the initial location where the high-temperature flame appeared. Furthermore, combining the spray combustion images acquired from diffused backlight illumination (DBI) and the apparent heat release rate (AHRR) by analyzing the in-cylinder pressure, the results clarified the effect of high injection pressure on reducing the heat transfer and soot formation by improving the combustion performance.