Experimental investigation of transition process from LTC to ITC and HTC during diesel spray combustion at low ambient temperatures

The dynamics of low temperature combustion (LTC) and intermediate temperature combustion (ITC) dramati-cally affect the combustion limits and properties of high temperature combustion (HTC) and engine performance. To reveal the transition from LTC to ITC and HTC and the characteristics of heat release in spray combustion under low ambient temperatures, optical experiments were conducted in a constant volume combustion chamber (CVCC). The high-speed natural luminosity method and the high-speed schlieren method were used to obtain images of the evolution of spray ignition and vapor-phase spray combustion, respectively. The results reveal a significant increase in CVCC pressure when the flame luminosity is not captured by the high-speed natural lu-minosity method at a low ambient temperature (740 K), which is attributed to heat release by the LTC process. The cumulative heat release obtained from the first law of thermodynamics based on pressure attains 29.72 % of the total lower heating value of the fuel. The transition from LTC to ITC and HTC is diagnosed based on the luminosity variation of the vapor-phase spray tip region in the schlieren images. Furthermore, the transition from LTC to ITC and HTC can be monitored based on the average luminosity of the spray tip. Finally, with the decrease in ambient temperature, the end of LTC is gradually delayed by a smaller magnitude and rate of change. These results demonstrate that the transition from LTC to ITC and HTC is sensitive to ambient temperature.

Automated summary

The dynamics of low temperature combustion and intermediate temperature combustion significantly affect high temperature combustion and engine performance. Optical experiments were conducted to reveal the transition from low temperature combustion to intermediate temperature combustion and high temperature combustion in spray combustion under low ambient temperatures. The results show that the pressure in the combustion chamber increases significantly at low ambient temperatures and the transition can be diagnosed based on luminosity variations.