Non-monotonic change of ignition delay with injection pressure under low ambient temperature for the diesel spray combustion

The impact of injection pressure on the startability of compression ignition (CI) diesel engines has not been thoroughly studied yet, especially for the startup at low-temperature conditions. This research investigates the effects of injection pressure on diesel spray and flame characteristics under low ambient temperatures (close to the critical ignition temperature of diesel spray) in a constant volume combustion chamber (CVCC) using Schlieren, Mie scattering, and direct photography. Different from past engine startability research, the ignition delay time under quasi-critical ignition temperature is measured to be first shortened then prolonged with increasing injection pressure. The primary cause of such phenomenon is analyzed to be the trade-off effects between spray atomization and heat convection from the fuel to the ambience, which is quantitatively validated by the analytical calculation based on the Arrhenius-type correlation.