Modeling and Experiments on Ignition of Fuel Sprays Considering the Interaction Between Fuel-Air Mixing and Chemical Reactions
This study aimed to elucidate the ignition processes in transient fuel-sprays over a wide range of ambient conditions corresponding to PCCI combustion, as well as diesel combustion. Ignition of n-heptane sprays was experimentally investigated by using a constant-volume vessel. The well-known temperature dependencies of ignition delays were observed at a high ambient pressure. On the other hand, a negative temperature coefficient (NTC) accompanying a two-stage pressure rise was detected for lower ambient pressures. High-speed shadowgraph images indicated that the temperature rise begins in the highly homogenous mixture along the combustion chamber wall. Enhancement of fuel-air mixing with elevated injection pressure and a reduced nozzle orifice delays the appearance of hot flame in the NTC condition. To better understand these phenomena, ignition processes were predicted using an ignition model including a stochastic turbulent mixing model and a reduced chemical reaction scheme.