Numerical Analysis on the Characteristics of the Pressure Wave Generation Initiated by the Onset of the Auto-Ignition in the End-Gas

The end-gas auto-ignition and associated pressure wave generation in a premixed gas with a spatial distribution is numerically investigated. This study assumes that the auto-ignition phenomenon in the end-gas of PCCI combustion, a next-generation combustion method which is expected to achieve both low fuel consumption and low emissions at a high level. Detailed numerical analysis considering the chemical kinetics on the one-dimensional compressible fluid flow with high spatial and time resolution was performed to clarify the detailed phenomena of the auto-ignition and onset of the pressure wave and its propagation in the end-gas. Followings are results. (1) The pressure wave generations related with the auto-ignition in the end-gas is categorized into two types. The cases that the auto-ignition velocity, which is the localized auto-ignitive propagation velocity relative to the unburned mixture, exceeded the local sound speed, or not. The spatial distribution of the equivalence ratio in the initial unburned mixture affects the auto-ignition velocity. (2) In the cases that the Mach number of the auto-ignition velocity was less than one, the intensity of the pressure wave associated with the auto-ignition is relatively small, and the pressure wave propagates quietly with sound speed. (3) On the other hand, in the cases that the Mach number of the auto-ignition velocity exceeded one, very strong pressure wave is initiated by the auto-ignition. The temperature rise due to the auto-ignition and the pressure rise propagates synchronously toward the unburned mixture.