Pressure wave evolution during two hotspots autoignition within end-gas region under internal combustion engine-relevant conditions

Abstract

To further understand the intense pressure wave formation mechanism induced by multiple spontaneous ignition kernels under internal combustion engine-relevant conditions, a one dimensional code to solve the Navier–Stokes equations for reactive flows is adopted in this parametric study. The multiple autoignition kernels occurring in the end-gas region are simplified into two neighboring hotspots. Stoichiometric mixtures of PRF40/air (without an obvious Negative Temperature Coefficient (NTC) behavior, and showing a certain degree of anti-knock property) and PRF0/air (exhibiting a strong NTC behavior and weak anti-knock property) are both used to explore the effect of fuel characteristic. The initial pressure is 30.0 atm. Unburnt gas temperatures of 800.0 K and 890.0 K are below and within the NTC regime of stoichiometric PRF0/air under the initial pressure. The hotspots are modeled as sine waves in the initial temperature field. Different sine wave amplitudes are adopted to examine the effect of temperature inhomogeneity. Within a limited computational domain, a detonation wave tends to form under the initial conditions with a small interval between hotspots, a low initial temperature of the unburnt mixture and a large temperature inhomogeneity. During the formation of detonation wave, a process similar to the “explosion in the explosion” phenomenon that are found in previous experiments has been detected. Moreover, at the low initial temperature, a large interval between hotspots reduces the maximum intensity of pressure wave. In contrast, a wide interval increases the maximum pressure intensity at a higher initial temperature. The strongest pressure intensity induced by PRF0/air mixture autoignition is generally higher than that during the autoignition of PRF40/air mixture under the same initial condition, but a common intense pressure wave generation mechanism is shared. Furthermore, compared with the autoignition of the PRF40/air mixture, the distance for detonation formation within PRF0/air mixture becomes shorter.