Unsteady deflagration speed in an auto-ignitive DME/Air mixture at NTC conditions

Abstract

In modern engine concepts such as homogeneous charge compression ignition (HCCI) and reactivity controlled compression ignition (RCCI) engines, the presence of a highly reactive premixed charge leads to the formation of deflagration fronts that have the characteristics of both autoignition and diffusion propelled propagation. The presence of such dual combustion modes in these engines presents difficulties in predicting combustion phasing as well as the rate of heat release. In this paper, the propagation speed of an auto-ignitive DME/Air mixture subjected to time-varying temperature fluctuations is computationally studied in a onedimensional flow configuration with reduced kinetics and transport. These studies are carried out at conditions within the Negative Temperature Coefficient (NTC) regime relevant to HCCI/RCCI engines. Different time scales of thermal stratification are simulated to investigate their influence on spontaneous propagation. The main goal is to determine how the propagation speed of a thermally stratified front varies compared to a homogeneous mixture.