Comparative investigation of homogeneous autoignition of DME/air and EtOH/air mixtures at low initial temperatures

The dynamics of homogeneous isochoric explosions of dimethylether (DME)/air and ethanol (EtOH)/air mixtures were studied and compared at relatively low initial temperatures (≤ 700 K) using algorithmic tools derived from the methodology of computational singular perturbation. In the DME case, it is shown that the low-temperature oxidation is dominated by reactions involving heavy carbonaceous species, in contrast to the high-temperature case where oxidation is dominated by reactions involving light carbonaceous species. Moreover, it is demonstrated that the outcome of the competition between two specific reactions is the cause of the exhibited negative temperature coefficient (NTC). In the EtOH case, the analysis points to the importance of carbonaceous species and in particular acetaldehyde, which is different from what happens at elevated initial temperatures (above 1000 K), where hydrogen chemistry dominates the entirety of the oxidation process. The autoignition dynamics of both mixtures are shown to be pretty much independent of initial pressure, with the exception of the NTC behaviour of DME.