Effects of argon/nitrogen dilution on explosion and combustion characteristics of dimethyl ether-air mixtures

In this study, an investigation of the explosion parameters, which include maximum explosion pressure (pmax), maximum rate of pressure rise (dp/dt)max, and combustion characteristics, i.e., laminar burning velocity (SL), activation temperature (Ta) and Zel'dovich number (Ze) of dimethyl ether (DME)-air-argon/nitrogen mixtures are systematically carried out. The dilution effects on the explosion and combustion characteristics are also explored through the addition of two diluents, i.e., argon (Ar) and nitrogen (N2), into the DME-air mixture. It is found from experiment that, the explosion parameters of fuel-lean and fuel-rich mixture exhibit different behaviors. For the fuel rich mixture, pmax decreases with increasing amount of Ar and N2 dilution, and a significant drop of (dp/dt)max is observed as the amount of added diluent increases. For the fuel lean mixture, pmax is first increased with increasing diluent, afterwards it decreases as inert gas dilution ratio larger than a critical value, it is also found (dp/dt)max fluctuates with more addition of diluent. The present results also confirm that SL decreases more abruptly in the DME-air mixtures with dilution of N2 than with Ar, which indicates that the increase in density dominates over the retarding effect for laminar burning velocity in the cases of inert gases dilution. The activation temperature of DME-air-Ar is larger than DME-air-N2 at the same condition, which demonstrates N2 dilution is more sensitive than N2 on the suppression of chemical reaction. Results illustrate that Ze goes up with the increase of dilution ratio, and the values of Ze for argon diluted mixtures are larger than that of nitrogen diluted.