Autoignition of DME/C₂H₆ Mixtures Under High-Pressure and Low-Temperature Conditions

The impact of ethane (C₂H₆) addition to ignition delay of dimethyl ether (DME) under high-temperature conditions is opposite to that of other small molecule alkanes, but the trend is still unclear under low-temperature conditions. Thus, ignition delays of DME/C₂H₆ mixtures (C₂H₆ blending ratio ranging from 0% to 70%) were measured at temperatures of 624–913 K, pressures of 9–35 bar, equivalence ratios of 0.5–1 and dilution ratios of 4 and 5.5 using a rapid compression machine. Chemical kinetic simulations were further carried out using the NUI Aramco Mech 2.0, and a good agreement between experimental and simulation results was demonstrated. Results show that DME/C₂H₆ mixtures exhibit two-stage ignition and negative temperature coefficient (NTC) characteristics. The ignition delays DME/C₂H₆ mixtures decrease with increasing pressure, decreasing dilution ratio and increasing equivalence ratio, and the ignition-promoting effects become more prominent in the NTC region compared to the lower temperature region. Unlike the addition of C₂H₆ to DME at high temperatures, it appears anomalous behavior with other small molecule alkanes, and the addition of C₂H₆ at low temperatures nonlinearly increases the ignition delay especially at lower pressures, which is consistent with that of other small molecule alkanes. Kinetic analysis indicates that the addition of C₂H₆ to DME reduces the low-temperature chain-branching routes and more fuel molecule undergoes chain propagation ones. In the DME/C₂H₆ binary mixtures, the oxidation of DME is inhibited while that of C₂H₆ is promoted and even exhibits two-stage characteristics, which is due to their competition for OH radicals dominantly produced by low-temperature chain-branching of DME. On the whole, the consumption of overall fuel is inhibited with C₂H₆ addition, leading to less OH radicals and heat release accumulated during the low-temperature oxidation and thus longer ignition delays.