Ziman Wang

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

ABSTRACT 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.