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.

KEYWORDS:

• Ignition delay
• DME/C₂H₆ mixtures
• high pressure
• low temperature
• rapid compression machine

Highlights

• Ignition delay data of DME/C₂H₆ mixtures were provided at low temperatures and high pressures.

• The ignition delays decrease with increasing pressure and equivalence ratio.

• C₂H₆ addition nonlinearly inhibits the ignition of DME especially at low pressures.

• C₂H₆ addition reduces low-temperature chain-branching routes and delays the development of radical pool.

Supplemental material

Supplemental data for this article can be accessed here.

Additional information

Funding

This work was sponsored by the National Natural Science Foundation of China: [Grant Numbers 51776005, 51806014 and 91741124].