An experimental and kinetic modeling study of the ignition of methane/n-decane blends

Abstract

An experimental and kinetic modeling study of the combustion of methane/n-decane blends is performed. Ignition delay times (IDTs) of the pure fuels in addition to their blends are measured using both a shock tube and a rapid compression machine at three different methane/n-decane (mol%) compositions of 99/1 (M99D1), 95/5 (M95D5), and 80/20 (M80D20) in ‘air’, over the temperature range of 610–1495 K, at a pressure of 30 bar. A new chemical kinetic mechanism, GalwayMech1.0, is proposed to describe the combustion of these blends and is validated against the new IDT data including 1st-stage and total IDTs as well as existing experimental n-decane data available in the literature. Sensitivity analyses reveal that H-atom abstraction from n-decane by methyl peroxy radicals (CH₃Ȯ₂) play an important role in promoting blend reactivity at intermediate temperatures, which is not observed for pure n-decane. By investigating the effect of the n-decane concentration on the ignition characteristics, we found that the low ignition temperature limit is extended with increasing n-decane content with a non-linear reactivity-promoting effect. Flux analyses reveal that CH₄ oxidation in the blends is initiated via CH₄ + ȮH = ĊH₃ + H₂O, driven by the ȮH radicals produced from the early oxidation of n-decane and the CH₃Ȯ₂ radicals formed from CH₄ oxidation which subsequently accelerates nC₁₀H₂₂ consumption via H-atom abstraction. Comparisons of CH₄/nC₁₀H₂₂ and H₂/nC₁₀H₂₂ blends from a previous study demonstrate consistently higher reactivity for hydrogen blending compared to methane and that the magnitude of this increase diminishes with increasing n-decane content. Finally, we also compare our current model predictions of our new data with other n-decane models available in the literature.