Ignition Characteristics of Methane–Ethylene Mixtures: Shock Tube Measurements and Chemical Kinetic Analysis

ABSTRACT In scramjet engines employing regenerative cooling, hydrocarbon fuels undergo endothermic cracking prior to injection, generating light hydrocarbons that strongly influence the ignition behavior. Among the major cracked products, methane and ethylene exhibited significantly different ignitabilities. However, the ignition characteristics of these mixtures under scramjet‐relevant conditions remain insufficiently understood. This study examined the ignition‐promoting effect of ethylene addition to methane using shock tube experiments and detailed chemical kinetics modeling. The ignition delay times were measured behind reflected shock waves at temperatures of 1100–1400 K and a pressure of approximately 7 atm for methane–ethylene mixtures ranging from 100/0 to 0/100 at equivalence ratios of and 1.0. Ignition delay was determined from chemiluminescence, and numerical simulations with sensitivity analyses were conducted. The results showed that the ignition delay decreased monotonically with increasing ethylene fractions. At , a 25% ethylene fraction reduced the ignition delay by 75%–80%, whereas reductions exceeding 90% were observed above 50% ethylene. Saturation behavior was observed for higher ethylene fractions. The USC Mech II model showed the best agreement with the experiments, indicating that ignition was governed by the chain‐branching reaction and ethylene‐specific vinyl radical pathways. Sensitivity analyses further indicated that methane mainly acts as an OH radical sink in the low‐temperature region. These findings provide ignition delay data and mechanistic insights relevant to scramjet combustion modeling.