Insight into High-temperature Ignition Processes of Methane-T425 Mixtures at Various Methane Contents: Experimental and Chemical Kinetic Analysis

A surrogate fuel model named as T425 was constructed for diesel with 57.5% n-heptane and 42.5% toluene by mole fraction, and then ignition characteristics of stoichiometric methane-T425 mixtures with various methane contents at elevated initial temperatures were investigated at initial pressures up to 30 atm via a shock tube facility. The result shows that behaviors of two reaction mechanisms studied in accurate prediction of ignition of methane-T425 mixture depend on initial pressure and temperature. At higher methane content, more significant change will occur in ignition delay time of the mixture if continually increasing the methane content. In the ignition process, methane is consumed through reactions with radicals in a short time near the ignition time point. Attacks from radicals to n-heptane dominate its consumption, but at initial stage of ignition period the decomposition reaction plays the major role for the consumption of n-heptane. Radicals including H and OH show the control over the consumption of toluene, and such consumption lasts for a relatively longer time compared to methane. When elevating the methane content, decomposition reactions for consumption of n-heptane are promoted, and reactions involving CH3 are enhanced in oxidation processes of methane and toluene.