Effect of Methane Addition on Transition to Detonation in Hydrogen-Air Mixtures Due to Shock Wave Focussing in a 90 - Degree Corner

The main purpose of this work is to investigate the influence of methane addition in methane-hydrogen-air mixture (φ = 0.8 – 1.6) on the critical conditions for transition to detonation in a 90-deg wedge corner. Similar to hydrogen-air mixtures investigated previously [1], methane-hydrogen-air mixtures results showed three ignition modes, weak ignition followed by deflagration with ignition delay time higher than 1 μs, strong ignition with instantaneous transition to detonation, and third with deflagrative ignition and delayed transition to detonation. Methane addition caused an increase in the range of 3.25 – 5.03% in the critical shock wave velocity necessary for transition to detonation for all mixtures considered. For example, in stoichiometric mixture with 5% methane in fuel (95% hydrogen in fuel) in air, the transition to detonation velocity was approx. 752 m/s (an increase of 37 m/s from hydrogen-air) corresponding to M = 1.89 (an increase of 0.14 from hydrogen-air) and 75.7% (an increase of 4.7% from hydrogen-air) of speed of sound in products. Also, similar to hydrogen-air mixture, the transition to detonation velocity increased for leaner and richer mixture. Moreover, it was observed that methane addition in general increased the pressure limit at the corner necessary for transition to detonation.