Effects of hydrogen addition on combustion and flame propagation characteristics of laser ignited methane/air mixtures.

In this study, effects of hydrogen addition on combustion and flame propagation characteristics of methane/air mixtures were investigated in a constant volume combustion chamber. Tested gas mixtures are 100% CH 4 , 05% H 2 – 95% CH 4 , 10% H 2 – 90% CH 4 and 15% H 2 – 85% CH 4 , and such mixtures were ignited using a passively Q-switched Nd:YAG laser ignitor which has a pulse energy of 12.3 mJ, pulse duration of 2.4 ns and wave length of 1064 nm. A Schlieren setup coupled with a high-speed camera enabled evaluating flame propagation behavior, while pressure curve analysis provided necessary data for characterization of combustion properties. Additionally, lean flammability limits of gas mixtures were also determined at the test conditions. The unique properties of hydrogen (such as low density, high reactivity, high diffusivity etc) widened lean flammability limit. Rate of pressure rise and measured pressure values increased with hydrogen addition, regardless of the air-fuel equivalence ratio (λ). Lastly, hydrogen addition uniformly affected flame propagation characteristics and flame luminosity. Combustion process became more stable with hydrogen addition. • 5%, 10% and 15% hydrogen (by volume) were added to methane. • H2/CH4 mixtures were ignited by a laser ignitor. • Hydrogen content and equivalence ratio (λ) effects were investigated. • Maximum heat release rate, ignition delay time and combustion duration were calculated. • Hydrogen addition improved all combustion performance metrics, irrespective of the λ. [ABSTRACT FROM AUTHOR]