Impacts of hydrogen-addition on methanol-air laminar burning coupled with pressures variation effects

Abstract

The effect of hydrogen addition on the methanol laminar flames under various pressures was investigated experimentally and kinetically. A constant volume chamber was used to perform the experiments. The flame propagation was recorded by a schlieren system and a high-speed camera. The CHEMKIN was used to calculate the detailed reaction process. The initial pressure was changed from 1 to 3 bar, and the hydrogen mole fraction was varied from 0 to 0.8. The experimental results show that the laminar burning velocity is increased when adding more hydrogen and lowing initial pressure. When improving hydrogen fraction and initial pressure, Markstein length is decreased. The hydrodynamic instability is enhanced under elevated pressure. The hydrodynamic factor destabilizes the flames of rich-fuel mixtures with less hydrogen blended. When adding more hydrogen, the thermal-diffusion factor contributes most to the flame instability. Almost all main reactions tend to be more sensitive under higher pressure, and blending hydrogen provides more promotion to reactions with the positive sensitivity coefficient. The multiplication of H atoms caused by hydrogen introducing is capable of the enhancement of burning velocity, and the obvious consumption of free radicals due to the improvement of initial pressure results in the inhibition of flame propagation.