Effect of Hydrogen Fraction on Laminar Flame Characteristics of Methanol-Hydrogen-Air Mixture at Atmospheric Pressure 2017-01-2277
Methanol has been regarded as a potential transportation fuel due to its advanced combustion characteristics and flexible source. However, it is suffering from misfire and high HC emissions problems under cold start and low load conditions either on methanol SI engine or on methanol/diesel dual fuel engine. Hydrogen is a potential addition that can enhance the combustion of methanol due to its high flammability and combustion stability. In the current work, the effect of hydrogen fraction on the laminar flame characteristics of methanol- hydrogen-air mixture under varied equivalence ratio was investigated on a constant volume combustion chamber system coupled with a schlieren setup. Experiments were performed over a wide range of equivalence ratio of the premixed charge, varied from 0.8 to 1.4, as well as different hydrogen fraction, 0%, 5%, 10%, 15% and 20% (n/n). All tests were carried out at fixed temperature and pressure of 400K and 0.1MPa. The results showed that addition of hydrogen is beneficial for enhancing the combustion process of methanol-air mixture, laminar burning velocity and flame propagation of methanol-air increased significantly with the increasing of hydrogen. The effect of hydrogen addition on the stability of flame depended on equivalence ratio. In the condition of lean burn, the increasing of hydrogen addition deteriorated the stability of the flame. However, when ϕ>1.2, the increasing of hydrogen fraction is able to stabilize the flame. Besides, the effect of equivalence ratio on the stability of flame is accordant for both methanol-air mixture and methanol-hydrogen-air mixture: the flame stability which obtained from Markstein length decreased with the increasing of equivalence ratio. A detailed discussion on the differences between various equivalence ratio and hydrogen fraction of methanol- hydrogen-air mixture combustion in terms of combustion characteristics has been presented.