Effects of Hydrogen Addition on Stretched Premixed Laminar Methane Flames. 1st Report, Effects on Laminar Burning Velocity.

Abstract

Natural gas is now considered as one of the most promising alternative fuel for vehicle engine to gasoline due to lower overall pollutant emissions and more excellent running performance and fuel economy. To improve this further, lean burning method of natural gas is receiving increased attention. Lean burning, however, can deteriorate some combustion properties such as lower burning velocity and local quenching, resulting in problems to be solved. In past studies, it has been suggested that these problems caused by lean combustion can be resolved through addition of hydrogen, which can sustain vigorous burning at lower temperatures compared to hydrocarbons. In addition, hydrogen addition has been found to affect not only unstretched premixed flames, but also stretched premixed flames that are expected to have a large impact on turbulent flame as well according to flamelet concepts. In this study the effects of hydrogen addition to methane flames over a wide range of equivalence from lean to rich were investigated with a presence of flame stretch experimentally and numerically in order to clarify the mechanism for improving turbulent combustion properties by hydrogen addition under some conditions. The stretch effect was interpreted in terms of Markstein number. Comparison of the results between experiment and calculation exhibited the same trends, being explained by preferential-diffusion of lighter reactants.