Effects of hydrogen-addition on the FREI dynamics of methane/oxygen mixture in meso-scale reactor

Abstract

FREI (Flame with Repetitive Extinction and Ignition) is a unique flame dynamic in the micro or meso combustor due to the scale effect of the combustor. To further understand the flame dynamics of the FREI, the flame propagating process of the methane-oxygen premixed gas with hydrogen addition is visualized and analyzed experimentally in a rectangle combustor with transparent wall. The equivalence ratio regimes of different flame behaviors are obtained by varying the hydrogen addition. The effect of hydrogen addition on the flame propagation speed, the flame amplitude and the frequency of the FREI is discussed in terms of methane and hydrogen properties, as well as combustor wall temperature. The results indicate that increasing the hydrogen addition will enlarge the amplitude and decrease the frequency of the FREI. However, the effects of hydrogen addition on the flame properties in the upstream and downstream parts of the combustor vary. When the hydrogen addition is increased under the FREI condition, the temperature profile becomes more uniform upstream. Meanwhile, the flame propagates faster with higher hydrogen addition. However, due to the combined effect of wall temperature and the hydrogen property, increasing the hydrogen addition will decrease the wall temperature and the flame propagating velocity at the downstream part when the equivalence ratio is less than 1.9.