Combustion Characteristics for the Stabilization of Nonpremixed Methane-Ammonia/Air Coflow Flames through Their Visualization

Abstract

In order to confirm the possible use of methane (CH 4 )ammonia (NH 3 ) blends as a low carbon fuel, the fundamental combustion characteristics for the stabilization of nonpremixed CH 4 − NH 3 /air flames using the coflow jet flame configuration are experimentally studied, observing the flame behaviors by the direct imaging, shadow-graph, and OH radical visualization systems. Two types of flames, attached and lifted flames, are observed, and extinction (blowout) occurs as the injection velocity of fuel u fuel increases. The occurrence of blowout for pure CH 4 /air flames depends on u fuel regardless of the injection velocity of coflow air u coflow , while it considerably depends on u coflow for CH 4 −NH 3 /air flames. The OH radical visualization reveals that NH 3 addition affects the overall reaction intensity and mechanism but does not reduce the average reaction region near the injector lip. Also, the addition of NH 3 reduces the formation of polycyclic aromatic hydrocarbons (PAHs) as a soot precursor. Direct images confirm the effects of NH 3 addition, u fuel , and u coflow on the flame length, and the liftoff height. The measured NO x emissions exhibit that the fuel NO x from NH 3 is dominant and the NO x emissions are considerably affected by the flame intensity and fluctuation.