Effect of wall surface reaction on a methane-air premixed flame in narrow channels with different wall materials

In order to elucidate effect of wall material on chemical quenching behavior, a methane-air premixed flame formed in 5-mm-wide channel is investigated. In the present study, platinum, quartz, alumina and chromium are chosen as the wall materials. Platinum, chromium and alumina thin films similar to 100 nm in thickness are deposited on quartz substrates using sputtering, vacuum arc plasma gun or atomic layer deposition techniques to establish equivalent thermal boundary condition with different wall chemical reactions. OH-PLIF/micro-OH-PLIF and numerical simulation with detailed reaction mechanisms are employed to examine interaction between the gas-phase and the wall surface reactions. It is clearly shown through the PLIF measurements that OH* mole fraction in the vicinity of the wall is the highest for alumina, while it is decreased in order of quartz, chromium, and platinum. On the platinum surface, the gas-phase combustion is suppressed due to fast consumption of the reactants by the catalytic reaction. On the other hand, on the other surfaces, radical quenching cause the reduction of OH* near the wall. By using a radical quenching model, the initial sticking coefficient associated with radical adsorption is evaluated. It is found that radical quenching does exist on the quartz wall, while the alumina surface works as an inert surface. (C) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.