2021 Volume 63 Issue 204 Pages 101-108
Wall chemical effect caused by radical adsorption and recombination on wall surfaces under flame-wall interactions is investigated by using two different types of plasma techniques as well as combustion diagnostics. In this paper, the main focus is placed on surface reaction of H-atoms, which play a key role in the wall chemical effect on hot flames. Firstly, H adsorption is directly measured through molecular beam scattering technique using a non-equilibrium plasma-driven beam source with an ultra-high vacuum chamber. The initial sticking coefficient S0 of H-atom on stainless-steel (SUS) wall is 0.49~0.53 at the wall temperature of 30~800 ℃. This result is in good agreement with S0 estimated in our previous combustion experiments as 0.1~1, and more precise value can be obtained here. Secondary, non-equilibrium plasma jets are employed to examine H-atom adsorption at atmospheric-pressure. H-atoms are successfully generated by the addition of appropriate amount of water vapor into the plasma feed gas. The produced H-atoms are issued onto quartz and alumina walls, and it is found that H-atoms could be adsorbed on the quartz wall. Finally, H-atom recombination on SUS wall is evaluated using a premixed flame formed in a stagnation flow near a heated SUS wall. In order to estimate the recombination rate, the near-wall H2 concentration is analyzed by gas-chromatography and compared with numerical results. The H-atom recombination rate constant is larger than 104 s-1, showing that the wall chemical effect is adsorption-limited.
