A numerical study of hydrogen enrichment effects on laminar methane/air flame propagation and emissions in crevices

Abstract

Crevices, i.e. narrow channels, inside combustion devices, have been found to be a major source of emissions, such as unburned hydrocarbons (uHC) and carbon monoxide (CO). In the present 2D model problem, a premixed laminar methane/air flame approaches a narrow enclosure with cold walls. The effects of the crevice height, the hydrogen enrichment, and the equivalence ratio on the flame propagation and formation of pollutants are investigated with direct numerical simulations. For the chosen geometry, the flame experiences a head-on quenching (HOQ), possibly followed by a side-wall quenching (SWQ) and second HOQ, depending on the chosen conditions. The present study concludes that, (I) the quenching Peclet number is a sufficient a priori tool for estimating the methane/hydrogen flame propagation into a crevice, (II) increasing the crevice height, H₂-enrichment level, and equivalence ratio (up to stoichiometry) improve the flame penetration into a crevice, (III) a reciprocal relationship is observed between the flame penetration distance and the uHC emissions left in the system after combustion, and (IV) both the CO and NO emissions have the same dominant production and consumption reactions, respectively, regardless of the quenching scenario (HOQ or SWQ).