Effect of Reynolds number on the spatial distribution of OH and formaldehyde in jet flames in a heated and diluted co-flow

Abstract

The spatial distribution of OH, formaldehyde (H2CO) and temperature imaged by laser diagnostic techniques are presented. The measurements are of nonpremixed jet flames in a hot and highly diluted co-flow. These conditions emulate those of Moderate and Intense Low Oxygen Dilution (MILD) combustion. This paper presents some results on the effect of O2 co-flow level and jet Reynolds number on the structure of the flames for various fuels (each diluted by hydrogen 1:1 vol/vol). A reduction of O2 levels is shown to lead to a substantial suppression of OH and a drop in peak temperatures. For strained flames, increased dilution of O2 also leads to reduction of H2CO. Reynolds number effects on the radial profiles of the flame species considered are shown to be minor compared to O2 levels. The drop of the peak temperature in a low O2 co-flow leads to a reduction of thermal gradients and hence a laminarisation of these flames. Strain rate does have a significant effect on the relative levels of H2CO however, with levels increasing markedly with higher Reynolds number.