Effects of Equivalence Ratio on Temperature and OH Radical Concentration in Laminar Premixed Biofuel and Diesel Vapor Flames

Abstract

3School of Aerospace and Mechanical Engineering, Uni versity of Oklahoma, Norman, OK, 73069 The effects of equivalence ratio on the mechanism o f formation of NO x in laminar flames of diesel and neat canola methyl ester (CME) biodie sel were investigated in this study. Equivalence ratios, ranging from 1.2 to 7, were sel ected to simulate the partially-premixed to near non-premixed flame combustion that exists in some combustors. Key parameters measured included flame length (residence time), OH concentration field, and flame temperature. These measurements were documented and correlated to the in-flame pollutant concentrations of NO x. It was found that at the lowest equivalence ratio , NO x production was a function of the flame length, temp erature, and OH concentration, therefore attributable to the thermal (Zeldovich) mechanism. At more fuel-rich equivalence ratios, a large amount of NO x was produced along or near the flame centerline in the nearburner region. At these conditions, no correlation between NO x formation and flame length, temperature, or radical concentrations was observed, thus was not attributable to the thermal mechanism. It was also observed that biofuel produced higher peak concentrations of NO x than diesel at all conditions, from 7% at φ = 1.2 to 90% at φ = 7.0.