Short communication - Effects of partial premixing on NOx emission indicesof soot-containing flames

NOx emission indices (NOxEI) of laminar high-pressure and turbulent liquid- fueled partially premixed flames are studied as a function of fuel tube equ ivalence ratio Phi(B.) In both cases, NOxEI behavior appears to be affected by changes in soot production. Soot levels were visually observed to decre ase with increasing levels of partial premixing (decreasing Phi(B)) The res ulting Variation in NOxEI with Phi(B) is vastly different from the variatio n observed for flames with negligible soot. For the soot containing flames, NOxEI increases continuously with increasing levels of partial premixing. The increase in NOxEI becomes more rapid beyond the point at which soot for mation is suppressed, with a subsequent sharp reduction in NOxEI for Phi(B) .less than or equal to 1.3. Based on these results, we suggest that optimum level of partial premixing can be designed to eliminate soot formation wit hout a steep NOxEI penalty in high-pressure flames.