INFLUENCE OF RADIATIVE LOSS ON NITRIC-OXIDE FORMATION IN COUNTERFLOW DIFFUSION FLAMES AT HIGH-PRESSURE

A theoretical analysis is given of the effect of nonluminous thermal radiation on the properties of counterflow diffusion flames at high pressure. The self-consistent analysis includes an expression for gas band radiant dissipation in the energy equation of a counterflow flame solver. NO(x) formation rates and other properties are studied as a function of strain rate for adiabatic, optically thin, and optical thickness-corrected flames. For adiabatic flames, NO(x) concentration and flame temperature increase continuously with decreasing strain rate. For radiating flames, a temperature level off is exhibited due to the competing effects of heat loss and extent of reaction as strain rate (inverse residence time) decreases. For the very lowest strain rates, up to 5% of the flame enthalpy is converted to radiation, and optical thickness corrections start to become important. Certain factors that need to be taken into account in relating the isolated flamelet results to practical gas turbine combustors are also discussed.