PDF MODELING AND ANALYSIS OF THERMAL NO FORMATION IN TURBULENT NONPREMIXED HYDROGEN AIR-JET FLAMES

A numerical model is developed based on the probability density function (pdf) approach to study the thermal No formation in turbulent nonpremixed hydrogen jet flames. In particular, the effects of nonequilibrium chemistry and radiation heat loss on the thermal NO formation are examined. The numerical results indicate that when the NOx emission index is scaled with a properly defined flame residence time, it shows the negative one-half power dependence on the Damkohler number as observed by Chen and Driscoll [Twenty-Third Symposium (International) on Combustion]. An analysis is performed suggesting that the observed power dependence is due to the nonequilibrium chemistry effect, and it depends on the self-similar laws for jets. Comparisons of numerical results obtained with and without radiation heat loss show a significant impact on the thermal NO formation for jet flames with radiant fractions greater than 5%.