Soot Predictions Within an Aero Gas Turbine Combustion Chamber

This paper presents two different soot production models and their predictions in a practical combustion chamber. These predictions are compared with detailed internal measurements of soot concentration by probe sampling. Both models solve two additional transport equations for soot mass concentration and number density, and incorporate representations of source terms for particle nucleation, surface growth, coagulation and oxidation. In one approach these rates are inferred from soot property measurements in a confined turbulent jet flame, and in the other from a flamelet-based approach employing computations of a kerosene laminar counter-flow flame which incorporates detailed reaction kinetics. Preliminary results from both models are encouraging. Although both over predict the peak levels of soot measured in a gas turbine combustor at 7 bar, these computations have neglected the effects of radiation, which will be included in subsequent calculations. The approach based on detailed chemistry captures more accurately the very high rate of oxidation towards the combustor exit which is a pronounced feature of the measurements and is missing in earlier reported studies. This is related to differences in the coagulation model. Calibration of model parameters for the empirical model from simple experiments leads to exaggerated coagulation at the higher combustor temperatures, reduced soot number densities and under-estimates effective surface area for oxidation. The suitability of laminar flamelet counter-flow flames as a route to generating the soot production relationships necessary for combustor predictions are carefully reviewed in the light of strain rate and residence time effects on detailed hydrocarbon pyrolysis.© 1997 ASME