Predicting the Effects of Fuel Composition and Flame Structure on Soot Generation in Turbulent Non-Premixed Flames

Abstract

Abstract : This project aimed to develop a reduced chemistry and soot model for making accurate predictions of soot emissions from military gas turbine engines. Measurements of soot formation were performed in laminar flat premixed flames and turbulent non-premixed jet flames at 1 atm pressure and in turbulent liquid spray flames under representative conditions for takeoff in a gas turbine engine. Fuels investigated included ethylene and a JP-8 surrogate consisting of n-dodecane and m-xylene. The pressurized turbulent jet flame measurements demonstrated that the surrogate fuel was representative of actual JP-8. The premixed flame measurements revealed that flame temperature has a strong impact on the rate of soot nucleation and particle coagulation. Mean and rms soot concentrations were measured throughout the turbulent non-premixed jet flames, together with soot concentration-temperature data, as well as spatially resolved radiant emission. A detailed chemical kinetic mechanism for ethylene combustion, including fuel-rich chemistry and benzene formation steps, was compiled, validated, and reduced. The reduced ethylene mechanism was incorporated into a high-fidelity large eddy simulation (LES) code, together with a moment-based soot model and different models for thermal radiation. The LES results highlight the importance of including an optically-thick radiation model to accurately predict gas temperatures and thus soot formation rates. When including such a radiation model, the LES model predicts mean soot concentrations within 30% in the ethylene jet flame.