Numerical Simulation Of Counterflow Diffusion Flames And Preliminary Study Of Non-premixed Turbulent Combustion Of Methane/air At High Pressures

In this thesis, a set of computational software modules, with accurate calculations of thermophysical and transport properties, was developed to study the counterflow diffusion flames and non-premixed turbulent combustion phenomena at high pressures, which have very important implications for air-breathing rocket and advanced gas turbine engines. We first numerically studied the counterflow diffusion flames of methane/air at various pressures, focusing mainly on the effects of the pressure and strain rate. Results indicate that the maximum flame temperature increases with the pressure and decreases with the strain rate. The flame width decreases with both pressure and strain rate as dlog δ/dlog(p·a)≈0.500. The total heat release rate varies with the pressure and strain rate in a relationship of d1gQrelease/d1g(p·a)≈0.518. The effects of the pressure and strain rate on species productions are quite complex, but in general, an increasing pressure leads to a more complete combustion process, while variations of the strain rate exert significant effects on the formation of chemical species, particularly the main pollutant NO, in the fuel-rich region. We next studied the non-premixed turbulent combustion processes of methane/air at high pressures, focusing on effects of the equivalent ratio, operating pressure and inlet-flow swirl number. Numerical results reveal that a proper increase of the operating pressure can improve the combustion efficiency. Variations of the equivalent ratio, ranging from0.5-1.0, lead to both high combustion efficiency and low pollutant emissions. Increasing the swirl number of the inlet air can help enhancing the mixing process of the fuel and air, and controlling the flame location. Under the tested conditions, a higher swirl number leads to a better mixing process.