Effects of pressure on the structure of partially premixed turbulent diffusion flames: Calculations using MMC-LES

Abstract

This study numerically investigates the detailed structure of twelve partially premixed turbulent diffusion flames of methane and air across a pressure range between 1 and 20 bar. The flames are computed using the multiple mapping conditioning / large eddy simulations (MMC-LES) approach. The model is first validated against available experimental data at atmospheric pressure. This is followed by simulations of a series of flames with increasing pressure while holding either the bulk jet velocity or the jet Reynolds number constant. Results show that local extinction increases as pressure increases in cases with fixed bulk jet velocity. Meanwhile, an instability induced by body forces gradually arises as pressure increases at constant Reynolds number, but can be mitigated by reducing the gravitational acceleration, and hence the body forces, proportional to the pressure increase. Consequently, flames become more stable with less localised extinction when increasing pressure at constant Reynolds number. The study accurately reflects the effects of finite-rate chemistry with increasing pressure, as evidenced in representative plots of a Damköhler number ratio. Additionally, the approach to blow-off at different pressures is examined, and trends in temperature and species are analysed. The calculations presented in this study align well with existing data at atmospheric pressure and provide reliable blind test results that await detailed comparison with measurements not yet available at high pressures.