Direct Numerical Simulation of Complex Fuel Combustion with Detailed Chemistry: Physical Insight and Mean Reaction Rate Modeling

Abstract

Direct numerical simulation (DNS) of freely-propagating premixed flames of a multi-component fuel is performed using a skeletal chemical mechanism with 49 reactions and 15 species. The fuel consists of CO, H2, H2O, CH4, and CO2 in proportions akin to blast furnace gas or a low calorific value syngas. The simulations include low and high turbulence levels to elucidate the effect of turbulence on realistic chemistry flames. The multi-component fuel flame is found to have a more complex structure than most common flames, with individual species reaction zones not necessarily overlapping with each other and with a wide heat releasing zone. The species mass fractions and heat release rate show significant scatter, with their conditional average however remaining close to the laminar flame result. Probability density functions of displacement speed, stretch rate, and curvature are near-Gaussian. Five different mean reaction rate closures are evaluated in the RANS context using these DNS data, presenting perhaps the most stringent test to date of the combustion models. Significant quantitative differences are observed in the performance of the models tested, especially for the higher turbulence level case.