Counterflow Spray Combustion Modeling with Detailed Transport and Detailed Chemistry

Abstract

Structures of axisymmetric and planar counterflow spray flames are investigated by means of numerical integrations. The study emphasizes the effects of both detailed transport and detailed chemistry on flame structure and extinction conditions. Comparison of results of an n-heptane/O2 flame with results from experiment shows the applicability of the model. Parameter studies are performed for methanol/air sprays where the fuel is carried by a nitrogen stream that is directed against a hot air stream. The effect of varying both initial droplet size and droplet velocity is investigated. The phenomenon of a reversal of droplet direction at high strain as well as droplet oscillation are identified, and regimes of premixed-like and diffusion-like spray flames are characterized. Extinction conditions are specified for both methanol/air and n-heptane/air spray flames where cold air is used as carrier gas against a cold air stream that may result in twin flames. N-heptane spray flames are more stable compared to methanol sprays under the same conditions since more fuel mass is vaporized for methanol because of its high stoichiometric ratio of fuel to air. The present model is suitable to predict formation of pollutants such as NO, CO, and HCN for the n-heptane spray flame.