Numerical Simulation of the Effect of Water Mist on the Flame Speed and Structure of Propane-Air Premixed Flame

Abstract

Water mist is expected to have physical and chemical effects on the laminar flame speeds. In the present study, the effect of water mist on the flame speed and structure of propane-air premixed flames is numerically simulated by using PREMIX code of CHEMKIN package, modified to include the evaporation process of water mist. Evaporation process was assumed to follow the Arrhenius law. Chemical kinetic models for propane oxidation were evaluated by comparison of simulated flame speeds with experimental data for the case without water mist. The effects of water mist on flame speeds are separated into the dilution and chemical effects of water vapor, and the thermal effect which includes the heat of evaporation of water mist. The most effective is the sensible heat of water vapor, which is followed by the heat of evaporation. The chemical effect is relatively small but cannot be neglected. When the water mist is added, the flame temperature decreases due to thermal effect which reduces the rates of chemical reactions involving the radicals such as O and H, which have the positive sensitivity of flame speed. Furthermore, three-body reactions involving H₂O are enhanced. These reactions have high negative sensitivity of flame speed due to high chaperon efficiency of H₂O.