NUMERICAL INVESTIGATION OF THE IGNITION OF DILUTE FUEL SPRAYS INCLUDING DETAILED CHEMISTRY

One-dimensional unsteady numerical calculations have been performed to study the ignition of dilute fuel sprays. Recent investigations in th is field employ global kinetic rate expressions to model the chemical reactions occuring in the gas phase. In the present paper a detailed k inetic mechanism is employed to describe the ignition process of dilut e methanol sprays in air, the mechanism for methanol comprises 23 spec ies and 168 elementary reactions. The present investigation accounts f or unsteady droplet heating and vaporization using a distillation-limi t model; temperature dependence of liquid phase properties is included . The study investigates uniform sprays; both monodisperse and bidispe rse sprays are considered. The quiescent mixture of fuel and air is ig nited by assuming hot air and cold fuel. The present study concerns ig nition of a fuel spray in a closed volume. Effects of varying paramete rs such as initial gas temperature, initial fuel-vapor concentration, pressure, droplet size in both monodisperse and bidisperse sprays as w ell as equivalence ratio on both ignition-delay time and on spray life time are investigated. It is shown that there is a minimum ignition-de lay time in dependence of both equivalence ratio and of initial drople t size for various conditions. Ignition-delay time of a bidisperse spr ay is dominated by the characteristics of the smaller droplets. There is a two-stage heating for small droplets caused by gas-phase characte ristics. Fuel-vapor accumulation leads to delayed ignition and to high er gas temperatures for small droplets. The results of the calculation s give profiles of radical concentrations such as OH as well as concen tration of pollutants.