Numerical Simulation of Transient Liquid Fuel Sprays Vaporization Under Engine-Like Conditions Using Diffusion Limit and Well Mixed Vaporization Models

The vaporization of n-dodecane sprays during the early stages of the vaporization process under engine-like conditions is studied numerically using Well-mixed (W-M) and diffusion-limit (DL) evaporation models. A spray with Sauter mean radius (SMR) of 12 mm at injection is considered. The initial droplet size distribution is obtained from a χ-squared distribution using a Monte Carlo sampling technique. The initial ambient air pressure and temperature are taken to be 45 bar and 800 K respectively. The effect of the injection velocity on the vaporization process is studied by considering two initial injection velocities 100 and 200 m/s.

A modified version of the finite volume code Kiva-II is used to solve the governing equations for both the gas and the liquid phase. To see the effect of the presence of many droplets in the system on the vaporization of individual droplets the simulation is also performed for the case when the energy and mass exchange between the liquid and gas phase is neglected. The results of the simulation are presented in terms of vaporization history of two selected droplet parcels with initial diameters of 22 and 50 mm at injection, and in terms of temperature and velocity distribution of the gas phase along the chamber axis. The vaporized amount of fuel and penetration depth of the liquid phase as functions of time are also presented. The study concludes that for the range of parameters studied, the adequate simulation requires employment of the DL-model.