Numerical Simulation of Evaporation in Fuel Spray Droplets in a Diesel Engine

Abstract

The objective of present thesis is to model thermophysical process of evaporation of diesel fuel spray in the combustion chamber of diesel engine numerically. Evaporation of fuel droplets has an impact on the efficiency and exhaust of engine that is quiet obvious in the literature. In this work evaporation of diesel fuel is modeled numerically in Ansys. Presents work takes into account the turbulence effects generated into the engine cylinder due to high pressure and high temperature inside. In the this work evaporation of different diesel fuels is modelled numerically taking into account the turbulence effects present in the cylinder due to high temperature and pressure using the RANS turbulence model. A realizable RANS turbulence model is applied to analyze the effects of turbulence. RANS model is used in the present study due to its low computation cost and an appreciable accuracy for the present problem. Evaporation of n-heptane and n-decane is governed by the conservation equations of mass, energy, momentum and species transport. Heat transfer to drop and mass lost by the drop is governed by the discrete phase model equations. Results are plotted by varying the droplet diameter and temperature. Results include the vapor mass fraction of droplet, decay in droplet diameter, and increase in the droplet temperature, effect on the velocity of droplet and temperature changes in the cylinder due to evaporation of fuel. It is observed that size of droplets, temperature of droplets, ambient temperature, injection pressure and velocity, and turbulence intensity have an acceptable effect on the evaporation time of diesel fuel droplets in the engine cylinder. Small droplets need short time to evaporate and droplets with larger diameter require more time to evaporate completely. Droplets having high temperature have short evaporation time and high evaporation rate. High ambient temperature also shows a good effect on the evaporation rate of droplets. Finally proposed evaporation model is implemented on the diesel engine and results are described.