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.
