The findings of this work provides an insight into the fundamental aspects of liquid droplet combustion modelling by developing different droplet sub models. An unsteady, spherically symmetric, sub critical, single component gas phase model is developed first and tested for various ambient conditions of temperature, pressure, composition and fuels.It is further extended to include the effects of convection, droplet heating and emissions.A high pressure droplet vaporization model is evolved in view of the supercritical vaporization occuring in diesel engines and liquid rockets.Also, simple and...