The atomization process influences combustion. The Sauter Mean Diameter (SMD), the pressure, and the temperature of the combustor play an important role in the progress of the combustion. The objective of this study is to develop a mathematical model to evaluate the effect of the gas pressure on the combustion chamber flow characteristics. Based on this model a computer program has been designed taking into account the effects of droplet internal circulation, change in combustion chamber gas temperature, the non-unitary Lewis number, the changing gas film thickness surrounding the droplet, the slip, the variable thermo-physical properties. The effect of gas pressure on Liquid Reynolds number, gas Reynolds number, non-dimensional radii, Lewis number, droplet velocity and droplet surface temperature is established. Increasing the gas pressure increases the vapor mass fraction, which affects all other parameters (thermal conductivity, diffusivity, specific heat of liquid and gas, mass and heat transfer number) and leads to a decrease in combustion time. The droplet surface is found to reach its maximum temperature in a shorter time if the pressure is higher. By increasing the gas pressure the droplet-evaporating rate increases, which leads to a decrease in evaporating time. Consequently the combustion chamber volume is decreased. Iterations on the chamber dimensions are done until the program converges.