چكيده به لاتين
Theoretical research on spray evaporation and combustion processes of liquid fuel consuming engines requires the calculation of droplet evaporation rates. Estimation of the important characteristics of the engine, such as fuel consumption and emissions, depends on the accuracy of the models provided for droplet evaporation. So in this thesis, transient evaporation of multicomponent droplet at high ambient temperature and pressure condition within microgravity environment has been modeled. In the gas phase, the equations of species, momentum, and energy, and in the liquid phase, the equations of species and energy have been solved in which the spatial and temporal variations of the properties with pressure and temperature were taken into account. These governing equations have been discretized using the finite volume method. In this study, the droplet is assumed to be spherical. To consider the real gas effect, the Peng-Robinson equation of state has been employed and phase equilibrium has been estimated using the fugacity of all species in the liquid and gas phase.
First, the results of the proposed model for mono- and binary-component liquid fuel droplets with a wide range of volatility in various temperatures and pressures have been validated. It was observed that the results of the present model were in good agreement with the experimental data in the literature. Then, the evaporation process of the binary-component droplet has been described, and the effect of pressure change on the evaporation of heptane-hexadecane droplet has been investigated. It was also observed that at a constant temperature, by increasing pressure up to 2 MPa the droplet lifetime was increased but further increase in pressure (up to 2.5 MPa) reduces droplet lifetime.
Then the effect of different equations of state on the prediction of binary droplet lifetime was studied. Also the effect of ambient temperature and pressure on the surface temperature of the droplet was investigated. It was observed that at high enough pressure and temperature, the droplet surface could reach the supercritical condition. Finally, the diesel fuel was considered as a combination of 6 components and its evaporation was studied at high pressure and various temperature ranges. The lifetime of the diesel droplet was decreased and increased by increasing the ambient temperature and pressure, respectively.
