Convective vaporization of a fuel droplet with thermal radiation absorption

The ‘extended’ and ‘effective-conductivity’ droplet vaporization models developed by Abramzon and Sirignano [Abramzon B, Sirignano WA. Droplet vaporization model for spray combustion calculations. Int J Heat Mass Transfer 1989;32(9):1605–18] are generalized to take into account the contribution of thermal radiation and the temperature dependence of liquid fuel properties. The thermal radiation effect is simulated using the simplified model for thermal radiation absorption suggested by Dombrovsky and Sazhin [Dombrovsky LA, Sazhin SS. Absorption of thermal radiation in a semi-transparent spherical droplet: a simplified model. Int J Heat Fluid Flow 2003;24: 919–27]. Physical properties of liquid fuel, including density, are evaluated at the average liquid temperature and updated at each time-step. These generalized models are applied to the analysis of the vaporization process of n-decane and diesel fuel droplets injected into hot air. It is pointed out that the radiation absorption in diesel fuel is generally stronger than in n-decane, and it needs to be taken into account in modelling the combustion processes in diesel engines. Calculations of the droplet vaporization rate performed using the simplified ‘effective-conductivity’ model with the internal radiation heat source uniformly distributed show exceptionally good agreement with results obtained based on the more accurate ‘extended’ vaporization model with the non-uniform distribution of radiation absorption. This allows us to recommend using the ‘effective-conductivity’ model with uniform radiation absorption for spray combustion calculations, including applications in internal combustion engines.