Controlling parameters and regimes for preferential vaporization of jet fuel droplet with liquid transport and convection

Abstract

Petroleum-based fuels and some biofuels contain hundreds of compounds with a wide range of volatilities. Vaporization of such fuels usually favors more volatile species throughout the process. Such preferential vaporization has prevailed in practical applications, such as direct-injection engine and gas turbine. To numerically study preferential vaporization of a liquid complex fuel, a 24-component jet fuel (RP-3) surrogate was used in the present study. The “film theory” and “effective thermal conductivity/effective diffusivity” (ETC/ED) for droplet vaporization considering forced convection were employed to study the preferential vaporization of jet fuel droplets. To quantitatively assess the preferential vaporization, degree of preferential droplet vaporization was quantified using the reciprocal of gasification of Peclet number. Three environmental factors of preferential droplet vaporization were investigated in this work to find the controlling factors of droplet preferential vaporization: ambient temperature (573–1073 K), ambient pressure (1–20 bar) and forced convection (0–6 m/s). The results show that the preferential droplet vaporization is determined by the combined action of droplet vaporization rate and liquid transport. Specifically, under different environmental factors, the controlling parameters for preferential vaporization are different. Under different ambient temperatures, the preferential vaporization is highly affected by the droplet vaporization rate. Under different ambient pressures, the preferential vaporization is determined by the liquid transport through the liquid Lewis number. Under different forced convection conditions, both vaporization rate and liquid transport are enhanced by forced convection, whose effects on droplet preferential vaporization are in competition. In such cases, two distinct regimes separated by a critical liquid Reynolds number are recognized, each of which exhibits independent controlling scheme for droplet preferential vaporization.