Numerical investigation of multi-component droplet evaporation and autoignition for aero-engine applications

Abstract

The droplet evaporation and autoignition behaviour of a three-component kerosene surrogate is numerically investigated for a wide range of ambient pressures and temperatures representing realistic aero-engine conditions. Vitiated air with different levels of dilution is considered to represent mixing of air with combustion products. Particular attention is given to the analysis of multi-component fuel effects at the various operating conditions. The investigation also considers the impact of fuel preheating and multiple initial droplet diameters, and extends to the quantification of NOx emissions at the droplet scale level. Considering pure evaporation, results show that preferential evaporation and variation of the droplet composition are mainly affected by the gas temperature. An increase of the pressure generally increases the duration of the droplet heat-up period and reduces the effects of preferential evaporation, especially when high temperatures are considered. Autoignition in vitiated air is strongly influenced by both the level of dilution and ambient pressure, with the latter playing an important role in determining the value of the initial droplet diameter below which no autoignition occurs. Lower pressures generally make the kerosene droplet more resistant to autoignition for the same level of dilution or gas temperature. Droplet preheating mainly affects the heat-up period and can be used as a design parameter to control the autoignition delay time. NOx levels are substantially related to the gas-phase temperature and the existence of a flame at the droplet scale. Potential implications for the design of future low-emission combustor technologies are discussed with an emphasis on the fuel preparation.