Numerical study on preferential evaporation and combustion characteristic of SAF/Jet A spray flames stabilized in a laminar counter-flow

Abstract

Understanding and modeling the preferential evaporation characteristics of spray flames of blended sustainable aviation fuels (SAFs) and conventional jet fuels are crucial for their clean and efficient use in aircraft engines. The present study aims to investigate the preferential evaporation and combustion characteristics of spray flames of blended SAFs and Jet A mixtures stabilized in a laminar counter-flow configuration using direct numerical simulations (DNSs) with the HyChem chemistry model. In particular, three droplet diameters and two strain rates are considered to study a wide range of Stokes numbers. An a priori study of an extended flamelet/progress variable (E-FPV) model is also conducted to evaluate its performance in reproducing the preferential evaporation effect. The results demonstrate that the spray flames of ATJ-SPK/Jet A exhibit flame structures similar to those of the single-component fuels studied in existing research. The preferential evaporation behavior under different spray flame structures is emphasized. At low Stokes numbers, single fuel-side premixed flames form, leading to weak preferential evaporation. As the Stokes number increases, diffusion flames resulting from internal droplet group combustion emerge, accompanied by double flame structures. They spatially separate different fuel streams, resulting in significantly stronger preferential evaporation. With a further increase in droplet penetration, the air-side flame front transitions to premixed flames associated with the envelope flame. This reduces mixing between fuel streams from different droplets, thereby enhancing preferential evaporation. In cases of strong preferential evaporation, the E-FPV model outperforms the conventional model, particularly in predicting minor species.