Soot formation study on JP-8 fuel with detail chemistry under diesel engine conditions using a two-stage Lagrangian (TSL) model

摘要

Single-Fuel Concept (SFC) has been developed for air and ground vehicles because of an ability of operating an engine with a blend fuel of F54 and JP-8 or JP-5 at low environmental temperature. Despite the fact that using JP-8 as a fuel has advantages including storage ability, and corrosion inhibition, its short in understanding and characterization in engine operation suggests greater fundamental study to improve power output, efficiency, stability, and operability. The impractical attempt of simulating real fuel which contains hundreds of component leads to a solution -of-developing a surrogate fuel that mimics real fuel characteristics such as distillation curve, flame speed, ignition delay, and emission. In this study, various sets of chemical kinetic mechanisms taken into account of real combustion properties including ignition delay and soot propensity are developed and computationally validated under diesel engine conditions. Closed reactor and two-stage Lagrangian (TSL) models were used to investigate the growth of polycyclic aromatic species (PAHs) as soot chemistry for n-heptane, diesel surrogate, and JP-8 surrogate fuels combustion with 15% oxygen level under high pressure and temperature ambient gas mixture conditions. First, closed reactor model using CHEMKIN code was used to calculate pyrene yield as soot precursor over a wide range of temperature and equivalence ratios for three fuels. Second, the two-stage Lagrangian (TSL) model capable of coupling detailed chemical kinetics with a simplified jet flow field were used to simulate high-pressure spray combustion by incorporating data on mixing or entrainment of fuel/air and flame liftoff length from published experimental data. Results indicated that closed reactor simulation showed similarity of yields of acetylene, benzene, and pyrene for three fuels. However, TSL model showed that soot region was shifted to lower equivalence ratio and higher temperature compared to closed reactor simulation due to a fact that the mixing of hot air into fuel spray would result in higher core temperature. Furthermore, the TSL mixing model provides an importance of mixing on fuel chemistry and results indicated that the mixing promoted chemical reaction considerably.