Abstract
Fuel properties, fuel injection, fuel-air mixing, and the resulting combustion processes strongly influence the functionality and performance of diesel engines. The Single-Fuel Concept (SFC) for application of JP-8 fuel to diesel engines contains potential problems for current and advanced combustion engines. In order to maximize efficiency while limiting emissions and maintaining robust combustion for these systems when using JP-8 as a fuel, fundamental spray, ignition, and combustion properties need to be thoroughly understood and characterized. Recently, surrogate fuels have been widely studied to simulate combustion characteristics of real fuels including diesel and JP-8. In this study, the combustion and polycyclic aromatic hydrocarbon (PAH) growth characteristics of JP-8 were investigated numerically through the surrogate components and results were compared with those of n-heptane under diesel in-cylinder conditions. The reaction mechanism of JP-8 surrogate fuel was modified with addition of soot chemistry from n-heptane reaction mechanism. First, closed reactor model using CHEMKIN code was used to calculate pyrene yield as PAH indicator over a wide range of temperature and equivalence ratios for both 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 lift-off length from published experimental data. Results indicated that closed reactor simulation showed similar yields of C_2H_2, C_6H_6, and pyrene for both fuels. However, TSL model showed that PAH 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.
