Ignition of Jet Fuel Assisted by a Hot Surface at Aircraft Compression Ignition Engine Conditions

摘要

Ignition characteristics of F-24 jet fuel injected into a combustion chamber with a hot surface probe were studied for reliable combustion of aviation compression ignition engines. The effects of the fuel injection pressure, hot surface temperature, and the location of the hot surface tip on ignition behavior at the aircraft operating conditions were examined using the design of experiments (DoE) analysis to optimize design parameters of ignition assistants with sufficient ignition performance. The DoE input factors were chosen based on the engine operating condition, geometry confinement, fuel spray behavior, and glow plug material aspect. 37 cases were selected for the numerical simulations by an optimal Latin hypercube sampling with coded factors. Ignition delays from pressure recovery, maximum pressure rise, and maximum heat release rate, and full pressure traces were considered as responses, and the log-scaled ignition delay based on pressure recovery was chosen to develop a predictive equation. The simulation results show two distinct major mechanisms of ignition enhancement, autoignition and spray combustion, and the spray combustion mode dramatically decreases the ignition delay. The quadratic predictive equation developed from the DoE analysis includes coefficients which suggest the dependency of each factor on ignition delay, and shows that the dominant factors are ignition assistant temperature and the horizontal tip location. The equation provides ignition delays over multi-dimensional factor space, and the modes of ignition enhancement by the hot surface probe can be also predicted. The calculated values were compared with the previous experimental data. The regime map of ignition enhancement modes by the hot surface probe was developed and the map suggests the optimized values of factors for and ranges of sufficient ignitability.