Ignition enhancement of f-24 jet fuel by a hot surface for aircraft propulsion systems

Ignition enhancement of F-24 jet fuel injection into a combustion chamber with a hot surface probe is investigated with the goal of achieving reliable compression ignition engines in aircraft systems. The main purpose of this study is to understand the interactions between the fuel jet and hot surface, and to promote optimized designs of hot surface for maximum ignition probability. Therefore, the numerical simulations focus on the detailed ignition enhancement mechanisms by the hot surface and modes of ignition mechanism. Numerical models for spray, chemical kinetics, thermal boundary layer, and heating element are investigated and integrated into the simulation. A validation of enhancement mechanisms is provided by experiments in a modified rapid compression machine. Two different major mechanisms of ignition enhancement are found: autoignition and ignition propagation from the spray for low and high glow plug temperature ranges, respectively. Both ignition mechanisms are enhanced by heating of the fuel jet when it touches the hot surface. In the spray combustion mode, the ignition enhancement is significant compared to the autoignition mode. The spray combustion starts from the bottom-surface of the probe tip, which has high temperature and equivalence ratio. The residence time and spray shape affect the temperature and equivalence ratio, respectively. Based on the local properties, the optimal hot surface location can be analyzed considering both residence time and fuel quantity at the most probable ignition point.