High-pressure fuel spray ignition behavior with hot surface interaction

Abstract Fuel-flexible aircraft propulsion systems using compression ignition engines will require novel strategies for reducing the ignition delay of low-reactivity fuels to feasible timescales. Hot surface ignition of fuel sprays has been implemented in some practical situations, but the complex nature of flame formation within the spray structure poses significant challenges. In order to design next-generation ignition devices, the capacity of hot surface heating elements to promote fuel spray ignition must be investigated. In this study, a rapid compression machine (RCM) was used to examine the ignition process of a single kerosene-based F-24 jet fuel spray with a cylindrical heating element inserted into the spray periphery. The experiments, performed with moderately high injection pressures of 40 MPa, have demonstrated two modes of ignition governed by surface temperature and insertion depth of the heating element. There exists an optimal position where the heating element tip is located in the fuel vapor cone around the liquid spray. For this configuration, a critical surface temperature was identified (∼1250 K), above which short ignition delays associated with a “spray ignition” mode are consistently achieved. In this case, a local ignition flame kernel propagates downstream to the flame lift-off length before full ignition of the spray. In comparison, below the critical temperature a slower “volumetric” mode results. The extended ignition delays associated with this mode may be impractical for compression ignition engines operating at high speeds and increased altitude.