Optimizing hot-surface-assisted ignition performance of high-pressure f-24 fuel sprays

Advancements in fuel efficiency and emissions reduction of commercial automotive vehicles as well as progress in the fuel flexibility of heavy-duty direct-injection natural gas (DING) engines demonstrate the utility of compression ignition (CI) engines in a wide range of engineering applications. However, the demand for a multi-fuel capable engine that can be implemented in aircraft by the U.S. Army presents its own unique challenges and requires the development of advanced ignition systems. Hot surface ignition devices exhibit the ability to support reliable engine operation with various liquid fuels, but progress is limited by the complex nature of the fuel spray ignition process and associated flow field. Furthermore, a heating element shield is required to achieve acceptable performance but must maintain adequate fuel/air mixing. This study investigates the effects of both nozzle-to-heating element distance and shield design on the ignition performance of a single high-pressure F-24 fuel spray. Results demonstrate that placing the heating element tip close to the liquid penetration length results in reduced ignition delays for high surface temperatures relevant to ignition-assisting operation in an engine environment. An oblique cut 45° shield exhibits superior ignition performance than a half-tube design does, regardless of mounting position. The 45° cut design allows ignition kernels formed at the hot surface to propagate quickly out of the shield and ignite the spray plume.