Assessment of flash-boiling for pulse detonation engines

Liquid-fueled pulse detonation engines must complete the process of feeding, mixing, and purging in milliseconds. Such an engine is extremely sensitive to the Sauter mean diameter (SMD - must be less than 10 μm) and particle size distribution of the fuel, requirements which are difficult if impossible for most fuel injectors to achieve. This study selected an injector from a direct injection engine and used the aviation fuel JP-8. Utilizing a wide range of operation pressure and duration time, the injection timing and equivalence ratio could be accurately controlled with good response time. The results of the experiment indicate that an SMD of less than 10 μm can be achieved with a fuel pressure greater than 8 MPa. This condition, however, resulted in an overly long injection penetration. This study further incorporated the concept of flash boiling to derive a smaller SMD. However, this causes carbon deposition to occur due to cracking or thermal reaction. To circumvent this phenomenon, this study established a deoxygenation device to mitigate oxidization, further investigating the influence of heating temperature on the generation of deposition. The results of spray distribution indicated that when the fuel is heated to 100 °C, only 6 MPa is necessary for achieving fuel droplet characteristics favorable for detonation. Regarding deoxygenation, the results were most significant in fuel heated to 500 °C.