An Experimental and Numerical Study on the Cavitation and Spray Characteristics of Micro-Orifice Injectors under Low-Pressure Conditions

A fuel injector plays a crucial role in an internal combustion engine, and the occurrence of cavitation inside the injector may affect the engine’s spray, atomization, and combustion efficiency. In this study, a micro-turbojet engine equipped with a micro-orifice fuel injector was developed that operated under low injection pressure (Pinj), that is, at a low Reynolds number (Re). Given the paucity of cavitation studies conducted under such conditions, the current study experimentally and numerically investigated the cavitation and spray characteristics of water and kerosene in a micro-orifice injector with a diameter of 0.3 mm. The results indicated that the water and kerosene exhibited no cavitation, cavitation, supercavitation, and hydraulic flip. However, the discharged jet was unaffected by internal flows, and the jet angles remained nearly constant, indicating that the cavitation in micro-orifice injectors at a low Re is less important than that at a high Re. Because cavitation in micro-orifice injectors under a low Re has no positive effects on the atomization and spray, determining the geometry of a micro-injector is essential. The injector with a length-to-diameter (L/D) ratio of 3 exhibited an approximately 25% higher discharge coefficient (Cd) than those of injectors with L/D ratios of 6 and 8 and, thus, is recommended for injectors in micro-turbojet engines.