Pulsed, supersonic fuel jets—A review of their characteristics and potential for fuel injection

High pressure fuel injection has provided considerable benefits for diesel engines, substantially reducing smoke levels while increasing efficiency. Current maximum pressures provide jets that are at less than the sonic velocity of the compressed air in the cylinders at injection. It has been postulated that a further increase into the supersonic range may benefit the combustion process due to increased aerodynamic atomization and the presence of jet bow shock waves that provide higher temperatures around the fuel. Pulsed, supersonic injection may also be beneficial for scramjet engines. The current program is examining pulsed, supersonic jets from a fundamental viewpoint both experimentally and numerically. Shock wave structures have been viewed for jets ranging from 600 to 2400 m/s, velocity attenuation and penetration distance measured, different nozzle designs examined and autoignition experiments carried out. Inside the nozzle, numerical simulation using the Autodyne code has been used to support an analytic approach while in the spray, the FLUENT code has been used. While benefits have not yet been defined, it appears that some earlier claims regarding autoignition at atmospheric conditions were optimistic but that increased evaporation and mixing are probable. The higher jet velocities are likely to mean that wall interactions are increased and hence matching such injectors to engine size and airflow patterns will be important.