Flash boiling hollow-cone fuel spray from a piezoelectric fuel injector under low ambient pressure

This study investigates the spray characteristics under flash boiling conditions from an outwardly opening piezoelectric injector in an optically accessible constant volume chamber. Distinct spray structure is noticed under flash boiling spray regime and spray deforms from a hollow-cone structure to a diamond-like shape with a long central plume at the downstream of the spray. Liquid signals of the plume are much weaker than the original hollow-cone shape region. A higher ambient pressure leads to a shorter central plume. Spray penetration length is greatly enlarged due to the change in spray structure. Fuel injection pressure and fuel injection duration has little effect on spray front penetration length. Especially, the highest spray front penetration velocity observed at 0.01 bar is expected to approach to the local sound speed. Compared to isooctane fuel, commercial gasoline generates stronger flash boiling due to the wide boiling range, but the spray structures are quite similar.