2-D Visualization of a Hollow-Cone Spray in a Cup-in-Head, Ported, I.C. Engine

Two dimensional visualization of a pulsating, hollow-cone spray was performed in a motored, ported, high swirl, cup-in-head I.C. engine, using exciplex-forming dopants in the fuel, which produced spectrally separated fluorescence from the liquid and vapor phases. Illumination was by a laser sheet approximately 200 µm thick from a frequency tripled Nd:YAG laser, and image acquisition was by a 100 × 100 pixel diode array camera interfaced to a personal computer. Liquid and vapor phase fuel distributions are reported for engine speeds of 800 rpm and 1600 rpm, over a crankangle range spanning the injection event and subsequent evaporation and mixing. The beginning of injection was at 33° BTDC at 800 rpm and 47° BTDC at 1600 rpm. At 800 rpm, the spray angle is narrower than the 60° poppet angle, as expected from previous observations in a near-quiescent spray chamber. At 1600 rpm, however, the spray angle is equal to or greater than 60°; this is attributed to the higher swirl velocity of the gas at the higher engine speed. Mixing after the end of injection is consequently enhanced at 1600 rpm, with an almost homogeneous vapor phase fuel distribution being produced in the cup within 1 ms of the end of injection (10 crankangle degrees). In contrast, at 800 rpm, mixing is much less rapid, with the vapor tending to remain concentrated near the center of the cup for a substantial period after the end of injection.