An Optical Study of Mixture Preparation in a Hydrogen-fueled Engine with Direct Injection Using Different Nozzle Designs

Mixture formation in an optically accessible hydrogen-fueled engine was investigated using Planar Laser-Induced Fluorescence (PLIF) of acetone as a fuel tracer. The engine was motored and fueled by direct high-pressure injection. This paper presents the evolution of the spatial distribution of the ensemble-mean equivalence ratio for six different combinations of nozzle design and injector geometry, each for three different injection timings after intake-valve closure. Asymmetric single-hole and 5-hole nozzles as well as symmetric 6-hole and 13-hole nozzles were used. For early injection, the low in-cylinder pressure and density allow the jet to preserve its momentum long enough to undergo extensive jet-wall and (for multi-hole nozzles) jet-jet interaction, but the final mixture is fairly homogeneous. Intermediately timed injection yields inhomogeneous mixtures with surprisingly similar features observed for all multi-hole injectors. Fuel is concentrated near the cylinder wall, an unfavorable scenario were the engine to be fired. Results for late injection depend more on the particular injector configuration. The 13-hole injector shows complete merging of all jets, consistent with results in the literature. The influence of intake-induced bulk-gas tumble is minor for the current injector and combustion-chamber configurations.