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An optically-accessible single cylinder small-bore HSDI diesel engine equipped with a Bosch common-rail injection system is used to study the effects of multiple injection. High-speed video is used to study the injector and spray behavior. Laser-induced exciplex fluorescence is used to obtain simultaneous liquid and vapor fuel distributions within the combustion chamber, with tetradecane-TMPD-naphthalene as the base fuel-dopant combination. Significant liquid impingement is seen in the single main injection case, while evidence of liquid impingement is seen only in the first stage of the multiple injection case. No appreciable liquid impingement is seen for the second stage of the multiple injection case. Vapor is seen throughout the jet cross-section regardless of the injection parameters. The majority of the vapor is confined to the bowl region in the single injection case while evidence of vapor is seen outside of the bowl for the multiple injection case.

A 2.5L, V-6, port-injected, spark-ignition engine was modified for optical access by separating the head from the block and installing a Bowditch extended piston with a fused-silica top and a fused-silica liner in one of the cylinders. Two heads were employed in the study. One produced swirl and permitted modulation of the swirl level, and another produced a tumbling flow in the cylinder. Planar laser-induced exciplex fluorescence, which allows the simultaneous, but separate, imaging of liquid and vapor fuel, was extended to capture components of different volatilities in a model fuel designed to simulate the distillation curve of a typical gasoline. The exciplex fluorescence technique was calibrated in a separate cell where careful control of mixture composition, temperature and pressure was possible. The results show that large-scale motion induced during intake is critical for good mixing during the intake and compression strokes.