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A single-cylinder, 4-stroke, 4-valve research engine was operated in CAI mode by using low lift and short duration valve lift profiles with a negative valve overlap to trap exhaust gases. The engine was fuelled with super-unleaded 98 gasoline and was tested in normally aspirated mode and with a boost of 0.18bar applied to the intake system. A centrally-mounted Orbital gasoline direct-injection system was used. The injection timing, as defined by the start of the air-assist injection (SOA), was varied, as was the air-assist injection duration (Adur). The SOA sweeps in normally aspirated mode showed that the IMEP varied with injection timing and highest IMEP occurred with early SOA. When the engine was boosted, the variation in IMEP over the SOA sweep was significantly less than the naturally aspirated test. In boosted mode, the lowest ISFC, ISCO and ISNOx emissions occurred at a SOA of 10°CA after the intake valve opened.

A drivetrain model incorporating detailed crankshaft and drivetrain dynamics has been incorporated into an unsteady gas dynamic computer simulation of a single-cylinder two-stroke engine. This study examines the change in predicted engine performance caused by relaxing the conventional assumption of constant crankshaft velocity, and a comparison of results is presented. Relaxing the assumption changed the predicted brake mean effective pressures by over 10%. Experimental validation of the simulation involved mounting an engine to a test bed and driving an inertia wheel through a fully characterized drivetrain. A high-speed data acquisition system measured signals from a position encoder mounted on the crankshaft and from a non-contact torque transducer. The time and position data were used to calculate instantaneous crankshaft speed, and these results were compared to the predicted profiles. Simulation results and experimental measurements are presented and discussed.