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A unique single cylinder engine was used to assess engine performance and combustion characteristics at three different strokes, with all other variables held constant. The engine utilized a production four-valve, pentroof cylinder head with an 86mm bore. The stock piston was used, and a variable deck height design allowed three crankshafts with strokes of 86, 98, and 115mm to be tested. The compression ratio was also held constant. The engine was run with a controlled boost-to-backpressure ratio to simulate turbocharged operation, and the valve events were optimized for each operating condition using intake and exhaust cam phasers. EGR rates were swept from zero to twenty percent under low and high speed conditions, at MBT and maximum retard ignition timings. The increased stroke engines demonstrated efficiency gains under all operating conditions, as well as measurably reduced 10-to-90 percent burn durations.

The objective of this work was to develop a methodology to rapidly assess comparative intake port designs for their capability to produce tumble flow in spark-ignition engine combustion chambers. Tumble characteristics are of relatively recent interest, and are generated by a combination of intake port geometry, valve lift schedule, and piston motion. While simple approaches to characterize tumble from steady-state cylinder head flow benches have often been used, the ability to correlate the results to operating engines is limited. The only available methods that take into account both piston motion and valve lift are detailed computational fluid dynamic (CFD) analysis, or optical measurements of flow velocity. These approaches are too resource intensive for rapid comparative assessment of multiple port designs. Based on the best features of current steady-flow testing, a simplified computational approach was identified to take into account the important effects of the moving piston.