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The combustion characteristics of three gaseous fuels (hydrogen, methane and ethane) in a direct-injection stratified-charge single-cylinder engine with a centered square head-cup operated at 800 rpm (compression ratio = 10.8, squish ratio = 75%, nominal swirl ratio = 4) were studied to assess the extent to which the combustion is controlled by turbulent mixing, laminar mixing and chemical kinetics. The injection of gaseous fuels was via a Ford AFI injector, originally designed for the air-forced injection of liquid fuel. Pressure measurements in the engine cylinder and in the injector body, coupled with optical measurements of the injector poppet lift and shadowgraph images of the fuel jets provided both quantitative and qualitative information about the in-cylinder processes. To make the cases comparable, the total momentum of the fuel jets and the total heat released by the three fuels was kept the same (equivalence ratio = 0.316, 0.363, 0.329 for H2, CH4 and C2H6, respectively).

The structure of turbulent flames was examined in a premixed-charge, spark-ignition ported engine using a three-dimensional visualization technique with 10 ns time resolution and 350 µm best spatial resolution. The engine had a pancake chamber, a compression ratio of 8, a TDC swirl number of 4 and was operated at 300, 1200 and 2400 rpm with stoichiometric and lean propane/air mixtures. The second and third harmonic beams of an Nd-YAG laser (532 nm and 355 nm), along with the two strongest beams (first Stokes (683 nm) and first anti-Stokes (436 nm)) from a hydrogen Raman shifter pumped by the second harmonic were used to create four parallel laser sheets each of less than 300 microns thickness. The laser sheets were passed through a transparent quartz ring in the cylinder head parallel to the piston top with vertical separations between successive sheets ranging from 1.5 to 0.9 mm.