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The ability of certain induction systems to enhance turbulence levels at the time of ignition, through formation of long-lived tumbling vortices on the plane of the valve and cylinder axes, has been investigated in a two-valve spark-ignition engine by rotating the intake port at 90° and 45° to the orientation of production directed ports. Detailed measurements of the three velocity components, obtained by laser velocimetry, revealed that the 90° port generated a pure tumble motion, with a maximum tumbling vortex ratio of 1.5 at 295°CA, zero swirl, and 42% turbulence enhancement relative to the standard configuration, while the 45° port gave rise to a combined tumble/swirl structure with a maximum tumbling vortex ratio of 0.5 at 285°CA, swirl ratio of 1.0 at TDC, and turbulence enhancement of 24%. The implications of the two types of flow structures for combustion are discussed.

Heat release analysis, ion current and laser Doppler velocimetry methods are combined to examine the effect of pre-spark turbulent mixture motion on flame propagation and combustion characteristics in the four-valve pentroof combustion chamber of a spark ignition engine. Two inlet port configurations leading to different strengths of induction-generated tumbling vortices are considered with emphasis on lean mixture operation under partial load conditions. The results show a good correlation between mixture turbulent characteristics at ignition and flame development, flame propagation rate, combustion duration and cyclic variability. It is shown that turbulence enhancement through induction-generated tumble counterbalances the lean mixture ignition delay by enhancing the flame propagation speed, leading to extension of the engine lean operating limits.

The interaction of fuel sprays and airflow in the intake system of a port fuel-injected spark-ignition engine has been examined experimentally in a pulsating-flow rig which comprised the cylinder head and intake manifold of a production engine connected to a large-capacity plenum chamber, with the camshaft of the intake valves driven by an electrical motor at engine speeds between 1000 and 5000 rpm and with air sucked through the system by a suction fan. Static pressure measurements in the intake port showed periodic pulsations with frequencies of 360 and 200 Hz with open and closed valves, respectively, and these corresponded to quarter- and half-waves in the manifold and were independent of engine speed.