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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.

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 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.

The effect of intake duct length on volumetric efficiency and in-cylinder flow field is investigated in a four-stroke single cylinder research DI Diesel engine, motored at 1000-3000 rpm. Three lengths of straight duct upstream of the helical inlet port of the engine are considered and measurements of instantaneous mass flow rate and pressure drop across the port are reported as a function of duct length and engine speed. The in-cylinder flow field is characterised by LDV measurements of swirl velocity at inlet valve closure and inside the piston bowl at top dead centre of compression. The results show a significant increase of swirl velocity magnitudes as resonance of the induction system is reached. Turbulence intensity is shown to be less affected by the inlet conditions.

Measurements of three velocity components and of the corresponding turbulent fluctuations are reported obtained by laser Doppler anemometry in the cylinder of a FIAT-IVECO 8140 DI Diesel engine motored at 1000 rpm with a 16:1 compression ratio. The results show that the air swirl velocities at inlet valve closure are axially stratified while the intake-generated axial flow structures persist, although decaying, up to 70° BTDC when the squish effect transforms the in-cylinder flow structure. The presence of a flow towards the piston crevice is detected at 20° BTDC while at TDC of compression the formation of at least, one toroidal vortex in the axial plane inside the piston bowl is detected. The findings of this investigation are compared with similar measurements in simplified engine configurations and reveal a satisfactory qualitative as well as quantitative agreement.

Measurements of three velocity components have been obtained by forward-scatter laser Doppler anemometry in the transparent cylinder of a modified production engine motored in the speed range 300-2000 rpm with a disc-type combustion chamber and a compression ratio of 7.4. The in-cylinder flow development has been examined in detail with and without induction swirl at an engine speed of 1000 rpm. In both cases turbulence was non-isotropic during compression with a tendency towards isotropy at TDC. The swirl velocities at TDC of compression scaled linearly with engine speed while the volume-averaged turbulence intensity varied more than linearly with engine speed for both induction system configurations, increasing from 0.45 to 0.6 times the mean piston speed in the absence of induction swirl and from 0.4 to 0.5 with induction swirl.

Multidimensional model predictions and laser Doppler anemometer measurements are presented of the flow in a motored model engine equipped with a central shrouded valve. Although the accuracy of prediction, as assessed against the data, is at best moderate, the simulation is sufficiently close to provide valuable insight into the flow behaviour. an important finding in this regard is that the shrouded valve generates a long-lived tumbling vortex which is sustained and amplified by the compression process and in turn causes amplification of the turbulence, the TDC levels of which are more than twice those observed in similar studies with non-shrouded valves. It is concluded that inlet arrangements which produce such tumbling motions are likely to lead to enhanced flame propagation rates.

Ensemble-averaged and in-cycle axial and swirl velocities have been measured by laser Doppler anemometry in the three-dimensional flow field of a four-stroke model engine motored at 200 rpm with a compression ratio of 6.7 and various cylinder head and piston geometries. The inlet configurations comprised an axisymmetric port with a shrouded valve and an off-centre port with two valve and swirl generating vane geometries. The piston configurations comprised flat, cylindrical and re-entrant axisymmetric piston-bowls. The results indicate that with the off-centre port a complex vortical flow pattern is generated during induction, which later either collapses in the absence of induction swirl or is transformed into a single rotating vortex in the transverse plane when swirl is present. The axisymmetric port with the shrouded valve gives rise to a double vortex structure and higher turbulence levels at TDC of compression compared to the off-centre port.