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Technical Paper

Velocity Measurements In Motored Engines - Experience and Prognosis

Measured values of velocity and associated turbulence properties have been obtained in a motored single-cylinder Diesel engine and in a plexiglass simulation engine. The quality of the signals obtained from thereal engine and the corresponding useful data rate are quantified and discussed. As a consequence, it is shown that measurements in real engines are likely to relate to crank-angle intervals of the order of 10 degrees. The implications of this conclusion are quantified by analysis and by measurements in the plexiglass engine. The results, from the motored Diesel engine, also show that values of velocity cannot be measured throughout the cylinder cavity.
Technical Paper

Tumbling Motion: A Mechanism for Turbulence Enhancement in Spark-Ignition Engines

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.
Technical Paper

Three-Dimensional Flow Field in Four-Stroke Model Engines

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.
Technical Paper

The Effect of Engine Speed on the TDC Flowfield in a Motored Reciprocating Engine

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.
Technical Paper

An Approach to Charge Stratification in Lean-Burn, Spark- Ignition Engines

A constant-volume combustion chamber was used to examine injection of a small quantity of slightly rich fuel/air mixture towards the spark plug around the time of ignition, in an overall very lean mixture rotating at velocities representative of modern spark-ignition engines. The results show that it is possible to achieve 100% ignitability with overall air-fuel ratios in excess of 50 and much faster burn rates than those with initially homogenous mixtures of the same equivalence ratio with high swirl and turbulence. The advantages of this method of local charge stratification have been demonstrated in terms of both pressure measurements and shadowgraphs of the early flame development while the transient characteristics of the injected rich mixture at the spark plug gap were monitored by a fast flame ionization detector.
Technical Paper

Air and Fuel Characteristics in the Intake Port of a SI Engine

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.