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.