Influence of induction swirl piston configuration on air flow in a four-stroke model engine

Measurements of ensemble-averaged mean, r.m.s. and cycle resolved instantaneous swirl velocities, obtained by laser-Doppler anemom-etry, are reported for the in-cylinder JIow in a four-stroke model engine motored at 200 rjmin. Variable induction swirl was created by 30 " and 60 " vanes located in axisymmetric and offkentre intake ports with,flut and re-entrant howl piston configurations. The results showed that the main features of the initial swirl velocity dislribution, which are determined by the inlake portj iulw geometry, persist through the compression stroke. The swirl centre performed in all cases u helical niotion whose development was a,function of the clearance volume at top dead centre; the weakness of this motion made it susceptible to cyclic oariations which were signijicantly reduced with the re-entrant piston bowl. High induction swirl resulted in lower turbulence intensity a6 top dead centre of compression, in the j u t piston case, and more complex vortex pattern inside the re-entrant piston bowl. T h e angular momentum decay from inlet value closure to top dead centre of compression was shown to depond on itiiiial swirl ratio and velocity distribution and calculated to be about 30 and 45 per cent for t h e j a t and re-entrant bowl piston, respectively. D IV