A Comparison of Cycle-Resolved and Ensemble-Averaged velocity variations in a Diesel Engine

Laser-Doppler anemometry was used to investigate mean flow and turbulence fields in a direct injection diesel engine, motored at speeds of 1500, 2250 and 3000 rev/min. Both cycle-resolved and ensemble-averaged measurements were made in the upper part of the cylinder during the inlet and compression strokes.

The cycle-resolved measurements in the inlet stroke indicated that the annular jet leaving the valve underwent rapid changes of direction at frequencies which varied from one point to another around the valve circumference. The cycle-resolved and ensemble-averaged measurements in the compression stroke both revealed a precession of the swirl centre around the cylinder axis, at a rate which was faster than the speed of rotation of the crankshaft.