The variation of Flow Pattern in a Diesel Engine Cylinder with Speed

The mean flow and turbulence fields in the cylinder of a HSDI Diesel engine were measured by laser-Doppler anemometry. The engine was motored at speeds from 1000-3000 rev/min at a compression ratio of 6.7. Particular attention was paid to the effect of engine speed on the interaction of the swirl and radial velocities near TDC of the compression stroke.

There was found to be a considerable difference between the radial flow patterns at high engine speeds (2250 and 3000 rev/min) and at low speeds (1000 and 1500 rev/min). Swirl velocities increased in proportion to engine speed in some locations and some crank angles but at others the increase was much less. Radial and tangential r.m.s. velocities increased at a greater rate than the piston speed in some parts of the flow.