Analysis of the Intake Flow in a Diesel Engine Head Using Dynamic Steady Flow Conditions

An experimental investigation, using the Laser Doppler Anemometry (LDA) technique, was carried out to investigate the complex structure of the intake flow in a commercial four-cylinder automotive Diesel engine. The attention was focused on the evaluation of the mean motion and turbulence intensity by using a steady state test rig with dynamic valve flow arrangements, supplying a flow rate of 17.4m³/h, that corresponds to the actual flow rate of the engine running at 2,000 rpm. The LDA tests were performed with the engine head mounted on a plexiglas cylinder, having the same diameter as that of the real engine, equipped with optical accesses. The intake manifold was connected to a flow bench tester to simulate the actual flow rates of the engine. Measurement points were located within the cylinder at different distances from the cylinder axis, on two orthogonal diameters, and at different depths from the engine head. The instantaneous velocities were processed by using an ensemble averaging technique in order to estimate the mean velocity and the turbulence intensity.

The main results showed that both the mean tangential and axial velocities increase during the valve opening period, reaching the maximum magnitude when the valve is closed for every measurement points. The velocities decrease subsequently to near zero values at 60° cam angle (c.a.) after the valve closure. Results highlighted a complicated flow field structure with a tumble motion in the vertical plane, which forms and grows during the valve lift and spreads until 60° c.a. after the valve closure. The turbulence intensity profile displayed a high level around the valve closure with a decaying trend until 60° c.a. after the valve closure.