The instantaneous two-dimensional velocity distribution around the intake valve of an internal combustion engine was investigated by using the Particle Image Velocimetry (PIV) technique and the results were checked measuring the mean velocity vector by using the Laser Doppler Anemometry (LDA) technique. PIV tests were performed, using a steady state test rig, on a vertical plane below the intake valve at two valve lifts. The LDA technique was used to calibrate the PIV, measuring the mean velocity vector on the same plane. Moreover, LDA measurements were taken, under motoring conditions, to investigate the complex flow at the intake and its evolution during the compression. The experimental set-up, for PIV and LDA steady state tests, consisted of a 4-cylinder diesel engine head mounted on a plexiglas cylinder of the same diameter as that of the real engine. The intake manifold was connected to a flow bench tester to simulate the actual intake flow rates of the engine. The PIV set-up consisted of a Nd:YAG laser able to generate a light sheet and a 35 mm camera set at 90° to the laser sheet. The double exposed frame was interrogated by using the Young''s fringe method. The experimental set-up for LDA measurements within the engine cylinder, under motoring conditions, was set using the same engine head modified with an optical access.The PIV results showed a flow field characterized by a large scale motion with recirculation zones. An upward flow below the intake valve, generated by the interaction of the strong jet motion along the valve surface with the stagnant air within the cylinder, was observed. The comparison between PIV and LDA gave a fair agreement although differences were noted in some locations due to the high fluctuation of the mean motion at the intake. Results obtained by LDA, under motoring conditions, showed a complex flow field during the intake valve opening interval with high velocity and turbulence levels. At the end of intake, the turbulence intensity decays to a value that remains constant until the middle of compression.
Flow field characterization of the intake flow in a diesel engine by lda and piv
1999
Aufsatz (Konferenz)
Englisch
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