PIV Characterization of a 4-valve Engine with a Camshaft Profile Switching (CPS) system

Particle Image Velocimetry (PIV) measurements were performed on a single cylinder optically accesible version of a 3.0L 4-valve engine using a Camshaft Profile Switching (CPS) system. The flow field was investigated at two engine speeds (750 and 1500 rpm), two manifold pressures (75 and 90 kPa) and two intake cam centerlines (maximum lift at 95° and 115° aTDCi respectively). Images were taken in the swirl plane at 10 mm and 40 mm below the deck with the piston at 300° aTDC of intake (60° bTDC compression) and BDC respectively. In the tumble plane, images were taken in a plane bisecting the intake valves with the piston at BDC and 300° aTDC. The results showed that the swirl ratio was slightly lower for this system compared with a SCV system (swirl control valve in the intake port) under the same operating conditions. The swirl and tumble ratios generated were not constant over the range of engine speeds and manifold pressures (MAP) but instead increased with engine speed and MAP. The induced swirl was due to in-cylinder flow asymmetry. The asymmetry, measured by the ratio of the mass of air flowing through the primary valve to the mass of air flowing through the secondary valve, increased with speed and MAP. This resulted in the average velocity in the swirl plane increasing with engine speed beyond that expected due to the increased piston speed. The velocities in the tumble plane scaled with the engine speed and the tumble ratio was only slightly affected by the CPS, mainly due to the coupling of the swirl and tumble in the engine. At 750 rpm, increasing the MAP was found to decrease cycle-to-cycle variation, as did increasing engine speed at low MAP.