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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.

Variable Cam Timing (VCT) has been proven to be a very effective method in PFI (Port Fuel Injection) engines for improved fuel economy and combustion stability, and reduced emissions. In DISI (Direct Injection Spark Ignition) engines, VCT is applied in both stratified-charge and homogeneous charge operating modes. In stratified-charge mode, VCT is used to reduce NOx emission and improve combustion stability. In homogeneous charge mode, the function of VCT is similar to that in PFI engines. In DISI engine, however, the VCT also affects the available fuel-air mixing time. This paper focuses on VCT effects on the induction process and the fuel-air mixing homogeneity in a DISI engine. The detailed induction process with large exhaust-intake valve overlap has been investigated with CFD modeling. Seven characteristic sub-processes during the induction have been identified. The associated mechanism for each sub-process is also investigated.

Swirl plane Particle Image Velocimetry (PIV) measurements were performed in a single-cylinder optically accessible gasoline direct injection (DISI) engine using a borescope introduced through the spark plug hole. This allowed the use of a contoured piston and the visualization of the flow field in and around the piston bowl. The manifold absolute pressure (MAP) was fixed at 90 kPa and the engine speed was varied in increments of 250 rpm from 750 rpm to 2000 rpm. Images were taken from 270° to 320° bTDC of compression at 10° intervals to study the evolution of the velocity fluctuations. Measurements were performed with and without fuel injection to study its effect on the in-cylinder flow fields. Fuel was injected at 10 MPa and 5 MPa. The 2-D spatial mean velocities of individual flow fields and their decompositions were averaged over 100 cycles and used to investigate the effects of engine speed and image timing on the flow field.