1995-10-01

Unsteady Intake Valve Gap Flows 952477

The performance of engine intake ports is traditionally characterized by pressure drop and in-cylinder swirl or tumble ill steady flow at discrete valve lifts. These characteristics are often complemented by velocity profiles in the cylinder and the valve gap, but the influence of valve and piston motion cannot be represented.
In this work the intake stroke simulation was improved with a moving piston, although the valve remained motionless. A simple port geometry was chosen, since it was not the intention to optimize the port design for a particular engine. Measurements of three mean velocity components and the corresponding turbulence intensities around the intake valve showed complex flow patterns, including separation from the valve seat and sealing faces and back-flow into the intake port near the cylinder wall.
Assuming quasi-steady flow conditions, i.e. a constant flow coefficient, flow velocities should scale with the instantaneous piston speed. It is demonstrated that normalized distributions of mean axial and radial velocity across the valve gap do indeed fit a single distribution at each azimuthal location at all crankangles. This normalization does not, however, eliminate engine speed dependence for the tangential mean velocity and all turbulence intensity components.

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