The Development of a Transparent Cylinder Engine for Piston Engine Fluid Mechanics Research

The development of a unique flow visualization engine is discussed. The new research engine, called the Flow Diagnostics Engine (FDE), is a single-cylinder engine with a transparent cylinder made from single-crystal sapphire. In contrast to previous efforts, the FDE has an internal geometry very similar to that of production engines. A computer-controlled valve-actuation system is used on the FDE. The valve actuators are last electro-hydraulic devices which with a minicomputer, provide complete control over the valve motion. To visualize the flows in the engine cylinder a special schlieren system was developed and demonstrated. In the new visualization system, a holographic optical element is used to correct system aberrations.

To demonstrate the feasibility and usefulness of the FDE system, flows in both conventional and swirl engine geometries were visualized and recorded with high-speed cinematography. The visualization provides qualitative information about the flow and allows observation of:

• the development and motions of large recirculation zones during the intake event.
• the appearance of small-scale turbulence and the changes in scale caused by compression and expansion.
• the expansion of ring crevice gases into the cylinder during the beginning of the exhaust evens, and
• the large-scale motions associated with intake swirl.

The FDE system is very versatile and can accommodate a wide variety of engine geometries, operating conditions, and optical diagnostics.