Cooling Effects of Air-Cooled Finned Cylinder Utilizing Contracted Flow 2009-01-0176

In air-cooled motorbike and stationary engines, waste heat dissipates from the cylinder through the cooling fins to the cooling air. In these engines, the cooling air flow follows the cylinder surface at the front of the cylinder, but separates at the rear, reducing cooling. To increase the distance over which the air flow follows the cylinder surface before it separates from the cylinder, and so to increase cooling at the rear, we experimented with cylinders utilizing contracted flow between fins. These cylinders have fins with different thickness at the front and the rear, so as to contract the air flow around the cylinder. We produced and tested three experimental cylinders with various lengths of contracted fins (tapered fins), in a wind tunnel at air velocities between 20 and 60km/h. We measured the temperature inside the cylinder over time to determine the heat release from the cylinder. We also measured the temperature on the fin surfaces to determine the temperature distribution around the circumference of the cylinder. To understand the effect of the contracted flow between fins on cylinder cooling, we visualized the air flow on the fin surfaces. Results indicated that, compared with conventional finned cylinders, our finned cylinders with contracted flow increased cylinder cooling. Furthermore, our finned cylinder with the contracted flow at the rear increased cylinder cooling, and decreased cylinder weight.