Air-Cooling Effects of Fins on a Motorcycle Engine∗

Effects of the number of fins, fin pitch and wind velocity on air-cooling were investigated using experimental cylinders for an air-cooled engine of a motorcycle. Experimental cylinders that had a various number of fins and fin pitches were tested in a wind tunnel. Then the temperature inside of the cylinder, on the surface of the fins and in the space between the fins was measured. Results indicated that the heat release from the cylinder did not improve when the cylinder had more fins and too narrow a fin pitch at lower wind velocities, because it was difficult for the air to flow into the narrower space between the fins, so the temperature between them increased. We also obtained the expression of average fin surface heat transfer coefficient derived from the fin pitch and the wind velocity. This expression is useful for the fin design of an air-cooled cylinder.