Optimum Fin Layout of Air-Cooled Engine Cylinder in Air Stream

It is important for an air-cooled engine to utilize fins with effective engine cooling and uniform temperature in the cylinder circumference. In order to permit the development of design data, an experimental cylinder was developed having variable fin pitch and number of fin capability. This experimental cylinder was tested in a wind tunnel. Experimental cylinders with five different fin pitches and twelve different numbers of fins were investigated over a range of air velocity between 0 and 60 km/h. The temperature inside the cylinder and on the fin surface was measured to determine the heat release from the cylinder and the fin surface heat transfer coefficient respectively. To understand the operation of cooling fins for each fin pitch, number of fins, and air speed, the temperature in the space between the fins was measured and the air flow between them was observed with a high-speed video camera using the smoke wire method. As a consequence, this experimentation clarified the fin pitch and number of fins required to provide more effective cooling. In addition, fin pitch was found to be important in improving cooling, especially in a lower air velocity. The expression of average fin surface heat transfer coefficient derived from fin pitch and air velocity was developed. This expression can be utilized to predict the improvement of cooling in the fin design process.