Improvement of Cylinder Cooling in Air-Cooled Engines by Utilizing Baffle Plates

In an air-cooled engine, the cooling air follows the cylinder surface at the front in an air stream. However, it separates from the cylinder at the rear reducing the cooling effect of the air stream on the rear of the cylinder. In order to improve the flow of air to the rear of the cylinder, baffle plates were mounted on the outside of the cylinder or between the fins symmetrically with respect to a plane through the axis of the cylinder. Experimental cylinders with baffle plates at various positions were investigated over a range of air velocities between 20 and 60 km/h in a wind tunnel. The temperature on the fin surfaces was measured to determine the temperature distribution provided to the circumference of the cylinder and the average fin surface heat transfer coefficient. To understand the effects of baffle plates on cylinder cooling, the air flow between the fins was observed with a high-speed video camera by the smoke wire method. Results indicated that cylinders with baffle plates mounted on the outside of the cylinder had more uniform temperature around the circumference of the cylinder. The average surface heat transfer coefficient was lower in a higher air velocity and with the baffle plates mounted nearer to the rear as compared to the cylinder without baffle plates. Cylinders with baffle plates mounted between the fins had not only more uniform temperature in the circumference but also a greater average surface heat transfer coefficient. The optimized baffle plates mounted between the fins gave an increase of 19 to 23 % in the average surface heat transfer coefficient as compared to the cylinder without baffle plates.