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In most air-cooled engines, aluminum cylinder blocks are lined with cast iron, which enjoys a higher wear resistance than aluminum. Recently, rather than a turned periphery, an increasing number of cast iron liners have employed as-cast periphery with projections, so the liner better adheres to the aluminum cylinder block, and improves heat transfer. This study attempts to maximize heat transfer while minimizing cylinder weight, by comparing four liners: (1) a cast iron liner with higher projections on its periphery, (2) a cast iron liner with lower projections, (3) a cast iron liner with lower projections, and aluminum-silicon coated on its periphery by thermal spraying, and (4) a high-silicon aluminum alloy liner with aluminum-silicon coated by thermal spraying. These four experimental liners were fitted in a die-cast low-silicon aluminum-alloy cylinder block, to investigate their joint and cooling characteristics.

We aim to maximize the performance of air-cooled engines (such as motorbike engines and small stationary engines) by increasing cylinder cooling and by maintaining uniform temperature around the cylinder circumference. In typical engine designs, air cools the front of the cylinder better than the rear. In an effort to increase cooling at the rear, this research experiments with tapered fins that contract air flow to the cylinder axis between the fins, and with baffle plates mounted between fins symmetrically with respect to a plane through the axis of the cylinder. In a wind tunnel at air velocities between 20 and 60 km/h, we compared cylinders with conventional fins, cylinders with tapered fins, cylinders with baffle plates between conventional fins, and cylinders with baffle plates between tapered fins.

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.

Several techniques facilitate the cooling of air-cooled motorbike engines. Baffle plates, mounted between cooling fins symmetrically with respect to a plane through the axis of the cylinder, maximize the distance that the cooling air follows the cylinder surface before it separates from the cylinder, when the motorbike is in motion. Cooling ports, drilled in the fins parallel to the axis of the cylinder, induce natural convection in the cylinder, when the motorbike is stationary. We produced cylinders with baffle plates between the fins, and with cooling ports, in order to improve cylinder cooling while motorcycles are both moving and stationary. We investigated experimental cylinders with baffle plates, cylinders with fins with cooling ports, and cylinders with both baffle plates and fins with cooling ports, all over a range of air velocities between 0 and 60 km/h.

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.