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In a cross-scavenged two-stroke engine, a piston with a deflector is often utilized to flow the fresh charge toward the cylinder head and away from the exhaust port. But flow-visualization studies have shown that the fresh charge flows toward the cylinder head even without the deflector. To find why the fresh charge flows toward the cylinder head, we used Fluent, a general purpose computational fluid dynamics (CFD) software, to simulate two- and three-dimensional flows in a cross-scavenged two-stroke engine. While the fresh charge entered from the scavenging port into the cylinder and flowed across the cylinder, we investigated the instantaneous fresh charge flow, velocity, and pressure distribution in the cylinder.

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.

An air-cooled engine with a finned cylinder may have residual heat between the fins. Residual heat decreases heat release from the cylinder when cooling air is not forced over the engine. In order to induce natural convection in the cylinder, cooling ports were drilled in the fins parallel to the cylinder axis to determine if residual heat could be decreased and additional cylinder cooling could be developed. The effects of the fin configurations on air-cooling were investigated to utilize the cooling ports for a stationary engine and a non-moving motorbike engine. The experimental cylinder design permitted variation in the number of fins and fin pitch. Numbers of fins that had various port sizes and port positions were investigated; in addition, the temperature inside of the cylinder and in the space between the fins was measured. Results indicated that heat release from the cylinder was increased by utilizing the fins with ports as compared to the fins without ports.

During the scavenging of a two-stroke engine, it can be assumed that a very small quantity of fresh mixture flows from the scavenging ports and also from the crankcase through the gap between the cylinder and the piston to the exhaust port, in order to assess the effects of these leakages on fuel economy and hydrocarbon emissions, the authors calculated the quantity of mixture lost using the time-areas of the flow paths and the pressure-time history in the crankcase, and found that this quantity was in the order of 1-3% of the inducted fresh mixture.

Special advantages of U-cylinder uniflow scavenged engines are that only a little amount of the fresh charge flows out through the exhaust port because of their one-way scavenging paths, and that the hydrocarbon concentration in the exhaust gas is considerably low. On these engines, however, we cannot expect, like other two-cycle engines, the perfect scavenging quality which four-cycle engines can normally achieve. In the case of U-cylinder uniflow scavenged engines the hydrocarbon concentration of the exhaust gas becomes naturally higher with increasing delivery ratio(SAE Paper 850181). The author has developed a U-cylinder uniflow engine in which the front of the fresh scavenging medium consists of air layer. The running performance of this engine was, however, not stable.

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.

The scavenging picture means here the velocity distribution of the scavenging flow in the cylinder measured by a pitot tube. The picture is often used to investigate the suitability of the design of the scavenging system in a two-stroke cycle engine. In measurements by pitot tube only the upward component of the velocity has been measured until now. By this improvement, however, it is well possible to measure the velocity in three dimensions. In other words, it is now possible to measure also the scavenging flow toward the exhaust port after the flow turns downward at the cylinder head.

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.

The authors have utilized a modified automobile engine with a transparent glass cylinder, which was driven by an electric motor. The effects of the positions of the piston ring gaps, the end clearance size and the shape of the piston ring gaps on the lubricating oil flow were examined using the modified engine. The results indicate that the main stream of the lubricating oil flow goes from the lower ring gap to the upper ring gap in all of the positions of the piston ring gaps and that the position of the oil ring upper side rail gap has a great influence on the lubricating oil flow.

The authors have constructed a modified engine with a transparent glass cylinder, for motoring experiments, to observe lubricating oil flow from the sump to the combustion chamber through the clearance between the piston and the cylinder. The modified engine was motored at engine brake condition and the oil flow was filmed by a video camera. The amount of actual oil flow was also measured. The effects of pressure difference between the intake manifold and the crankcase, oil temperature, and oil ring tension on oil flow through the piston ring belt were studied. The results indicate that the main stream of oil flow increases with pressure difference and with oil temperature, and that oil flow is increased when a higher tension oil ring with excessive spacer expander circumference is utilized. Measuring equipment was also developed to examine the deflection of the oil ring underside in the cylinder when the expander circumference was varied.

In an air-cooled engine, waste heat dissipates from the cylinder, through the cooling fin, to the cooling air. This cooling air is kept moving by a cooling fan in most utility engines, and by the relative motion in moving motorbikes. However, such cooling becomes less efficient when air is not forced around the cylinder, e.g., in utility engines without cooling fans and in stationary motorbike engines. Here, the temperature may increase in the space between the fins, decreasing the heat release from the cylinder. In an effort to increase natural convection in the cylinder, and so decrease the temperature between the fins, we produced special cooling fins with slits arranged in a fixed equiangular spiral. We tested experimental cylinders, varying the fin slit widths and slit setting positions, and measured the temperature inside the cylinder to determine the heat release from the cylinder.

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.

Two-stroke engine cylinders have ports to exchange gas. While the engine runs, the piston and its piston rings slide over these ports in the cylinder walls, and the rings may project into the ports. This paper explores this, first, by reporting a simple model of material mechanics that predicts rings might project into ports, and second, our experimental verification. We installed strain gauges on the bottom of the top and second rings, over the intake and exhaust ports, and ran signal wires out of the engine. We then examined the variations of strain while running the engine. Our analysis confirmed how the dimensions and the tension of the rings, and the dimensions of the ports, affect ring projection into ports as static displacements.

Using a modified engine with a transparent glass cylinder for motoring equipment, the effects of the structure in the vicinity of the oil ring groove drain back slots of the inside of the piston, the end clearance size of the oil ring side rail gaps and the shape of the top ring gap on the lubricating oil flow were examined. The results indicate that the amount of undesirable oil flow was reduced by utilizing a piston with the covers installed under the drain back slots on the inside of the piston, the side rails with the optimized upper and lower side rail gap size and the top ring with a special joint (triangle step joint) as compared to a standard piston and standard piston rings. Furthermore, the amount of undesirable oil flow was considerably reduced by utilizing the combination of the modified piston and rings.