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To accurately measure piston ring radial-force, we constructed an instrument arraying 12 measuring assemblies, spaced 30º apart around the ring circumference, each comprising a roller, a slider, a load cell in a holder, and a micrometer head. Using this measuring device, we investigated the radial-force distribution in several compression rings with various ovalities. For each ring, we first measured the radial force at 30º intervals around the ring circumference, avoiding the ring gap, and then we displaced the ring 15º in the circumferential direction, and set a custom jig between the ring gap and the measuring assembly. Thus we were able to measure the radial-force at 15º intervals around the entire circumference, including the ring gap position.

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.

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.

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.

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.

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.

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.

An all aluminum cylinder block with a Metal Matrix Composite (MMC) cylinder bore was developed which made it possible to re-design the base engine for high performance with a bore-to-bore distance as narrow as 5.5mm. The cylinder block is an open deck type and the MMC preform consists of alumina-silica fibers and mulite particles. A laminar flow die cast process was selected to ensure defect-free MMC bore quality. To insure good lubrication, electrochemical machining was applied to the bore surface. By use of radioisotope(RI) measurements, MMC reinforcement was optimized for wear characteristics. Particular attention was paid to use of fuels with high sulfur levels.

A study was conducted to reduce unburned oil fractions in diesel particulate matter (PM) by improving oil consumption. A method utilizing radioisotope 14C was developed to measure the unburned oil fractions separately for the four paths by which oil is consumed: valve stem seals, piston rings, PCV system, turbocharger. The conversion ratio of oil consumption to PM was calculated by comparing the unburned oil emission rates with oil consumption rates, which were obtained by the use of the 35S tracer method. The result in an experimental diesel engine shows the highest conversion ratio for the oil leaking through the valve stem seals. The modifications to the engine were thereby focused on reducing the leakage of the stem seals. This stem seal modification, along with piston ring improvements, reduced oil consumption, resulting in the unburned oil fractions in PM being effectively reduced.

The EHD lubrication model of connecting rod big end bearings is compared with experiments using an automotive diesel engine. The axial load and the bending moment near the middle of rod length were derived from strain measurements and compared with the theoretical results based on engine dynamics. Although oscillation appeared on bending moment at 5000 rpm, the theoretical load almost agreed with the experiment. The EHD lubrication theory and the experiments were compared by the histories of clearances and the journal center orbits in the bearing. The theoretical results agreed well with the experimental one. The deformation of the bearing appeared both in the theory and in the experiment at 3000 rpm or above; these results confirm the necessity of the EHD lubrication theory.

Temperature distributions on the surface of a connecting rod big end bearing were measured to understand the margin to the allowable limiting temperature. The results show that the temperature difference between the bearing surface and the feed oil is independent of the engine load but quadratically increased with the engine speed, and that the bearing surface temperature on the rod side is higher than those on the cap side, and that the high temperature regions appeared near the edges on the rod side of the bearing under high speed operations. The results were analyzed by the observation of rubbing traces on the bearing surface and the EHD lubrication theory.

The influence of engine oil viscosity on the wear of piston rings and cam faces has been investigated by fired engine tests using a radioisotope (RI) tracer technique. High-temperature and high-shear-rate (HTHS; 150°C, 1O6 s-1) viscosities of the experimental oils prepared are 2.2, 2.4, 2.6 and 3.1 mPa•s. At an oil temperature of 90°C the wear of piston rings and cam faces did not increase, even if the HTHS viscosity was lowered down to 2.2 mPa•s. However, both piston rings and cam faces exhibited an increase in wear below 2.4 mPa•s at 130°C. It was also recognized that valve train wear did not significantly increase with reducing viscosity in the motored engine tests at a temperature of 50°C. From these test results, it was suggested that the oil with the HTHS viscosity of 2.6 mPa•s sufficiently demonstrates the antiwear performance equivalent to that with around 3.0 mPa•s for application to piston rings and cam faces.

Oil consumption mechanism was analyzed by measuring the radial movement of the upper side rail in a three piece type oil ring, together with the piston movement. Ultra-miniature inductive displacement sensors were designed to measure the oil ring movement and fitted on the upper side rail with a part of the 3rd land cut out. The clearance between the side rail and the cylinder wall was measured under various operating conditions. The results showed that the radial movement of the oil ring was affected by the piston movement, which results in the possibility of degrading the oil control ability for the cylinder wall because the oil ring temporarily moves with the piston. Accordingly, the designs to improve the piston movement or to be less affected by the movement proved to be an important factor for the reduction of the oil consumption.

In the measurement of engine oil consumption the conventional radiometric method is more rapid and precise than the drain-weigh method, but the former method-a batch type-is inapplicable to measurements in transient engine operations which are inevitable in real driving. In the present study, a reliable method was developed to measure continuously the consumption rate through all phases of engine operation. Oleic acid sulfide containing S35 was selected as a radioactive tracer to be added to the engine oil. Engine exhaust gas containing the discharged oil was burned in an electric furnace and a gas burner and reacted with aqueous H2O2 solution, converting the S35O2 into H2S35O4. A plastic bead scintillator used for the detection of β-rays from the aqueous solution was sensitive enough to measure the consumption rate as low as 0.4 g/h.