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The improvement of fuel consumption is the most important issue for engine manufactures from the viewpoint of energy and environment conservation. A piston-cylinder system plays an important role for the reduction of an engine friction. For the improvement of the frictional behavior of the piston-cylinder system, it is beneficial to observe and analyze the frictional waveforms during an engine operation. To meet the above-mentioned demand, frictional waveforms were measured with using the renewed floating liner device. In the newly developed floating liner device, an actual cylinder block itself was used as a test specimen. The measured single cylinder was an aluminum monolithic type made of hypereutectic Al-17%Si alloy using a high pressure die casting process. The combined piston was a light weight forged piston and a DLC coated piston ring was used. For the measurement, 110cc air cooled single cylinder engine was used.

A simple method is frequently used to calculate a reciprocating engine’s bearing load from the measured cylinder pressure. However, it has become apparent that engine downsizing and weight reduction cannot be achieved easily if an engine is designed based on the simple method. Because of this, an actual load on a bearing was measured, and the measured load values were compared with a bearing load distribution calculated from cylinder pressure. As a result, it was found that some of actual loads were about half of the calculated ones at certain crank angles. The connecting rod’s elastic deformation was focused on as a factor behind such differences, and the rod’s deformation due to the engine’s explosion load was studied. As a result, it was found that the rod part of the engine’s connecting rod was bent by 0.2 mm and became doglegged. Additional investigation regarding these findings would allow further engine downsizing.

For various densities of gas jets including very light hydrogen and relatively heavy ones, the penetration length and diffusion process of a single high-speed gas fuel jet injected into air are computed by performing a large eddy simulation (LES) with fewer arbitrary constants applied for the unsteady three-dimensional compressible Navier-Stokes equation. In contrast, traditional ensemble models such as the Reynolds-averaged Navier-Stokes (RANS) equation have several arbitrary constants for fitting purposes. The cubic-interpolated pseudo-particle (CIP) method is employed for discretizing the nonlinear terms. Computations of single-component nitrogen and hydrogen jets were done under initial conditions of a fuel tank pressure of gas fuel = 10 MPa and back pressure of air = 3.5 MPa, i.e., the pressure level inside the combustion chamber after piston compression in the engine.

In order to verify cooling loss reduction effect of internal combustion engine, method for measuring wall surface temperature and heat flux with high accuracy is required. Various methods have been proposed for measuring the cooling loss from the combustion gas to the combustion chamber wall, newly coaxial type thin-film temperature sensor was developed for wall temperature and heat flux measurement by the authors. This sensor consists of thin-film and body and center wire have three junction positions in the case where three materials are different. Therefore, it is necessary to use the same materials for thin-film and body or thin-film and center wire to make two junction points. In this study, sputtering method that can be formed various kinds of alloy materials and film thickness of 0.1~1μm on the sensor surface was chosen.

The piston rings, the engine sliding parts, are required to further contribute on mechanical loss reduction in order to improve fuel efficiency. However, many cases of the abnormal combustion due to oil upward flow, as well as the increase in oil consumption have been reported. Therefore, elucidation of the mechanism of those phenomena is still an urgent task. It is widely known that the distribution of the sliding face pressure in between the piston ring and the cylinder bore largely influence the oil flow via the sliding face of the piston ring. However, there are many unknown aspects in this field. Therefore, verification of the sliding face pressure during the actual operation is necessary in order to elucidate the mechanism of oil consumption. The thin-film sensor, since it has little influence on shape, is widely used as a measurement method of the sliding face pressure between two different faces, however this method has never been applied to the piston ring in the past.

The friction reduction of a piston/piston-ring assembly is effective for fuel economy of an engine, and a friction measurement method is required for developing low friction pistons, piston-rings and lubricants. Most suitable method for friction measurement for piston assemblies is “floating liner method”. It has load sensors between a floating cylinder liner and cylinder block, and the sensors can detect friction force acting on the liner. Many apparatuses using floating liner method are developed. They are roughly divided to two categories. In one of them, floating liner is supported by load-washers which axis is set parallel to the center line of the cylinder liner. In another type, floating liner is supported by three-component force sensors installed on the side face of the cylinder. In this paper, five types of floating liner devices were compared.

1 Piston design approach for automotive engines has been advanced from both experimental and calculation analysis. However, the developments of experimental analysis method that can verify the accuracy of the calculation analysis are required. In this paper, multi-point thin-film pressure sensor for piston pin-boss part (hereinafter pin-boss) was sputtered on piston pin sliding surface and oil-film pressure distribution was measured in axial and circumferential direction using the pin-boss fatigue tester. Two kinds of pistons with different pin-boss shape (tapered shape) were used in the experiment. The peak pressure of piston with large tapered shape was higher about 20%, compared to the piston with the small tapered shape. As a result of oil film pressure distribution in circumferential direction, it has measured that the oil-film pressure at near side relief was higher than that of piston top side.

The reduction of friction losses is a subject of central importance in a diesel engine. The piston frictions of low viscosity engine oil and molybdenum dialkyl dithiocarbamate (MoDTC) have been measured by floating liner method. It was found that the low viscosity engine oil lower than 5W-30 is not effective against the reduction of friction mean effective pressure (FMEP) related to the fuel consumption. MoDTC showed a good performance against the reduction of FMEP. In the friction measurement points, the reduction ratio of 10W-30 with MoDTC to 10W-30 was greater than that of 5W-30 to 10W-30.

Clarifying the mechanism of oil transporting upward at around an oil ring of a piston is necessary for calculating engine oil consumption. This study aimed to clarify the function of oil drain holes in the oil ring groove of a piston. The effect of the oil drain holes in the groove on oil consumption was investigated. Also the pressure balance around the oil ring was measured. It was found that the drain holes in the groove lowered oil consumption. It was assumed that lower pressure in the groove with the drain holes caused less oil flow into the third land.

The authors have previously proposed a plume ignition and combustion concept (i.e., PCC combustion), in which a hydrogen fuel is directly injected to the combustion chamber in the latter half of compression stroke and forms a richer mixture plume. By combusting the plume, both cooling losses and NOx formation are reduced. In this study, thermal efficiency was substantially improved and NOx formation was reduced with PCC combustion by optimizing such characteristics as direction and diameter of the jets in combination with combustion of lean mixture. Output power declined due to the lean mixture, however, was recovered by supercharging while keeping NOx emissions at the same level. Thermal efficiency was further improved by slightly re-optimizing the jet conditions.

In order to establish standard method to evaluate cooling loss in combustion chamber of internal combustion engines based on measurement of instantaneous heat flux / wall temperature with higher response and accuracy than previously reported coaxial type thin-film temperature sensor by applying thin film fabrication technology based on PVD method (Physical Vapor Deposition method) which improved to realize higher responsiveness than the conventional sensor was developed by the authors, and it was confirmed that the sensor has sufficient durability in conditions in which the hydrogen jet and flame directly contacts surface of the sensor by thin-film material change. The influence of the improvement on the measurement accuracy was verified by numerical analysis including thermoproperty evaluation. In this report, the configuration of measurement system that can measure minute voltage from the sensor with low noise and high response is reported.

Hydrogen ICE can achieve carbon neutrality and is adaptable to medium and heavy-duty vehicles, for which electricity is not always a viable option. It can also be developed using high-quality conventional diesel/gasoline engine technology. Furthermore, it allows for the conversion of existing engines to hydrogen ICE, making it highly marketable. The reliability and durability of MPI hydrogen ICE is better than that of DI, and MPI has an advantage over DI in terms of cruising range because the low-pressure injection of hydrogen reduces the remaining hydrogen in the tank. Improving MPI output is, however, an important subject, and achieving this requires suppressing abnormal combustion such as pre-ignition. In this study, an inline four-cylinder 5L turbo-charged diesel engine was converted to a hydrogen engine. Hydrogen injectors were installed in the intake ports and spark plugs were installed instead of diesel fuel injectors.

The mechanism of lubricant dilution by post injection fuel in a diesel engine was investigated. The operating conditions of the engine were changed, and oil was sampled from each part of the piston and the crankcase, and the dilution ratio was analyzed. Also, photochromism was used to visualize the oil and fuel flow. Dilution ratios obtained from oil sampling and photochromism showed the same tendency.