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Furuhama(1)* proposed the new two ring package consist of a pressure ring and a narrow single-rail oil ring (NSOR) in 1985. Number of studies(2) have been done for the purpose of reducing the oil consumption (OC) in this ring package. However, OC reduction problem has been still remaining to solve as only one serious problem of this ring package. The reasons of a larger OC in the new ring package than the conventional three ring has been hardly understood, considering the OC control ability on second ring in three ring package will not so large since the fact that the oil film thickness is thicker than that of the oil ring. In this study, the mechanism of OC increase in new ring package was found out at last, as a result, OC of new ring package piston was improved up to the same level of conventional three ring package piston.

The purpose of this study is to clarify the state of heat loss to the cylinder liner of the tested engine of which piston and cylinder head were previously measured. The authors' group developed an original measurement technique of instantaneous surface temperature at the cylinder liner wall using thin-film thermocouples. The temperature was measured at 36 points in total. The instantaneous heat flux was calculated by heat transfer analysis using measurement results of the temperature at the wall. As a result, the heat loss ratio to all combustion chamber walls is evaluated except the intake and exhaust valves.

This paper describes measurements of oil film thickness of piston ring packages which have different oil control rings. The oil film thickness measurements were taken at three points, namely, the piston thrust side, front side and rear side, by the Laser Induced Fluorescence Method(LIF). One of the main findings is that the oil film thickness on the thrust side varies greatly from cycle to cycle, while cyclic variations are smaller on the front and rear sides. This difference is due to the smaller inclination of the oil control rings on the front and rear sides, compared with that on the thrust side. It is also found that oil consumption has a good correlation with oil film thickness on the thrust side and that the thrust side oil film thickness becomes thinner as the oil ring becomes narrower.

Thermodynamic characteristics of premixed compression ignition combustions were clarified quantitatively by heat balance estimation. Heat balance was calculated from temperature, mole fractions of intake and exhaust gases, mass and properties of fuels. Heat balance estimation was conducted for three types of combustion; a conventional diesel combustion, a homogeneous charge compression ignition (HCCI) combustion; fuel is provided and mixed with air in an intake pipe in this case, and an extremely early injection type PREmixed lean DIesel Combustion (PREDIC). The results show that EGR should be applied for premixed compression ignition combustion to complete combustion at lower load conditions and to control ignition timing at higher load conditions. With an application of EGR, both HCCI and PREDIC showed low heat loss characteristics at lower load conditions up to 1/2 load.

One of the problems in HCCI combustion is a knocking in higher load conditions. It governs the high load limit, and it is suggested that the knock increases heat loss[1], because it breaks the thermal boundary layer. But it is not clear how much knock affects on heat loss in the HCCI combustion in various conditions, such as ignition timing and load. The motivation of this study is to clarify the ratio of heat loss caused by knock in HCCI engines. The heat loss from zero-dimensional calculations with modified heat transfer coefficient, which is considering the effect of knock by adding a term of cylinder pressure rising rate dp/dt, agreed well with the results from the thermodynamic analysis in various conditions. And the results show that it is possible to avoid heat loss by knock by controlling the ignition timing at appropriate timing after T.D.C. and it will be possible to expand the load range if knock can be avoided.

One of the phenomena accompanying the lightweight/compact/high power output feature of engines is the cylinder bore deformation, which may readily cause increased oil consumption, gas leakage, unusual wear, scuffing, etc.. The authors have had experiences that piston rings had generated contact failure during engine operation (1)*. Such deformation is generated as a combination of the static deformation due to head bolt tightening, crankshaft installation, etc., and the deformation by the operating factors; thermal load and combustion pressure. Countermeasure of design have been made for the former (2)*, and prediction of the deformation during actual operating have been tried using FEM analysis, etc. for the latter (3)*. Therefore, the accurate measurement result have been required strongly, for a long time. But it could not be realized in the past.

An unique measurement method was developed for measurement of the piston outer surface during the engine operation. The method was realized by embedding a gap sensor into a cylinder bore and by rotating the cylinder in the circumferential direction. By means of this method, interesting data of skirt deformation of a gasoline engine caused by temperature, pressure and the slap force were obtained.

In order to establish hydrogen engines for practical use, it is important to overcome difficulties caused by unique characteristics of hydrogen fuel. A hydrogen engine with direct injection right before top dead center(TDC) and spark ignition has advantages such as prevention of abnormal combustion and realization of high power output near the stoichiometric air-fuel ratio, in comparison with an engine with external mixture. On the other hand, it has been pointed out that ignition and combustion for this type of hydrogen engines should be improved and that further studies on mixture formation of air and injected hydrogen are necessary for the improvement. For the direct injection hydrogen engine, mixture is formed both by air flow inside the combustion chamber and by injected hydrogen jet.

Local heat flux from the flame to the combustion chamber wall, q̇, was measured the wall surfaces of a rapid compression-expansion machine which can simulate diesel combustion. Temperature of the flame zone, T1, was calculated by a thermodynamic two-zone model using measured values of cylinder pressure and flame volume. A local heat transfer coefficient was proposed which is defined as q̇/(T1-Tw). Experiments showed that the local heat transfer coefficient depends slightly on the temperature difference, T1-Tw, but depends significantly on the velocity of the flame which contacts the wall surface.

This study has been aimed at the reduction of the intense piston skirt friction force that appears in the expansion stroke out of all piston friction forces generated in gasoline engines. The friction characteristics at the piston skirt have been analyzed according to the measured results at piston friction forces and the shapes of wears at the piston skirt in actual engine operations. It is found from the above that the majority of the side force working on each piston is supported by the oil film on the skirt, while only some of the side force is supported by the portion in metallic contact with the cylinder. It is also found through experiments that the metallic contact portion has a great effect on the friction force at the skirt. The effect of piston posture in expansion stroke on the friction force has been also analyzed based on the measured results of piston slap motions.

The aim of this research was to analyze the lubrication conditions of piston pin boss bearings used in the press-fit piston pins of automobile gasoline engines. An original pin boss friction measuring device was developed and used to successfully obtain measurements. It was revealed that the friction force peaks twice every cycle at high engine loads, and non-fluid lubrication characteristics are displayed. The friction forces for various differing piston pins and pin boss bearings were analyzed, and it was shown that reducing piston pin length or thickness to reduce piston weight, or reducing the pin boss bearing clearance to reduce noise worsen the friction characteristics and increase the possibility of abnormal bearing friction as well as seizure.

How much reduction in piston friction loss can be achieved by the piston design? Piston friction force measurements have been carried out using the measuring method developed by the authors to obtain the effects of piston clearance, surface roughness, lubricant and ring size and contact pressure on the piston friction forces. A particular emphasis is placed on the study of effects of the piston rings by the experimental and theoretical analyses, since friction forces of piston rings accounted for 3/4 or more of the total piston friction force.

Diesel engines make a shrill noise called “idle knock” under low temperature idling operation. This causes a serious noise pollution problem in automobile diesel engines. It was clarified by this study that one important source of this noise was piston slap impulse. Piston slap motion was measured under usual operating conditions and a condition with additional oil supplied into the piston clearance. The piston slap motion was calculated taking into account the frictional resistances of the crank mechanism and squeeze action of oil film. It was concluded that only a negligible amount of oil existed in the piston clearance for the squeeze action.

It is desired to minimize clearance between the piston and the cylinder to reduce noise and suppress vibration. Although significant effort has been made for this purpose, increased piston friction force and the occurrence of seizure still prevent the ideal clearance from being realized. In order to determine the lower limit of the piston clearance, it is crucial to clarify the following unknowns; which part of piston contributes to friction increase as the piston clearance is decreased, during which phase of the piston motion the friction increase occurs, and how the piston clearance affects lubrication phenomena. Measurements of piston friction force under operating conditions were made by applying the Floating Liner Method(1),(2)* to a single-cylinder test gasoline engine. The measurement revealed how the piston friction varied as the piston clearance decreased. Lateral motion of the piston was also measured.

The hydrogen combustion characteristics have been studied in a late-injection (near TDC) hot surface ignition engine. As a supplemental experiment, the mode of combustion was observed in a constant volume combustion chamber by the schlieren method. Consequently the combustion process, that was the flame propagation initiated by a hot surface through heterogeneous hydrogen jets, was not the same as that of a diesel engine. The experimental results in test engine showed the optimum number of injection holes and the effect of intake air swirl for better mixture formation. It was observed that the combustion was frequently accompanied by non-negligible combustion pressure vibrations at all engine operating conditions.

Considerable amount of research work on hydrogen fueled engines has been conducted for 17 years in Musashi Institute of Technology. The primary purpose of the research has been to develop a hydrogen powered autmobile, and in order to realized it, various innovations have been applied and tested. The newest outcome of this 17 years research was Musashi-7 Track, which demonstrated its performance in Innovation vehicle Design Competition held in Vancouver in July 1986. Musashi-7 Track was a modified medium duty truck, which was originally made by Hino Motors, and had a hydrogen powered engine. The track was equipped with 150 ℓ liquid hydrogen (LH2) tank and 8 MPa high pressure LH2 pump. The pump delivered 8 MPa high pressure hydrogen gas to the engine and the fuel was injected to a hot surface igniter in DI combustion chamber. This type of hydrogen enigne has following advantages. Firstly, fuel corrier weight and volume can be much smaller than those of metal-hydrides (MH).

A thin film thermocouple with a high accuracy was developed by means of computer analysis, which allowed measurements of instantaneous temperatures and heat fluxes on combustion chamber walls. Conventional Al-alloy and ceramic plates were compared in terms of the heat loss at the upper surface of each piston during combustion, using a gasoline engine and a diesel engine in the series of experiments. It was found by the comparison that the ceramic plates subjected to higher temperatures had greater heat losses in both the gasoline and diesel engines contrary to the anticipation.

Accurate measurements of combustion gas temperature and the coefficient of heat transfer between the gas and the combustion chamber wall of internal combustion engine in cyclic operations are difficult at present. Hence the only method available for determination of states of thermal load and heat loss to the combustion chamber wall in a cycle is to measure the instantaneous temperature on the combustion chamber wall surface accurately and precisely using proper thin-film thermocouples, then to calculate the instantanenous heat flux flowing into the wall surface by means of numerical analysis. However, it is necessary to pay adequate attention to the effects of thermophysical properties of the thermocouple materials on the measured values, since any thermocouple consists of several kinds of materials which are different from those of portions to be measured.

Oil film thicknesses of the piston top ring and the second ring of a truck diesel engine have been measured simultaneously by embedding capacitance type clearance sensors in the ring sliding surfaces. Owing to the above, several phenomena such as the variation in oil film thickness of each ring in one cycle, correlation between the rings, difference in oil film thickness between the thrust and counter thrust-sides, effects of engine operating conditions on oil film thickness, etc. have been determined. Efforts have been also made to analyze the causes of such phenomena according to the measured results of piston slap motion and ring motions, and the calculated results of oil film thickness.

There have been strong demands recently for reductions in the fuel consumption and exhaust emissions of diesel engines from the standpoints of conserving energy and curbing global warming. A great deal of research is being done on new emission control technologies using direct-injection (DI) diesel engines that provide high thermal efficiency. This work includes dramatic improvements in the combustion process. The authors have developed a new combustion concept called Modulated Kinetics (MK), which reduces smoke and NOx levels simultaneously by reconciling low-temperature combustion with pre-mixed combustion [1, 2]. At present, research is under way on the second generation of MK combustion with the aim of improving emission performance further and achieving higher thermal efficiency [3]. Reducing heat rejection in the combustion chamber is effective in improving the thermal efficiency of DI diesel engines as well as that of MK combustion.