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Recently the analysis of air-fuel mixing and combustion has become important under the stringent emissions regulations of diesel engines. In the case of gasoline engines, the KIVA computer program has been developed and used for the analysis of combustion. In this paper, the calculations of combustion phenomena in DI diesel engines are performed by modifying the KIVA program so as to be applicable to multi-hole nozzles and arbitrary patterns of injection rate. The thermophysical and ther-mochemical properties of gasoline are altered to those diesel fuel. In order to investigate the ability of this modified program, the calculations are compared with the experiments on single cylinder engines concerning the pressure, flame temperature and mass change of chemical species in cylinders. Furthermore, the calculation for the heavy duty DI diesel engine is performed with this diesel combustion program.

In a diesel engine, the mixing of the fuel spray and in-cylinder air controls rate of beat release during combustion, namely it will determine the thermal efficiency, maximum output and gas or noise emission, etc. Therefore, it is important to measure the droplet size and its volume density distribution in diesel fuel sprays. The optical measuring method, which includes a light scattering and holographic technique, seems the only feasible method for analysing these unsteady characteristics of fuel sprays. The light scattering technique described herein was based upon Mie scattering theory, and the droplet size and volume density distribution of fuel sprays were calculated from the combination of the light extinction and the forward-to-backscattering ratio of Mie scattering intensity. The volume density and droplet size distribution of fuel sprays were obtained from the light intensity distribution on a photograph of fuel sprays.

A new concept for diesel combustion was investigated by means of numerical simulation, engine experiment, and combustion observation in order to realize a simultaneous reduction of NOx and particulate emission. This concept (HiMICS: Homogeneous charge intelligent Multiple Injection Combustion System) is based on pre-mixed compression ignition combustion combined with multiple injection. Combustion characteristics of HiMICS concept was investigated by comparing with both a standard single injection and a pilot injection. In HiMICS concept, the pre-mixture is formed by a preliminary injection performed during a period from the early stage of the induction stroke to the middle stage of the compression stroke. Modified KIVA-II code was used to predict engine performances and emissions of each injection method. The simulation results show a capability of considerable improvement in the trade-off relation between NOx emissions and fuel consumption of HiMICS.

A new concept for diesel combustion has been investigated by means of engine experiments and combustion observations in order to realize a simultaneous reduction of NOx and particulate emissions. The concept is based on pre-mixed compression ignition combustion combined with multiple injection. In this method, some part of fuel is injected at an early stage of the process to form a homogeneous lean pre-mixture, then the remaining fuel is injected at around the TDC in the same manner as a conventional diesel injection. The emissions, ROHR (rate of heat release), and combustion pictures of conventional combustion, pilot injection combustion, and this new combustion concept were compared and analyzed. Engine tests were carried out using a single cylinder research engine equipped with a common rail injection system.

The Dual-Fuel (DF) combustion is a promising technology for efficient, low NOx and low exhaust particulate matter (PM) engine operation. To achieve equivalent performance to a DF engine with only the use of conventional liquid fuel, this study proposes the implementation of an on-board fuel reformation process by piston compression. For concept verification, DF combustion tests with representative reformed gas components were conducted. Based on the results, the controllability of the reformed gas composition by variations in the operating conditions of the reformer cylinder were discussed.

In heavy duty (HD) trucks cruising on expressway, about 60% of input fuel energy is wasted as losses. So it is important to recover them to improve fuel economy of them. As a waste heat recovery system, a Rankine cycle generating system was selected. And this paper mainly reports it. In this study, engine coolant was determined as main heat source, which collected energies of an engine cooling, an EGR gas and an exhaust gas, for collecting stable energy as much as possible. And the exergy of heat source was raised by increase coolant temperature to 105 deg C. As for improving the system efficiency, saturation temperature difference was expanded by improving performance of heat exchanger and by using high pressure turbine. And a recuperator which exchanges heat in working fluid between expander outlet and evaporator inlet was installed to recover the heat of working fluid at turbine generator. Then a working fluid pump was improved to reduce power consumption of the system.

The requirements for emission control, lower fuel consumption and higher engine output have changed the engine valve train system to 4-valve/cylinder and higher cam lift designs, and these changes make the cam/tappet lubrication conditions more severe than before. Under such a working condition, there is a high possibility that cam/tappet surface damages such as scuffing, pitting and wear may occur. Among the damages, the wear of cam/tappet is the most difficult to predict since the wear mechanism still remains unclear. To understand the lubrication condition and therefore, the wear mechanism at the cam/tappet contact, friction was measured with a newly developed apparatus. Measurement results showed that the lubrication condition between cam and tappet is predominantly in the mixed and boundary lubrication conditions.

To improve the thermal efficiency of an engine, it is particularly important to reduce the cooling loss from the combustion gas to the combustion chamber wall, which constitutes a major proportion of the total loss [1]. Previous studies addressing cooling loss reduction attempted to use ceramic in place of the conventional aluminum or iron alloys, but this led to a reduction in the volumetric efficiency and increased smoke emissions. This was caused by the ceramics having both a low thermal conductivity and high heat capacity, relative to aluminum and iron. These characteristics cause the piston wall temperature, which rises during combustion, to remain high during the intake stroke, thus increasing the intake temperature and reducing the volumetric efficiency. This increases the smoke emissions [2].

Reduction of oil consumption of engines is required to avoid a negative effect on engine after treatment devices. Engines are required fuel economy for reduction of carbon-dioxide emission, and it is known that reduction of piston frictions is effective on fuel economy. However friction reduction of pistons sometimes causes an increase in engine oil consumption. Therefore reduction of engine oil consumption becomes important subject recently. The ultimate goal of this study is developing the estimation method of oil consumption, and the mechanism of oil upward transport at oil ring gap was investigated in this paper. Oil pressure under the oil ring lower rail was measured by newly developed apparatus. It was found that the piston slap motion and piston up and down motion affected oil pressure rise under the oil ring and oil was spouted through ring-gap by the pressure. The effect of the piston design on the oil pressure generation was also investigated.

The necessity of the reduction of the lubricating oil consumption of diesel engines has been increasing its importance to reduce the negative effect of exhausted oil on after treatment devices for exhausted gas. The final purpose of the studies is clarifying the mechanism of the oil consumption and developing the method of its estimation. For the basic study, the mechanism of oil film generation on the piston skirt could be explained by hydrodynamic lubrication in our first and second reports [1, 2]. In this paper, the piston skirt was calculated using the measured piston motion to clarify the effect of the piston motion to the piston skirt oil film behavior.

Clarifying the mechanism of the oil consumption of engines is necessary for developing its estimation method. Oil moves upwards on the piston to the combustion chamber through ring sliding surfaces, ring backs and ring gaps. The mechanisms of oil upwards transport through the ring gaps are hardly analyzed. In this report, oil pressure just under the oil ring was successfully measured by newly developed method to clarify the oil transport mechanism at the ring gap. It was showed that the generated oil pressure pushed up the oil at the ring gap.

Decrease of engine lubricating oil consumption is necessary to reduce environmental impact. Usually oil consumption is estimated experimentally at the engine development stage, and it is expensive in terms of both time and cost. Therefore it is essential to develop its calculation method. The purposes of this study are clarifying the mechanism of engine lubricating oil consumption and developing the calculation method for the estimation of oil consumption. In this report, oil film on the piston skirt, which affected on oil volume supplied to the oil ring, was observed. Furthermore the effect of piston skirt design on oil consumption was investigated. Findings showed that the splashed oil on the cylinder liner had much effect on the oil film on the piston skirt hence oil consumption. It was suggested that the splashed oil on the cylinder liner affected on supply oil volume and it should be considered in the calculation of oil consumption.

Hino Motors, Ltd. has added to its line of charge-cooled engines for heavy duty trucks a higher power version which is called EP100-II. To meet the recent customers' demands for rapid transportation with better fuel economy, this engine was developed on the uprating program for the original EP100 which was introduced in 1981 as the first Japanese turbo-charged and air to air chrge-cooled engine. EP100-II has the same displacement as the original EP100, 8.8 liters, and is an in-line six cylinder engine with 228kW (310PS)/2,100rpm (JIS) output that provides the world's utmost level specific output of 25.8 kW (35.1PS)/ liter. Also this engine achieved a maximum BMEP of 16.8 bar/1,300 rpm and best BSFC of 199 gr/kWh at 1,500 rpm. This paper describes the advanced technology for increasing horsepower and improving fuel consumption such as the so-called multi harmonized inertia charging system, the electronically controlled waste gate valve of turbocharger.

As a result of the stringent noise regulations for heavy-duty vehicles, the use of shields and enclosures for engine compartment has been increasingly applied, but it is difficult for a conventional axial flow fan to provide the required airflow against higher resistance caused by such shields and enclosures. To solve this problem, a new, mixed flow fan (hereafter called MF fan) which is suitable for the higher resistance has been developed and this paper describes the development process of the MF fan. The design criteria of the MF fan were experimentally investigated with a test rig, and an optimum combination of design parameters were established. The airflow was improved approximately 6 % without any additional power loss in comparison with the conventional axial flow fan.

When the engine oil evaporates in the crankcase, it is necessary to discharge to the outside of the engine or returns to the intake air as part of blow-by gas. The amount of oil content in the blow-by gas is preferable to be as small as possible. This paper researched the evaporation characteristics of diesel engine oil for heavy duty into blow-by gas using 5W-30 and 10W-30 engine oils with the equivalent to Noack. As a result, it is found that evaporate phenomenon cannot be explained well enough by just Noack and clarified of the oil evaporation mechanism in blow-by gas.

Experiments on a large number of soluble fuel additives were systematically conducted for diesel soot reduction. It was found that Ca and Ba were the most effective soot suppressors. The main determinants of soot reduction were: the metal mol-content of the fuel, the excess air factor, and the gas turbulence in the combustion chamber. The soot reduction ratio was expressed by an exponential function of the metal mol-content in the fuel, depending on the metal but independent of the metal compound. A rise in excess air factor or gas turbulence increased the value of a coefficient in the function, resulting in larger reductions in soot with the fuel additives. High-speed soot sampling from the cylinder showed that with the metal additive, the soot concentration in the combustion chamber was substantially reduced during the whole period of combustion. It is thought that the additive acts as a catalyst not only to improve soot oxidation but also to suppress soot formation.

In a DI diesel engine, THC emissions increase significantly with lower compression ratios, a low coolant temperature, or during the transient state. During the transient after a load increase, THC emissions are increased significantly to very high concentrations from just after the start of the load increase until around the 10th cycle, then rapidly decreased until the 20th cycle, before gradually decreasing to a steady state value after 1000 cycles. In the fully-warmed steady state operation with a compression ratio of 16 and diesel fuel, THC is reasonably low, but THC increases with lower coolant temperatures or during the transient period just after increasing the load. This THC increase is due to the formation of over-lean mixture with the longer ignition delay and also due to the fuel adhering to the combustion chamber walls. A low distillation temperature fuel such as normal heptane can eliminate the THC increase.

The thermal cracking and polyaromatic hydrocarbon (PAH) formation processes of dimethyl ether (DME), ethanol, and ethane were investigated with chemical kinetics to determine the soot formation mechanism of oxygenated fuels. The modeling analyzed three processes, an isothermal constant pressure condition, a temperature rising condition under a constant pressure, and an unsteady condition approximating diesel combustion. With the same mole number of oxygen atoms, the DME rich mixtures form much carbon monoxide and methane and very little non-methane HC and PAH, in comparison with ethanol or ethane mixtures. This suggests that the existence of the C-C bond promotes the formation of PAH and soot.

Direct injection of various ignition suppressors, including water, methanol, ethanol, 1-propanol, hydrogen, and methane, was implemented to control ignition timing and expand the operating range in an HCCI engine with induced DME as the main fuel. Ultra-low NOx and smoke-less combustion was realized over a wide operating range. The reaction suppressors reduced the rate of low-temperature oxidation and consequently delayed the onset of high-temperature oxidation. Analysis of the chemical kinetics showed a reduction of OH radical in the premixed charge with the suppressors. Among the ignition suppressors, alcohols had a greater impact on OH radical reduction resulting in stronger ignition suppression. Although water injection caused a greater lowering of the temperature, which also suppressed ignition, the strong chemical effect of radical reduction with methanol injection resulted in the larger impact on suppression of oxidation reaction rates.

Light naphtha, which exhibits two-stage ignition, was induced from the intake manifold for ignition enhancement and a low ignitability fuel or water, which does not exhibit low temperature oxidation, was directly injected early in the compression stroke for ignition suppression in an HCCI engine. Their quantitative balance was flexibly controlled to optimize ignition timing according to operating condition. Ultra-low NOx and smokeless combustion without knocking or misfiring was realized over a wide operating range. Alcohols inhibit low temperature oxidation more strongly than other oxygenated or unoxygenated hydrocarbons, water, and hydrogen. Chemical kinetic modeling for methanol showed a reduction of OH radical concentration before the onset of low temperature oxidation, and this may be the main mechanism by which alcohols inhibit low temperature oxidation.