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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.

Characteristics of diesel combustion with high pressure fuel injection were investigated, using a supercharged and charge air cooled single cylinder engine. Observation and analysis of combustion was performed using high speed schlieren photography at a definite low level NOx emission, while varying the parameters of both injection pressure and swirl ratio. Engine performance at a high injection pressure was evaluated in combination with shallow dish type combustion chamber and 8 hole nozzle. Two different intake ports (higher and lower swirl ratio) were used for the evaluation. Conventional injection system in combination with toroidal cavity and 4 hole nozzle was compared as a base line. It is generally said that quiescent combustion system is suitable for higher injection pressure configuration. According to the observed result of combustion photographs, however, higher swirl ratio shows better mixing than a lower swirl ratio, which was also confirmed by the performance test.

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].

Approximately 200,000 units of Hino J-series diesel engine were produced for 7 years. The J-series engines had a reputation all over the world for their performance, reliability, lightweight, and installation ability. They are composed of 4, 6 cylinders engines and unique 5-cylinder engine J07C. In 2002, newly modified J-series engines, which met the Japan 2001 noise emission regulations, were developed and J07C-TI, 5-cylinder TI engine, equipped with a common-rail fuel injection system was added in the J-series. Common-rail fuel injection system was equipped in order to achieve the emission targets in the future as well as to meet the current emission regulations. Achieving higher injection pressure level through the all engine speed, include excess low speed, was effective in reduction of PM emissions and in increasing of low engine speed torque drastically.

A current unmodified and modified engines with different amounts of thermal insulation have been used to generate data from which changes in bsfc, cooling loss, emissions, exhaust loss were determined. Since legislative requirement exists for allowable emission of NOx, fuel injection timing and other controllable factors were adjusted to maintain constant NOx emission except a test of influence on NOx emission according to the rate of heat insulation (adiabaticity). The effect of higher combustion temperature on the combustion phenomena is discussed.

This paper describes the investigation of the mechanisms of engine front noise generation and the corresponding countermeasures employed in the development of Hino's medium duty diesel engine. The engine front noise, which had a noise peak in the 630 Hz 1/3 octave band, was investigated by experiment and it was concluded that there were two mechanisms as follows: 1) Combustion pressure excites the crankshaft. Noise is generated by the crankshaft pulley which vibrates with the crankshaft system mode shapes. 2) The cavity between the torsional damper and the timing gear case resonates as a result of the vibration of the torsional damper. Noise caused by the acoustic resonance is emitted to the front of the engine. Using both experimental and analytical methods, crankshaft vibration and acoustic resonance were reduced, thus yielding a substantial noise reduction.

Fuel injection timing retardation for reducing exhaust emission of direct injection diesel engines prolongs the period to complete cold starting. Engine speed at this period varies through some accelerating and faltering stages. The speed variation and relating combustion characteristics was investigated through the measurement of cylinder pressure for each cylinder as well as the dynamic fuel injection timing and instantaneous engine speed. An improvement of cold start was shown by application of afterheat of a sheathed type glow plug and an electronic fuel injection timing control device.

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.

This paper describes the combustion optimizations of heavy-duty diesel engines for the anticipated future emissions regulations by means of an electronically controlled common rail injection system. Tests were conducted on a turbocharged and aftercooled (TCA) prototype heavy-duty diesel engine. To improve both NOx-fuel consumption and NOx-PM trade-offs, fuel injection characteristics including injection timing, injection pressure, pilot injection quantity, and injection interval on emissions and engine performances were explored. Then intake swirl ratio and combustion chamber geometry were modified to optimize air-fuel mixing and to emphasize the pilot injection effects. Finally, for further NOx reductions, the potentials of the combined use of EGR and pilot injection were experimentally examined. The results showed that the NOx-fuel consumption trade-off is improved by an optimum swirl ratio and combustion chamber geometry as well as by a new pilot concept.

Diesel Particulate active Reduction system (DPR) is a system that traps particulate matter in diesel exhaust gas with a particulate filter and actively regenerates the filter when PM accumulates to a specific level. In 2003, DPR was installed on Hino's light-, medium-, and heavy-duty diesel engines, and about 50,000 units of these DPR-equipped diesel engines are currently on the market. This paper reports results of further progress made on optimization of the active regeneration function of DPR. The goal of successful development of DPR is to optimally control the system under various engine-operating conditions to regenerate the filter without producing abnormal combustion of PM and to minimize the amount of unburned PM to keep the filter from clogging. To improve the control of DPR, the combustion phenomena of PM collecting on the filter were studied through visualization, and the factors influencing combustion were determined.

Historically the high speed diesel engine for commercial vehicles has been developed along with its combustion system in compliance with political and economical changes. After the 1970's, stricter exhaust emission regulations and fuel economy requirements induced combustion developments and application of turbocharged and inter cooled engines. From the late 1980's, high pressure fuel injection has been investigated and recognized as an essential tool for lowering emissions especially of particulate matter. Although turbulence effects on both in-cylinder air motion and during the combustion process are quite effective, they show different phenomena in conventional and advanced high pressure fuel injection systems. In the 1990's, multiple injection with high pressure has been attempted for further reduction of NOx and particulate matter.

Hino has developed new J-series medium-duty diesel engines for trucks and buses. The new J-series comprises four, five and six-cylinder engines with the same cylinder bore and stroke and with both naturally aspirated and charge air cooled. Both output and torque have been enhanced along with fuel efficiency in an engine that is lighter and more compact than ever and reaches new heights of durability and reliability. J-series engine features a 4-valve system and OHC valve train design, which achieved an uniform combustion by a centered nozzle and combustion chamber design. This decreases the maximum combustion temperature and hence improved the NOx,smoke and PM emissions. And a reduced pumping loss results in improving the fuel consumption. J-series engines thus meet the Japanese 1994 emission regulations. Another feature is a fully electronically controlled common-rail fuel injection system, which is equipped in a specified engine of naturally aspirated 6 cylinder.

The spark-assisted methanol engine has disadvantages like poor fuel economy especially at light load and low spark plug durability affected by combustion characteristics. Investigations of combustion characteristics of the spark ignition system and the autoignition system in the methanol engine and discharge characteristics of a spark plug are described in this paper. It is clear that effective autoignition was accomplished by increasing the compression ratio and adopting an EGR system in the spark-assisted methanol engine. This new improved methanol engine which is named HAMS achieved good fuel economy at light load, a low NOx emission and longer spark plug life. And a heat insulated piston with a stainless steel cap is being investigated for further improvement of autoignition combustion characteristics.

A new combustion system for a light duty D.I. diesel engine was developed, and a 3.5 ton payload truck (6.5 ton G.V.W.) equipped with this D.I. diesel engine and this combustion system realized good fuel economy and lower exhaust gas emission. Generally, light duty vehicles have to operate over a wide engine speed range. Therefore application of a D.I. diesel engine to light duty vehicles is difficult because of combustion tuning requirements over a wide engine speed range. Up to now, most of the diesel engines for light vehicles have been of the I.D.I. type. But the D.I. diesel engine has an evident advantage of lower fuel consumption. In these circumstances the authors developed a new combustion chamber shape for a small D.I. diesel engine with turbulence induced intake port and optimum fuel injection equipment. Various combustion chamber geometries were tested and evaluated.

A new combustion system for a light duty D. I. diesel engine was developed and introduced (1)*. The combustion chamber, which was used in the combustion system, has 4 concaves on the periphery of the inner wall and was calld HMMS-III. This combustion chamber realized better fuel consumption and lower smoke level over a wide speed range. However, the effects of HMMS-III combustion chamber on in-cylinder air motion and combustion characteristics were not yet clarified in the previous paper. In this study, in order to clarify the effects of HMMS-III combustion chamber on in-cylinder air motion and characteristics, analysis of flow direction and streak line via oil film method was carried out in comparison with flat dish and re-entrant type combustion chambers. Further, measurement of in-cylinder air motion by L.D.V. and observation of mixture formation and burning process via high speed schlieren photography were carried out.

For the 1990's diesel engines, particulate control has been an important problem. The purpose of this paper is to discuss emission control needs for heavy duty diesel truck engines for the 1990's. This paper will focus on the factors such as fuel injection pressure and fuel properties which most affect particulate emission. The characteristics of diesel spray in the atmosphere and also actual combustion of a turbocharged and charge-cooled H.D. D.I diesel engine were studied as a function of injection pressure ranging from 50 to 150 MPa. Experimental results show that high pressure injection improves the atomization and air entrainment. Though Bosch smoke level, fuel consumption and combustion period decreased with the rise of injection pressure, particulate emission in EPA transient test cycle did not decrease dut to an increase of SOF.

This paper describes the experimental studies of turbocharged and intercooled diesel engines with particular emphasis on combustion characteristics following increase of boost pressure. Through these studies, it has become possible to determine the optimum air quantity for minimizing fuel consumption at each engine speed range under the restrictive conditions of NOx emission, exhaust smoke and maximum cylinder pressure. Discussed also is the lack of air quantity in the low engine speed range of high-boost turbocharged diesel engines. Various turbocharging systems to improve air quantity in this speed range are introduced herein. Practically the engine performance of conventional turbocharging, waste gate control turbocharging and variable geometry turbocharging are discussed from the viewpoint of torque recovery in the low engine speed range.