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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.

In order to improve the brake thermal efficiency of the engine, such as cooling and friction losses from the theoretical thermal efficiency, it is necessary to minimize various losses. However, it is also essential to consider improvements in theoretical thermal efficiency along with the reduction of the various losses. In an effort to improve the brake thermal efficiency of heavy-duty diesel engines used in commercial vehicles, this research focused on two important factors leading to the engine's theoretical thermal efficiency: the compression ratio and the specific heat ratio. Based on the results of theoretical thermodynamic cycle analyses for the effects of the above two factors, it was predicted that raising the compression ratio from a base engine specification of 17 to 26, and increasing the specific heat ratio would lead to a significant increase in theoretical thermal efficiency.

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.

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.

Urea selective catalyst reduction (SCR) systems have a high NOx conversion rate because the ammonia formed by the hydrolyzing urea solution reacts with NOx efficiently as a reducing agent. Systems combining urea-SCR and a diesel particulate filter (DPF) have been adopted in heavy duty vehicles to meet the post new long term emissions regulations in Japan. This study examined the emissions reduction performance of these systems after 160,000 km. The emissions that were examined included both regulated emissions (NOx, PM, HC, and CO) and unregulated emissions. As a result, the cleanness of diesel emissions from a urea-SCR and DPF system was confirmed.

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.

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.

The U.S. Environmental Protection Agency (EPA) issued new emissions regulations, which came into effect in January, 2010. These EPA 2010 regulations are the most stringent emissions standards in the world, reducing both particulate matter (PM) and nitrogen oxides (NOx) to nearly zero levels. Hino Motors improved upon its previous EPA 2007-compliant engine, developing a new exhaust after-treatment system in which a Diesel Particulate active Reduction System (DPR), a Urea-Selective Catalytic Reduction (SCR) System and a Burner System are employed to meet EPA 2010 emissions regulations for medium duty commercial vehicles. DPR was already developed and utilized to reduce PM to meet EPA 2007 standards, but the Urea-SCR System is newly developed technology used to reduce NOx emissions to comply with EPA2010 emissions regulations. In addition, a Burner System is used to elevate exhaust gas temperatures in order to improve both SCR performance and DPR active Regeneration.

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.

The new Diesel Particulate active Reduction (DPR) system was developed for a medium-duty commercial vehicle as a deNOx catalyst combined with the conventional DPR system to achieve the Japan Post New-Long-Term (JPNLT) emissions regulations. It consists of a catalyst converter named as the new DPR cleaner, a fuel dosing injector, NOx sensors, temperatures and pressure sensors. The new DPR cleaner was constructed from a Front Diesel Oxidation Catalyst (F-DOC), a catalyzed particulate Filter (Filter), and a Rear Diesel Oxidation Catalyst (R-DOC). A newly developed Hydrocarbon Selective Catalyst Reduction (HC-SCR) catalyst was employed for each catalyst aiming to reduce NOx emissions with diesel fuel supplied from the fuel dosing injector. While the total volume of the catalyst was increased, the compact and easy-to-install catalyst converter was realized through the optimization of the flow vector and flow distribution in it by means of Computational Fluid Dynamics (CFD) analysis.

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.

This paper presents technical solutions and a development process to accomplish not only superior fuel economy but also excellent driveability with a turbocharged diesel engine for heavy duty trucks. For better fuel economy, one of the basic considerations is how to decrease the friction losses of the engine itself while keeping the required horsepower and torque characteristics. A high boost turbocharged small engine offers this possibility, but it has serious disadvantages such as inferior low speed torque, poorer accelerating response, insufficient engine braking performance, and finally not always so good fuel consumption in the engine operating range away from the matching point between engine and turbocharger. These are not acceptable in complicated traffic conditions like those in Japan - a mixture of mountainous and hilly roads, city road with numerous traffic signals, and freeways.

Gaseous emission measurements of a diesel engine including hydrocarbons (HC), carbon monoxide (CO), and oxide of nitrogen (NOx) are made in accordance with the procedures specified in the Federal Register. However, it is very difficult to maintain constantly the accuracy of these emission measurements due to failure of the emission analyzer. The authors have thus developed the Pre-Alarm Diagnostic System for a Diesel Emission Analyzer. Firstly, the authors have carried out analysis of all failure modes that are classified into initial failure, random failure and wearing-out failure, plus tolerance level for prediction of failures and method of predicting failures. Next, the authors have developed the Pre-Alarm Diagnostic System that is able to easily discover these failures before the exhaust emission test. In this system, 40 sensors, such as pressure, temperature, voltage etc, are laid in each pipe line of connection between exhaust emission sampling pump and analyzer.

The emissions reduction potential of neat GTL (Gas to Liquids: Fischer-Tropsch synthetic gas-oil derived from natural gas) fuels has been preliminarily evaluated by three different latest-generation diesel engines with different displacements. In addition, differences in combustion phenomena between the GTL fuels and baseline diesel fuel have been observed by means of a single cylinder engine with optical access. From these findings, one of the engines has been modified to improve both exhaust emissions and fuel consumption simultaneously, assuming the use of neat GTL fuels. The conversion efficiency of the NOx (oxides of nitrogen) reduction catalyst has also been improved.