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In-Direct Injection (IDI) system are mainly used in off-road diesel engines with output of less than 19 kW. These engines generally employ a mechanical injection system. Since it is difficult for these engines to flexibly control the injection timing and injection quantity, there are restrictions on improving fuel efficiency and emission performance. Therefore, we have developed an electronically controlled fuel injection system that is optimal for small diesel engines. We adopted injectors used in relatively inexpensive direct-injection gasoline engines for automobiles, instead of injectors for common rail systems, which are often used in diesel engines. The adopted injector is a multi-hole nozzle, and its spray behavior is different from that of the pintle nozzle used in swirl-chamber diesel engines.

With the strengthening of exhaust gas regulations such as EU Stage 5 and China’s 4th regulation, the engine such as external EGR and aftertreatment device has become complicated. In addition, Kubota’s industrial engines are used not only in agricultural and construction machines but also in various machines with different applications around the world, there are many variations of intake and exhaust systems, and the engines are diversified. For an engine adopting an external EGR and a aftertreatment device, a hot wire type mass air flow rate sensor is widely adopted in an intake piping in order to control the EGR valve appropriately and the regeneration control of the DPF. However, it is known that the sensitivity of this sensing system varies depending on the shape of the intake piping. When the sensitivity varies, the engine is controlled based on the incorrect air mass flow rate, so that the exhaust performance may be deteriorated.

In recent years, since the demands for comfortable operation and low fuel consumption are increasingly enhanced on the industrial machines, non-road engines as power sources on agriculture, landscape and construction applications are required to be achieved high power, low fuel consumption and low noise. Also, even for small engines, it is necessary to keep up with the trend of electronic control devices on these machines. Based on such backgrounds, we developed new non-road direct injection diesel engines with common rail system to satisfy those demands. This paper reviews the technologies to achieve the adoption of common rail system onto such small displacement industrial engines and to optimize the combustion system and injection characteristics.

In accordance with the rising concern about global environmental protection, exhaust emissions regulations for industrial diesel engines are also being strengthened worldwide in stages. In order to comply with the EPA Tier3 and interim Tier4 level, EGR (Exhaust Gas Recirculation) system is recognized as one of the most potential technologies to reduce Nitrogen Oxide (NOx), but there were concerns about durability deriving from the fuel quality and cost increase from additional parts like as EGR cooler, reed valve and EGR valve. To overcome these problems and to fulfill the market demands for industrial diesel engines, such as low cost, compactness, high output and high durability, most appropriate system should be chosen for each engine type.

Optimization of combustion system is important element to design reciprocating engines and Computational Fluid Dynamics (CFD) approach is an effective tool for it. Though CFD approach is widely used to analyze air motion now, further improvement is needed for fuel spray applications especially practical use, such as requirement of special knowledge and its complicated behavior. In this thesis, CFD approach was applied to the free spray in the test rig to understand the diesel spray characteristics and applicability for practical design. A spray visualization techniques including Phase Doppler Particle Analyzer (PDPA) were combined for further understanding. As a result, fuel injection systems were evaluated by CFD approach, that showed the potential to use for practical design process.

In recent years, small diesel engines for industrial use are required to achieve still higher power output per engine size (higher power density) and to have the performance to comply with stringent exhaust emissions standards as well. Therefore, engine makers need to meet these two demands in a short term. In this paper, we introduced techniques for lower exhaust emissions such as optimization of combustion system and higher power density such as reduction of heat load, noise and vibration. These techniques were utilized in process of a new DI diesel engine development effectively.

Lately, numerical approach plays an important role in developing reciprocating engines due to the requirement of both higher performance and environmental protection, such as exhaust emission. Using numerical approach, the performance of each engine parts can be predicted before testing and some behavior which are difficult to be visualized directly can be understood. Especially, the engines in this paper have their particular characteristics to be solved. Evaluation of In-Direct Injection system (IDI) is key issue to improve exhaust emissions. Their small dimensions also cause some difficulties to design and development. In this paper, some numerical approaches including Computer Fluid Dynamics were used to solve these tasks. In the end, we could introduce the new small IDI diesel engines with high performance, low exhaust gas emissions and good NVH characteristics.

In designing new valve train system, it is useful to predict the complicated dynamic characteristics correctly by CAE simulation at the initial stage. In this paper, a modeling technique of mechanical system simulation and the simulation results about the dynamic characteristics of the diesel engine valve train are shown. From the measured results, it is found that the valve spring plays an important role in the dynamic characteristics of valve train. Based on the results, we propose a new model which use beam coupled the displacement and shearing stress and gap elements to express the valve spring. The model is proved very well to express not only the same-pitch valve spring but also the different-pitch valve spring. As a result, the prediction of the dynamic characteristics of the valve train provides a lot of effective data and hint for the developing valve train design of a newly designed diesel engine.

In recent years, small diesel engines for industrial use are required to achieve still higher power output per engine size (high power density) and to have the performance to comply with stringent exhaust emissions standards as well. To meet these social demands and market requirements, there are various engineering tasks yet to accomplish. In this paper, two important technical issues have been focused, those are, combustion system improvement to enable lower exhaust emissions and higher power output than conventional models and new cooling system as a solution for increased heat load issue accompanying the progress of high power density. Firstly, for combustion system improvement, the swirl adjustment technique has been developed that will optimize the swirl ratio for each engine application with different load and speed condition.

The simulation techniques play important role on contemporary engine design. In this study, computer fluid dynamics approach (CFD) was focused to design the intake and combustion system of the direct injection diesel engine for versatile use. A practicality was stressed as much as an accuracy to correspond to designer and researcher's requirements, such as close relationship to the engine performance and short period of computation. The correlation of the trapping efficiency and the swirl ratio was mainly focused. A steady flow rig tests and engine operation data were combined to improve their quality mutually.

Recently, the demand for comfort with environmental protection has been increasing considerably. This is not only the concern of industry, but also of the entire society. Therefore, it's required as an indispensable element for engines as power sources of machineries to have characteristics such as low noise and pollution output, as well as high performance and reliability. There have been various studies on this theme and steady achievements have been made so far. However, the conventional technologies have their limitations, having reached the highest level that they can possibly achieve, so now new technologies and new thinking are needed to meet the environmental theme. This report discusses a new approach to the 92.4mm Stroke Series next generation engines, which have reduced noise by using noise quality analysis and other techniques. This report also presents the optimization of the combustion system by utilizing numerical simulation techniques such as fluid flow analysis.

With a drastic advance of computing software and hardware, recently, simulation techniques play snore important role in development and design of diesel engines. Especially, Finite Element Method (FEM) is indispensable for design of diesel engine components, as a tool of optimizing each part and selecting the Materials. Meanwhile, it is one of the greatest theme for all engine designers to raise compactability and high-performance of small engines. At the same time, we have to respond to social needs, that is safety, reliability, durability, and comfortability, for reduction of noise and vibration. Moreover, for design of engine components, we always try to reduce a period of development and make more economical components because we have to consider those cost. To meet this severe requirement, it is needed not to apply the simulation techniques just as they are, but to establish the higher and more useful ones.