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Hydrogen engines have problems of knocking, lower thermal efficiency and NOX emission. These problems are caused by the hydrogen characteristics of high burning velocity. This study tried to reduce rapid combustion of hydrogen. Hydrogen was injected directly into the combustion chamber and the hydrogen-jet was ignited by a spark plug. Moreover, this kind of combustion system was applied to a newly developed engine employing Z-crankshaft mechanism. This mechanism can realize a quasi-constant volumetric cycle. In the result, the engine realizes knock-less combustion with low NOX emission. In addition, Z-crankshaft engine can keep high thermal efficiency even at late ignition timing.

This study investigates the effect of using waste cooking oil (WCO) and Bio-diesel Fuel (BDF) of WCO on combustion performance and exhaust emissions compared with diesel fuel (JIS#2) in a direct injection diesel engine. Results show that WCO and BDF emit higher concentration of SOF at low load compared with JIS#2. A study on blending WCO and BDF with several percentage of JIS#2 reveals that reduction of kinematic viscosity would be able to improve SOF emissions at low load. SOF emission also can be reduced by using high squish combustion chamber which continues high turbulence combustion in the chamber.

The aim of this study is to clarify the mixture formation in the combustion chamber of our developed natural gas engine incorporating the sub-chamber injection system, in which natural gas is directly injected into a combustion sub-chamber in order to completely separate rich mixture in the sub-chamber, suitable for ignition, from ultra-lean mixture in the main chamber. Mixture distributions in chambers with and without sub-chamber were numerically simulated at a variety of operating conditions. The commercial software of Fluent 16.0 was used to conduct simulations based on Reynolds averaged Navier-Stokes equations in an axial 2 dimensional numerical domain considering movements of piston. Non-reactive flow in the combustion chamber was simulated before the ignition timing at an engine speed of 2000 rpm. The turbulence model employed here is standard k-ε model. Air-fuel ratio is set with a lean condition of 30.

This study investigates the effects of fuel properties on combustion characteristics and emissions such as NOx, smoke, THC and particulates in a direct-injection diesel engine. Fuel properties, such as cetane number and aromatic content, are varied independently in the experiments to separate their effects. The engine tests are carried out at steady operation with changed load, injection timing and injection pressure. The results show that reducing cetane number results in the increase of NOx and decrease of particulate emission at high load. This is because the low cetane number fuel has the long ignition delay and causes the high maximum heat release rate and the short combustion duration. However, high THC emission is produced at low load for the low cetane number fuel.

In this study it is tried to reduce NOx and particulate emissions simultaneously in a direct injection diesel engine based on the concept of two-stage combustion. At initial combustion stage, NOx emission is reduced with fuel rich combustion. At diffusion combustion stage, particulate emission is reduced with high turbulence combustion. The high squish combustion chamber with reduced throat diameter is used to realize two-stage combustion. This combustion chamber is designed to produce strong squish that causes high turbulence. When throat diameter of the high squish combustion chamber is reduced to some extent, simultaneous reduction of NOx and particulate emissions is achieved with less deterioration of fuel consumption at retarded injection timing. Further reduction of NOx emission is realized by reducing the cavity volume of the high squish combustion chamber. Analysis by endoscopic high speed photography and CFD calculation describes the experimental results.

This study tries to reduce SOF (Soluble Organic Fraction) emissions at low load by improving spray characteristics of rape-seed oil and avoiding wall-impingement of the spray to the piston wall in a real direct-injection diesel engine applying rape-seed oil directly. High swirling air motion and squish flow caused by the piston configurations are taken as measures. Further, flat bottom shape of the piston is applied. Results show that emissions can be improved by the support of air motions. High swirl with toroidal piston is effective to reduce SOF emissions. Re-entrant piston with flat bottom shape offers the best emission performance. Raising gas temperature is also effective to reduce SOF emissions at low load.

Sub-chamber is a useful device with regard to sustaining stable operation of compressed natural gas (CNG) engines under lean burn conditions. In our previous studies, we applied a sub-chamber injection system to CNG engines, in which a single injector and a spark plug are mounted in a small sub-chamber. The aim of this study is to investigate the effect of the sub-chamber configuration on heat release in the main combustion chamber. 11 types of sub-chamber with different nozzle number, nozzle diameter, and sub-chamber volume were examined under a condition that pressure is 2.3 MPa, and global equivalence ratio is 0.6. When the sub-chamber with smaller nozzles are used, the penetration velocity of burned gas jet increases. In addition, the velocity also increases with an increasing sub-chamber volume. The high-speed penetration of burned gas jet shortens the period of initial flame development.

Many technologies for reducing exhaust emissions of wide variety of diesel engines from small size to large size ones have been considered with the improvement throughout the combustion process. To reduce emissions, mixing of fuel and air is still important phenomena. Purpose of this study is to clarify the relation between mixture formation during the ignition delay period and burning process in diesel combustion that strongly affects the exhaust emissions. In this study, a rapid compression machine was used to simulate actual phenomenon inside the combustion chamber with changing ambient density. In addition, swirl velocity and injection pressure were changed as experimental parameters to improve mixture formation at high ambient density. This study constructed schlieren photography system with a high-speed digital video camera to investigate the detail behavior of mixture formation during ignition delay period.