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It is widely known that direct application of biomass fuels oil to DI diesel engines increases the carbon deposit in the engine. To minimize this effect, biomass fuel is subjected to transesterification process. Nevertheless, it is still desirable to use biomass fuel without transesterification. As diesel engine combustion and emissions are strongly dependent on spray characteristics and mixture formation, this study tries to clarify the spray characteristics of rape-seed oil (SVO) including spray structure, spray development, fuel evaporation, and droplets atomization. Optical observation reveals that rape-seed oil (SVO) spray forms a stick-like structure without branching structure at spray boundary and has heterogeneous density distribution in a liquid column at spray centerline. SVO spray hardly penetrates at exceedingly initial stage of injection, in particular at low injection pressure.

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.

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 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.