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Spray development and fuel-air mixture formation are important process early in diesel combustion. Moreover, wall impingement of spray and spray interaction also affect combustion process greatly. The spray interaction happens in multi-hole injector. This study investigated influence of spray combustion accompanied with wall impingement and spray interaction on heat release history. The experiment observed initial spray development by shadowgraph technique using a constant volume spray chamber. The injectors were a single-hole injector and multi-hole injectors with the hole-number of 8, 6 and 4. The combustion experiment observed flame development. The spatial distribution of the flame temperature and the soot oxidation were analyzed by the flame images. Results of the unburned spray images revealed the difference of mixture formation and initial combustion between single-hole and multi-hole sprays.

It is well known that indirect injection (IDI) diesel engines have better exhaust performance but lower fuel economy than direct-injection (DI) diesel engines. In recent years, fuel efficiency has been strongly demanded to reduce global warming. Therefore, the IDI engine is required to reduce fuel consumption. According to past research, fuel injection control can be one of the means to improve fuel efficiency in the IDI system. This paper tried to apply two-stage fuel injection as one of the fuel injection control methods to improve fuel efficiency while suppressing exhaust emissions. Particularly, since it is considered necessary to reduce the amount of injection during the ignition delay period in the sub-chamber with the IDI type, two-stage injection with a small amount of pilot injection was applied.

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.