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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.

Diesel spray evaporation in a high pressure and high ambient temperature close to actual diesel engine condition was investigated in this study. A nano-spark shadowgraph photography technique and a rapid compression machine were applied in this experiment. By using this method, relatively clear image of liquid phase, vapor phase and droplets was obtained. In order to quantify the spray characteristics in the spray liquid area and vapor phase area, an image analysis method was applied. An algorithm was developed to quantify the droplets size and number of the droplets characteristic in the vapor phase. Experimental results have revealed that the injection pressure and the ambient temperature do not affect the spray penetration length apparently. In the case of ambient temperature Ti = 700K, the liquid core is observed in the region near the spray axis. Meanwhile, the vapor exists mostly in the outer region in the middle of the spray.

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.

The chemical behaviors of diesel fuel and the effects of aromatic content on combustion characteristics and NOx histories were experimentally investigated using a rapid compression machine and a total-gas sampling device. The aromatic content was changed under constant cetane number. Composition of the individual hydrocarbons, inorganic gases and NOx under various ambient temperatures and fuel injection pressures were analyzed with aromatic-free and aromatic-containing fuels. The results indicate that injected fuel is rapidly decomposed and dehydrogenated during the ignition delay period. The decomposed low boiling-point hydrocarbons consist of mainly unsaturated hydrocarbons such as C2H4, C2H2 and C3H6 at the initial combustion phase. At the diffusion combustion phase, the low boiling-point hydrocarbons consist of mainly CH4.

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.