Study of Thermal Efficiency Improvement by Multi-Hole Nozzle

A truck and bus transportation which support logistics and people, diesel engines are highly expected to have high thermal efficiency and low exhaust emissions over the next few decades. Effective methods to achieve even higher thermal efficiency are to reduce a cooling loss from combustion chamber wall. A multi-hole diesel injector has a significant impact on improving engine thermal efficiency by enhancing a combustion activity and reducing a cooling loss. In this study, two types of diesel injectors - 8-hole and 14-hole - with the same flow rate were tested under heavy-duty diesel engine condition. Heat release rate, energy balance and engine emissions were investigated using the single-cylinder engine with displacement of 1,478 cc. Furthermore, an optical engine was used to observe quantitative spray penetration and flame development from shadowgraph imaging and analyze flame temperature by a two-color method. The results of the single-cylinder engine showed that the 14-hole injector exhibited higher indicated thermal efficiency thanks to lower cooling loss than 8-hole results. However, we observed a slightly higher exhaust loss in the case of 14-hole injector. In addition, 14-holes were less exhaust emission than 8-holes. Coupling with optical observation, 14-hole injector support those results derived from shorter spray penetration and lower flame temperature than 8-hole injector. According to Newton’s law of cooling, these are factors that contribute to reducing a cooling loss by to relieve a difference in temperature between the flame and the combustion chamber wall and to reduce contact time with the flame and the combustion chamber wall.