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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.

To improve the thermal efficiency of an engine, it is particularly important to reduce the cooling loss from the combustion gas to the combustion chamber wall, which constitutes a major proportion of the total loss [1]. Previous studies addressing cooling loss reduction attempted to use ceramic in place of the conventional aluminum or iron alloys, but this led to a reduction in the volumetric efficiency and increased smoke emissions. This was caused by the ceramics having both a low thermal conductivity and high heat capacity, relative to aluminum and iron. These characteristics cause the piston wall temperature, which rises during combustion, to remain high during the intake stroke, thus increasing the intake temperature and reducing the volumetric efficiency. This increases the smoke emissions [2].

The application of high-efficiency diesel engines, hybrid systems, waste heat recovery (WHR) systems, aftertreatment systems, and advanced drivetrains were all examined as possible approaches to improve the fuel consumption of heavy-duty, long-haul commercial trucks that mainly drive on highways. In this study, the strategies that were employed in an effort to improve the fuel consumption performance of the diesel engine itself and the results of evaluating and testing the actual engine are reported.