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A hybrid electric vehicle (HEV) system of heavy duty truck (HDT) for long haul application was studied to improve the fuel economy (FE). At first, the HEV system configuration and control functions were defined and optimized. Secondly the test vehicle was constructed and a test drive was carried out on Tomei express way, and then, 10% FE improvement compared to non-hybrid HDT was achieved. Additionally, HEV system with coasting technology, which had become attractive as a FE improvement technology for non-hybrid HDT, was considered to obtain further FE benefit. The effective usage of both “Electrical energy regeneration control” for HEV system and “Kinetic energy control” for coasting was studied with simulation. As a result, it was clarified that the effects for FE improvement depended on route profile and those combined operations advantaged for FE improvement compared to each individual operation.

Reduction of smoke emission from diesel engines is important in order to meet upcoming stringent exhaust gas regulations and also for improving fuel economy. In this paper, the reduction of smoke from DI diesel engines for heavy duty vehicles is discussed. A single cylinder engine test and three dimensional numerical analysis were carried out in order to obtain necessary and useful information for designing a combustion chamber and a fuel injection nozzle that could realize reduced smoke emission. This study is focused particularly on the behavior of the fuel spray which impinges on the piston cavity wall in the case of a reentrant type combustion bowl. As a result, it was found that the spray wall-impingement angle performs an important role in promoting fuel-air mixing. It is thus an important parameter which controls the main combustion region.