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In heavy duty diesel engines, the waste heat recovery has attracted much attention as one of the technologies to improve fuel economy further. In this study, the available energy of the waste heat from a high boosted 6-cylinder heavy duty diesel engine which is equipped with a high pressure loop EGR system (HPL-EGR system) and low pressure loop EGR system (LPL-EGR system) was evaluated based on the second law of thermodynamics. The maximum potential of the waste heat recovery for improvement in brake thermal efficiency and the effect of the Rankine combined cycle on fuel economy were estimated for each single-stage turbocharging system (single-stage system) and 2-stage turbocharging system (2-stage system).

A study has been made of an automotive direct-injection diesel engine in order to identify the effects of the combustion chamber geometry on combustion, with special emphasis focused on a re-entrant combustion chamber. Conventional combustion chambers and a re-entrant one were compared in terms of the combustion process, engine performance and NOx and smoke emissions. Heat transfer calculations and heat release analyses show that the re-entrant chamber tends to reduce ignition lag due to the higher temperatures of the wall on which injected fuel impinges. Analyses of turbulent flow characteristics in each chamber indicate that the re-entrant chamber enhances combustion because of the higher in-cylinder velocity accompanied by increased turbulence. Further, analyses of in-cylinder gas samples show lower soot levels in the re-entrant chamber. As a result, a good compromise can be achieved between fuel economy and exhaust emissions by retarding the fuel injection timing.

More stringent emission regulations call for high-efficiency engines in the heavy-duty vehicle sector. Towards this goal, reduced heat losses, as well as increased work output, are needed. In this study, a multiple injector concept to control the combustion as well as reduce the hot boundary zones is proposed. Earlier studies have proven that multiple injectors experience lower heat losses and higher efficiency. However, a comprehensive investigation of the causes for experimental heat loss was not performed in depth. Experiments in a heavy-duty CI engine equipped with three injectors were thus performed. Engine configurations of single, dual and triple injectors were compared for a single-injection case as well as a multi-injection (Sabathe-cycle) case. Heat losses, efficiency and the emission levels were quantified and investigated. Optical experiments were performed to investigate the temperature field as well as flame behavior.