Research of Fuel Components to Enhance Engine Thermal Efficiency Part II: Consideration of Engine Combustion Characteristics

To correspond to the social requirements such as climate change, air pollution, and energy security, enhancing the engine thermal efficiency is strongly required in these days. As for the specific engine technologies to improve the engine thermal efficiency, Atkinson cycle, cooled EGR (Exhaust Gas Recirculation), and low friction technologies have been developed [1–4]. In regard to combustion technology, lean boosted concept has a potential to reduce CO₂ emission because lean boosted concept is expected to enhance the engine thermal efficiency. Although expanding lean combustion limit is important for both increasing the engine thermal efficiency and reducing NO_x emission, there is a limitation to realize stable lean combustion with SI (Spark Ignition) gasoline engine. In this study, fuel effects on the combustion characteristics from the viewpoint of chemical reaction capability are focused on. In consequence, it is demonstrated that the some molecules with high laminar burning velocity expand the lean combustion limit and enhance the engine thermal efficiency. In other words, those candidate molecules show the potential to realize compatible characteristics both lean combustion stability and knocking resistance. They also reduce THC at lean operating condition.