2022 Volume 64 Issue 210 Pages 360-366
As part of global efforts to reduce GHG emissions, there is a strong demand to reduce CO2 emissions in the transportation sector by improving the thermal efficiency of internal combustion engines. As a technology for improving the thermal efficiency of gasoline engines, super lean-burn is known, in which the air-fuel mixture in the cylinders of the engine is burned with a leaner air-fuel ratio than the stoichiometric air-fuel ratio. By reducing energy loss such as cooling loss and improving the specific heat ratio, thermal efficiency is improved, leading to a reduction in CO2 emissions. However, there is a limit point (lean limit) at which combustion becomes unstable as the air-fuel mixture becomes leaner. If the lean limit is exceeded, misfiring occurs in the engine and stable operation becomes impossible. This makes it difficult to obtain sufficient output, and adversely affects the running of the vehicle. To further improve thermal efficiency, it is necessary to expand the lean limit, and various methods have been proposed as engine technologies, such as increasing ignition energy and improving in-cylinder flow. In this study, as a fuel technology, we tried to expand lean limit by changing fuel composition and molecular structure. As a result, the fuel which have a lower molecular weight and high reactivity at around 1000K showed good lean limit expansion property. Specifically, it can be said that olefins and the like are excellent molecular structures.
