Development of 50% Thermal Efficiency S.I. Engine to Contribute Realization of Carbon Neutrality

To prevent global warming, many countries are making efforts to reduce CO₂ emissions toward achieving 2050 carbon neutrality. In order to reduce CO₂ concentration quickly, in addition to spread of renewable energy and expansion of BEV, it is also important to reduce CO₂ emissions by improving thermal efficiency of ICE (internal combustion engine) and utilizing carbon neutral fuels such as synthetic fuels and biofuels. It is well known that lean burn is an effective technology to increase thermal efficiency of engine highly. However, since NOx emission from lean burn engine cannot be reduced with three-way catalyst, there have been issues such as complicated system configuration due to the addition of NOx reduction catalyst or limiting lean operation to narrow engine speed and load in order to meet emission regulation of each country. This paper introduces super lean burn engine with over lambda 2.5 that achieves both high thermal efficiency and significantly low NOx emission in order to solve the issues of conventional lean burn engine. Key technologies for combustion such as ignition, flame propagation, and unburned HC reduction are described firstly, and then the possibility of further improvement of thermal efficiency and combustion effect by applying ethanol as CN (Carbon neural) fuel to the super lean burn engine is indicated.