Takahashi, D., Nakata, K., Yoshihara, Y., Ohta, Y. et al., "Combustion Development to Achieve Engine Thermal Efficiency of 40% for Hybrid Vehicles," SAE Technical Paper 2015-01-1254, 2015, doi:10.4271/2015-01-1254.
In recent years, enhancing engine thermal efficiency is strongly required. Since the maximum engine thermal efficiency is especially important for HVs, the technologies for improving engine thermal efficiency have been developed. The current gasoline engines for hybrid vehicles have Atkinson cycle with high expansion ratio and cooled exhaust gas recirculation (EGR) system. These technologies contribute to raise the brake engine thermal efficiency to more than 38%.In the near future the consumers demand will push the limit to 40% thermal efficiency. To enhance engine thermal efficiency, it is essential to improve the engine anti-knock quality and to decrease the engine cooling heat loss. To comply with improving the anti-knock quality and decreasing the cooling heat loss, it is known that the cooled EGR is an effective way. Therefore the cooled EGR technology is widely spread throughout the world and ESTEC (Economy with Superior Thermal Efficient Combustion) has been introduced in some papers.This paper describes some concepts like high tumble that are able to expand the EGR limit and to realize the engine thermal efficiency of 40%.