Takahashi, D., Nakata, K., Yoshihara, Y., and Omura, T., "Combustion Development to Realize High Thermal Efficiency Engines," SAE Int. J. Engines 9(3):1486-1493, 2016, doi:10.4271/2016-01-0693.
Improving vehicle fuel economy is a central part of efforts toward achieving a sustainable society, and an effective way of accomplishing this aim is to enhance the engine thermal efficiency. Measures to mitigate knocking and reduce engine cooling heat loss are important aspects of enhancing the engine thermal efficiency. Cooled exhaust gas recirculation (EGR) is regarded as a key technology because it is capable of achieving both of these objectives. For this reason, it has been adopted in a wide range of both hybrid vehicles and conventional vehicles in recent years.Cooled EGR has the potential to achieve further lower fuel consumption if the EGR ratio can be increased. Fast combustion is an important and effective way for expanding the EGR ratio. The engine combustion enhancement can be categorized into measures to improve ignition characteristics and methods to promote flame propagation. Ignition characteristics can be improved by increasing the length of the arc discharge or intensifying ignition energy when the air flow around the spark plug is increased. Measures to promote flame propagation include intensifying in-cylinder turbulence through flows such as swirl, squish, and tumble. Toyota has been introducing these technologies as ESTEC (Economy with Superior Thermal Efficient Combustion) in these years.This paper describes how air flow and air turbulence contribute to enhancing combustion by using the results of several different engines and lead to enhance the engine thermal efficiency. Especially the merits of high tumble concept are mentioned.