Baek, H., Lee, S., Han, D., Kim, J. et al., "Development of Valvetrain System to Improve Knock Characteristics for Gasoline Engine Fuel Economy," SAE Technical Paper 2014-01-1639, 2014, doi:10.4271/2014-01-1639.
It is difficult to reach higher compression ratios of the gasoline engine even though higher compression ratios improve thermal efficiency. One of the barriers is large torque drop led by knocking. Extensive researches to suppress knocking of the gasoline engine have been conducted. It is focused on lowering the temperature of fuel mixture in combustion chamber at compression top dead center (TDC). This paper covers the new valvetrain system to decrease the temperature of exhaust valve bottom (combustion) side. Hollow head and stem sodium filled valve (HHSV) have shown more heat transfer from combustion chamber to valve seat insert and valve guide, and higher thermal conductivity valve seat insert (HVSI) and valve guide (HVG) help to decrease valve temperature lower by higher heat transfer. This combination generates a synergy effect to decrease exhaust valve bottom temperature much lower and improve knock behavior, which contributes to improve engine fuel consumption and valvetrain durability.