Investigations of Valve Recession Mechanism in Flex Fuel Engines

Valve recession is a phenomenon observed in internal combustion engines, in which the set of valve and valve seat presents excessive wear in the contact region, causing poor sealing of the combustion chamber and, hence, loss of engine power. It is known that the wear mechanism depends on several variables such as the fuel type. Because of the growing Flex Fuel vehicle sales and therefore the usage in large-scale of hydrated ethanol, it was necessary to perform new studies and actions for continuous improvement on engine optimization to minimize the valve recession levels. One alternative to expedite engine testing and follow valve recession is to run it on dynamometer and perform measurements of valve wear with pre-set frequencies. Based on the engine design, a maximum recession level is calculated and exceeding this number would cause stated failure modes. Supported by a 6-Sigma approach, distinct sources of degeneration of the valve set could be observed, which were consistently worsen by the usage of ethanol. This paper shows the study performed with the objective to reduce valve recession on Flex Fuel engines by experimentally evaluating combinations of valves and valve seats materials with different characteristics of hardness and heat dissipation, which, as observed, were the main factors influencing valve recession.