Wear of diesel engine inlet valves and seat inserts

Valve wear has been a problem to engine designers and manufacturers for many years. Although new valve materials and production techniques are constantly being developed, these advances have been outpaced by demands for increased engine performance. The aim of this work was to establish the effect of engine operating parameters on diesel engine inlet valve recession and to screen potential new seat materials using test apparatus designed to simulate the loading environment and contact conditions to which a valve and seat are subjected. These data were then used, along with the mechanisms of wear identified during previous work [1-3], to develop a quantitative model for predicting valve recession. Valve recession was shown to increase with combustion loading, valve closing velocity and misalignment of the valve. Drip feed lubrication of the valve/seat interface reduced valve recession, on the material combination tested, by a factor of 3.5. The lubricant, however, was supplied in a larger amount and at a lower temperature than would be experienced in an engine. Two materials, of those tested, stand out as having improved wear resistance. These are maraging steel and ductile cast iron. Both gave significantly higher wear resistance than the other seat materials tested. The semi-empirical valve recession model, based on the fundamental mechanisms of valve and seat wear, provides a good approximation of valve recession for both engine tests and tests run on the hydraulic loading apparatus. Modelling of a diesel engine test indicated that impact was the major cause of valve recession.