Comparison of the wear exerted on engine valves and seat inserts under various speeds and mileages

Abstract

Under actual engine driving conditions, there is a possibility of engine valve and seat insert wear occurring as a result of various speed changes and accumulation of mileage. It is therefore necessary to examine the wear-related problems of engine valves and seat inserts and to determine by comparison whether speed or mileage inflicts the greater wear. This work focuses on the various degrees of wear produced at three different singular test speeds (10 Hz, 25 Hz, and multi-Hz) and two different cycle numbers (2.1 — 106 and 6.0 — 106). Throughout all tests performed in this study, the temperature of the outer surface of the seat insert was controlled at 350°C and the test load was 1960 N. Wear depths were measured using a confocal laser microscope, and wear mechanisms were observed using a scanning electron microscope. The extent of wear produced at higher speeds (25 Hz) was found to be greater than that produced at lower speeds (10 Hz) under identical test conditions (temperature, valve displacement, cycle number, and test load). Although test cycle numbers were increased by a factor of 3, for example from 2.1 — 106 to 6.0 — 106, the wear depths were not proportionally increased. Wear occurred rapidly during the initial stages of the test and wear depths increased less significantly with each cycle number. Wear depth of the 2.1 — 106 cycle number test at 25 Hz was much larger than that of the 6.0 — 106 cycle number test at 10 Hz in both the valve and the seat insert. Therefore, this result indicates that speed (Hz) might have a greater effect than mileage (cycle number) on the valve and seat insert while the engine is running. As the cycle number was increased, the wear depth at multi-Hz showed a tendency to near the wear depth at 25 Hz (high speed) rather than that at 10 Hz (low speed). Adhesive wear and shear strain were observed in the wear mechanisms of the valves. Furthermore, adhesive wear and surface fatigue wear were observed in the wear mechanisms of the seat inserts.