Sundaram L. Narasimhan

The effect of operating conditions on heavy duty engine valve seat wear

Abstract Engine valve seat wear affects engine performance. To improve valve quality and life is a common goal for both valve and engine manufacturers. By performing tests on a valve seat wear simulator, the effect of cycles, load and temperature on heavy duty intake valve/insert seat wear was investigated. The test temperatures ranged from 180 to 650 °C, the number of cycles was varied from 150 000 to 3 420 000, and the test loads were applied from 6615 to 24 255 N. The relationship of valve and insert seat wear as a function of cycles, load and temperature was experimentally established. A load dependent wear transition was found to exist and suggests different wear mechanisms operating in these different regions. Higher temperatures produced lower seat wear, which was attributed to parting agents or oxide films and valve head deformation. The intake valve/insert (Silcrome 1/Silcrome XB) seat wear mechanisms were found to be a complex combination of adhesion, shear strain and abrasion. Shear strain or radial flow was found to be an important valve seat wear mechanism from the microstructure analysis of cross-sectioned valve seats, and two-dimensional and three-dimensional worn seat profiles. The oxide films which formed during testing were found to play a significant role. They can prevent the direct metal to metal contact and reduce the coefficient of friction on the seat surface, thus reducing adhesive wear and deformation controlled wear.

Wear and wear mechanism simulation of heavy-duty engine intake valve and seat inserts

A silicon-chromium alloy frequently used for heavy-duty diesel engine intake valves was tested against eight different insert materials with a valve seat wear simulator. Wear resistance of these combinations was ranked. For each test, the valve seat temperature was controlled at approximately 510 °C, the number of cycles was 864,000 (or 24 h), and the test load was 17,640 N. The combination of the silicon-chromium valve against a cast iron insert produced the least valve seat wear, whereas a cobalt-base alloy insert produced the highest valve seat wear. In the overall valve seat recession ranking, however, the combination of the silicon-chromium valve and an iron-base chromium-nickel alloy insert had the least total seat recession, whereas the silicon-chromium valve against cobalt-base alloy, cast iron, and nickel-base alloy inserts had significant seat recession. Hardness and microstructure compatibility of valve and insert materials are believed to be significant factors in reducing valve and insert wear.The test results indicate that the mechanisms of valve seat and insert wear are a complex combination of adhesion and plastic deformation. Adhesion was confirmed by material transfer, while plastic deformation was verified by shear strain (or radial flow) and abrasion. The oxide films formed during testing also played a significant role. They prevented direct metal-to-metal contact and reduced the coefficient of friction on seat surfaces, thereby reducing adhesive and deformation-controlled wear.