Search Results

This paper is a review of ceramic tribological characteristics and application of silicon-based ceramics as engine valves and seat inserts. This review has shown that wear of ceramics is not an intrinsic material property or a constant, rather it depends on the operating conditions as well as on microstructure, environment, measurement techniques and material properties. The review also found that the dominant ceramic wear mechanism is a fracture/crack controlled process. There have been many models developed to describe the wear of ceramics, however, the complexity of the wear and the existence of wear transitions suggest that satisfactory results can be obtained for each wear model/equation only for the operating conditions for which it was derived. The application of silicon-based ceramics for engine valves and seat inserts is also reviewed and field engine test results are presented. The advantages and disadvantages of ceramics for engine valves and seat inserts are discussed.

In this investigation, more than one hundred valves from forty seven fired engines have been examined. The worn surfaces of valve and insert seats from a wide variety of engines were studied using optical microscopy, SEM and EDX. The purpose of this investigation is to obtain a fundamental understanding of the primary wear mechanisms on the valve/insert seat of the engines. The wear mechanism which dominates the valve/insert seat wear depends on the engine operating conditions, seat contact configurations, valve/insert seat materials, and dynamics etc. Besides adhesion, corrosion and abrasion wear mechanisms, this study also found that shear strain is a major factor contributing to engine valve/insert seat wear. When shear strain at the seat surface exceeds the limit of the material, delamination wear is produced.

The new two-microphone acoustic intensity technique has been applied to the determination of the transmission paths of sound into an airplane cabin interior. It appears that, provided sufficient care is taken in the measurements, accurate quantitative information can be obtained with this technique on the dominant paths of acoustic energy transmission. This information can be used to make design changes to the fuselage wall to reduce interior cabin noise.