Corrosion and wear resistance of some novel and current diesel exhaust valve materials

Abstract

This paper summarizes the work undertaken in a five year collaborative project aimed at developing improved materials and coatings for exhaust valves in diesel engines for marine service, operating on residual fuel oils. Eighty candidate materials were assessed using a range of laboratory tests designed to simulate various aspects of engine conditions. Of particular interest to this paper are those relating to high temperature corrosion and corrosive wear in this diesel engine environment. Following these laboratory tests, prototype engine valves were produced in 15 different combinations of the most promising materials and their performance was compared in severe engine trials with that of the best currently used commercial materials. Some experimental nickel alloys, coatings and hardfacings showed considerable promise together with a cheaper, coated iron-based valve alloy. In addition to, and as a result of, these material evaluation programmes a life prediction model has been devised which gives engine valve lives as a function of alloy composition and valve seat operating temperature for engines operating on residual fuels oils.

Keywords:

• diesel exhaust valves
• material evaluation programmes
• life prediction model