The operating properties of exhaust valves under heavy thermal and mechanical loads are dependent on the strength of steel i.e. resistance to mechanical deformations under increased and high temperatures and high temperature corrosive action of hot exhaust gas. Long term operation of exhaust valves under the conditions of cyclic thermal and mechanical tensions in the environment of diesel exhaust gas where the main oxidizing components are oxygen, carbon dioxide and overheated steam leads to a corrosion of the steel surface and diffusion processes on the thin surface layer of steel, which, under extreme conditions, may lead to a deformation of the valve, an increased leakage of the combustion chamber and a damage or destruction of the engine.
The investigations of the corrosion resistance of valve steel in diesel exhaust gas containing 5, 10 and 20 % of FAME were conducted on the durability test stand of BOSMAL Automotive Research and Development Institute in Bielsko-Biała in the oxidation catalyst chamber under the conditions simulating the operation of exhaust valves in diesel engines. The tests have confirmed that the corrosion resistance of valve steel in diesel exhaust gas decreases with an increased content of FAME in the fuel and as the content of Cr, Si, Ni is reduced in the tested valve steel and the content of Mn is increased in the tested valve steel.
Laboratory evaluation of ceramic coatings for diesel exhaust valves. Final technical report