Abstract
Out of the many components of four-stroke diesel engines the exhaust valves are under significant constant thermal and mechanical loads. They operate in a highly corrosive environment of hot exhaust gases. The durability of these elements is determined by the creep resistance of steel i.e. simultaneous resistance to mechanical deformations under high temperatures and the resistance of the surface to corrosive hot exhaust gases. Long term cyclic heating and burning of the exhaust valves in the exhaust gases whose main components are oxygen, carbon dioxide and superheated steam results in a simultaneous rrosion of the steel surface and core diffusion of carbon and alloy elements in the thin layer of the steel surface. In extreme operating conditions this may lead to a deformation of the exhaust valves, a reduction of the air tightness of the combustion chamber or damage or destruction of the engine. The paper discuses the results of investigations of the influence of Cr, Ni, Mn and Si on the oxidation rate of high alloy austenitic valve steel in the diesel oil exhaust gases containing 5% of biocomponents. The corrosion tests were conducted in the temperate of 973 K and 1173 K under the conditions simulating the operation of the exhaust valves in diesel engines under heavy thermal loads. Based on the conducted research significant influence of the said alloy elements on the oxidation rate of the valve steel in the exhaust gases has been observed. The tests were conducted on the engine durability test stand in Automotive Research and Development Institute BOSMAL in Bielsko-Biała.
Highlights
The exhaust valves controlling the air tightness of the combustion chamber and the flow of highly corrosive hot exhaust gases to the exhaust manifold have great impact on the durability and operational parameters of combustion engines and their exhaust systems including catalytic converters.The measurements of the temperatures of the exhaust valves operating in diesel engines under high thermal and 1
The measurements of the temperatures of the exhaust valves operating in diesel engines under high thermal and Zawory wylotowe, decydując o szczelności komory spalania oraz przepływie niezwykle agresywnych korozyjnie gorących gazów spalinowych do układu wydechowego, wywierają duży wpływ na trwałość i walory eksploatacyjne silników spalinowych oraz układów wydechowych i katalizatorów spalin
In order to ensure high creep resistance of the exhaust valve i.e. great resistance to heat in a highly corrosive environment of the diesel exhaust gases [3] (Tab. 1) including high resistance to low and high temperature creeping [4] the valve heads of moderns bimetallic exhaust valves are usually made from four types of high alloy austenitic valve steel of the chemical composition and mechanical properties given in Table 2 and 3
Summary
The exhaust valves controlling the air tightness of the combustion chamber and the flow of highly corrosive hot exhaust gases to the exhaust manifold have great impact on the durability and operational parameters of combustion engines and their exhaust systems including catalytic converters
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