Alternative designs towards thermal optimization of coated valves using space‐time finite elements

Heat transfer and stress analysis in metallic and coated exhaust valves are performed by an adaptive space‐time finite element method. Results indicated that coatings of ordinary thickness cannot protect a coated valve operating in an uncooled engine. A new approach for designing the inner geometry of the metallic part in a coated hollow valve is presented. The purpose of the cavity is changed from cooling to insulating. Controlling the valve temperature and the heat flows out is done by changing the geometry of the cavity. The optimum is sought between the hollow geometry of the valve and its coating thickness while the outer geometry is that of an ordinary valve. Exhaust valves with optimal geometry are presented. A reduction of 40% of the heat flows out is obtained, compared to the heat flows out from a metallic valve operating in a cooled engine. By comparison, reduction of the heat flows out from a coated, ordinary geometry valve amounts to only 20%.