Feasibility and Reliability Study on GH4169/Cast Iron Bimetallic Exhaust Valves

Key words:  Bimetallic exhaust valves  Dynamic behaviour  Temperature distribution  Feasibility assessment.

Abstract:

In order to extend the service life of exhaust valves in high power density diesel engines, bimetal can be used for exhaust valves. A GH4169/cast iron bimetal was made with Laser Powder Bed Fusion (LPBF) tech, and the feasibility and dependability under exhaust valve operating conditions were thoroughly examined. This study determined the temperature distribution and stress distribution of the exhaust valve under service conditions using steady-state thermal analysis and dynamic mechanical analysis. The reliability of GH4169/cast iron bimetal applied to exhaust valves was evaluated through tensile and fatigue testing. From research findings, it can be seen that increasing the ratio of cast iron in bimetallic exhaust valves improves the overall heat conduction performance of the exhaust valve. There is a significant stress concentration in the geometric transition area of the exhaust valve, and the stress can reach 166.5 MPa when combustion occurs. From the experimental data, we can see that when porosity is less than 2.68%, fatigue mainly depends on the propertities of the cast iron rather than on porosity. The tensile strength of the GH4169/cast iron bimetal is 478.51 MPa at 400 ℃, 490.40 MPa at 500 ℃, and 462.24 MPa at 600 ℃. All corresponding fatigue strength values are over 135 MPa, far above the working stress of the exhaust valve stem. To take into account the exhaust valves"" thermo-mechanical behavior as well as the bimetal’s properties at higher temperatures, placing the bimetal interface on the stem would work. When the interface is in position 2, the bimetal offers the best balance of performance and cost.