Working conditions of exhaust valves in Marine diesel engine fittings

The working conditions of the exhaust valve are very bad, the bottom surface of the valve is in direct contact with high temperature combustion products, and it is also subjected to high temperature (900~ 1000*C) and high speed (up to 600m/s) of corrosive gases during the opening of the valve, and the center temperature of the valve is as high as 700~800°C, in the middle of the transition arc between the valve disc and the valve stem. The temperature is also 600~700°C, and the exhaust valve operating temperature distribution.

Excessive temperature will reduce the mechanical properties of metal materials, and the material will have thermal deformation. When the valve surface seal is not strict, it will cause high-temperature gas to burn the valve surface. When the valve is seated, under the combined action of the inertia force and spring force of the valve and the valve seat, it also bears a considerable impact alternating load, which will be significantly increased when the valve pulsates or the valve clearance, increase, and increase. The impact of the valve and the seat is easy to form the deformation of the sealing surface and serious wear. Because most of the Marine diesel engines are supercharged diesel engines, because the fresh air pressure in the intake port prevents the possibility of obtaining oil from the valve conduit, dry friction between the metals is easy to occur.

There is always a layer of lubricating oil or smoke oil between the alloy surface of the air valve of the general diesel engine parts and the exhaust valve seat of the supercharged diesel engine. In addition, there will be wear between the valve stem and the conduit, and the top and end of the valve stem will be impacted and worn by the rocker arm. Therefore, these bad habits of operation and maintenance of diesel engines are also factors that cause diesel valve failure.