Solving Valve Train Wear Problems in Medium Speed High BMEP Diesel Engines 2011-01-2217
A major task ahead of engine manufacturers today is to extract the maximum power output from the engine while improving the reliability and durability, this is even more significant in case of applications such as power generation where engine experiences high loads for a prolonged period of time. Durability of valve train components in such cases greatly affects the overall engine life and service intervals.
Majority of power generation engines running at medium speed employ pushrod type valve train. The high valve train inertia along with continuous operation at high loads poses as different set of problems for such engines. A significant amount of wear can occur at various valve train part interfaces which eventually leads to change in valve lash. A large change in valve lash beyond a certain point deteriorates the engine performance and emissions; it also accelerates the wear further. The work presented here is carried out to identify and solve valve train wear issues for such medium speed high BMEP engines.
To exactly evaluate the life of a valve train assembly, a test cycle was developed which accelerated the wear during engine durability testing. A methodology was developed by means of dimensional checks and profile measurements to exactly evaluate the valve train wear at various interfaces. The wear characteristics of various engine parts/ interfaces were studied in detail from design, manufacturing and metallurgy point of view. The parts/ part pairs causing the maximum contribution to the overall wear were identified and root cause matrix was developed for each part/ part pair.
For each root cause identified the design was improved in terms of dimensions/, material/, manufacturing process. 1D kinematic simulation was used to improve the cam profile design, 3D CFD was used to study the cooling aspect especially in the valve guide and valve seat region. FEA was also used for carrying out stiffness and stress analysis of individual valve train components. The modified valve train assembly was tested for durability and the improvement in wear rates and hence the valve train life was evaluated. A significant improvement was observed in wear rates and hence the overall valve train life.