Research On Monitoring And Diagnosis For Exhaust Valve Of Diesel Engines Based On Acoustic Emission Signals

In recent years, with the slow recovery of the international economy, the shipowners put forward higher requirements on the economy of the ship. Additionally, the International Maritime Organization (IMO) will officially implement Tier III standard in2016, which induces more stringent emission requirement on newly-built ships. Therefore, an energy-saving and environment-friendly ship will become the new favorite of the ship market. As the "heart" of ships, marine diesel engines are the key devices to guarantee the reliability, reduce emissions, and improve efficiency of the ship. Because of the complex structure of a marine diesel engine and harsh working conditions, a marine diesel engine is subject to failure. As one of the important parts of a diesel engine, the exhaust valve easily suffers from leak fault under the alternating load of thermal and mechanical, because of working conditions even worse. Exhaust valve failure will affect the economy and emissions of the diesel engine. The MAN6L16/24diesel engine is taken as the research object in this dissertation, monitoring and diagnosis of diesel engine exhaust valves based on acoustic emission technique is introduced. Firstly, the valve seated force is calculated. Secondly, calculate the acoustic emission caused by the exhaust valve seated force and validate the calculation results. Last, Research acoustic emission diagnostic mechanism, and study the acoustic emission laws of valve normal state and fault state. In accordance with the conclusion of the theoretical analysis, by fault simulation experiments, study the feature extraction method of acoustic emission, and provide the theoretical basis and technical reference for the diagnosis and monitoring of the exhaust valve of diesel engines based on acoustic emission signals. The main content is as follows.(1) The multi-body dynamics model and rigid-flexible dynamic model of MAN6L16/24diesel engine valve train is built, and the exhaust valve seated force is simulated in different valve clearance and speed, by using the ADAMS software. The simulation results reveal the change rule of the valve seated force, and the result is the boundary conditions of acoustic emission theoretical calculation.(2) The model of MAN6L16/24diesel engine cylinder head is built to calculate the acoustic emission signal under the exhaust valve normal and exhaust valve clearance, by using the ANSYS software. The relationship between the exhaust valve seated force and the acoustic emission is revealed.(3) The MAN6L16/24diesel engine being chosen as the test object, the acoustic emission test research was implemented. Under different operating conditions of the diesel engine, the acoustic emission signals are measured, and the theoretical results is verified. The excitation source of the acoustic emission and the characteristic of acoustic emission signal is analyzed.(4) Through the valve failure simulation test of a high-speed diesel engine and the exhaust valve testing of a large low-speed marine diesel engine, the acoustic emission signals is further analyzed and the feature of acoustic emission signal is extracted.