Research On Magnetism Monitoring Technology Of Piston Ring Wear For Marine Diesel Engine

A large low-speed marine diesel engine is the power source of a ship and its working fault has been threatening the ship’s safety. Due to the poor working condition of the diesel engine, there is a great possibility of diesel engine working fault. As the key parts of diesel engine, piston rings operation state affects the performance of the diesel engine directly. However, it is difficult to monitor piston rings wear on-line accurately considering those sealing working environment. The diesel engine faults caused by the piston rings wear of diesel engine occupy a large proportion of the shipping faults. Therefore it is significant to research the monitoring of the marine diesel engine piston rings wear. The main work and research results are as follows:1. As the accuracy of the two-dimensional magnetic finite element calculation model is limited, the three-dimensional finite element calculation model including a piston, piston rings, a cylinder liner, a magneto-resistive sensor was developed based on the theory of electromagnetic field. The compare between the three-dimensional magnetic finite element simulation and the ship test had been carried out, the two exists consistency. It was validated that the simulation model, calculation method and conclusions are correct. It found out that there is a single corresponding relationship between the piston ring wear and magnetic field changes on the monitoring point through simulation. The calculation results confirmed that the monitoring method which is based on magneto-resistive sensor can diagnose marine diesel engine piston rings wear.2. Steel magnet (strong magnet) was adopted as permanent magnet for the original magnetic sensors, while the field change caused by piston ring wears belongs to the feeble magnetic field which was generated after the iron sexual material magnetization. A ferrite magnet was selected instead of the original strong magnets to provide the magnetic field which is perpendicular to the sensitive direction of sensor to magnetize piston rings in this paper. And the internal structure of the sensor was optimized by calculating, piston rings wear monitoring sensor and the pretreatment circuits (the set/reset circuit, the signal amplifier and filter circuit, the zeroing circuit of bias voltage) was developed. And the patent,’A monitoring device of piston rings wear for marine diesel engine’, was obtained (the application number is201110327110.5).3. As there was no calibration device for the original monitoring system. It is difficult to determine the corresponding relationship between the piston rings wear and the sensor output voltage. A calibration equipment of piston rings wear monitoring sensor was devised, and the calibration experiment was carried out in this paper. The calibration experiment result shows that the sensor meets the requirements of wide wear range and high resolution. The patent,’A calibration equipment of the monitoring device of piston rings wear for marine diesel engine’, was obtained (the application number is201120409959.2).