Experimental Research On Knock And Misfire And Development Of Monitoring System For Marine Medium Speed Gas Engine

In the face of the increasingly stringent emission regulations of International Maritime Organization(IMO),the advantages and the prospects of natural gas as a clean fuel has become a new research hotspot and development direction for medium speed fuel engines in controlling the pollutant emissions and reducing operating costs.Due to the narrow working range of the gas engine,it is prone to misfire and to knock during the operation,which brings a great security risk to the gas engine.Therefore,it is of great significance to carry out the fault monitoring and the diagnosis of the knocking and the misfiring for the gas engine.The type ACD320 marine medium-speed gas engine is taken as research subject in the thesis.The experimental research on the technologies of monitoring and diagnosing the knocking and misfiring for the gas engine is carried out,the main research work and the conclusions are shown below:(1)The test and analysis methods of detecting the knocking and the misfiring for engines are summarized.The monitoring and diagnosing principles of the knocking and misfiring of the gas engine are analyzed.The research routes of monitoring and diagnosing the knocking and misfiring by using vibration method and the instantaneous speed method respectively are determined.(2)The knocking experiments are carried out on the type ACD320 marine medium-speed engine test bench,and the cylinder pressure signals and the vibration signals of the engine are measured synchronously.The knocking condition of the engine is determined by analyzing the cylinder pressure signals.The vibration signals on the engine body in the knocking condition and the good condition are analyzed in the frequency domain and the time domain.It is found that the vibration energy during firing time in the good condition of the gas engine is concentrated in the low frequency band and that the vibration energy during firing time in the knocking condition of the gas engine is transferred to the high frequency band and the RMS value,variance and kurtosis of the vibration signals are increasing respectively.The relative energy and RMS value,variance and kurtosis coefficient of the vibration signals in the characteristic frequency segment are extracted as the characteristic parameters of diagnosing the knocking for the gas engine.And the diagnosing knocking coefficient based on the characteristic parameters of the vibration signals during the firing time of the engine is put forward to.(3)The misfiring experiments is carried out on the test bench of the type ACD320 marine medium-speed gas engine.The instantaneous speed and the top dead center(TDC)signals of the gas engine in the misfiring condition and in the good condition are measured synchronously.The instantaneous speed signals are analyzed in the time domain and the frequency domain respectively.It is found that the low harmonic amplitudes of the instantaneous speed in the misfiring condition of the gas engine change obviously and that the fluctuation peak of the instantaneous speed in the misfiring condition cylinder of the gas engine is lower than that in the good condition cylinder of the gas engine.The ratio of the harmonics amplitude of the instantaneous speed of the medium-speed gas engine is extracted as the characteristic parameters of diagnosing misfiring and the misfiring cylinder is identified by the fluctuation peak of the instantaneous speed.The rule of diagnosing misfiring of the medium-speed gas engine is established.(4)The safety monitoring system of the gas engine based on LabVIEW is developed,the on-line monitoring and alarming knocking and misfiring of condition of the gas pipeline of the gas engine are realized.