of the non-linear model is based on its partial linearization, use of the least squares method as well as on application of the optimum determination methods known in the theory of experiment. The model makes it possible to determine TDC location on indicator diagram dealing with combustion, determination of total compresion ratio, pressure value of indicator diagram truncation, as well as determination of maximum values of compression pressure on the diagrams in which self-ignitionoccurs before reaching the TDC.
The paper analyses the current offer of combustion pressure sensors for use on marine engines under operating conditions, methods of data acquisition, methods of determining TDC position and methods of obtaining diagnostic information from the indicator diagrams. Terms of continuous work on marine engines themselves only: new ABB cylinder pressure sensor, the piezoelectric sensors from KISTLER and AVL companies, but with limitations, the main ones being stability at high temperature. Another important issue for the accuracy of mean indicated pressure and heat released characteristics determination is referred to TDC position on the indicator diagrams. TDC is appropriate thermodynamic point, it is hardly determinable in the presence of interference and lack of sufficient information-but is used, for example in ABB solution. One of the sources of diagnostic information is to analyse trends in some parameters, which, unfortunately, is very difficult in environments with varying engine loads. Further progress in the diagnostic use of indicator diagrams should be associated with the use of the heat released characteristics and the net internal efficiency, which as shown by the results of preliminary tests can be used to assess the accuracy of the injection and combustion of fuel, including gas fuel. Supplementing these methods may be the use of vibration and noise to detect certain malfunctions.
In this paper -on the basis of indicator diagram processing taken as an example -were shown possibilities of the smoothing-out and decomposing of run disturbances with the use of the movable multiple approximation based on the least squares criterion. The notion was defined of movable approximating object and constraints used to form approximation features. It was demonstrated that the multiple approximation can be used to decompose disturbances out of an analyzed run. The obtained smoothing-out results were compared with those obtained from full-interval approximation of runs by means of splines as well as wavelet decomposition with using various wavelets, Wavelet Explorer and Mathematica software.Smoothing-out quality was assessed by comparing runs of first derivatives which play crucial role in the advanced processing of indicator diagrams.
Analysis of the indicator diagram is the basis of technical state evaluation of marine diesel engines. The indicator diagram contains a large amount of diagnostic information. A major problem for the diagnostic use of the indicator diagram is the pressure sensor location. Indicator channel and valve may introduce significant distortions in the resulting pressure. The paper presents results of research conducted on the medium speed laboratory engine Al 25/30. Pressure measurement (indication) was made by the sensor placed directly in the cylinder (instead of starting air valve), before the indicator valve (with special Kistler adapter) and on the indicator valve. Distortion of heat release characteristics for the sensor placed on the indicator valve is important, but it is estimated that diagnostic information is not erased. For medium speed engines is to be expected the use of a portable pressure sensors placed on the indicator valve. For this reason, further research is needed to assess the impact of channels and valves on different cylinders. During the research the course of heat release rate q and the heat released Q were determined. The curve of heat release rate q is a full equivalent to fuel injection pressure curve in the fuel pipes. It allows identification of the failure of the injection system. The curve of Q allows such determination and assessment of internal efficiency of the cylinder.
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