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2 Łutowicz M.

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Asymmetry increase in the course of compression pressure as a measure of obstruction in indicating channel

Łutowicz M.

Journal of KONES

2016

Vol. 23, No. 3

311--316

Indicating process of large combustion engines for both marine and industrial applications is performed using the indicating channels with valves. The impact of these channels on the values of parameters obtained from engine’s indication is significant. In previous studies, it had been shown that during exploitation accidental degradation of the indicating channels occurs. Carbon deposits, which appear in the channels, are limiting their patency. Leaks in channels connections are also appeared. Disregarded state of degradation of indicating channels will change the image of indicated pressure course, different for each cylinder of the engine. When cylinders are indicated using commercial instruments, the status of the channel is not in any way taken into account. At one gas compressing station in Poland, which has compressor diagnostic system, developed by the author, with stationary indicator, inverted IIR filter has been used. This filter is used to adjust the recorded waveforms of indicated pressure on motor-compressors GMVH type, and the filter coefficient is chosen to offset the associated throttling signal delay. Information about the delay of the signal is missing, however, in the case of popular portable indicators that do not use tags from crankshaft position. The paper presents a method for assessing the state of the indicating channel, based on the asymmetry measurement of compression course obtained after cut-off the fuel supply to the tested cylinder. The study model shows that leakage from the combustion chamber, interference in cooling and other defects cause only slight and predictable disruption of symmetry. The analysis of compression pressure course (without fuel delivery) immediately prior to each cylinder indication, in the case of positive verification, increases the reliability of diagnosis. In the case of negative verification, measure of the asymmetry could be the basis for the adjustment of acquired pressure waveforms and achieved from them parameters.

Reverse IIR filter as a tool for cylinder indicating channel patency impact correction on measured cylinder pressure waveform

Łutowicz M.

Journal of KONES

2013

Vol. 20, No. 2

253--259

Indicating of large marine and industrial diesel engines is made with using indicating channels in cylinder head with valves. The impact of these channels on the value of the parameters obtained from indicating is significant. However, indicating is commonly used for comparative tests assuming that this error is the same on all cylinders of the same engine in identical conditions. As a result of operation especially in cylinders with irregular combustion process the coke occurs in the channel limits its patency. It causes changes in the image of indicated pressure. In such a situation defined parameters are subject of considerable random error. In the earlier studies on the engine Sulzer type 6AL20/24 cylinder channel failure was simulated and channel chocking symptom was observed as apparent TDC shift relative to a reference mark connected with the shaft. As part of ongoing studies attempt to reconstruct distorted pressure curve by chocked indicating channel was made. It is assumed that the channel with the valve is only connection between throttling element in the form of a channel with the much greater volume of the valve. Such a structure was modeled as IIR filter. For this type of filter, there is an unequivocal inverse transformation, which, at least in theory gives possibility to reconstruct the distorted pressure waveform. The reconstruction was carried out by selection of the filter coefficients so as to eliminate the shift of TDC. In practice it turned out that the reconstruction is not perfect. All obtained pressure waveforms are slightly noisy and distorted in the first phase of expansion. Despite this, there was a significant reduction in errors of some parameters determined from the reconstructed pressure waveform.