Abstract
The aim of the article is to present the concept of an indirect diagnostic method using the assessment of the variability of the amount of released heat (mass fraction burn) and the heat release rate. The Wiebe function for the assessment of variability has been used. The Wiebe function parameters from the course of the high-pressure indication in the cylinder of internal combustion engine using linear regression have been calculated. From a sufficiently large number of measured samples, the upper and lower limits of the Wiebe function parameters have been statistically determined. Lower and upper limits characterize variability of the heat release process not only in terms of quantity but also in terms of heat release rate. The assessment of variability is thus more complicated than using one integral indicator, typically the mean value of amount of the released heat. The procedure enabling a more accurate estimation of heat generation beginning has been shown. For the combustion process variability assessment of the engine, statistical test of relative frequencies has been used.
Highlights
The internal combustion engines diagnostics has an extensive history and a lot of diagnostic methods have been applied
The method evaluates the variability of the combustion process using the Indicated Mean Effective Pressure (IMEP) parameter
The Covariance method (CoV) IMEP method in principle works with the mean value of the indicated pressure, i.e. with one integral parameter, but there is no information about the distribution of the heat release rate
Summary
The internal combustion engines diagnostics has an extensive history and a lot of diagnostic methods have been applied. The method is described in [34], where it is shown that the course of the indicated pressure depends on the amount of released heat during the fuel combustion process. The CoV IMEP method in principle works with the mean value of the indicated pressure, i.e. with one integral parameter, but there is no information about the distribution of the heat release rate. The utilization of the Wiebe function provides information about the distribution of the heat release rate This can be advantageously utilized for the better assessment of the variability between each engine cycles, because of uses of two parameters for the burning description. The calculation of the parameters of the Wiebe function is performed from this fictitious course This procedure does not allow to assess the variability of the combustion process. If the test result exceeds the confidence level α, the diagnosed engine shows greater combustion process variability, than corresponds to the expected values, shows the poor technical condition of the engine
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