Method for Selecting the Disсretization Step of Indicator Diagrams in Digital Methods of Internal Combustion Engines Parameters Monitoring

Abstract

Peculiarities of measuring equipment usage in the field of internal combustion engines and the rationality of methods for testing and results processing are considered. It is shown that one of the most difficult tasks in the study of the working processes of engines is to obtain a reliable indicator diagram with a given accuracy. It is noted that it is important to consider the features of the flow of rapidly changing and non-stationary processes in the internal combustion engine: high rates of processes change, a wide frequency spectrum, non-identity flow of the processes flow from cycle to cycle. This causes specific requirements to the methodological plan, as well as to measuring instruments themselves in terms of speed, recording frequency and rationality of the techniques of performing the experimental studies. It is proved that in the process of the engines investigation it is necessary to have both single-cycle indicator diagram and averaged, for several hundreds cycles, indicator diagram. It is shown that the objective of the work is to improve the methodology for choosing the discretization step and choosing the number of recorded ordinates of the internal combustion engine indicator diagram during one working cycle, depending on the approximation error and the rate of pressure increase. A general method for determining the sampling frequency of indicator diagrams depending on the required accuracy of its approximation is described; improved expressions for its determination are given. A scheme for determining the sampling frequency by the angle of crankshaft rotation is presented. The essence of improving the methodology for choosing the discretization step of the indicator diagram by dividing it into zones and selecting different sampling steps in each zone is considered in detail. The use of a digital microprocessor complex for the study of the working processes of a particular diesel engine is considered. The initial data and values of discretization angles, necessary for the experiment were determined.