ANALYTICAL DESCRIPTION OF INDICATOR DIAGRAMS

Introduction. The disadvantage of presenting indicator diagrams in engine condition monitoring systems is their representation using splines. The structure of polynomials, which describe the links of splines, does not reflect the laws of thermodynamics, mechanics, chemical kinetics and heat transfer, which are the corresponding processes during the operating cycle of the engine. Purpose. To substantiate the structure of the analytical description of the indicator diagram for a two-stroke diesel engine on the basis of piecewise continuous functions. Develop an algorithm for approximating the indicator diagram with a piecewise continuous function using the tools of the DirectSearch package. Results. Finding the numerical values of the parameters of the approximating function is carried out by solving the problem of nonlinear conditional optimization using the method of conjugate directions with orthogonal shift. Processing of test experimental dependences has shown the possibility of finding the indicators of physical and chemical processes of the engine cycle (on the example of a twostroke diesel engine) with satisfactory accuracy according to the indicator diagram. Conclusions. Approximation of indicator diagrams by piecewise continuous functions, which include functions with physical and chemical content, allows for theoretical analysis of the quality of engine cycles. The function proposed for the approximation of the indicator diagram can be considered as a semi-local approximating spline, the links of which have a smooth connection of the order of C0 . Its individual links are described by linear functions, polytropic functions, a function that is a modified derivative of the Vibe function, a function that simulates gas leakage from the tank in the critical mode. Prospects for further research are related to increasing the accuracy of the approximation by increasing the number of units of the piecewise function, which corresponds to the approximation of the indicator diagram with a larger number of polytropic curves. This, in turn, provides a more adequate description of the indicator chart by highlighting the links on which the heat capacity of the working fluid can be considered constant or varying in polynomial dependences.