Авіаційно-космічна техніка та технологія (Mar 2019)
INFLUENCE OF WORKING MEDIUM LEAKS ON THE POINT POSITION OF MAXIMUM COMPRESSION PRESSURE RISE RATE
Abstract
The article discusses the analysis of the parameters of the compression process, which is carried out according to the results of engine indication. The solution to this problem allows us to evaluate the technical condition of the cylinder-piston group parts. According to the requirements of most classification societies, the deviation of the compression pressure on this cylinder from the engine average should not exceed 2.5%. The dependence of the compression pressure value on the pressure of the supercharger makes it difficult to obtain correct diagnostic conclusions about the condition of the cylinder-piston group when the technical condition of the gas turbine compressor deteriorates. The existing publications investigated the position on the indicator diagram of the point at which the rate of increase in compression pressure reaches its maximum, and its position was demonstrated to be almost invariant with respect to pressure. This fact makes it possible to calculate its position relative to the top dead center of the engine even before the start of indexing and to accept the calculated value as a first approximation in the algorithmic synchronization of the display results. However, the leakage of the working medium, inevitably present in the engine, was not considered. Therefore, the problem of the displacement of the coordinate point of the maximum rate of pressure increase in the presence of leaks is legitimate. The task is solved applying a mathematical model consisting of three equations (condition, mass conservation and the first law of thermodynamics), written in a differential form and integrate at each calculated step. As an argument, the selected angle of rotation of the crankshaft of the engine. Nevertheless, to solve such systems of equations analytically considering the leaks in the full formulation is extremely difficult. Therefore the effective flow area of the piston rings was given in modeling the workflow is considered to be constant throughout the calculations. The modeling results determine the position of the point of maximum pressure rise rate on the indicator diagram, which can be used as an indirect indicator in the integral analysis of the engine technical condition
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