Mathematical modeling and simulation of a multi-cylinder automotive compressor
Abstract
A simulation model for a multi-cylinder automotive compressor has been developed. The equations for the compression cycle based on the first law of thermodynamics are derived to calculate the instantaneous pressure in the cylinder. During the suction process, the dynamic motion of an automotive valve between a stop and seat are approximated as one-dimensional in the transverse direction and a linear beam model is used to describe these motions. Also the mass flow rate equation through the valve port is derived assuming one-dimensional compressible flow in a squared-edge orifice. After it is demonstrated that the simulation model predicts the thermodynamic processes and the valve dynamics well, it is used to analyze gas pulsations in the suction manifold. A complicated real suction manifold connected to an anechoic pipe is modeled as a simplified annular cavity with an area change. Then linear acoustic plane wave theory and a four pole parameter formulation are used to derive and solve the governing inhomogeneous equation for the forced pressure responses in the manifold. Along with the resultant mathematical models, a characteristic cylinder method is used in order to reduce the computational time. The method is proven to be reliable in predicting gas pulsations. Because the assumption of the anechoic condition of the suction line is restricted to academic type experiments, the simulation procedure for predicting gas pulsations in the suction manifold connected to a finite inlet pipe is described. Then several parametric studies are performed including changes of the inlet and the discharge locations and the addition of an area change. The inclusions of the suction mufflers are also considered to examine the influence on gas pulsations. The four pole parameters for mufflers and the suction line with temperature variation are formulated and then used as fundamental tools to investigate the temperature effects on the gas pulsations. The valve opening time and clearance volume of the piston are also changed in order to understand the effects of variability from valve-to-valve as are the effects of changes in the characteristics and phases of the mass flow rate through the suction valves.
Degree
Ph.D.
Advisors
Adams, Purdue University.
Subject Area
Mechanical engineering
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