Modeling and Simulation of the Suction Process in a Multi-Cylinder Automotive Compressor

Thermodynamics, valve dynamics and piston kinematics are considered in order to model the gas flows through compressor suction valves. The equations for the compressor processes based on the first law of thermodynamics are derived to calculate the instantaneous cylinder pressure and temperature. During the suction process, the dynamic motions of an automatic valve between a stop and seat are approximated as one -dimensional in the transverse direction and a linear elastic beam model is used to describe those motions. The finite difference method is then used to solve the equation of the valve. The mass flow rate through the valve is estimated assuming onedimensional compressible flow through an orifice. All of the equations that are derived are then solved simultaneously to obtain the pressure in the cylinder, valve response and the mass flow rate. Using the calculated mass flow rate, pressure pulsations in a simplified cylindrical annular cavity with an area change to consider ‘mode splitting’ are predicted based on the characteristic cylinder method. 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 response in the manifold. It is shown that the estimate of the gas pulsation in the suction manifold is in good agreement with experimental results.