Thermal efficiency degradation analysis of compressor under multi-failure coupling with stepless capacity control condition.

A stepless capacity-control system drives a compressor suction valve to operate independently at high frequencies and speeds. Failures, such as unloader wear, valve plate leakage, and control system performance degradation, significantly alter the thermodynamic processes of the compressor. This study established a new compressor model accounting for independent collaborative operation of multiple valves coupled with diverse fault modes. The model comprehensively considers unloader driving force, displacement, and action time parameters, incorporating independently parameterized valve dynamic motion equations and valve clearancecylinder fluid flow equations. Simultaneously, it integrates fault influence parameters (leakage rate, unloader wear) with solving equations for multi-valve partial faults. The model was validated through a constructed compressor simulation monitoring test rig, demonstrating less than 5% error under normal operating conditions. Furthermore, the research revealed thermodynamic performance distortion characteristics in complex operating conditions and identified characteristic parameters of sudden multi-valve local faults under variable loads. The extracted fault patterns include valve unloader wear, valve leakage, and coupled faults. Analytical results demonstrate that the comprehensive impact intensity of concurrent multi-valve faults exhibits significant nonlinear superposition effects. Coupled fault modes display mutually inverse characteristics in fault parameters such as indicated work and discharge capacity, while specific fault categories can be differentiated through inward contraction or expansion trends in dynamic pressure profiles.