The present article focuses on a stepless capacity regulation system for reciprocating compressors in the capacity range between 0 and 100 per cent. This system is based on the so-called reverse flow regulation principle. The principle works by reversing part of the total gas that has been taken into the cylinder by conveying it back to the suction chamber by holding the suction valve open for a controlled and variable proportion of the compression stroke. Therefore the discharge capacity and power reduction are virtually proportional. In this study, the thermal cycle of reciprocating compressors in the case of stepless capacity regulation is analysed. The theoretical model of the thermodynamics cycle is first established. The relationship between the variation of the capacity and the opening time of the suction valve in a compression stroke can be obtained. Based on this approach, a new stepless capacity regulation system is designed, which consists of a hydraulic unit, a distributor, an unloader, and a control system. The resulting system is applied to a type 3L-10/8 reciprocating compressor to demonstrate its effectiveness. The experimental results show that the capacity of the compressor can be regulated steplessly, and the energy consumption is reduced proportionally with respect to the reduction in the capacity.

The existing researches of stepless capacity regulation system by depressing the suction valve for reciprocation compressor always adopt hypothesis that the compressor valves are open or close instantaneously, the valve dynamic has not been taken account into thermal cycle computation, the influence of capacity regulation system on suction valves dynamic performance and cylinder thermal cycle operation has not been considered. This paper focuses on theoretical and experimental analysis of the valve dynamic and thermal cycle for reciprocating compressor in the situation of stepless capacity regulation. The valve dynamics equation, gas forces for normal and back flow, and the cylinder pressure varying with suction valve unloader moment during compression thermal cycle are discussed. A new valve dynamic model based on L-K real gas state equation for reciprocating compressor is first deduced to reduce the calculation errors induced by the ideal gas state equation. The variations of valve dynamic and cylinder pressure during part of compression stroke are calculated numerically. The calculation results reveal the non-normal thermal cycle and operation condition of compressor in stepless capacity regulation situation. The numerical simulation results of the valve dynamic and thermal cycle parameters are also verified by the stepless capacity regulation experiments in the type of 3L-10⁻⁸ reciprocating compressor. The experimental results agree with the numerical simulation results, which show that the theoretical models proposed are effective and high-precision. The proposed theoretical models build the theoretical foundation to design the real stepless capacity regulation system.

In this study, the effects of residual stress induced by three different cooling methods during heat treatment on the crack propagation behaviour of the GH4169 disc were investigated. Different levels of stress fields were induced to the specially designed discs by using air cooling (AC), air jetting cooling (AJC) and water quenching (WQ) methods and were quantitated by numerical simulation. These discs were then subjected to prefabricated cracking, and crack propagation tests were conducted on a spin tester with two load spectrums. Crack growth behaviour was depicted via the surface replica technique and fracture morphology. Regarding the linear superposition of residual stress and centrifugal force, the crack propagation behaviour of different discs was simulated using the FRANC3D software. AJC and WQ introduced compressive residual stress (−259 MPa and −109 MPa, respectively) into the disc compared with the AC method (about −1.5 MPa). The AJC method increases the crack propagation life of the disc by introducing residual compressive stress into the area near the surface of the central hole to inhibit the opening of the crack surface. When the fatigue load was low, this inhibition effect was more significant.

The labyrinth-honeycomb seal has been widely used in gas turbine engines as an abradable gas path seal to protect the rotor from wear and damage in rubbing