Experimental study on the indicating diagram of an oil-injected twin screw compressor

Through experimental study on the indicating diagram, the working process of an oil-injected twin screw compressor can be understood thoroughly and this is beneficial to advanced optimum design. A small pressure sensor built into the tooth root of the discharge side of the female rotor was used to measure the pressure changes in the groove, ranging from the midpoint of the suction process to the completion of the discharge. By comparing the indicating diagrams at various working conditions, the influence of the parameters such as discharge pressure, rotating speed and oil-gas ratio on performance was analyzed. It is shown that the great change in discharge pressures has not caused evident iso-volumetric compression, and the indicating diagram and the corresponding performance have changed a littler in a wide range of rotating speeds. However, the oil-gas ratio seems to have a great influence. About 1%-2% of oil-gas volume ratio can provide a comparatively good performance. Furthermore, a rapid pressure rise at the end of discharge stage has been found in the indiating diagram and a flow-guided slot should be designed to avoid it.