Effect of oil-injection on twin screw compressor performance

Oil-injection improves twin-screw compressor performance significantly and its overall effect depends on the working fluid mass flow rate, the shaft speed, the injection position and the injected oil temperature. However, the individual contribution of each of these variables to the machine performance is yet not fully researched. Therefore, tests have been carried out on an air compressor with a male rotor diameter of 98mm, with injection nozzle sizes of 2, 3 and 4mm and with a nozzle of multiple holes. Tests were carried out with discharge pressures of 6.5, 8.5, 10.5 and 12.5 bar and rotor shaft speeds of 3000, 4000 and 5000 RPM. The results from the tests were compared with performance estimates at the same operating conditions as measurements against the standard injection nozzle of 5mm diameter. It was found that there is an optimum quantity of oil injected to obtain the best performance. (paper)