Within the European research project ATOS (Advanced Transmission and Oil System Concepts) a systematic study of the separation efficiency of a typical aero-engine air/oil separator design was conducted. The main objectives were to obtain a basic understanding of the main separation mechanisms and to identify the relevant parameters affecting the separation efficiency. The results of the study contribute to an optimised separator technology. Nonintrusive optical measurement techniques like laser diffraction and multiple wavelength extinction were applied to analyse the separation efficiency and identify potential optimisation parameters. Oil mist with defined oil droplet size distribution was supplied to the breather. By simultaneously measuring particle size and oil concentration upstream and downstream of the breather the separation mechanism was analysed and the separation efficiency was assessed. In addition, the pressure drop across the separator was measured. The pressure drop is an important design feature and has to be minimised for proper sealing of the engine bearing chambers. The experimental programme covered a variation of airflow, oil flow, shaft speed, and droplet size. The main emphasis of the investigations was on the separation of small droplets with a diameter of up to 10 μm. The following trends on separation efficiency of small droplets were observed: the separation efficiency increases with increasing rotational speed, with increasing particle size and with decreasing air flow rate. In parallel, the pressure drop across the breather increases with increasing speed and increasing airflow.

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