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Trends in aircraft engine design have caused an increase in mechanical stress requirements for rolling bearings. Consequently, a high amount of heat is rejected, which results in high oil scavenge temperatures. An RB199 turbofan bearing and its associated chamber were modified to carry out a survey aiming to reduce power losses in bearing chambers. The test bearing was a 124 mm PCD ball bearing with a split inner ring employing under-race lubrication by two individual jets. The survey was carried out in two parts. In the first part, the investigations were focused on the impact on the power losses in the bearing chamber of the operating parameters, such as oil flow, oil temperature, sealing air flow, bearing chamber pressure, and shaft speed. In the second part, the investigations focused on the reduction of the dwell time of the air and oil mixture in the bearing compartment and its impact on the power losses. In this part, porous screens were introduced around the bearing. These screens would aid the oil to flow out of the compartment and reduce droplet-droplet interactions as well as droplet-bearing chamber wall interactions. The performance of the screens was evaluated by torque measurements. A high-speed camera was used to visualize the flow in the chamber. Considerable reduction in power loss was achieved. This work is part of the European Research programme GROWTH ATOS (Advanced Transmission and Oil Systems).

Aiming in the direction of designing more efficient aero engines, various concepts have been developed in recent years, among which is the concept of an intercooled and recuperative aero engine. Particularly in the area of recuperation, MTU Aero Engines has been driving research activities in the last decade. This concept is based on the use of a system of heat exchangers mounted inside the hot-gas exhaust nozzle (recuperator). Through the operation of the system of heat exchangers, the heat from the exhaust gas, downstream the LP turbine of the jet engine is driven back to the combustion chamber. Thus, the preheated air enters the engine combustion chamber with increased enthalpy, providing improved combustion and by consequence, increased fuel economy and low-level emissions. If additionally an intercooler is placed between the compressor stages of the aero engine, the compressed air is then cooled by the intercooler thus, less compression work is required to reach the compressor target pressure. In this paper an overall assessment of the system is presented with particular focus on the recuperative system and the heat exchangers mounted into the aero engine’s exhaust nozzle. The herein presented results were based on the combined use of CFD computations, experimental measurements and thermodynamic cycle analysis. They focus on the effects of total pressure losses and heat exchanger efficiency on the aero engine performance especially the engine’s overall efficiency and the specific fuel consumption. More specifically, two different hot-gas exhaust nozzle configurations incorporating modifications in the system of heat exchangers are examined. The results show that significant improvements can be achieved in overall efficiency and specific fuel consumption hence contributing into the reduction of CO2 and NOx emissions. The design of a more sophisticated recuperation system can lead to further improvements in the aero engine efficiency in the reduction of fuel consumption. This work is part of the European funded research program LEMCOTEC (Low Emissions Core engine Technologies).

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Operating conditions in high speed mainshaft ball bearings applied in new aircraft propulsion systems require enhanced bearing designs and materials. Rotational speeds, loads, demands on higher thrust capability, and reliability have increased continuously over the last years. A consequence of these increasing operating conditions are increased bearing temperatures. A state of the art jet engine high speed ball bearing has been modified with an oil channel in the outer diameter of the bearing. This oil channel provides direct cooling of the outer ring. Rig testing under typical flight conditions has been performed to investigate the cooling efficiency of the outer ring oil channel. In this paper, the experimental results including bearing temperature distribution, power dissipation, and bearing oil pumping and the impact on oil mass and parasitic power loss reduction are presented.