In response to the public consultation on Clean Aviation Partnership: A short comment on ultra-efficient gas turbines and sustainable aviation fuels

This two-page comment on the Clean Aviation SRIA, contains output from two Horizon 2020 projects, ULTIMATE (ultra-efficient engines) and ENABLEH2 (hydrogen aircraft). The report has also been updated by a coordinated effort on collecting strategic inputs from Chalmers University of Technology.\ua0Some output from efforts on road-mapping conducted together with leading aero engine manufacturers is also supporting this comment. The comment concentrates on giving input on the two key thrusts “3. Ultra-efficient Aircraft and Gas Turbines” and “4. Sustainable Aviation Fuels enabled Aircraft”. However, for all four thrust areas, it is noted that as aircraft design complexity increases the need for dynamic modelling, energy management and optimal control increases

Design Considerations of Low Bypass Ratio Mixed Flow Turbofan Engines with Large Power Extraction

The possibility of extracting large amounts of electrical power from turbofan engines is becoming increasingly desirable from an aircraft perspective. The power consumption of a future fighter aircraft is expected to be much higher than today\u27s fighter aircraft. Previous work in this area has concentrated on the study of power extraction for high bypass ratio engines. This motivates a thorough investigation of the potential and limitations with regards to performance of a low bypass ratio mixed flow turbofan engine. A low bypass ratio mixed flow turbofan engine was modeled, and key parts of a fighter mission were simulated. The investigation shows how power extraction from the high-pressure turbine affects performance of a military engine in different parts of a mission within the flight envelope. An important conclusion from the analysis is that large amounts of power can be extracted from the turbofan engine at high power settings without causing too much penalty on thrust and specific fuel consumption, if specific operating conditions are fulfilled. If the engine is operating (i) at, or near its maximum overall pressure ratio but (ii) further away from its maximum turbine inlet temperature limit, the detrimental effect of power extraction on engine thrust and thrust specific fuel consumption will be limited. On the other hand, if the engine is already operating at its maximum turbine inlet temperature, power extraction from the high-pressure shaft will result in a considerable thrust reduction. The results presented will support the analysis and interpretation of fighter mission optimization and cycle design for future fighter engines aimed for large power extraction. The results are also important with regards to aircraft design, or more specifically, in deciding on the best energy source for power consumers of the aircraft

Conceptual Design of a Compressor Vane- HEX for LH2 Aircraft Engine Applications

In order to meet the ambitious environmental targets set by the Paris Agreement, new sustainable carbon neutral aviation fuels need to be introduced. The high gravimetry energy density of hydrogen, makes it a prime candidate for a future aviation fuel. However, the associated poor volumetric energy density, requires an increased aircraft volume and associated penalty in aerodynamic performance. The required volume occupied by the hydrogen fuel can be decreased in half, if stored in its liquid form. This however requires that the liquid hydrogen (LH2) is kept at cryogenic temperatures, requiring adequate tank insulation. Moreover, to increase the effective heating value of hydrogen, the fuel distribution system will include heat exchanger technology to increase the fuel temperature before injection in the combustion chamber. The present work provides an outlook of different heat exchanger technology for application in hydrogen fueled gas turbine aero engines. The heat exchangers can be placed in the vicinity of the engine to reject the heat generated by the gas core to the hydrogen fuel. Ideally, they are strategically located to use heat management to maximize the engine efficiency and ensuring sufficient component durability. Moreover, the combination of liquid hydrogen’s high specific heat with cryogenic storage temperatures results in a formidable cooling capacity that can be explored by more compact heat exchanger solutions

Quantifying the Environmental Design Trades for a State-of-the-Art Turbofan Engine

Aircraft and engine technology have continuously evolved since their introduction and significant improvement has been made in fuel efficiency, emissions, and noise reduction. One of the major issues that the aviation industry is facing today is pollution around the airports, which has an effect both on human health and on the climate. Although noise emissions do not have a direct impact on climate, variations in departure and arrival procedures influence both CO2 and non-CO2 emissions. In addition, design choices made to curb noise might increase CO2 and vice versa. Thus, multidisciplinary modeling is required for the assessment of these interdependencies for new aircraft and flight procedures. A particular aspect that has received little attention is the quantification of the extent to which early design choices influence the trades of CO2, NOx, and noise. In this study, a single aisle thrust class turbofan engine is optimized for minimum installed SFC (Specific Fuel Consumption). The installed SFC metric includes the effect of engine nacelle drag and engine weight. Close to optimal cycles are then studied to establish how variation in engine cycle parameters trade with noise certification and LTO (Landing and Take-Off) emissions. It is demonstrated that around the optimum a relatively large variation in cycle parameters is allowed with only a modest effect on the installed SFC metric. This freedom in choosing cycle parameters allows the designer to trade noise and emissions. Around the optimal point of a state-of-the-art single aisle thrust class propulsion system, a 1.7 dB reduction in cumulative noise and a 12% reduction in EINOx could be accomplished with a 0.5% penalty in installed SFC

Design of Chalmers new low-pressure compressor test facility for low-speed testing of cryo-engine applications

As a part of the ongoing Horizon 2020 ENABLEH2 project, a new low-speed compressor test facility is being constructed at the Chalmers University Laboratory of Fluids and Thermal Sciences. The ENABLEH2 project investigates critical technologies for cryogenic H2 applications in commercial aviation, including new combustion and heat management systems. This paper revolves around the design and construction of a core cooling flow facility which was commissioned to study and verify the potential benefits of incorporating a heat management system into the intermediate compressor duct (ICD).The test facility is designed to operate continuously at rotor midspan chord Reynolds number up to 600,000 to allow for detailed aerothermal studies at a technical readiness level four. The two-stage axial compressor is representative of the low-pressure compressor and ICD of a mid-size commercial jet engine. The compressor is powered by a 147kW electric motor at 1920 RPM. The mass-flow and pressure ratio are controlled by restricting valves located at the inlet of the facility. A compact volute settling chamber, with an integrated thermal control system is used to control the inlet temperature and remove flow non-uniformities downstream the restrictor valves before entering the compressor. At the compressor inlet, a turbulence mesh is mounted to increase the turbulence intensity levels to 3-4% at the leading edge of the variable inlet guide vanes. The compressor is mounted vertically to allow for easy access to the downstream ICD and mitigate non-axisymmetric mechanical loads. The compressor unit allows for optical and traverse access at two +- 9-degree sectors for all the rotor-stator interfaces. Upstream the OGV, there are four independent $\pm$ 180-degree access traverse systems. In the ICD, measurements are carried out by a single ABB robot with a U-shaped probe mount, providing full volume probing access of the ICD. At the first design iteration the ICD is designed to be instrumented with multi-hole probes, hot-wire anemometry and heat transfer measurement using IR-thermography.The paper describes the facility and the process of achieving a high case similarity (engine representative) while maximising the quality of the experimental data over a large test domain, targets that often produce conflicting design demands

Development of fuel and heat management systems for liquid hydrogen powered aircraft

The presentation describes the recent developments in the design of the fuel and heat management systems for liquid hydrogen powered aircraft within the H2020 project ENABLEH2. The fuel distribution system main task is to deliver the right amount of hydrogen to the combustion chamber at an adequate pressure. This requires the usage of fuel pumps, valves, insulated piping, and a fuel control system to adjust the fuel flow for a given engine rating. Moreover, since liquid hydrogen is stored at cryogenic temperatures (-253C), it also requires the integration of heat exchanger technology to increase the fuel temperature up to a state where it can be efficiently mixed with air and combusted. The combination of hydrogen high specific heat with cryogenic temperatures results in formidable cooling capacity that can be explored by compact heat-exchanger solutions. Concepts that use existing engine aero-surfaces located after rotating turbomachinery are currently being investigated a Chalmers University of Technology.\ua0 A recently commissioned facility to investigate the potential benefits of a compressor flow cooling heat rejection system will also be discussed.\ua0 The test facility comprises a vertically mounted low-speed 2.5 stage compressor designed to operate continuously at rotor mid-span chord Reynold number up to 600,000, which is representative of a large-size future geared turbofan engine. Detailed aerothermal studies at TRL4 will be conducted to calibrate in-house design methods for radical core integrated heat exchangers. The facility is driven by a 147kW electric drive at a nominal speed of 1920 RPM. Traverse access is included in two 18-degree sectors for all the rotor-stator interfaces. At the upstream plane of the compressor outlet-guide-vane, four independent access traverse systems are included for a 360-degree access. Downstream, an ABB robot arm with a U-shaped probe mount provides full volume probing access in the exit compressor duct

Assessment of CO2 and NOx emissions in intercooled pulsed detonation turbofan engines

In the present paper, the synergistic combination of intercooling with pulsed detonation combustion is analyzed concerning its contribution to NOx and CO2 emissions. CO2 is directly proportional to fuel burn and can, therefore, be reduced by improving specific fuel consumption and reducing engine weight and nacelle drag. A model predicting NOx generation per unit of fuel for pulsed detonation combustors, operating with jet-A fuel, is developed and integrated within Chalmers University\u27s gas turbine simulation tool GESTPAN. The model is constructed using CFD data obtained for different combustor inlet pressure, temperature and equivalence ratio levels. The NOx model supports the quantification of the trade-off between CO2 and NOx emissions in a 2050 geared turbofan architecture incorporating intercooling and pulsed detonation combustion and operating at pressures and temperatures of interest in gas turbine technology for aero-engine civil applications