Stefan Donnerhack

Ultra Low Emission Technology Innovations for Mid-century Aircraft Turbine Engines

Commercial transport fuel efficiency has improved dramatically since the early 1950s. In the coming decades the ubiquitous turbofan powered tube and wing aircraft configuration will be challenged by diminishing returns on investment with regards to fuel efficiency. From the engine perspective two routes to radically improved fuel efficiency are being explored; ultra-efficient low pressure systems and ultra-efficient core concepts. The first route is characterized by the development of geared and open rotor engine architectures but also configurations where potential synergies between engine and aircraft installations are exploited. For the second route, disruptive technologies such as intercooling, intercooling and recuperation, constant volume combustion as well as novel high temperature materials for ultra-high pressure ratio engines are being considered. This paper describes a recently launched European research effort to explore and develop synergistic combinations of radical technologies to TRL 2. The combinations are integrated into optimized engine concepts promising to deliver ultra-low emission engines. The paper discusses a structured technique to combine disruptive technologies and proposes a simple means to quantitatively screen engine concepts at an early stage of analysis. An evaluation platform for multidisciplinary optimization and scenario evaluation of radical engine concepts is outlined.

Composite Cycle Engine Concept with Hectopressure Ratio

The investigated concept targets a significant increase in core engine efficiency by raising the overall engine pressure ratio to over 100 (hectopressure ratio) by means of discontinuous cycles allowing for closed volume combustion. To this end, piston engines enable isochoric combustion and augment the conventional Joule/Brayton cycle, thereby producing a composite cycle. An engine concept is chosen based on idealized parametric studies of simplified representations of the cycle as well as qualitative measures embracing weight, size, efficiency, emissions, operational behavior, and the life cycle. The most beneficial mechanical representation of the composite cycle engine in this study features crankshaft-equipped piston engines driving separate piston compressors, a high-pressure turbine driving an axial intermediate pressure turbocompressor, and a low-pressure turbine driving the fan. The powerplant performance calculations show radical improvements in thrust-specific fuel consumption of 17.5% during c...

Derivation of an Anisotropic Model for the Pressure-Loss Through a Heat Exchanger for Aero Engine Applications

We present an effort to model the pressure loss together with the heat transfer mechanism, in a heat exchanger designed for an integrated recuperative aero engine. The operation of the heat exchanger is focusing on the exploitation of the thermal energy of the turbine exhaust gas to pre-heat the compressor outlet air before combustion and to decrease fuel consumption and pollutant emissions. Two basic parameters characterize the operation of the heat exchanger, the pressure loss and the heat transfer. The derivation of the pressure loss model is based on experimental measurements that have been carried-out on a heat exchanger model. The presence of the heat exchanger is modeled using the concept of a porous medium, in order to facilitate the computational modeling by means of CFD. As a result, inside the integrated aero engine, the operation of the heat exchanger can be sufficiently modeled as long as a generalized and accurate pressure drop and heat transfer model is developed. Hence, the porosity model formulation should be capable of properly describing the overall macroscopic hydraulic and thermal behavior of the heat exchanger. The effect of the presence of the heat exchanger on the flow field is estimated from experimental measurements. For the derivation of the porous medium pressure loss model, an anisotropic formulation of a modified Darcy-Forchheimer pressure drop law is proposed in order to take into account the effects of the three-dimensional flow development through the heat exchanger. The heat transfer effects are taken also into account with the use of a heat transfer coefficient correlation. The porosity model is adopted by the CFD solver as an additional source term. The validation of the proposed model is performed through CFD computations, by comparing the predicted pressure drop and heat transfer with available experimental measurements carried-out on the heat exchanger model.© 2009 ASME

LEMCOTEC: Improving the Core-Engine Thermal Efficiency

This paper describes the research carried out in the European Commission co-funded project LEMCOTEC (Low Emission Core Engine Technology), which is aiming at a significant increase of the engine overall pressure ratio. The technical work is split in four technical sub-projects on ultra-high pressure ratio compressors, lean combustion and fuel injection, structures and thermal management and engine performance assessment. The technology will be developed at subsystem and component level and validated in test rigs up to TRL5. The developed technologies will be assessed using three generic study engines (i.e. regional turbofan, mid-size open rotor, and large turbofan) representing about 90% of the expected future commercial aero-engine market. Two additional study engines from the previous NEWAC project will be used for comparison. These are based on intercooled and intercooled-recuperated future engine concepts.The compressor work is targeting efficiency, stability margin and flow capacity by improved aerodynamic design. High-pressure and intermediate-pressure compressors are addressed. The mechanical and thermo-mechanical functions, including the variable-stator-systems, will be improved. Axial-centrifugal compressors with impeller and centrifugal diffuser are under investigation too.Three lean burn fuel injection systems are developed to match the technology to the corresponding engine pressure levels. These are the PERM (Partially Evaporating Rapid Mixing), the MSFI (Multiple Staged Fuel Injection) and the advanced LDI (Lean Direct Injection) combustion systems. The air flow and combustion systems are investigated. The fuel control systems are adapted to the requirements of the ultra-high pressure engines with lean fuel injection. Combustor-turbine interaction will be investigated. A fuel system analysis will be performed using CFD methods.Improved structural design and thermal management is required to reduce the losses and to reduce component weight. The application of new materials and manufacturing processes, including welding and casting aspects, will be investigated. The aim is to reduce the cooling air requirements and improve turbine aerodynamics to support the high-pressure engine cycles.The final objective is to have innovative ultra-high pressure-ratio core-engine technologies successfully validated at subsystem and component level. Increasing the thermal efficiency of the engine cycles relative to year 2000 in-service engines with OPR of up to 70 (at max. condition) is an enabler and key lever of the core-engine technologies to achieve and even exceed the ACARE 2020 targets on CO2, NOx and other pollutant emissions:• 20 to 30 % CO2 reduction at the engine level, exceeding both, the ACARE 15 to 20% CO2 reduction target for the engine and subsequently the overall 50% committed CO2 and the fuel burn reduction target on system level (including the contributions from operations and airframe improvements),• 65 to 70 % NOx reduction at the engine level (CAEP/2) to attain and exceed the ACARE objective of 80% overall NOx reduction (including the contributions from both, operational efficiency and airframe improvement), reduction of other emissions (CO, UHC and smoke/particulates) and• Reduction of the propulsion system weight (engine including nacelle without pylon).Copyright

Best Strategies for the Development of a Holistic Porosity Model of a Heat Exchanger for Aero Engine Applications

In an attempt to manage CFD computations in aero engine heat exchanger design, this work presents the best strategies and the methodology used to develop a holistic porosity model, describing the heat transfer and pressure drop behavior of a complex profiled tubular heat exchanger for aero engine applications. Due to the complexity of the profile tube heat exchanger geometry and the very large number of tubes, detailed CFD computations require very high CPU and memory resources. For this reason the complex heat exchanger geometry is replaced in the CFD computations by a simpler porous medium geometry with predefined pressure loss and heat transfer.The present work presents a strategy for developing a holistic porosity model adapted for heat exchangers, which is capable to describe their macroscopic heat transfer and pressure loss average performance. For the derivation of the appropriate pressure loss and heat transfer correlations, CFD computations and experimental measurements are combined. The developed porosity model is taking into consideration both streams of the heat exchanger (hot and cold side) in order to accurately calculate the inner and outer pressure losses, in relation to the achieved heat transfer and in conjunction with the selected heat exchanger geometry, weight and operational parameters. For the same heat exchanger, RAM and CPU requirement reductions were demonstrated for a characteristic flow passage of the heat exchanger, as the porosity model required more than 80 times less computational points than the detailed CFD model. The proposed porosity model can be adapted for recuperation systems with varying heat exchanger designs having different core arrangements and tubes sizes and configurations, providing an efficient tool for the optimization of the heat exchangers design and leading to an increase of the overall aero engine performance.Copyright

A Composite Cycle Engine Concept with Hecto-Pressure Ratio

This paper describes research carried out in the European Commission funded Framework 7 project LEMCOTEC (Low Emission Core Engine Technologies). The task involved significant increase in core engine efficiency by raising the overall engine pressure ratio to over 100 (hecto-pressure ratio) by means of discontinuous cycles allowing for closed volume combustion. To this end, piston engines enable isochoric combustion and augment the conventional Joule/Brayton-cycle, thereby producing a composite cycle. An engine concept was chosen based on idealized parametric studies of simplified representations of the cycle as well as qualitative measures embracing weight, size, efficiency, emissions, operational behavior and the life cycle. The most beneficial mechanical representation of the Composite Cycle Engine in this study features crankshaft equipped piston engines driving separate piston compressors, a high pressure turbine driving an axial intermediate pressure turbo compressor, and a low pressure turbine driving the fan. The power plant performance calculations showed radical improvements in thrust specific fuel consumption of 17.5% during cruise. Although engine weight increases correspondingly by 31%, at aircraft level, a fuel burn reduction of 15.2% could be shown for regional operations relative to year 2025 engine technology. The concept is capable of meeting the emission reduction targets for CO2 and NOx aspired to by the LEMCOTEC project and the Strategic Research and Innovation Agenda (SRIA) targets for CO2 in 2035, and for NOx in 2050.

Performance Investigation of Cycle-Integrated Parallel Hybrid Turboshafts

Motivated by long term target settings for research and innovation in Europe and in North America initial investigations of parallel hybrid electric power plant systems have already shown a significant fuel reduction potential for the transport aircraft. Within the classical parallel hybrid topology, an electric motor assists the gas turbine by suppling mechanical power to the power shaft. In this paper, the implications of a more sophisticated parallel hybrid variant, namely the CycleIntegrated Parallel Hybrid (CIPH) is investigated with regard to an advanced turboshaft engine application for helicopters. For this purpose several compressor stages of a baseline turboshaft (TS) power plant, and, are thereby decoupled from the turbine section offering an independent drive and control of the compressor stages. The baseline power plant of the investigated concept is derived for a 12-ton-helicopter accommodating 19 passengers on a 450nm mission. It consists of an axialcentrifugal compressor powered by the high pressure turbine, and, a free low pressure (power) turbine delivering a maximum power of 3300 kW at constant rotational speed. For the presented study the axial compressor section is electrified with the help of linear electric motors mounted at the blade tips. Due to the implications of the electric motor counter rotating stages are considered most appropriate for the design and performance investigations. The electric motor energy is supplied by a power management and distribution system with built-in redundancies, and, energy storage via batteries are taken into account. A hybrid electric topology can be easily characterized by the degree of power hybridization, HP, being defined as the ratio of installed electric power to the total power installed. With this configuration a CIPH TS with a HP of 19.7% is identified to be a suitable solution. With the implementation of electric power within the cycle, an additional degree of freedom controlling the power plant can be established. During part load conditions a power specific fuel consumption improvement of over 45% and an increase in overall efficiency of more than 90% compared to the conventional TS was found. The investigation of the usable part load range has shown that the maximum installed electric power imposes an additional limiting factor. At the vehicular level, a retrofitted version of the reference helicopter equipped with the CIPH turboshaft features a range reduction of more than 50%, but simultaneously offering an energy reduction potential of over 28% and a CO2 reduction potential of over 42%. NOMENCLATURE APSS Advanced Propulsion System Synthesis CIPH Cycle-Integrated Parallel Hybrid DC Direct Current E-BREAK Engine Breakthrough Components and Subsystems EIS Entry Into Service EPS Energy and Power System HP Degree of Power Hybridization HPT High Pressure Turbine ISA International Standard Atmosphere LEM Linear Electric Motor

Efforts to improve aero engine performance through the optimal design of heat recuperation systems targeting fuel consumption and pollutant emissions reduction

The present work is focused on the conceptual development and numerical assessment of various new heat recuperation system configurations, specifically designed and optimized for a state-of-the-art turbofan application developed by MTU Aero Engines AG. The optimization efforts were performed through CFD computations, experimental measurements and aero engine thermodynamic cycle analysis. A critical part of the optimization phase was conducted using a customizable numerical tool modelling the recuperation system heat transfer and pressure loss characteristics and including the effect of important heat exchanger design decisions. The numerical tool was based on an advanced porosity model approach in which the heat exchangers macroscopic behaviour was included through the integration of predefined heat transfer and pressure loss correlations, calibrated through CFD computations and experimental measurements. The optimization led to two new recuperation configurations with significant improvements regarding the aero engine fuel consumption and pollutant emissions reduction providing direct environmental and economic benefits.

Thermodynamics Cycle Analysis, Pressure Loss and Heat Transfer Assessment of a Recuperative System for Aero Engines

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).Copyright