Konstantinos Kyprianidis

Assessment of Future Aero-engine Designs With Intercooled and Intercooled Recuperated Cores

Reduction in CO2 emissions is strongly linked with the improvement of engine specific fuel consumption, as well as the reduction in engine nacelle drag and weight. Conventional turbofan designs, however, that reduce CO2 emissions—such as increased overall pressure ratio designs—can increase the production of NOx emissions. In the present work, funded by the European Framework 6 collaborative project NEW Aero engine Core concepts (NEWAC), an aero-engine multidisciplinary design tool, Techno-economic, Environmental, and Risk Assessment for 2020 (TERA2020), has been utilized to study the potential benefits from introducing heat-exchanged cores in future turbofan engine designs. The tool comprises of various modules covering a wide range of disciplines: engine performance, engine aerodynamic and mechanical design, aircraft design and performance, emissions prediction and environmental impact, engine and airframe noise, as well as production, maintenance and direct operating costs. Fundamental performance differences between heat-exchanged cores and a conventional core are discussed and quantified. Cycle limitations imposed by mechanical considerations, operational limitations and emissions legislation are also discussed. The research work presented in this paper concludes with a full assessment at aircraft system level that reveals the significant potential performance benefits for the intercooled and intercooled recuperated cycles. An intercooled core can be designed for a significantly higher overall pressure ratio and with reduced cooling air requirements, providing a higher thermal efficiency than could otherwise be practically achieved with a conventional core. Variable geometry can be implemented to optimize the use of the intercooler for a given flight mission. An intercooled recuperated core can provide high thermal efficiency at low overall pressure ratio values and also benefit significantly from the introduction of a variable geometry low pressure turbine. The necessity of introducing novel lean-burn combustion technology to reduce NOx emissions at cruise as well as for the landing and take-off cycle, is demonstrated for both heat-exchanged cores and conventional designs. Significant benefits in terms of NOx reduction are predicted from the introduction of a variable geometry low pressure turbine in an intercooled core with lean-burn combustion technology.

Future Aero Engine Designs : An Evolving Vision

Gas turbine engines will still represent a key technology in the next 20-year energy scenarios, either in stand-alone applications or in combination with other power generation equipment. This book intends in fact to provide an updated picture as well as a perspective vision of some of the major improvements that characterize the gas turbine technology in different applications, from marine and aircraft propulsion to industrial and stationary power generation. Therefore, the target audience for it involves design, analyst, materials and maintenance engineers. Also manufacturers, researchers and scientists will benefit from the timely and accurate information provided in this volume. The book is organized into five main sections including 21 chapters overall: (I) Aero and Marine Gas Turbines, (II) Gas Turbine Systems, (III) Heat Transfer, (IV) Combustion and (V) Materials and Fabrication.

EVA: A Tool for Environmental Assessment of Novel Propulsion Cycles

This paper presents the development of a tool for EnVironmental Assessment (EVA) of novel propulsion cycles implementing the Technoeconomical Environmental and Risk Analysis (TERA) approach. For nearly 3 decades emissions certification and legislation has been mainly focused on the landing and take-off cycle. Exhaust emissions measurements of NOx, CO and unburned hydrocarbons are taken at Sea Level Static (SLS) conditions for 4 different power settings (idle, descent, approach and take-off) and are consecutively used for calculating the total emissions during the ICAO landing and take-off cycle. With the global warming issue becoming ever more important, stringent emissions legislation is soon to follow, focusing on all flight phases of an aircraft. Unfortunately, emissions measurements at altitude are either extremely expensive, as in the case of altitude test facility measurements, or unrealistic, as in the case of direct in flight measurements. Compensating for these difficulties, various existing methods can be used to estimate emissions at altitude from ground measurements. Such methods, however, are of limited help when it comes to assessing novel propulsion cycles or existing engine configurations with no SLS measurements available. The authors are proposing a simple and fast method for the calculation of SLS emissions, mainly implementing ICAO exhaust emissions data, corrections for combustor inlet conditions and technology factors. With the SLS emissions estimated, existing methods may be implemented to calculate emissions at altitude. The tool developed couples emissions predictions and environmental models together with engine and aircraft performance models in order to estimate the total emissions and Global Warming Potential of novel engine designs during all flight phases (i.e. the whole flight cycle). The engine performance module stands in the center of all information exchange. In this study, EVA and the described emissions prediction methodology have been used for the preliminary design analysis of three spool high bypass ratio turbofan engines. The capability of EVA to radically explore the design space available in novel engine configurations, while accounting for fuel burn and global warming potential during the whole flight cycle of an aircraft, is illustrated.

Multidisciplinary Analysis of a Geared Fan Intercooled Core Aero-Engine

The reduction of CO2 emissions is strongly linked with the improvement of engine specific fuel consumption, along with the reduction of engine nacelle drag and weight. One alternative design approach to improving specific fuel consumption is to consider a geared fan combined with an increased overall pressure ratio intercooled core performance cycle. The thermal benefits from intercooling have been well documented in the literature. Nevertheless, there is very little information available in the public domain with respect to design space exploration of such an engine concept when combined with a geared fan. The present work uses a multidisciplinary conceptual design tool to analyze the option of an intercooled core geared fan aero engine for long haul applications with a 2020 entry into service technology level assumption. With minimum mission fuel in mind, the results indicate as optimal values a pressure ratio split exponent of 0.38 and an intercooler mass flow ratio of 1.18 at hot-day top of climb conditions. At ISA midcruise conditions a specific thrust of 86 m/s, a jet velocity ratio of 0.83, an intercooler effectiveness of 56%, and an overall pressure ratio value of 76 are likely to be a good choice. A 70,000 lbf intercooled turbofan engine is large enough to make efficient use of an all-axial compression system, particularly within a geared fan configuration, but intercooling is perhaps more likely to be applied to even larger engines. The proposed optimal jet velocity ratio is actually higher than the value one would expect by using standard analytical expressions, primarily because this design variable affects core efficiency at midcruise due to a combination of several different subtle changes to the core cycle and core component efficiencies at this condition. The analytical expressions do not consider changes in core efficiency and the beneficial effect of intercooling on transfer efficiency, nor do they account for losses in the bypass duct and jet pipe, while a relatively detailed engine performance model, such as the one utilized in this study, does. Mission fuel results from a surrogate model are in good agreement with the results obtained from a rubberized-wing aircraft model for some of the design parameters. This indicates that it is possible to replace an aircraft model with specific fuel consumption and weight penalty exchange rates. Nevertheless, drag count exchange rates have to be utilized to properly assess changes in mission fuel for those design parameters that affect nacelle diameter.

Optimization Study of an Intercooled Recuperated Aero-Engine

The design space of an intercooled recuperated aero-engine has been explored using detailed engine and aircraft performance, weight, and dimensions modeling. The design parameters of the engine fan, core, intercooler, recuperator, cooling-air ratio, and variable-geometry settings for the low-pressure turbine have been optimized for minimum mission fuel. Analysis shows that the improvement achieved in terms of performance against the datum design can be attributed primarily to an increase in thermal efficiency. A parametric study has also been carried out around the optimal design to understand the impact of the chosen design parameters on mission fuel burn. The study demonstrates in detail the substantially more complex interrelationship that the different fan design parameters have in terms of engine performance compared to what is typical for conventional turbofan designs. Furthermore, the optimal pressure ratio split between the low-pressure compressor and the high-pressure compressor aligns well with a previous analytical study. It is also revealed that the increased amount of cooling air required when a hot bleeding concept is adopted is in fact beneficial for mission fuel burn. Finally, the study concludes that the potential of using variable geometry in the low-pressure turbine for improving fuel burn is limited by the high-pressure turbine blade-metal temperature.

On Intercooled Turbofan Engines

Public awareness and political concern over the environmental impact of the growth in civil aviation over the past 30 years have intensified industry efforts to address CO2 emissions [5]. CO2 emissions are directly proportional to aircraft fuel burn and one way to minimise the latter is by having engines with reduced Specific Fuel Consumption (SFC) and installations that minimise nacelle drag and weight. Significant factors affecting SFC are propulsive efficiency and thermal efficiency. Propulsive efficiency has been improved by designing turbofan engines with bigger fans to give lower specific thrust (net thrust divided by fan inlet mass flow) until increased engine weight and nacelle drag have started to outweigh the benefits. Thermal efficiency has been improved mainly by increasing the Overall Pressure Ratio (OPR) and Turbine Entry Temperature (TET) to the extent possible with new materials and design technologies.

Conceptual Design and Mission Analysis for a Geared Turbofan and an Open Rotor Configuration

In this multidisciplinary study a geared open rotor configuration is assessed and compared to an ultra high bypass ratio geared turbofan engine. Both designs assume a 2020 entry into service level of technology. The specific thrust level for minimizing block fuel and the resulting engine emissions for a given mission is sought. The tool used contains models that effectively capture: engine performance, mechanical and aerodynamic design, engine weight, emissions, aircraft design and performance as well as direct operating costs. nThe choice of specific thrust is a complex optimization problem and several disciplines need to be considered simultaneously. It will be demonstrated, through multidisciplinary analysis, that the open rotor concept can offer a substantial fuel saving potential, compared to ducted fans, for a given set of design considerations and customer requirements.

Dynamic performance investigations of a turbojet engine using a cross-application visual oriented platform

This paper presents the development of visual oriented tools for the dynamic performance simulation of a turbojet engine using a cross-application approach. In particular, the study focuses on the feasibility of developing simulation models using different programming environments and linking them together using a popular spreadsheet program. As a result of this effort, a low fidelity cycle program has been created, capable of being integrated with other performance models. The amount of laboratory sessions required for student training during an educational procedure, for example for a course in gas turbine performance simulation, is greatly reduced due to the familiarity of most students with the spreadsheet software. The model results have been validated using commercially available gas turbine simulation software and experimental data from open literature. The most important finding of this study is the capability of the program to link to aircraft performance models and predict the transient working line of the engine for various initial conditions in order to dynamically simulate flight phases including take-off and landing.

On the trade-off between minimum fuel burn and maximum time between overhaul for an intercooled aeroengine

A large variety of promising power and propulsion system concepts are being proposed to reduce carbon dioxide and other emissions. However, the best candidate to pursue is difficult to select and it is imperative that major investments are correctly targeted to deliver environmentally friendly, economical and reliable solutions. To conceive and assess gas turbine engines with minimum environmental impact and lowest cost of ownership in a variety of emission legislation scenarios and emissions taxation policies, a tool based on a techno-economic and environmental risk assessment methodology is required. A tool based on this approach has been developed by the authors. The core of the tool is a detailed and rigorous thermodynamic representation of power plants, around which other modules can be coupled (that model different disciplines such as aircraft performance, economics, emissions, noise, weight and cost) resulting in a multidisciplinary framework. This approach can be used for efficient and cost-effective design space exploration in the civil aviation, power generation, marine, and oil and gas fields. In the present work, a conceptual intercooled core aeroengine design was assessed with component technologies consistent with 2020 entry into service via a multidisciplinary optimisation approach. Such an approach is necessary to assess the trade-off between asset life, operating costs and technical specification. This paper examines the influence of fuel consumption, engine weight and direct operating costs with respect to extending the engine life. The principal modes of failure such as creep, fatigue and oxidation, are considered in the engine life estimation. Multidisciplinary optimisation, comprising the main engine design parameters, was carried out with maximum time between overhaul as the objective function. The trade-off between minimum block fuel burn and maximum engine life was examined; the results were compared against the initial engine design and an assessment was made to identify the design changes required for obtaining an improved engine design in terms of direct operating costs. The results obtained from the study demonstrate that an engine optimised for maximum time between overhaul requires a lower overall pressure ratio and specific thrust but this comes at the cost of lower thermal efficiency and higher engine production costs.

Applications of near-infrared spectroscopy (NIRS) in biomass energy conversion processes : A review

ABSTRACT Biomass used in energy conversion processes is typically characterized by high variability, making its utilization challenging. Therefore, there is a need for a fast and non-destructive method to determine feedstock/product properties and directly monitor process reactors. The near-infrared spectroscopy (NIRS) technique together with advanced data analysis methods offers a possible solution. This review focuses on the introduction of the NIRS method and its recent applications to physical, thermochemical, biochemical and physiochemical biomass conversion processes represented mainly by pelleting, combustion, gasification, pyrolysis, as well as biogas, bioethanol, and biodiesel production. NIRS has been proven to be a reliable and inexpensive method with a great potential for use in process optimization, advanced control, or product quality assurance.