Optimizing Separate Exhaust Turbofans for Cruise Specific Fuel Consumption

2017 ◽  
Vol 139 (12) ◽  
Author(s):  
Syed J. Khalid
Keyword(s):  
Fuel Consumption ◽  
Control Algorithm ◽  
Velocity Ratio ◽  
Transmission Efficiency ◽  
Specific Fuel Consumption ◽  
Variable Geometry ◽  
Nozzle Throat ◽  
Propulsive Efficiency ◽  
Turbofan Engines ◽  
Bypass Ratio

Cruise specific fuel consumption (SFC) of turbofan engines is a key metric for increasing airline profitability and for reducing CO2 emissions. Although increasing design bypass ratio (BPR) of separate exhaust turbofan configurations improves cruise SFC, further improvements can be obtained with online control actuated variable geometry modulations of bypass nozzle throat area, core nozzle throat area, and compressor variable vanes (CVV/CVG). The scope of this paper is to show only the benefits possible, and the process used in determining those benefits, and not to suggest any particular control algorithm for searching the best combination of the control effectors. A parametric cycle study indicated that the effector modulations could increase the cruise BPR, core efficiency, transmission efficiency, propulsive efficiency, and ideal velocity ratio resulting in a cruise SFC improvement of as much as 2.6% depending upon the engine configuration. The changes in these metrics with control effector variations will be presented. Scheduling of CVV is already possible in legacy digital controls; perturbation to this schedule and modulation of nozzle areas should be explored in light of the low bandwidth requirements at steady-state cruise conditions.

Optimizing Separate Exhaust Turbofans for Cruise Specific Fuel Consumption

2016 ◽  
Author(s):  
Syed Khalid
Keyword(s):  
Fuel Consumption ◽  
Control Algorithm ◽  
Velocity Ratio ◽  
Transmission Efficiency ◽  
Specific Fuel Consumption ◽  
Variable Geometry ◽  
Nozzle Throat ◽  
Propulsive Efficiency ◽  
Turbofan Engines ◽  
Bypass Ratio

Cruise specific fuel consumption (SFC) of turbofan engines is a key metric for increasing airline profitability and for reducing CO2 emissions. Although increasing design bypass ratio (BPR) of separate exhaust turbofan configurations improves cruise SFC, further improvements can be obtained with control actuated variable geometry modulations of core nozzle throat area, bypass nozzle throat area, and compressor variable vanes (CVV). The scope of this paper is to show only the benefits possible, and the process used in determining those benefits, and not to suggest any particular control algorithm for searching the best combination of the control effectors. A parametric cycle study indicated that the effector modulations could increase the cruise BPR, core efficiency, transmission efficiency, propulsive efficiency, and ideal velocity ratio resulting in a cruise SFC improvement of as much as 2.6% depending upon the engine configuration. The changes in these metrics with control effector variations will be presented. Modulation of CVV is already possible in legacy digital controls, and modulation of nozzle areas should be explored in light of the low bandwidth requirements at steady-state cruise conditions.

Cycle Optimization of Mixed High Bypass Turbofan

2014 ◽  
Author(s):  
Adel Ghenaiet
Keyword(s):  
Fuel Consumption ◽  
Engine Performance ◽  
Feasibility Studies ◽  
Specific Fuel Consumption ◽  
Design Parameters ◽  
Optimization Approach ◽  
Propulsive Efficiency ◽  
Turbofan Engines ◽  
Passenger Aircraft ◽  
Analytical Expressions

This paper presents a parametric study and an optimization approach, targeting the design of optimum mixed turbofan engines employed by long-range passenger aircraft. The first part of this paper concerns a parametric analysis carried out with the aim of highlighting the effects of principal design criteria on engine performance in terms of specific thrust and specific fuel consumption. The second part deals with the optimization to find the design parameters concurrently minimizing the specific fuel consumption at cruise. The backbone of the optimization approach consists of a genetic algorithm and a developed engine performance analysis method for both design point and off-design operations. This latter employs closed form analytical expressions instead of numerical solution using pre-defined components’ maps. This approach is deemed sufficient for simple feasibility studies carried out during the course of conceptual and preliminary designs. The strong coupling between the core and bypass streams has constrained the range of physical properties and reduced the space of search for the optimum. The results show possible benefits from utilizing the mixing of gases and a common propelling nozzle, which in some cases may increase the propulsive efficiency.

scholarly journals Study of Bypass Ratio Increasing Possibility for Turbofan Engine and Turbofan with Inter Turbine Burner

2019 ◽  
Vol 26 (2) ◽  
pp. 61-68
Author(s):  
Robert Jakubowski
Keyword(s):  
Fuel Consumption ◽  
Energy Input ◽  
Pressure Ratio ◽  
Specific Fuel Consumption ◽  
Additional Energy ◽  
Fast Analysis ◽  
Turbofan Engine ◽  
Turbofan Engines ◽  
Specific Thrust ◽  
Bypass Ratio

Abstract Current trends in the high bypass ratio turbofan engines development are discussed in the beginning of the paper. Based on this, the state of the art in the contemporary turbofan engines is presented and their change in the last decade is briefly summarized. The main scope of the work is the bypass ratio growth analysis. It is discussed for classical turbofan engine scheme. The next step is presentation of reach this goal by application of an additional combustor located between high and low pressure turbines. The numerical model for fast analysis of bypass ratio grows for both engine kinds are presented. Based on it, the numerical simulation of bypass engine increasing is studied. The assumption to carry out this study is a common core engine. For classical turbofan engine bypass ratio grow is compensated by fan pressure ratio reduction. For inter turbine burner turbofan, bypass grown is compensated by additional energy input into the additional combustor. Presented results are plotted and discussed. The main conclusion is drawing that energy input in to the turbofan aero engine should grow when bypass ratio is growing otherwise the energy should be saved by other engine elements (here fan pressure ratio is decreasing). Presented solution of additional energy input in inter turbine burner allow to eliminate this problem. In studied aspect, this solution not allows to improve engine performance. Specific thrust of such engine grows with bypass ratio rise – this is positive, but specific fuel consumption rise too. Classical turbofan reaches lower specific thrust for higher bypass ratio but its specific fuel consumption is lower too. Specific fuel consumption decreasing is one of the goal set for future aero-engines improvements.

Multidisciplinary Analysis of a Geared Fan Intercooled Core Aero-Engine

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
Konstantinos G. Kyprianidis ◽  
Andrew M. Rolt ◽  
Tomas Grönstedt
Keyword(s):  
Exchange Rates ◽  
Fuel Consumption ◽  
Pressure Ratio ◽  
Velocity Ratio ◽  
Specific Fuel Consumption ◽  
Design Parameters ◽  
Aircraft Model ◽  
Aero Engine ◽  
Jet Velocity ◽  
Analytical Expressions

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 mid-cruise 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.

Analyses and Optimization of a Propulsion Cycle for Unmixed High Bypass Turbofan

2008 ◽  
Author(s):  
Adel Ghenaiet
Keyword(s):  
Fuel Consumption ◽  
Pressure Ratio ◽  
Specific Fuel Consumption ◽  
Design Parameters ◽  
Inlet Temperature ◽  
Turbine Inlet Temperature ◽  
High Pressure Ratio ◽  
Turbine Inlet ◽  
Design Variables ◽  
Bypass Ratio

This paper deals with a parametric study and an optimization for the design variables of a high bypass unmixed turbofan equipping commercial aircrafts. The objective of the first part of this study is to highlight the effects of the principal design parameters (bypass ratio, compression ratios, turbine inlet temperature etc..) on the uninstalled performance, in terms of specific thrust and specific fuel consumption. The second part concerns the optimization, aiming at finding the optimum design parameters concurrently minimizing the specific fuel consumption at cruise, and meeting the thrust requirement at takeoff. The cycle analyzer (on-design and off-design) as coupled to the optimization algorithm MMFD by adopting a random multi-starts search strategy is shown to be stable and converging. The predefined requirements and constraints have dictated utilizing an engine with a high-bypass ratio, high-pressure ratio and a moderate turbine inlet temperature. In general, the obtained results compare fairly well with typical data available for an equivalent ‘reference’ engine. This elaborated methodology is shown to be consistent with the conceptual design requirements and accuracy, because, it does not use components’ characteristics, and operates on simplifying assumptions. This present methodology can be readily adapted for other configurations of aero-engines as well, and easily integrated in a multi-disciplinary design approach.

Fundamental Differences Between Conventional and Geared Turbofans

2009 ◽  
Author(s):  
Joachim Kurzke
Keyword(s):  
Fuel Consumption ◽  
Real Option ◽  
Pressure Ratio ◽  
Thermodynamic Cycle ◽  
Specific Fuel Consumption ◽  
Thermodynamic Efficiency ◽  
Aircraft Engines ◽  
Direct Drive ◽  
Significant Difference ◽  
Bypass Ratio

The potential for improving the thermodynamic efficiency of aircraft engines is limited because the aerodynamic quality of the turbomachines has already achieved a very high level. While in the past increasing burner exit temperature did contribute to better cycle efficiency, this is no longer the case with today’s temperatures in the range of 1900...2000K. Increasing the cycle pressure ratio above 40 will yield only a small fuel consumption benefit. Therefore the only way to improve the fuel efficiency of aircraft engines significantly is to increase bypass ratio — which yields higher propulsive efficiency. A purely thermodynamic cycle study shows that specific fuel consumption decreases continuously with increasing bypass ratio. However, thermodynamics alone is a too simplistic view of the problem. A conventional direct drive turbofan of bypass ratio 6 looks very different to an engine with bypass ratio 10. Increasing bypass ratio above 10 makes it attractive to design an engine with a gearbox to separate the fan speed from the other low pressure components. Different rules apply for optimizing turbofans of conventional designs and those with a gearbox. This paper describes various criteria to be considered for optimizing the respective engines and their components. For illustrating the main differences between conventional and geared turbofans it is assumed that an existing core of medium pressure ratio with a two stage high pressure turbine is to be used. The design of the engines is done for takeoff rating because this is the mechanically most challenging condition. For each engine the flow annulus is examined and stress calculations for the disks are performed. The result of the integrated aero-thermodynamic and mechanical study allows a comparison of the fundamental differences between conventional and geared turbofans. At the same bypass ratio there will be no significant difference in specific fuel consumption between the alternative designs. The main difference is in the parts count which is much lower for the geared turbofan than for the conventional engine. However, these parts will be mechanically much more challenging than those of a conventional turbofan. If the bypass ratio is increased significantly above 10, then the geared turbofan becomes more and more attractive and the conventional turbofan design is no longer a real option. The maximum practical bypass ratio for ducted fans depends on the nacelle drag and how the installation problems can be solved.

scholarly journals ANALYSIS OF THE EFFECT OF BYPASS RATIO ON PERFORMANCE ENGINE CFM56-5A1 IN CRUISING CONDITIONS

Vortex ◽  
2020 ◽  
Vol 1 (1) ◽  
pp. 39
Author(s):  
Opri Surya Yustinoto
Keyword(s):  
Fuel Consumption ◽  
Engine Performance ◽  
Specific Fuel Consumption ◽  
Bypass Ratio ◽  
Consumption Value

The value of engine performance is known to decrease and increase with increasing and decreasing variation of the value of the parameter bypass ratio, so that if the value of these parameters is greater, then the fuel consumption when the aircraft operates will be less and the thrust will decrease. In addition to changing the value of the specific fuel consumption due to the influence of the bypass value, variations in altitude are also very influential where the higher the aircraft, the resulting specific fuel consumption value will be smaller 

scholarly journals ОСОБЕННОСТИ РАСЧЕТА И РЕГУЛИРОВАНИЯ ДВУХКОНТУРНОГО ТУРБОРЕАКТИВНОГО ДВИГАТЕЛЯ С ФОРСАЖНОЙ КАМЕРОЙ СГОРАНИЯ В НАРУЖНОМ КОНТУРЕ НА ПРЯМОТОЧНЫХ РЕЖИМАХ РАБОТЫ

2020 ◽  
pp. 15-23
Author(s):  
Олег Владимирович Кислов ◽  
Михаил Анатольевич Шевченко
Keyword(s):  
Mathematical Model ◽  
Fuel Consumption ◽  
Control Program ◽  
Critical Section ◽  
Specific Fuel Consumption ◽  
Outlet Section ◽  
Nozzle Outlet ◽  
Turbofan Engine ◽  
Turbofan Engines ◽  
Ramjet Engines

A promising direction in aviation is the creation of anaircraft for supersonic cruise speeds (Mach 3...4). It is known that ramjet engines are more preferable for Mach numbers larger 3. However, they do not have starting thrust and uneconomical at subsonic flight speeds. At the same time, at subsonic flight speeds, turbofan engines are the most expedient. The combination of the positive properties of turbofan engines at subsonic speeds and a ramjet engines at supersonic speeds is possible by using duct-burning turbofan engine, which can operate at the ramjet mode with the blocked gas turbine duct at supersonic flight conditions. At this mode, duct-burning turbofan engine turns into ramjet engine, which, however, has special features due to the presence of fan in front of the combustion chamber, which operates in turbine mode or in zero power mode and also because of the outlet jet, which has annular shape, flows out from the duct causes the appearance of bottom drag. The presence of bottom drag requires both the development of a mathematical model for its calculation and taking into account its influence on the choice of the control law for the nozzle outlet area. The article presents a mathematical model of the working process of duct-burning turbofan engine at ramjet mode, taking into account the presence of fan in the flow path and bottom drug. Using the developed mathematical model, the regularities of changes in the internal and effective thrust, as well as the specific fuel consumption, depending on the relative fuel consumption and the critical section of the nozzle at a given altitude and flight speed are established. The critical section of the nozzle is the main regulating factor, and the relative fuel consumption is related to the main regulating factor - the fuel consumption. These patterns are useful for choosing a control program.There is such a combination of regulating factors whichprovides two extremes in the regularities of trust and specific fuel consumption changes: the mode of minimum specific fuel consumption and the mode of maximum thrust. In addition, the influence of gas underexpansion in the nozzle on the thrust-economic parameters of the engine and the required area of the nozzle outlet section were estimated. The obtained regularities are advisable to use when engine control program is chosen.

Feasibility Study of Some Novel Concepts for High Bypass Ratio Turbofan Engines

2009 ◽  
Author(s):  
Dipanjay Dewanji ◽  
G. Arvind Rao ◽  
Jos van Buijtenen
Keyword(s):  
Fuel Consumption ◽  
Substantial Reduction ◽  
Substantial Improvement ◽  
Fuel Price ◽  
Turbofan Engine ◽  
Turbofan Engines ◽  
Fuel Flow ◽  
Blade Tip ◽  
Fan Blade ◽  
Bypass Ratio

The soaring fuel price and the burgeoning environmental concerns have compelled global research towards cleaner engines, aimed at substantial reduction in emission, noise and fuel consumption. In this context, the present research investigates the feasibility of some novel engine concepts, namely Geared Turbofan and Intercooled Recuperated Turbofan concepts, by hypothetically applying them into an existing state-of-the-art high bypass ratio engine. This paper made an effort to estimate the effects on the baseline engine performances due to the introduction of these two concepts into it. By performing steady state simulations, it was found that the incorporation of the Geared Turbofan concept into the existing Turbofan engine caused a significant reduction in thrust specific fuel consumption, engine weight, and fan blade tip speed. However, when simulations were also carried out by incorporating the Intercooler and Recuperator concept in the baseline turbofan engine, it did not demonstrate any substantial improvement in fuel consumption. It was observed that the fuel flow rate was influenced to a large extent by heat exchanger’s effectiveness and the pressure drop within it. The overall engine weight was also found to get increased due to the inclusion of massive heat exchangers necessary for the system.

scholarly journals The Potential of Sequential Combustion for High Bypass Jet Engines

1998 ◽  
Author(s):  
Konrad Vogeler
Keyword(s):  
Fuel Consumption ◽  
Specific Fuel Consumption ◽  
Maximum Pressure ◽  
Jet Engines ◽  
Gas Temperature ◽  
Core Mass ◽  
New Family ◽  
Fuel Flow ◽  
Lp Turbine ◽  
Bypass Ratio

ABB has designed a new family of industrial gasturbines for power generation using a Sequential Combustion Cycle (SCC) on a large single shaft engine. This concept allows considerable increase in power density and efficiency by only increasing pressure without raising the maximum hot gas temperature of the cycle. Instead a second combustion after an HP-turbine is used to reheat the gas before the final expansion in an LP-turbine. This concept is applied to the analysis of a high bypass ratio jet engine. In an engine with a single combustor, thrust is a function of bypass ratio and the combination of maximum pressure and temperature in the cycle. The proposed SCC allows increased thrust without pushing technology on materials and cooling. A modern twin spool engine is taken as reference. When total inlet massflow is kept constant, increasing bypass ratio decreases core mass flow. This limits the fuel flow for the HP-spool and hence total energy input to the engine. Introduction of the SCC gives another parameter of freedom to the cycle design. However the twin spool concept is now a disadvantage. The low fuel flow for the HP-spool due to high bypass ratio means there is not enough energy available to build up the necessary pressure for an economical expansion in the LP-turbine after the second combustion. Specific fuel consumption will be unacceptable. It is proposed to apply the SCC concept in a single spool engine with a geared fan. Both turbines can now support the compression. The fan is operated as a constant speed propeller with variable blade pitch. This engine concept allows for a given inlet massflow a substantially higher bypass ratio and hence decreases specific fuel consumption while specific thrust can be kept on a level which will be considerably higher than it would be in todays engines with comparable bypass ratio.

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