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at SciVerse ScienceDirect Energy 58 (2013) 550e560 Contents lists available Energy journal homepage: www.elsevier .com/locate/energy Exergo-sustainability indicators of a turboprop aircraft for the phases of a flight Hakan Aydın a, Önder Turan b,*, T. Hikmet Karakoç b, Adnan Midilli c a TUSAŞ Engine Industries, Eskisehir, Turkey b Faculty of Aeronautics and Astronautics, Anadolu University TR-26470 Eskisehir, Turkey c Energy Division, Department of Mechanical Engineering, Faculty of Engineering, Recep Tayyip Erdo�gan University, Rize 53100, Turkey a r t i c l e i n f o Article history: Received 19 February 2013 Received in revised form 5 April 2013 Accepted 7 April 2013 Available online 29 June 2013 Keywords: Exergy Sustainability Energy: aviation Turboprop Environment * Corresponding author. Tel.: þ90 222 3350580; fa E-mail addresses: tei.hakan@gmail.com (H. Aydın) science.onder.turan@gmail.com (Ö. Turan), (T.H. Karakoç), adnan.midilli@erdogan.edu.tr (A. Midi 0360-5442/$ e see front matter Crown Copyright � http://dx.doi.org/10.1016/j.energy.2013.04.076 a b s t r a c t One of the key challenges for sustainable aviation is to reduce global and local environmental impacts. The scope of this study is analysed and discussed in detail for better understanding of sustainability performances of a turboprop aircraft. In this regard, this study presents exergetic sustainability indicators of the turboprop engine for eight flight phases. The results show that exergetic efficiency approaches a maximum value to be 29.2%, waste exergy ratio (to be 70.8%), exergetic destruction ratio (to be 0.41) and environmental effect factor (to be 2.43) become minimum values, whereas exergetic sustainability index approaches a maximum value (to be 0.41). The phases of taxi and landing for the turboprop aircraft have minimum exergy efficiency (to be 20.6%) and minimum exergetic sustainability index (to be 0.26). Accordingly, the exergetic efficiency, waste exergy ratio and exergetic sustainability index of the aircraft are reasonably well in the climb, maximum cruise/continuous, normal/maximum take-off and APR (automatic power reverse) phases. Finally, it is supposed that studying exergetic indicators for an aircraft enables how much improvement is possible for aircraft engines to achieve better sustainable aviation. Crown Copyright � 2013 Published by Elsevier Ltd. All rights reserved. 1. Introduction Energy is an important tool for the sustainable development and environmental sustainability. In the last decade, the need for en- ergy sustainability is rapidly increasing in theworld, which is called a solution of ecological, economical and developmental problems. In this regard, sustainable development demands a sustainable supply of energy at reasonable cost, and can be utilized without causing negative environmental impacts. Therefore, energy con- sumption plays a crucial role to achieve sustainable development; balancing economic and social development. Consequently, the potential usefulness of energy analysis in addressing sustainability issues is substantial [1e6]. Energy and exergy concepts have been utilized to ensure the environmental, economic and social sustainability. In order to reduce the negative impacts created by the pollutant emissions, the energy sources should be efficiently utilized. If one wants to approach environmental considerations incorporated with x: þ90 222 3221619. , onderturan@anadolu.edu.tr, hikmetkarakoc@gmail.com lli). 2013 Published by Elsevier Ltd. All sustainability and thermodynamics, there are twomethods: energy analysis through the first-law of thermodynamics and exergy analysis through the second-law of thermodynamics [2]. Many engineers and scientists suggest that the thermodynamic perfor- mance is best evaluated using exergy analysis [6]. Wall [7] sug- gested exergy as a suitable measure of environmental impact of waste emissions. Exergy as the thermodynamic departure between a substance and its surrounding has been gradually accepted as a unified measure for the environmental impact of waste emissions [8e11]. The exergy of an emission to the environment, therefore, is a measure of the potential of the emission to change or impact the environment. The exergy of an emission is zero only when it is in equilibrium with the environment and thus benign. These points suggest that exergy may be, or provide the basis for, an effective indicator of the potential of an emission to impact the environment [5]. There have been various assessments used for waste gases emitted from transportation sectors as well [12,13]. The importance of energy efficiency for sustainable aviation is also linked to environmental problems, such as global warming, noise problem and atmospheric pollution. Passenger traffic in aviation sector around the world will average 5.1% growth and cargo traffic will average 5.6% growth [14e18]. Effects of energy consumption in aviation sector give rise to potential environmental hazards [19,20]. Emissions from aviation currently account for only rights reserved. Delta:1_given name Delta:1_surname Delta:1_given name Delta:1_surname mailto:tei.hakan@gmail.com mailto:onderturan@anadolu.edu.tr mailto:science.onder.turan@gmail.com mailto:hikmetkarakoc@gmail.com mailto:adnan.midilli@erdogan.edu.tr http://crossmark.dyndns.org/dialog/?doi=10.1016/j.energy.2013.04.076&domain=pdf www.sciencedirect.com/science/journal/03605442 http://www.elsevier.com/locate/energy http://dx.doi.org/10.1016/j.energy.2013.04.076 http://dx.doi.org/10.1016/j.energy.2013.04.076 http://dx.doi.org/10.1016/j.energy.2013.04.076 H. Aydın et al. / Energy 58 (2013) 550e560 551 a small proportion of GHG (global greenhouse gases) emissions, around 2% of global man-made CO2 emissions, however, if the current growth rate of air travel continues, this trend is forecast to grow to around 3% by 2050 [21]. Air transport GHG emissions could be lowered by reducing activity, improving the energy efficiency of transport modes [22e24]. The aviation industry has successfully made consistent, continued efforts to reduce the fuel burn, emis- sions and noise produced by aircraft. Growing focus on emissions and noise along with high fuel prices are favouring turboprops demand growth. In 2010 there were 2080 turboprops in service with an average age of 15 years. By 2030, 2440 new turboprops will be delivered and the total turbo- prop fleet will increase to 3295 aircraft. From 2011 to 2030, 660 new turboprops will be delivered: 41% to replace old aircraft and 59% to support market growth [25]. Between 2010 and 2029, Embraer forecasts that 32% of aircraft deliveries in the 30e120 seat range will be turboprops and Bombardier forecasts that 39% of aircraft deliveries in the 20e99 seat range will be turboprops [26]. The latest technology turboprops will remain an essential part of the world’s regional aircraft fleet. The high fuel prices have high- lighted one of the principal benefits of the twin turboprop over the regional jet: Its low fuel consumption and unrivalled economics on short-haul connections. By using turboprop engines on an aircraft, the following advantages are yielded: a) the engine can be run under more efficient and economical conditions at low and me- dium altitudes b) the amount of power available for propulsion is largely independent of the forward speed of the aircraft. Exergy efficiency is a useful metric for evaluating aircraft envi- ronmental performance. Moreover, technology has a vital role to play in mitigating the environmental impacts of air transport. If so, the most direct way for an airline to improve its fuel efficiency with new aircraft and its components incorporating the latest available technology [27e29]. In this regard, the scientists, researchers, and engineers, who work on useful solutions for the aircraft gas turbine engines, aim at maximizing the energy saving, minimizing the energy consump- tion, and thus, developing the environmentally benign propulsion systems, which isreducing environmental impacts for sustainable aviation. If so, the promotion of the aircraft propulsion systems, such as turboprop engines should become one of the primary goals of designers for airliners, aircraft and aero engine manufacturers. In this regard, it should be emphasized that, in terms of exergo- sustainability, turboprop engines can play an important role to ensure the environmental sustainability in the regional air trans- portation. As a conclusion, in terms of the second-law of thermo- dynamics, minimizing irreversibilities in the turboprop engines also becomes significant challenge for better efficiency, environ- ment and sustainability. Under these important considerations, a detailed literature re- view has been performed on exergy and sustainability analysis [30,31]. The exergy studies related to gas turbine engines have been first done on stationary gas turbines. In the literature, the various exergy and exergo-economic analysis of aero engines have been re- ported [32e43]. In terms of exergy analysis of the turboprop engines, Aydın et al. (2012a, 2012b) examined some exergetic aspects of the CT7 engine. Aircraft selected the CT7 turboprop version of the GE T700 turboshaft engine topower their newSaab340 regional airliner [44]. Aydın et al. [33] measured and calculated operating mass flow rates, inlet and outlet temperatures and pressures, work and power of the turboprop engine and its components. In addition to this, they calculated the inlet and outlet exergy values and exergetic effi- ciencies. They observed that component exergy efficiencies were highly affected by varying shaft torque as a function of free power turbine work. Nevertheless, exergo-sustainability indicators have not beendeveloped for the aircraft gas turbineengines.However, it is also possible to find some applications on exergy-based sustain- ability indicators for different study in the literature [45e60]. How- ever, no studies exist on the sustainability evaluation of the turboprop engine. Therefore, this study is analysed and discussed in detail for better understanding the power turbine shaft torque (or shaft load) effects on the sustainability and environmental perfor- mances of the turboprop aircraft in various flight phases. Lack of sustainability information of the turboprop engine emphasizing the originality of this article is the motivation behind this study. Nowadays there is a great interest in studying the linkages be- tween exergy and sustainability. As differing from the above- mentioned studies, in this study, we bring completely new exer- getic aspects about the turboprop engine to contribute to sustain- ability. For this purpose, some exergetic indicators of the turboprop engine for exergo-sustainability are investigated and discussed by taking into account its flight characteristics. Through a literature review, it is noticed that there is no work to be studied about exergo-sustainability indicators for the turboprop engine in the open literature. Lack of this makes the paper original and becomes main motivation for turboprop, turbojet, turboshaft and turbofan engines and aircrafts during typical flight. Finally, this work including all details on exergo-sustainability of the turboprop engine, aims to contribute to introduce the concepts about exergo-sustainability indicators of a turboprop engine, come up with new exergo-sustainability indicators for the turboprop engine, encourage the use of turboprop engines for ensuring exergo-sustainability and develop sustainability policies on other aircraft propulsion and power systems. 2. Exergo-sustainability indicators for the turboprop engine For better understanding the main operating principle and the main roles of the turboprop engine components, Fig. 1 is illustrated. To develop the exergo-sustainability indicators of the turboprop engine, the first step should be to perform the exergy analysis of the engine by employing the second-law of thermodynamics. Actually, the main objective of this study is not to perform an exergy analysis for a turboprop engine. Such an analysis and more details on the turboprop engine can be found in the literature [32,33]. To inves- tigate the exergo-sustainability aspects of the engine, we first make some assumptions and secondly derive the exergo-sustainability indicators for the turboprop engine. Some assumptions related to the engine are made as follows: i. Dead state conditions are 281 K of temperature and 92.4 kPa of pressure. ii. Kerosene (Jet A-1; chemical formula is C12H23) is selected to be the main fuel for the engine. iii. The combustion process is completely performed. iv. Compressor and turbines are assumed to be adiabatic. v. Cooling air from the compressor (from station 3B) is used for gas turbine (station B1) and power turbine (station B2). Considering the above assumptions, the general exergy balance of a TP (turboprop engine) can be shown in Fig. 2. Considering Fig. 2, the exergy balance of a turboprop engine can be written as X _Ex TP in ¼ X _Ex TP u;out þ X _Ex TP loss þ X _Ex TP dest (1) The following exergo-sustainability indicators can be consid- ered and rearranged for the engine a) Exergy efficiency (hTPex) b) Waste exergy ratio (rTPwex) c) Recoverable exergy rate (rTPrex) Air 1 Axial-centrifugal Compressors (c) Combustor (comb) 3f fuel 3 4.54.1 Gas generator Turbine (gg) Power Turbine (pt) 5 0 B1 B2 3B Propeller gear box Exhaust (exh) Fig. 1. The flow chart of the turboprop engine. H. Aydın et al. / Energy 58 (2013) 550e560552 d) Exergy destruction factor (f TPexd) e) Environmental effect factor (f TPeef ) f) Exergetic sustainability index (QTPesi) 2.1. Exergy efficiency (hTPex ): Exergy efficiency of the turboprop engine will be calculated by dividing the total useful exergy output (shaft power) to the total exergy input should be taken into consideration [1,2,61]. If so, from this expression the exergetic efficiency (hTPex) of the engine can be calculated as below: hTPex ¼ X _Ex TP u;out= X _Ex TP in ¼ _Wpt= � _Ex3f þ _Ex1 � (2) 2.2. Waste exergy ratio (rTPwex): The main target of aircraft engine is to generate thrust to accelerate and make flight the aircraft. Waste exergy ratio will be calculated by division of total waste exergy to the total inlet exergy. Waste exergy can be classified in two categories as reusable and unusable waste exergies. In the turboprop engine all waste exergy is in unusable category since the emissions released from exhaust cannot be recovered. The total waste exergy can easily be calculated by subtracting the useful exergy from total inlet exergy as given below [1,2,61]: Waste exergy ratio ¼ ðtotal waste exergy outputÞ=ðtotal exergy inputÞ (3a) Fig. 2. Exergy balance diagram of the turboprop engine. The waste exergy ratio ðrTPwexÞ can be calculated as: rTPwex ¼ �X _Ex TP lossþ X _Ex TP dest �.X _Ex TP in ¼ � _Exexhþ _Ex c destþ _Ex comb dest þ _Ex gg destþ _Ex pt dest �.� _Ex3f þ _Ex1 � (3b) rTPwex ¼ 0 BBBBBBB@ _Exexh þ _Wc þ _Ex1 � � _Ex3 þ _Ex3B � þ � _Ex3f þ _Ex3 � _Ex4:1 � þ � _Ex4:1 þ _ExB1 � _Ex4:5 � _Wgg � þ � _Ex4:5 þ _ExB2� _Ex5 � _Wpt � 1 CCCCCCCA ,� _Ex3f þ _Ex1 � (3c) 2.3. Recoverable exergy ratio (rTPrex) Recoverable exergy amount is zero since the emissions released from exhaust cannot be recoverable in the engine. So the recover- able exergy ratio is also zero for the turboprop engine for all torques from the following formula [1,2,61]. Recoverable exergy ratio ¼ ðrecoverable exergyÞ=ðtotal exergy inputÞ (4a) rTPrex ¼ X _Ex TP ru= X _Ex TP in ¼ _Exexh= � _Ex3f þ _Ex1 � ¼ 0= � _Ex3f þ _Ex1 � ¼ 0 (4b) 2.4. Exergy destruction factor (f TPexd) Exergy destruction factor is an important parameter indicating the decrease of the positive effect of the engine on exergo- sustainability. Exergy destruction factor is found by dividing the total exergy destruction into total exergy input. Exergy destruction factor (fTPexd) of the turboprop engine has been formulatedas below [1,2,61]: fTPexd ¼ X _Ex TP in �X _Ex TP in ¼ � _Ex c destþ _Ex comb dest þ _Ex gg destþ _Ex pt dest �.� _Ex3f þ _Ex1 � (5a) Table 1 Typical turboprop performance ratings. Engine rating Power (shp) Up to ambient temperature Automatic power reverse 1870 38 �C Take-off 1750 38 �C Maximum continuous 1750 41 �C Maximum cruise 1700 15 �C Source : [63] H. Aydın et al. / Energy 58 (2013) 550e560 553 B _Wc þ _Ex1 � _Ex3 þ _Ex3B� � C fTPexd ¼ 0 BBBBBB@ � � þ _Ex3f þ _Ex3 � _Ex4:1 þ � _Ex4:1 þ _ExB1 � _Ex4:5 � _Wgg � þ � _Ex4:5 þ _ExB2� _Ex5 � _Wpt � 1 CCCCCCA ,� _Ex3f þ _Ex1 � (5b) 2.5. Environmental effect factor (f TPeef ) Environmental effect factor of a turboprop engine is an impor- tant parameter to indicate whether or not it damages the envi- ronment because of its unusable waste exergy output (exergy loss) and exergy destruction. Environmental effect factor can be rear- ranged as in the following form, ranging from 0 to þN [1,2,61]: Environmental effect factor ¼ ðwaste exergy ratioÞ=ðexergy efficiencyÞ (6a) fTPeef ¼rTPwex=nTPex ¼ ��X _Ex TP lossþ X _Ex TP dest �.X _Ex TP in �. �X _Ex TP u;out= X _Ex TP in � ¼ �X _Ex TP lossþ X _Ex TP dest �.�X _Ex TP u;out � (6b) Table 2 Standard definitions the phases of a flight. Phase Symbol Definition Standing STD Prior to pushback or taxi, or after arrival, At the gate or parking area, while the aircraft is st Pushback/Towing PBT Aircraft is moving in the gate, ramp, or parking ar Taxi TXI Aircraft is moving on the ground under its own po after landing Take-off TOF From the application of take-off power through ro of 35 feet above runway elevation Initial Climb ICL From the end of the take-off to the first prescribed reaching 1000 feet above runway elevation En Route ENR From completion of Initial Climb through cruise a of controlled descent to the Initial Approach Fix Maneuvering MNVR Low altitude/aerobatic flight operations Approach APPR From the Initial Approach Fix to the beginning of Landing LDG From the beginning of the landing flare until aircr comes to a stop on the runway Emergency descent EMG A controlled descent during any airborne phase in emergency situation Uncontrolled descent UND A descent during any airborne phase in which the controlled flight Post-impact PIM Any of that portion of the flight which occurs afte object, obstacle Source : [63] B _Exexh þ _Wc þ _Ex1 � � _Ex3 þ _Ex3B � � � C fTPeef ¼ 0 BBBBBB@ þ _Ex3f þ _Ex3 � _Ex4:1 þ � _Ex4:1 þ _ExB1 � _Ex4:5 � _Wgg � þ � _Ex4:5 þ _ExB2� _Ex5 � _Wpt � 1 CCCCCCA , _Wpt (6c) 2.6. Exergetic sustainability index (QTPesi) Exergetic sustainability index is an important parameter for the exergo-sustainability of the turboprop engine. Exergetic sustain- ability index can be found by division of 1 to environmental effect factor. The range of this index is between 0 and 1. The exergetic sustainability index is developed as below [1,2,61]: Exergetic sustainability index ¼ 1=ðenvironmental �effect factorÞ (7a) QTPesi ¼1=fTPeef ¼ nTPex=rTPwex ¼ �X _Ex TP u;out= X _Ex TP in �. ��X _Ex TP loss þ X _Ex TP dest �.X _Ex TP in � ¼ X _Ex TP u;out= �X _Ex TP loss þ X _Ex TP dest � (7b) QTPesi ¼ _Wpt= 0 BBBBBBB@ _Exexh þ _Wc þ _Ex1 � � _Ex3 þ _Ex3B � þ � _Ex3f þ _Ex3 � _Ex4:1 � þ � _Ex4:1 þ _ExB1 � _Ex4:5 � _Wgg � þ � _Ex4:5 þ _ExB2� _Ex5 � _Wpt � 1 CCCCCCCA (7c) Sub-phases ationary Engine(s) i) not operating ii) start-up iii) Operating iv) shut-down ea, assisted by a tow vehicle Engine(s) i) not operating ii) start-up iii) Operating iv) shut-down wer prior to take-off and i) Power back ii) taxi to runway iii) taxi to take-off position iv) taxi from runway tation and to an altitude i) Take-off ii) rejected take-off power reduction, or until e ltitude and completion i) Climb to cruise ii) cruise iii) change of cruise level iv) descent v) holding i) Aerobatics ii) low flying the landing flare. i) Initial approach ii) final approach iii) missed approach/go-around aft exits the landing runway, i) Flare ii) landing roll iii) aborted landing after touchdown response to a perceived e aircraft does not sustain e r impact with a person, e Table 3 Main control parameters of the turboprop engine in different phases of a flight. Ngg(%) Npt(%) ITT (�C) Torque (%) Start 65e75 18e24 480e600 0 Taxiing 70e76 73 600e650 10e25 Take-off 95e102 100 800e944 (Max. 950) 75e100 (107 APR) Climb 90e95 88e100 800e875 70e95 Landing 75e80 100 600e700 25e35 Max. reverse 80e85 90 650e700 30e50 Source: [63] H. Aydın et al. / Energy 58 (2013) 550e560554 3. Results and discussion This study presents exergo-sustainability indicators of the turboprop engine by using the experimental data in the literature [33]. To evaluate the variations of the exergo-sustainability indicators of the turboprop engine as a function of shaft torque, the following indicators are taken into consideration: (a) exergy efficiency, (b) waste exergy ratio, (c) recoverable exergy ratio, (d) exergy destruction factor, (e) environmental effect factor, (f) exergetic sustainability index. The CN-235-300 aircraft is capable of air transport and powered by two CT7-9C turboprop engines, driving four bladed propellers. It is necessary to definite the phases of flight for an aircraft. The phase of flight definitions given in Table 2 consist of broad operational phases. Most of them have sub-phases. This table can be used for powered fixed-wing land and rotorcraft operations [62]. Status of main parameters of the turboprop engine for different flight phases are given in Table 3 [62]. In the event of turboprop engine failure during take-off, the integral Automatic Power Reserve (APR) in- creases the power of the remaining engine to 1870 shp, also at sea level up to an airfield ambient temperature of 38.5 �C. The installed turboprop engine performance for sea level static, 100% propeller rpm and ISA (international standard atmosphere) conditions is summarised in Table 1 [63]. In this table, maximum continuous power is the maximum power approved for continuous operation under emergency conditions. Maximum cruise power is the maximum power approved for normal continuous operation. Table 4 Flight phases correlation as a function of turboprop engine torque. Nomenclature Taxi and Landing TX-LDG Climb CLM Maximum cruise MX-CRS Normal take-off NR-TOF Maximum continuous MX-CNT Automatic power reverse APR Maximum take-off MX-TOF Symbol of each phases Considering the flight phases as a function of engine torque and shaft horsepower, the flight phases can be split into seven parts in this study: a) landing b) climb c) maximum cruise d) normal take- off e) maximum continuous f) automatic power reverse g) maximum take-off. Concerning the classification of flight phases as an engine power or torque level, it is difficult to see many examples in the literature. In this context, a typical flight phases are demonstrated with engine torque in Table 4. Figs. 3e6 demonstrate the variations of exergy input and output values of the compressor, combustor, gas generator and power turbine as a function of shaft torque, respectively. On the other hand, before analysing and evaluating the results in these figures, it should first be emphasized that the principal objective of this study are not to determine the exergetic performance for the turboprop engine. Rather, studying engine torque values at the dynamic and unsteady conditions aims how much improvement is possible for the turboprop engine for better exergo-sustainability. Fig. 7 presents the variations of exergy efficiency as a function of flight phases based on the shaft torque of the turboprop engine. The exergy efficiency, one of the most important indicators for exergo- sustainability of the engine, is mainly based on the exergy input and the required output. Moreover, the shaft torque and hence shaft horsepower is another important variable affecting the exergy efficiency. In addition to this, it is noticed that the exergy efficiencyof the turboprop engine highly affected by the inputeoutput exergetic values of the each engine component at various shaft torques as shown in Figs. 3e6. When the engine or aircraft runs at the taxi and landing, this causes the decrease of the exergy effi- ciency. On the contrary, shaft torque increases the exergy efficiency. The results show that the exergy efficiency ranges from 0.206 to 0.292 in all flight phases. As can be seen in Fig. 7, exergy efficiency changes between 0.274 and 0.284 in both climb and maximum cruise. There is good relationship between exergy efficiency and shaft torque. In same figure, as expected, exergy efficiency increases with shaft torque in all phases. In maximum-continuous and normal take-off conditions, exergy efficiency ranges from 0.284 to 0.289. Fig. 8 clearly illustrates the variations of waste exergy ratio as a function of shaft torque, and hence, six flight phases. From this figure, waste exergy ratio decreases with shaft torque increases. This leads to provide better results for the automatic power reverse, Torque (N m) shp z240, z350 745 485 � CLM � 552 1500 � CLM � 1709 485 � MX-CRS � 552 1500 � MX-CRS � 1709 552 � NR-TOF � 580 1709 � NR-TOF � 1835 552 � MX-CNT � 580 1709 � MX-CNT � 1835 580 � APR � 630 1835 � APR � 1948 580 � MX-TOF � 630 1835 � MX-TOF � 1948 Fig. 3. Exergy inputeoutput relation of the compressor as a function of the shaft torque. H. Aydın et al. / Energy 58 (2013) 550e560 555 normal/maximum take-off, climb, maximum cruise/continuous flight phases. It is seen that waste exergy ratio of the engine ranges from 70.60% to 72.60% in these flight conditions. In same figure, waste exergy ratio is found to be from 75.80% to 79.40% in both taxi and landing. It is clear from Fig. 8 that waste exergy ratio is mini- mum at high torques. Figs. 9 and 10 show the exergy destruction ratio and environ- mental effect factor in the different phases of flight, respectively. The exergy destruction ratio and environmental effect factor should be taken into consideration to show their effects on exergo- sustainability of the turboprop aircraft. When the shaft torque goes up, the exergy destruction ratio and environmental effect Fig. 4. Exergy inputeoutput relation of the com factor decrease as shown in these figures. Therefore, to minimize the exergy destruction ratio and environmental effect factor, high torque should be considered. It is observed that the maximum exergy destruction ratio range from 47% to 48% (its theoretical values range from 0 to 1) and higher value of the environmental effect factor is found to be in the range of 3.14 and 3.85 (its theo- retical values range from 0 to þN) in both taxi and landing phases. In Fig.11, effects of shaft torque togetherwithflight phases on the exergetic sustainability index of the turboprop are shown. Consid- ering the investigated flight conditions, it is revealed that exergetic sustainability index is significantly low in taxi and landing phases (its theoretical values range from0 to 1). According to the Fig.11, the bustor as a function of the shaft torque. Fig. 5. Exergy inputeoutput relation of the gas generator turbine as a function of the shaft torque. H. Aydın et al. / Energy 58 (2013) 550e560556 average exergetic sustainability index is calculated to as 0.40 in automatic power reverse, climb, maximum cruise/continuous, normal/maximum take-off phases. Value of exergetic sustainability index for taxi and landing is obtained as up to 0.32 from 0.26. In terms of the exergy, all exergetic outputs become meaningful for the turboprop engine and aircraft because aero engines have potential to generate entropy in the environment. Aircraft engines Fig. 6. Exergy inputeoutput relation of the pow produce waste exhaust energy emission and releases heat from the primary and secondary nozzles. So the recoverable exergy ratio is also zero for the turboprop engine for all flight phases. Therefore, in terms of the second-law of thermodynamics, the waste emissions by the engine are very important waste products because it transports waste exergy to the environment and can cause the environmental destruction. er turbine as a function of the shaft torque. Fig. 7. Exergy efficiency of turboprop aircraft at the different phases of flight. H. Aydın et al. / Energy 58 (2013) 550e560 557 At the end of the discussion, final remarks can be summarized according to the reference values of the above presented parame- ters as follows: � As exergy efficiency approaches a maximum value, the waste exergy ratio, exergetic destruction ratio and environmental effect factor become minimum values, whereas exergetic sus- tainability index approaches a maximum value. � The taxi and landing phases of the turboprop aircraft have minimum exergy efficiency and exergetic sustainability index with the value of 0.206 and 0.26, respectively. It can be seen that this phase has also maximum waste exergy ratio, exergy destruction ratio and environmental effect factor with the value of 79.4%, 48% and 3.85, respectively. Moreover, exergy inputs and outputs for the compressor, combustor, gas gener- ator and power turbines are directly proportional to shaft torque. Fig. 8. Waste exergy ratio of turboprop air � Owing to the rise of shaft torque from 240 to 630 N m, the exergetic sustainability index increases from 24% to 29.2%, waste exergy ratio decreases from 79.40% to 70.80%, exergy destruction ratio decreases from 48% to 41%, environmental effect factor decreases from 3.85 to 2.43, and exergetic sus- tainability index increases from 0.26 to 0.41. � A comparison of exergy destruction ratio and environmental effect factor variation with shaft torque during all flight phases indicates an exponential trend of decrease of these indicators. In order to model this trend, therefore, an exponential function can be used for future sustainability aspect. � Finally, in the climb, maximum cruise and continuous, normal and maximum take-off and automatic power reverse phases, exergy efficiency, waste exergy ratio and exergetic sustain- ability index of the turboprop aircraft are reasonably well. These indicators were found to be in the range of 0.274e0.290, 0.726e0.708 and 0.380e0.410, respectively. craft at the different phases of flight. Fig. 9. Exergy destruction ratio of turboprop aircraft at the different phases of flight. Fig. 10. Environmental effect factor of turboprop aircraft at the different phases of flight. Fig. 11. Exergetic sustainability index of turboprop aircraft at the different phases of flight. H. Aydın et al. / Energy 58 (2013) 550e560558 H. Aydın et al. / Energy 58 (2013) 550e560 559 4. Conclusions This study is to define a set of exergo-sustainability indicators for a turboprop aircraft for sustainable aviation and corresponding methodologies and guidelines. The exergo-sustainability indicators for the engine are exergy efficiency, waste exergy ratio, exergy destruction ratio, and environmental effect factor and exergetic sustainability index. The turboprop engine torque values are clas- sified as flight phases of the aircraft and modelled with flight models of their sustainability performance capability. Typically, a comprehensive flight phase model of the aircraft, as selected of this study includes: a) taxi and landing b) climb/maximum cruise c) maximum continuous/normal take-off d) automatic power reverse and maximum take-off. We can then extract some concluding remarks as follows: a) Exergy efficiency changes between 0.274 and 0.284 in both climb and maximum cruise. In maximum-continuous and normal take-off conditions, exergy efficiency ranges from 0.284 to 0.289. In order to increase the exergetic sustainability index of an aircraft and its propulsion system, exergy efficiency should be increased while waste exergy ratio, exergy destruc- tion ratio, environmental effect factor should be decreased. The turboprop engine has high waste exergy ratios in taxi and landing phases, waste exergy ratio is found to befrom 75.80% to 79.40% in both taxi and landing. Besides, higher value of the environmental effect factor is found to be in the range of 3.14 and 3.85 in the same flight phases. Furthermore, value of exergetic sustainability index for taxi and landing is obtained as up to 0.32 from 0.26. If so, it needs further improvement for better sustainable environment. In this regard, effects of irre- versibility due to friction, turbulence, imperfect combustion and thermal losses in the compressor, combustor and turbines should be minimized. b) The present results are consistent with the view that, during climb, take-off, continuous and automatic power reverse, maintaining high shaft torque provides better sustainability. The exergetic relationship developed in this study can also be useful for aircrafts and aircraft engines. c) An understanding of the relation between flight profile and exergetic sustainability will allow the energy saving potential. In addition, the use of exergy indicators based on the second law of thermodynamics may be possible to assess the sus- tainability and environmental effect for air transportation. The results should provide a realistic and meaningful in the performance evaluation of these power systems, which may be useful in the analysis of similar turboprop, turboshaft and industrial gas turbines. In a future study, we will focus on exergo- environmental analysis of the turboprop engine at the different phases of flight and effects of biofuel on the exergetic sustainability of the turboprop engines. Alternative fuels, such as biofuel, can be blendedwith kerosene fuel without having to bring changes to aero engine design. Acknowledgement The authors would like to express their appreciation to TUSAS Engine Industries (TEI) in Eskisehir city of Turkey for full support throughout the preparation of this study, while they would like to thank the reviewers for their valuable comments, which hel- ped in increasing the quality of the paper. They are also grateful for the support provided for the present work by Anadolu Uni- versity, Eskisehir and Recep Tayyip Erdo�gan University, Rize, Turkey. Nomenclature Ex exergy rate (MW) f factor GHG greenhouse gases ISA international standard atmosphere Q environmental sustainable index r ratio shp shaft horsepower _W power (MW) Greek letters h efficiency j flow exergy (kJ kg�1) Subscripts and superscripts c compressor comb combustor dest destruction eef environmental effect exh exhaust ex exergy esi environmental sustainable index exd exergy destruction f fuel gg gas generator turbine in inlet out outlet pt power turbine rex recoverable exergy TP turboprop u useful wex waste exergy 0,1,2.B1,B2 station numbering of the engine component References [1] Midilli A, Dincer I. Development of some exergetic parameters for PEM fuel cells for measuring environmental impact and sustainability. Int J Hydrogen Energy 2009;34:3858e72. [2] Midilli A, Dincer I. Effects of some micro-level exergetic parameters of a PEMFC on the environment and sustainability. Int J Glob Warm 2010;2(1): 65e80. 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http://refhub.elsevier.com/S0360-5442(13)00454-4/sref46 http://refhub.elsevier.com/S0360-5442(13)00454-4/sref47 http://refhub.elsevier.com/S0360-5442(13)00454-4/sref47 http://refhub.elsevier.com/S0360-5442(13)00454-4/sref47 http://refhub.elsevier.com/S0360-5442(13)00454-4/sref48 http://refhub.elsevier.com/S0360-5442(13)00454-4/sref48 http://refhub.elsevier.com/S0360-5442(13)00454-4/sref48 http://refhub.elsevier.com/S0360-5442(13)00454-4/sref48 http://refhub.elsevier.com/S0360-5442(13)00454-4/sref49 http://refhub.elsevier.com/S0360-5442(13)00454-4/sref49 http://refhub.elsevier.com/S0360-5442(13)00454-4/sref49 http://refhub.elsevier.com/S0360-5442(13)00454-4/sref49 http://refhub.elsevier.com/S0360-5442(13)00454-4/sref50 http://refhub.elsevier.com/S0360-5442(13)00454-4/sref50 http://refhub.elsevier.com/S0360-5442(13)00454-4/sref50 http://refhub.elsevier.com/S0360-5442(13)00454-4/sref51 http://refhub.elsevier.com/S0360-5442(13)00454-4/sref51 http://refhub.elsevier.com/S0360-5442(13)00454-4/sref51 http://refhub.elsevier.com/S0360-5442(13)00454-4/sref52 http://refhub.elsevier.com/S0360-5442(13)00454-4/sref52 http://refhub.elsevier.com/S0360-5442(13)00454-4/sref52 http://refhub.elsevier.com/S0360-5442(13)00454-4/sref53 http://refhub.elsevier.com/S0360-5442(13)00454-4/sref53 http://refhub.elsevier.com/S0360-5442(13)00454-4/sref53 http://refhub.elsevier.com/S0360-5442(13)00454-4/sref54 http://refhub.elsevier.com/S0360-5442(13)00454-4/sref54 http://refhub.elsevier.com/S0360-5442(13)00454-4/sref55 http://refhub.elsevier.com/S0360-5442(13)00454-4/sref55 Exergo-sustainability indicators of a turboprop aircraft for the phases of a flight 1 Introduction 2 Exergo-sustainability indicators for the turboprop engine 2.1 Exergy efficiency (ηexTP): 2.2 Waste exergy ratio (rwexTP): 2.3 Recoverable exergy ratio (rrexTP) 2.4 Exergy destruction factor (fexdTP) 2.5 Environmental effect factor (feefTP) 2.6 Exergetic sustainability index (ΘesiTP) 3 Results and discussion 4 Conclusions Acknowledgement Nomenclature References
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