Włodzimierz Balicki, Paweł Głowacki, Stefan Szczeciński, Ryszard Chachurski, Jerzy Szczeciński
`Effect of the Atmosphere on the Performances of Aviation Turbine Engines
`
`EFFECT OF THE ATMOSPHERE ON THE PERFORMANCES
`OF AVIATION TURBINE ENGINES
`
`Włodzimierz BALICKI*, Paweł GŁOWACKI*, Stefan SZCZECINSKI*, Ryszard CHACHURSKI**, Jerzy SZCZECIŃSKI***
`
`*Aviation Institute, Propulsion Department, Al. Krakowska 110/114, 02-256 Warszawa, Poland
`**Military University of Technology, Faculty of Mechatronics and Aviation, ul. Sylwestra Kaliskiego 2, 00-908 Warszawa, Poland
`***GE Poland, Al. Krakowska 110/114, 02-256 Warszawa, Poland
`
`Balicki@ILot.edu.pl, Pawel.Glowacki@ILot.edu.pl, Ryszard.Chachurski@WAT.edu.pl; Jerzy.Szczecinski@GE.com
`
`Abstract: The paper presents how the parameters defining the state of the atmosphere: pressure, temperature, humidity, are affecting
`performance of the aircraft turbine engines and their durability. Also negative impact of dust pollution level is considered as an important
`source of engine deterioration. Article highlights limitation of the aircraft takeoff weight (TOW) and requirements for length of the runways
`depending on weather condition changes. These problems stem from the growing "demand" of gas turbine engines for an air. The highest
`thrust engines have air mass flow more than 1000 kg/s. Engine inlet ice formation is presented as a result of weather conditions and inlet
`duct design features.
`
`Key words: Power Plant, Aircraft Engine, Turbine Engine, Inlet Icing, Standard Atmosphere
`
`1. INTRODUCTION
`
`Aviation, like any other form of transport is dependent on the
`atmosphere conditions (weather). Hence the need to analyze the
`impact of the environment on the lift force, drag, and a thrust
`of the aircraft engines. The values of these parameters are pro-
`portional to the density of the air.
`While in practice, the effect of an altitude on the engine thrust
`is considered, influence of the temperature and humidity is often
`overlooked. Higher values of these two parameters are decreas-
`ing the lift force and engine thrust. Such conditions are limiting
`safe takeoff of heavy loaded aircraft (including aerostats). Higher
`humidity increases the likelihood of inlets icing and can cause
`engine shutdown during flight.
`The phenomenon, which is hard to observe is a gradual loss
`of thrust due to the erosive effects of dust on the aerodynamic
`profiles of the blades and vanes, and its deposition in cavities
`of engine ducts where locally speed is reduced or direction
`of airflow is changed. The source of dust are mainly contaminated
`runways, industry, and occasionally volcanic eruptions or dust
`storms.
`Considerations were done for engines performances on take-
`off ranges. The values of the engine parameters (rotor speed
`and exhaust gas temperature) are limited by the control system.
`
`2. CLIMATE AND THE AIRPORT ALTITUDE INFLUENCE
`ON THE ENGINE TAKEOFF PERFORMANCES
`
`Assuming that a jet engine has fuel mass flow supplied to the
`combustor much smaller than the air mass flow, and assuming the
`full expansion in the exhaust nozzle, thrust of the engine can be
`described by the relation:
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`
`
` ̇ ( ) ( )
`
` (1)
`
`where: ̇ – air mass flow, – exhaust gases velocity, – air-
`speed, – volumetric airflow, – air density
`Atmospheric air parameters (pressure, temperature and den-
`sity) are changing with altitude above sea level (ASL), which
`of course affects the performance of aircraft engines. Lowermost
`airports are located at altitudes close to sea level, while some
`of them are in the Andes and the Himalayas at altitudes exceed-
`ing 3000 m, and even reaching 4500 m
`For engine performances comparison, generally is used mod-
`el of the International Standard Atmosphere (ISA), in which it is
`assumed that at sea level ( ) the air pressure is 101325 Pa,
`temperature of an air is equal to 288.15 K, and the air density
`is 1.225 kg/m3. This model does not consider humidity changes.
`Calculation of engine performances assumes that the air is com-
`pletely "dry". Besides the standard atmosphere, due to the con-
`siderable diversity of climatic conditions in the world, additional
`models of the atmosphere - cold, hot and tropical (Trop) also has
`been developed, for which the adopted pressure changes are the
`same as for the standard atmosphere model but different changes
`in temperature, and hence the change in air density. The de-
`scribed models depending on the airport height above sea-level
`are shown on Figs. 1, 2 and 3.
`The need to take into account temperature changes depend-
`ing not only on the altitude at which the airport is situated but
`depends also on latitude. Airports located on similar altitudes
`for the polar circle have OAT -50°C, while in the airports located
`in Africa and Asia OAT exceeds + 50°C.
`In the case of relative humidity we have to consider that
`in= tropical regions often exceeds 90% at the temperatures ap-
`prox. +30 ... +35°C, while in the same time at the airports located
`on the same altitude, but in Central Europe conditions may prevail
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`acts medlanica elauhrnafica Vol.8 no.2 [@141 DOI 10.2478/ama-2014-0012
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`Fig. 4. Changes of the engine thmst with the altitude and the
`temperatures from 35°C to +35°C (dark dot — the conditions
`corresponring to ISA, generated by GasTurb 12 program)
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`3.
`
`INFLUENCE OF ATMOSPHERIC CONDITIONS (T,,, P" )
`AND AIRPORT ALTITUDE ON AIRCRAFT
`PERFORMANCES
`
`Fonnulas for lift force P, and for drag force I’, of the aircraft
`are including multiplier — atmospheric air density pH (2).
`
`P2=§'cz'VI¥'S'PHrPx=%'Cx'VI¥'S'PH (2)
`
`where: cz — lift force coeflicient, cx — drag force coefficient,
`VH — flight speed, S — wing lifting surface.
`This uses that changes of the lift force and the drag force
`with changes in temperature and altitude of the airport are propor-
`tional to changes in the density of the air. Since the lift force coef-
`ficient is much greater than the coefficient of drag force the de-
`crease in air density decreases drag force, but much more lift
`force is reduced. During takeoff pilot can increase lift force by
`flap extension, but this increases the drag force. As a result, the
`necessary value of the lift force n be achieved by increase of V2
`speed. This causes building of the longer mnways, and in addition
`as already mentioned before, under such conditions the crew has
`less thnist from the engines. For example, while Chopin Airport
`ninways have length of
`2 800 m and 3 620 m ninway
`of Daocheng Airport at an altitude of 4 411 m has a length
`of 4 200 m and located slightly below Bamda Qamdo Airport has
`a runway with astonishing length of 5 500 m.
`
`4.
`
`INFLUENCE OF AIR HUMIDITY ON ENGINE
`AND AIRCRAFT PERFORMANCES
`
`Changes of the engine thrust as a function of the relative hu-
`midity signifintfy are affected by OAT. In the ISA temperature
`increase in relative humidity from 0 to 100% uses a slight de-
`crease ot thrust (1 .. 2%), but in tropical conditions ISA +30°C
`in the same humidity changes as above uses decrease of thnist
`approx. 16% of which 4% solely from the change of relative
`humidity of the air (Fig. 5).
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`in where the temperature will correspond to standard conditions
`and the relative humidity does not exceed 10%.
`Calculations carried out for the model of turbofan engine
`at standard conditions with a thrust approx. 100 kN are showing
`that when the engine is mnning and the pressure corresponds to
`the standard (Fig. 4) it has thnist 12% higher at the temperature
`less by +35°C than the reference, and 22% lower if the ambient
`temperature rises by the same amount in relation to the reference
`temperature.
`In case, if that engine will operate from airport situated on alti-
`tude close to 4500 m, the thrust will be about 38% less than this
`can be achieved at the airport, located at sea level.
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`Altitude [Inn]
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`Fig. 2. Changes of the air temperature with the altitude
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`Fig. 3. Changes ofthe air densitywith thealfifude
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`

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`Ryszard Chachilski. JHZV
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`the Assessment
`perfomtances (Recommended Practices for
`of the Effect of Atmosphere Water Ingestion on the Perfonnance
`and Operability of Gas Turbine Engines, 1995). In subsequent
`stages of the compressor the air temperature rises due to the
`pressure increase. Water sucked into the compressor duct
`is gradually evaporating. Nonnally water in liquid form is rejected
`due to the centrifugal force by the rotor blades on the surface
`of compressor duct and then flows towards the combustion cham-
`ber. This water can get into the bleed valves. If all of the water
`does not evaporate in the compressor or will not be removed by
`bleed valves n enter the combustor and may lead to the engine
`shutdown. Large amount of water vapor worsen preparation and
`combustion of the air —fuel mixture and moreover, water can
`rapidly (quasi detonation) vaporize becoming anaerobic filler
`of the air stream in the combustion chamber causing flame out.
`If there is airframe icing, then decreases the lift force, drag
`force increases, and further increases the weight of the aircraft.
`For example, if the lifting surfaces of the A380—800 have an ice
`layer with a thickness of 1 mm, than the aircraft weight would be
`increased by about 780 kg.
`Different anti icing systems are used depends on aircraft type
`to protect the engine and an airframe. It should be remembered
`that when anti ice system works causes a decrease in engine
`thnist, especially when system is heated by the air from the com-
`pressor.
`
`5.
`
`INFLUENCE OF OTHER EXPLOITATION CONDITIONS
`ON ENGINE PERFORMANCES
`
`Engines are important for flight safety but hail, sand, dust
`and salt flowing with the air through engine ducts are fonning
`deposits on flow pass surfaces and airfoils or even using me-
`chanical damages to the engine. Engine performances are deteri-
`orating hence aircraft characteristics are different than calculated.
`Engines are damaged most often during taxiing,
`take—off
`and landing by objects ejected from the ground by landing gear
`or thrust reverser. Also in|et—vortex (or ground—vortex) phenome-
`non uses FOD. In order to prevent engine against FOD a num-
`ber of organizational and design measures are taken by the indus-
`try. Firstly, risk awareness training for ground staff. Secondly,
`development of a suitable methodologies for takeoff and landing.
`Design features include installation of particle separators on
`helicopter inlets or special shapes of the engines inlet ducts.
`Suction of dust, even particles with a small diameter is leading to
`wear of engine parts and as a consequence efficiency reduction,
`which in the turn induces an increase of EGT (Exhaust Gas Tem-
`perature) beuse of higher fuel consumption in order to keep
`required performance level of the engine.
`Takeoff EGT depends on the OAT (Outside Air Temperature)
`and control system settings. EGT increases with increasing
`of OAT (Fig. 6a) while the maximum engine thrust is constant.
`When OAT exceeds certain value EGT is limited by the engine
`control system, which means further increase of the ambient
`temperature decreases
`available
`engine
`thrust
`(Fig.
`6b).
`The maximum temperature value (corner point) below which
`engine thrust is not decreasing varies between 30°C....35 °C.
`For each type of the engine manufacturer specifies the maxi-
`mum pennissible limit of the EGT. For example, for CFM5f‘r3
`engines the exhaust gas temperature limit is 1230 K.
`
`Fig. 5. Changes of the engine thnist with the relative speed N2
`for a different relative humidity and OAT
`(generated by GasTurb 12 program)
`
`Steam in the air reduces the mass flow, which leads to a re-
`duction in engine thnist or power. We should also remember that
`is like anaerobic filling of the air, which in the case of large quanti-
`ties, eg. due to evaporation of water along gas path of the com-
`pressor or evaporation it in large quantities directly in the combus-
`tion chamber, can lead to the flame out, which means uncom-
`manded engine shutdown.
`High humidity can also cause icing of the engine, which can
`occur in temperatures between +10°C
`+15°C and correspond-
`ing relative humidity. Icing fomiations depend on engine design,
`as well as inlets position on the airframe and their structure. For
`example, during flight aircraft powered by turbofan engines with
`high by pass ratio under conditions of super cooled water drop
`lets, may have ice fomiation on: the inlet leading edge, inlet duct,
`spinner and on the fan blades as well as on 0GV's, low pressure
`compressor IGV's and first stage blades. Three shalt engines can
`face in such flight
`icing conditions on IGV's and lPC's first stage
`blades.
`
`Ice formation on the inlet duct surface sand directly on the
`compressor inlet, changes the geometry and cross section diame-
`ter of the duct and as a consequence reduces airflow and the
`parameters of airflow before compressor inlet (Chachurski, 2009).
`These negative changes are decreasing compressor pressure
`ratio which leads to engine thnist or power reduction, oflen to
`compressor instability and as a result high vibration or even en-
`gine shutdown.
`Instability of
`the compressor
`is also caused
`by distortion of duct ribs, vanes and blades airfoils.
`Reduced airflow, distortion of the velocity, pressure and tem
`perature circumferential distribution as well as inlet and IGV's
`airfoils distortion uses also negative circumferential distribution
`and increase of the temperature before turbine.
`Small amount of water injection before compressor inlet irr
`creases engine thnist by improving efficiency of its themiodynam-
`ic cycle and the growth of mass flow (Water injected before the
`compressor
`gradually evaporates, absorbs heat from the air
`reducing the temperature,
`increasing its density, which at a con-
`stant volumetric flow increases the air mass flow (m = p - Q)
`due to increase in air density and in addition weight of the inject-
`ed water. In contrast,
`steam is only anaerobic filler decreasing
`amount of the air entering the engine.). Opposite, water inform
`of liquid or as snow, ice or slush, which gets to the inlet and then
`passes through the duct leading to serious dismption of engine
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`EGT during takeoff (but also during lower ranges of engine
`operation) increases with the engine deterioration. Lower efficien-
`cy of the engine main modules (in particular compressor), requires
`more fuel delivered to the combustor in order to keep the same
`rotor speed (same engine thrust) to compensate lower compres-
`sor pressure ratio.
`Higher EGT may indicate erosive wear of the compressor
`or turbine blades, increased tip clearances or distortion of airfoils
`by dirty deposit of oil and dust mixture (Dunn et all., 1987;
`Tabakoff and Hamed, 1984. At the beginning of engine operation
`after installation on the aircraft EGT is growing rapidly (about
`12°C .. 15oC during the first 1000 cycles) compared to the test –
`cell and then stabilizes at 8°C .. 10°C per 1000 cycles (Fig. 6c).
`The large EGT increase in the initial period of engine operation in
`relation to the values measured in the test – cell is due to the fact
`that there are ideal conditions during manufacturer engine tests.
`As a result of engine deterioration, EGT margin becomes
`smaller (Fig. 6d).
`
`
`
`Fig. 6. OAT influence on EGT (a) and the thrust K (b); EGT (c) and EGT
`margin ΔT (d) changes depending on the number of cycles:
`1 – EGT limit, 2 – New engine takeoff EGT, 3 – Takeoff EGT
`of the deteriorated engine , 4 – available thrust of a new engine,
`5 – available thrust of a deteriorated engine,6 – EGT of the “dirty”
`engine, 7 – mean EGT, 8 – EGT of the “clean” engine, 9 – not
`washed engine, 10 – of the washed engine, 11 – limit,
` – OAT limit for a new engine, – OAT limit for deterio-
`rated engine, – the number of engine cycles, - the number
`of engine cycles when is decreasing per 1000 cycles, –
`the number of engine cycles for repair.
`
`In order to improve the efficiency of the engine by removing
`dirty deposit accumulated on the blades and vanes operators are
`performing washing and cleaning of the engine at regular intervals
`recommended by the engine manufacturer, but operators have
`the right to adjust these intervals to suit their needs resulting from
`the specific engine operating conditions (dust, humidity, hot
`or cold temperatures, short or long flight routes, etc.). These
`processes are also used in case of an excessive reduction of ,
`and after FOD or bird strikes, etc.
`
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`acta mechanica et automatica, vol.8 no.2 (2014), DOI 10.2478/ama-2014-0012
`
`6. FINAL COMMENTS
`
`Any unexpected to pilot thrust decrease during takeoff has
`adverse impact on safety. In extreme cases - the accumulation
`of factors that reduce thrust: heat, high humidity and low pressure
`– even threatened disaster. Under the influence of extremely
`adverse weather conditions the engine may shutdown automati-
`cally as a result of the compressor instability. Engine thrust can be
`unexpectedly reduced (or even the engine can shutdown) by the
`automatic control system to protect power plant from being dam-
`aged due to excessive increase in exhaust gas temperature.
`With this in mind the technical staff and flight crew should
`possess the ability to predict the impact of current or forecasted
`weather conditions on the aircraft and helicopters and their power
`plant performances.
`
`REFERENCES
`
`1. Balicki W., Chachurski R., Głowacki P., Godzimirski J., Kawalec
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`K., Kozakiewicz A., Pągowski Z., Rowiński A., Szczeciński J.,
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`Exploitation – Diagnostic. Part II, Scientific Publications of the
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`of the Institute of Aviation, no 4/2009 (199), 31-49, (in Polish).
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`Ingestion on the Performance and
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