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An Early Evaluation Method of the Compatibility of Alternative Jet Fuels with Elastomer Seals

Dullovi, Eriona LU (2024) KETM05 20232
Chemical Engineering (M.Sc.Eng.)
Abstract
The aviation industry is a contributor to the global greenhouse gas emissions. Moving away from fossil-based fuels has proven to be more difficult than expected. One possibility for the aviation industry is the development of sustainable aviation fuels (SAFs), produced from renewable sources such as biomass and waste. Certain problems have been discovered with using SAFs, however. The fuels are usually not compatible with the elastomer seals in engines. The elastomer usually swells in contact with conventional fuels making it more compact and a better seal. Elastomer seals in contact with alternative fuels tend to shrink and harden, causing leakages. This issue has been traced to the inherent low content of aromatics in SAFs. The testing... (More)
The aviation industry is a contributor to the global greenhouse gas emissions. Moving away from fossil-based fuels has proven to be more difficult than expected. One possibility for the aviation industry is the development of sustainable aviation fuels (SAFs), produced from renewable sources such as biomass and waste. Certain problems have been discovered with using SAFs, however. The fuels are usually not compatible with the elastomer seals in engines. The elastomer usually swells in contact with conventional fuels making it more compact and a better seal. Elastomer seals in contact with alternative fuels tend to shrink and harden, causing leakages. This issue has been traced to the inherent low content of aromatics in SAFs. The testing of the effect of fuels on materials in standards such as ASTM occurs after much fuel is already used. This study aimed therefore to find a rapid method of getting an early indication of the effect of a fuel on elastomer seals.
Previous studies on the subject have focused on the testing of volume change to determine the compatibility of fuels and materials. Volume change is a basic response for a material in contact with a fuel and many other properties will vary proportionally. The change in volume is determined by two processes, the material absorbing fuel components (causes swelling) and the fuel extracting components from the material (causes shrinking). Eventually an equilibrium is reached, and the volume remains constant. Volume swell is mostly tested by using Optical dilatometry, a method in which an elastomer is submerged in a fuel and images are taken at a specified time interval. These images are then analyzed, and the volume change is calculated by assuming isotropic volume change.
The optical dilatometry method was used to test the effect of fuels on a nitrile rubber O-ring. The fuels used were kerosene, HVO and RME. Every test used 10 mL of fuel in a volumetric flask, with a 2-3 mm cross-section of O-ring. Each fuel was tested in its pure form, tests were also done with a mix of kerosene and HVO. Pieces of elastomer were also aged in kerosene for 3 days and then switched to pure HVO and a blend of kerosene and HVO. All tests were done at room temperature. A Matlab script was used to detect the area of the elastomer in pixels.
The result of the tests showed that the kerosene fuel caused swelling immediately. The volume change reached a plateau of almost 12% volume swell within the first 24 hours. Testing of HVO showed some weak initial swelling and then consistent shrinking (about 1-2%). Testing of RME showed a swell of about 30-35%. The elastomer is assumed to have been dissolving in the fuel due to polar parts in both the elastomer and the fuel. Blends of HVO and kerosene showed similar swelling to that of pure kerosene but limited to around 5%. Aged elastomers showed a dramatic shrinking when switched to HVO and a blend of HVO and kerosene. This showed that a used elastomer is more strongly affected by a switch to a low aromatic fuel than a completely new elastomer.
It was concluded that testing volume swell by using optical dilatometry is a relatively simple way of testing material compatibility. Conclusions could be drawn from the results within the testing period. For faster results, higher temperatures could be used. Ageing the elastomers is necessary to see the effect of a new fuel on used elastomers. Other materials than nitrile rubber should also be tested. (Less)
Popular Abstract (Swedish)
Klimatomställningar har gjorts inom de flesta delar av transportsektorn, som ofta pekas ut som boven i dramat när det kommer till utsläpp av koldioxid. Bilar som går på elektricitet är ett typiskt exempel. Denna omställning är svårare att göra när det gäller flygindustrin. Elektriska flygplan är inte realistiska just nu då batterierna hade behövt vara enorma.
Fördelen med flytande bränslen är att de bränns upp under resan, vilket gör flygplanet lättare med tiden. Därför har industrin börjat utveckla bränslen som produceras från förnybara resurser såsom växtolja, biomassa och avfall. Dessa bränslen har potential att vara klimatneutrala från en livscykelanalys. Det finns sådana bränslen som har godkänts för kommersiell användning, men de... (More)
Klimatomställningar har gjorts inom de flesta delar av transportsektorn, som ofta pekas ut som boven i dramat när det kommer till utsläpp av koldioxid. Bilar som går på elektricitet är ett typiskt exempel. Denna omställning är svårare att göra när det gäller flygindustrin. Elektriska flygplan är inte realistiska just nu då batterierna hade behövt vara enorma.
Fördelen med flytande bränslen är att de bränns upp under resan, vilket gör flygplanet lättare med tiden. Därför har industrin börjat utveckla bränslen som produceras från förnybara resurser såsom växtolja, biomassa och avfall. Dessa bränslen har potential att vara klimatneutrala från en livscykelanalys. Det finns sådana bränslen som har godkänts för kommersiell användning, men de måste blandas med fossila bränslen för att få användas. Detta är för att rena biobränslen ofta inte är kompatibla med elastomera (en typ av polymer) tätningsmedel i flygmotorer. Fossila bränslen innehåller aromater (cykliska kolväten) som absorberas av elastomeren och orsakar svällning. Svällningen gör elastomeren mer kompakt vilket förbättrar dess förmåga att förhindra läckor. Biobränslen innehåller inte aromater vilket orsakar att bränslet i stället extraherar komponenter från elastomeren. Detta gör att elastomeren krymper, vilket i sin tur orsakar läckor. Syftet med denna studie var att hitta en snabb metod för att få en indikation av hur ett bränsle kommer påverka ett elastomeriskt tätningsmedel.
För att uppnå detta testades volymsvällningen genom att använda en metod som kallas optisk dilatometer. Volymsvällning är en grundläggande reaktion hos ett material i kontakt med bränslen och många andra egenskaper kommer att variera proportionerligt. Testmetoden går ut på att man skär upp en bit av en O-ring (som är ett vanligt elastomeriskt tätningsmedel), lägger den i ett kärl och häller i ett bränsle. Under kärlet placeras en kamera som tar bilder en gång i timmen. En lampa placeras ovanför kärlet.
Experimenten genomfördes i ca 3–4 dygn i rumstemperatur. Bilderna analyserades genom att använda ett datorprogram (MatLab). Volymändringen räknades ut genom att använda arean från bilderna i en ekvation som antar att volymändringen är likadan i alla riktningar. Tre olika bränslen användes, ett vanligt fossilt fotogen och två biodieslar (HVO och RME).
Hur bränslet påverkade materialet kunde observeras inom tiden för testning. Fotogenet orsakade svällning som planade av under det första dygnet. HVO orsakade krympning av elastomeren under hela testperioden. Elastomeren svällde upp till 35%, i RME, vilket misstänkts är på grund av att RMEn löser upp materialet. Tydligast effekt skedde i de tester där elastomeren först ”åldrades” i 3 dygn i fotogen och sedan testades med HVO. Då krympte elastomeren dramatiskt inom det första dygnet. Detta visade att tätningsmedel som redan varit i bruk kommer att påverkas mer av ett byte till ett lågaromatiskt biobränsle än ett helt nytt tätningsmedel.
Därför rekommenderas bränsleutvecklare att testa nya bränslen på båda nya och använda material. Dessutom bör de testa bränslet på flera olika material då dessa kan reagera olika. För snabbare metod, bör experiment utföras med högre temperatur. (Less)
Please use this url to cite or link to this publication:
author
Dullovi, Eriona LU
supervisor
organization
course
KETM05 20232
year
type
H2 - Master's Degree (Two Years)
subject
keywords
Alternative jet fuels, elastomers, optical dilatometry, volume swell, chemical engineering
language
English
id
9151663
date added to LUP
2024-05-20 12:09:52
date last changed
2024-05-20 12:09:52
@misc{9151663,
  abstract     = {{The aviation industry is a contributor to the global greenhouse gas emissions. Moving away from fossil-based fuels has proven to be more difficult than expected. One possibility for the aviation industry is the development of sustainable aviation fuels (SAFs), produced from renewable sources such as biomass and waste. Certain problems have been discovered with using SAFs, however. The fuels are usually not compatible with the elastomer seals in engines. The elastomer usually swells in contact with conventional fuels making it more compact and a better seal. Elastomer seals in contact with alternative fuels tend to shrink and harden, causing leakages. This issue has been traced to the inherent low content of aromatics in SAFs. The testing of the effect of fuels on materials in standards such as ASTM occurs after much fuel is already used. This study aimed therefore to find a rapid method of getting an early indication of the effect of a fuel on elastomer seals.
Previous studies on the subject have focused on the testing of volume change to determine the compatibility of fuels and materials. Volume change is a basic response for a material in contact with a fuel and many other properties will vary proportionally. The change in volume is determined by two processes, the material absorbing fuel components (causes swelling) and the fuel extracting components from the material (causes shrinking). Eventually an equilibrium is reached, and the volume remains constant. Volume swell is mostly tested by using Optical dilatometry, a method in which an elastomer is submerged in a fuel and images are taken at a specified time interval. These images are then analyzed, and the volume change is calculated by assuming isotropic volume change. 
The optical dilatometry method was used to test the effect of fuels on a nitrile rubber O-ring. The fuels used were kerosene, HVO and RME. Every test used 10 mL of fuel in a volumetric flask, with a 2-3 mm cross-section of O-ring. Each fuel was tested in its pure form, tests were also done with a mix of kerosene and HVO. Pieces of elastomer were also aged in kerosene for 3 days and then switched to pure HVO and a blend of kerosene and HVO. All tests were done at room temperature. A Matlab script was used to detect the area of the elastomer in pixels.
The result of the tests showed that the kerosene fuel caused swelling immediately. The volume change reached a plateau of almost 12% volume swell within the first 24 hours. Testing of HVO showed some weak initial swelling and then consistent shrinking (about 1-2%). Testing of RME showed a swell of about 30-35%. The elastomer is assumed to have been dissolving in the fuel due to polar parts in both the elastomer and the fuel. Blends of HVO and kerosene showed similar swelling to that of pure kerosene but limited to around 5%. Aged elastomers showed a dramatic shrinking when switched to HVO and a blend of HVO and kerosene. This showed that a used elastomer is more strongly affected by a switch to a low aromatic fuel than a completely new elastomer. 
It was concluded that testing volume swell by using optical dilatometry is a relatively simple way of testing material compatibility. Conclusions could be drawn from the results within the testing period. For faster results, higher temperatures could be used. Ageing the elastomers is necessary to see the effect of a new fuel on used elastomers. Other materials than nitrile rubber should also be tested.}},
  author       = {{Dullovi, Eriona}},
  language     = {{eng}},
  note         = {{Student Paper}},
  title        = {{An Early Evaluation Method of the Compatibility of Alternative Jet Fuels with Elastomer Seals}},
  year         = {{2024}},
}