Draining water from aircraft fuel using nitrogen enriched air

Research output: Contribution to journalArticle

Abstract

This paper concerns a computational study of the process of removing water from an aircraft’s fuel tank by pumping nitrogen enriched air (NEA) from the bottom of the tank. This is an important procedure for the smooth, efficient, and safe operation of the aircraft’s engine. Due to the low partial pressure of water in the pumped NEA, it absorbs water from the fuel. The water-laden bubbles enter the ullage, the empty space above the fuel, and escape into the environment. The effects of the number of NEA inlets and the NEA mass flow rate on the timescale of the NEA pumping were investigated using Computational Fluid Dynamics. The results reveal that the absorption of water by the NEA bubbles is low and is not affected by the number of the inlets used. Yet, the water content in the fuel decreases fast during the procedure, which is the desired outcome. We show that this is due to the relatively dry NEA entering the ullage and displacing the moist air, thus reducing the partial pressure of water at the fuel/ullage interface. This shift from equilibrium conditions forces water to evaporate from the fuel’s entire surface. Furthermore, the amount of water migrating from the fuel directly into the ullage is significantly greater than that absorbed by the rising bubbles. In turn, the rate of decrease of the water content in the ullage is determined by the total NEA mass flow rate and this is the dominant contributor to the draining time, with the number of NEA nozzles playing a minor role. We confirmed this by pumping NEA directly into the ullage, where we observe a significant decrease of water even when the NEA is not pumped through the fuel. We also show that doubling the mass flow rate halves the draining time. When considering the capability of most modern aircraft to pump NEA through the fuel as part of their inerting system, the proposed method for removing water is particularly attractive, requiring very little (if at all) design modification.
LanguageEnglish
Article number908
Number of pages16
JournalEnergies
Volume11
Issue number4
Early online date12 Apr 2018
DOIs
StateE-pub ahead of print - 12 Apr 2018

Keywords

  • fuel tank
  • water
  • nitrogen enriched air (NEA)
  • aircraft
  • inerting system
  • dehydrate

Cite this

@article{d0c085b53cb04b598d065324bc9fa778,
title = "Draining water from aircraft fuel using nitrogen enriched air",
abstract = "This paper concerns a computational study of the process of removing water from an aircraft’s fuel tank by pumping nitrogen enriched air (NEA) from the bottom of the tank. This is an important procedure for the smooth, efficient, and safe operation of the aircraft’s engine. Due to the low partial pressure of water in the pumped NEA, it absorbs water from the fuel. The water-laden bubbles enter the ullage, the empty space above the fuel, and escape into the environment. The effects of the number of NEA inlets and the NEA mass flow rate on the timescale of the NEA pumping were investigated using Computational Fluid Dynamics. The results reveal that the absorption of water by the NEA bubbles is low and is not affected by the number of the inlets used. Yet, the water content in the fuel decreases fast during the procedure, which is the desired outcome. We show that this is due to the relatively dry NEA entering the ullage and displacing the moist air, thus reducing the partial pressure of water at the fuel/ullage interface. This shift from equilibrium conditions forces water to evaporate from the fuel’s entire surface. Furthermore, the amount of water migrating from the fuel directly into the ullage is significantly greater than that absorbed by the rising bubbles. In turn, the rate of decrease of the water content in the ullage is determined by the total NEA mass flow rate and this is the dominant contributor to the draining time, with the number of NEA nozzles playing a minor role. We confirmed this by pumping NEA directly into the ullage, where we observe a significant decrease of water even when the NEA is not pumped through the fuel. We also show that doubling the mass flow rate halves the draining time. When considering the capability of most modern aircraft to pump NEA through the fuel as part of their inerting system, the proposed method for removing water is particularly attractive, requiring very little (if at all) design modification.",
keywords = "fuel tank, water, nitrogen enriched air (NEA), aircraft, inerting system, dehydrate",
author = "Michael Frank and Dimitris Drikakis",
year = "2018",
month = "4",
day = "12",
doi = "10.3390/en11040908",
language = "English",
volume = "11",
journal = "Energies",
issn = "1996-1073",
number = "4",

}

Draining water from aircraft fuel using nitrogen enriched air. / Frank, Michael; Drikakis, Dimitris.

In: Energies, Vol. 11, No. 4, 908, 12.04.2018.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Draining water from aircraft fuel using nitrogen enriched air

AU - Frank,Michael

AU - Drikakis,Dimitris

PY - 2018/4/12

Y1 - 2018/4/12

N2 - This paper concerns a computational study of the process of removing water from an aircraft’s fuel tank by pumping nitrogen enriched air (NEA) from the bottom of the tank. This is an important procedure for the smooth, efficient, and safe operation of the aircraft’s engine. Due to the low partial pressure of water in the pumped NEA, it absorbs water from the fuel. The water-laden bubbles enter the ullage, the empty space above the fuel, and escape into the environment. The effects of the number of NEA inlets and the NEA mass flow rate on the timescale of the NEA pumping were investigated using Computational Fluid Dynamics. The results reveal that the absorption of water by the NEA bubbles is low and is not affected by the number of the inlets used. Yet, the water content in the fuel decreases fast during the procedure, which is the desired outcome. We show that this is due to the relatively dry NEA entering the ullage and displacing the moist air, thus reducing the partial pressure of water at the fuel/ullage interface. This shift from equilibrium conditions forces water to evaporate from the fuel’s entire surface. Furthermore, the amount of water migrating from the fuel directly into the ullage is significantly greater than that absorbed by the rising bubbles. In turn, the rate of decrease of the water content in the ullage is determined by the total NEA mass flow rate and this is the dominant contributor to the draining time, with the number of NEA nozzles playing a minor role. We confirmed this by pumping NEA directly into the ullage, where we observe a significant decrease of water even when the NEA is not pumped through the fuel. We also show that doubling the mass flow rate halves the draining time. When considering the capability of most modern aircraft to pump NEA through the fuel as part of their inerting system, the proposed method for removing water is particularly attractive, requiring very little (if at all) design modification.

AB - This paper concerns a computational study of the process of removing water from an aircraft’s fuel tank by pumping nitrogen enriched air (NEA) from the bottom of the tank. This is an important procedure for the smooth, efficient, and safe operation of the aircraft’s engine. Due to the low partial pressure of water in the pumped NEA, it absorbs water from the fuel. The water-laden bubbles enter the ullage, the empty space above the fuel, and escape into the environment. The effects of the number of NEA inlets and the NEA mass flow rate on the timescale of the NEA pumping were investigated using Computational Fluid Dynamics. The results reveal that the absorption of water by the NEA bubbles is low and is not affected by the number of the inlets used. Yet, the water content in the fuel decreases fast during the procedure, which is the desired outcome. We show that this is due to the relatively dry NEA entering the ullage and displacing the moist air, thus reducing the partial pressure of water at the fuel/ullage interface. This shift from equilibrium conditions forces water to evaporate from the fuel’s entire surface. Furthermore, the amount of water migrating from the fuel directly into the ullage is significantly greater than that absorbed by the rising bubbles. In turn, the rate of decrease of the water content in the ullage is determined by the total NEA mass flow rate and this is the dominant contributor to the draining time, with the number of NEA nozzles playing a minor role. We confirmed this by pumping NEA directly into the ullage, where we observe a significant decrease of water even when the NEA is not pumped through the fuel. We also show that doubling the mass flow rate halves the draining time. When considering the capability of most modern aircraft to pump NEA through the fuel as part of their inerting system, the proposed method for removing water is particularly attractive, requiring very little (if at all) design modification.

KW - fuel tank

KW - water

KW - nitrogen enriched air (NEA)

KW - aircraft

KW - inerting system

KW - dehydrate

UR - http://www.mdpi.com/journal/energies

U2 - 10.3390/en11040908

DO - 10.3390/en11040908

M3 - Article

VL - 11

JO - Energies

T2 - Energies

JF - Energies

SN - 1996-1073

IS - 4

M1 - 908

ER -