Aircraft Fuel Tanks Research Articles

Effect of Structure on Reactor Performance in Fuel Vapor Catalytic Inerting System for Aircraft Fuel Tanks

Effect of Structure on Reactor Performance in Fuel Vapor Catalytic Inerting System for Aircraft Fuel Tanks

Impact of Internal Baffle Designs on Liquid Hydrogen Sloshing in Cryogenic Aircraft Fuel Tanks

Hydrogen because of its zero carbon emissions and highly energy-dense nature has a strong potential to be used as an aviation fuel. There are currently two main ways that hydrogen is being considered for use in aircraft: it can be vaporized and mixed with air before being burned in the jet engine, or it can be used to power fuel cells that generate electricity, which can be used to power electric motors. Both these scenarios would require storing liquid hydrogen (LH2) in cryogenic tanks on board as it minimizes the tank size. But a major challenge with cryogenic hydrogen storage is the dynamic movement of the fuel which can lead to fuel boil off and bubble formation. In the current paper, the sloshing motion of LH2 in a CHEETA type thin-walled composite fuel tank, under acceleration data obtained from an Airbus A-320 in cruising conditions, is investigated. The dynamic fluid structure interaction problem is solved numerically using the Coupled Eulerian-Lagrangian (CEL) technique in ABAQUS. The developed modelling strategy is then employed to study the impact of various internal baffle designs on the sloshing behavior of the fuel under different fill levels. This study not only establishes that sloshing is a major cause for concern when it comes to LH2 aircraft fuel storage, but also advances our understanding in devising potential mitigative strategies.

Spectroscopic and Microscopic Characterization of Microbial Biofouling on Aircraft Fuel Tanks.

Avoiding microbial contamination and biofilm formation on the surfaces of aircraft fuel tanks is a major challenge in the aviation industry. The inevitable presence of water in fuel systems and nutrients provided by the fuel makes an ideal environment for bacteria, fungi, and yeast to grow. Understanding how microbes grow on different fuel tank materials is the first step to control biofilm formation in aviation fuel systems. In this study, biofilms of Pseudomonas putida, a model Gram-negative bacterium previously found in aircraft fuel tanks, were characterized on aluminum 7075-T6 surfaces, which is an alloy used by the aviation industry due to favorable properties including high strength and fatigue resistance. Scanning electron microscopy (SEM) coupled with energy-dispersive X-ray (EDX) showed that extracellular polymeric substances (EPS) produced by P. putida were important components of biofilms with a likely role in biofilm stability and adhesion to the surfaces. EDX analysis showed that the proportion of phosphorus with respect to nitrogen is higher in the EPS than in the bacterial cells. Additionally, different morphologies in biofilm formation were observed in the fuel phase compared to the water phase. Micro-Fourier transform infrared spectroscopy (micro-FTIR) analysis suggested that phosphoryl and carboxyl functional groups are fundamental for the irreversible attachment between the EPS of bacteria and the aluminum surface, by the formation of hydrogen bonds and inner-sphere complexes between the macromolecules and the aluminum surface. Based on the hypothesis that nucleic acids (particularly DNA) are an important component of EPS in P. putida biofilms, the impact of degrading extracellular DNA was tested. Treatment with the enzyme DNase I affected both water and fuel phase biofilms─with the cell structure disrupted in the aqueous phase, but cells remained attached to the aluminum coupons.

Nonequilibrium model of water generation in Aircraft Fuel Tanks

To investigate the formation of water contaminants in fuel tanks, a nonequilibrium model based on heat and mass transfer is established, and the dissolved water, suspended water, condensed water, free water are analyzed under different conditions. The results show that: With the increase in the heat transfer time constant between fuel and ullage, the volume of condensed water and free water will reach its maximum. The largest volume of free water calculated in this research occurs when the heat transfer time constant between fuel and ullage is equal to 1 ms−1 and 0.8889 L of free water are produced. The time constant of condensation has a similar effect on the volume of condensed and free water as the heat transfer time constant between fuel and ullage. Compared with the effect of the heat transfer time constant between fuel and ullage, the volume change of condensed water and free water is smaller. When the time constants are less than 1 ms−1, the volumes of suspended water, condensate water, and free water increase obviously with the increase of the time constants, and the volume of dissolved water decreases gradually, but these phenomena become less obvious after the time constants increase to 1 ms−1.

Prediction of Lightning Currents on Fastening Assemblies of an Aircraft Fuel Tank With Machine Learning Methods

An important challenge for the aircraft industry consists to predict the currents on the fastening assemblies in order to avoid sparking, which can lead to accident, especially for fuel tank fasteners. In the literature, it has been demonstrated that the contact resistance plays a major role in the current path on fasteners. Nevertheless, these contact resistances cannot be well determined and vary greatly. As a result, the prediction of current must be done in a statistical way. Usually, it requires several aircraft simulations with several set of contact resistances, which represents a significant computational cost. This article proposes a machine learning model, which allows us to predict the currents in the fastening assemblies of an aircraft fuel tank in a few seconds. This model is built from a database of FDTD simulations of the aircraft fuel tank in the lightning frequency range 100 Hz to 1 MHz. The FDTD modeling is depicted in detail in this article based on previous work. From this database, several machine leaning approaches are explored ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$k$</tex-math></inline-formula> -nearest neighbors, support vector regression, XGBoost, and a neural network). As a result of this study, XGBoost presents the best performances. Further investigations using XGBoost highlights the ability of the model to predict well the current for most fasteners and frequencies, even with a small amount of simulations as training data. Moreover, the proposed model allows us to perform a parametric analysis, which underline the ability of the model to provide results in agreement with the physical effects of the issue (current paths, resistive effects, inductive effects, etc.). The results presented are promising for the use of the proposed methodology in the aeronautical industry.

Segmentation and Evaluation of Crack Image From Aircraft Fuel Tank via Atrous Spatial Pyramid Fusion and Hybrid Attention Network

Jet fuel leaks not only waste resources and increase costs but also pose a risk of emergency landings and aviation accidents. With the blossom and implementation of deep learning, crack segmentation techniques have been rapidly developed in many fields. However, it is struggle to get accurate and complete crack segmentation results because of images’ complex background environment. To address this issue, we collected and labeled a dataset of 2824 crack images from the surface of aircraft fuel tank, named CAFT2800. And this article presents an atrous spatial pyramid fusion and hybrid attention network based on deep learning to deal with the complicated environment. The backbone of network uses a hierarchical structure Swin Transformer to extract features. In the neck of the network, an atrous spatial pyramid fusion module is proposed to further capture contextual information in multiple scale. Unlike the ASPP module, which aggregates image-level information with pooling, we abandon this operation according to the characteristics of crack. And the neck structure is designed for fusing high-level semantic information to all scales. At the gate between the neck and the decoder head, a SK (selective kernel) block is embedded into the network to recalibrates channel-wise feature responses. Due to the morphological characteristics of crack, we propose an evaluation index, Thinning F1 score (TFscore), which is more meaningful compared to the commonly used F1 score. Sufficient control experiments were conducted on the CAFT2800 dataset and two complicated environment benchmarks (DeepCrack and GAPs) to test the effectiveness of the network, and our method achieved superior performance. Source code and the CAFT2800 are available at https://github.com/Gu-EH/CAFT2800.

Raw Scanned Point Cloud Registration with Repetition for Aircraft Fuel Tank Inspection

The aircraft fuel tank, as the source of fuel supply, is one of the key components for an aircraft. It is fastened to the fuselage with thousands of rivets, in which each rivet is sealed carefully to prevent the leakage. Thus, the sealing quality of the aircraft fuel tank needs to be precisely measured to ensure its normal function. To achieve the measurement, the complete 3D point clouds captured by 3D scanning are usually utilized. Therefore, it is necessary to align the different views of the aircraft fuel tank point clouds, to obtain the complete data. However, the aircraft fuel tank consists of abundant repetitive structures, such as the regular-distributed rivets, which can lead to mismatches in the aircraft fuel tank point clouds if using the conventional registration methods. In order to address the challenges, we propose a new registration framework, which is able to handle the point cloud match under the repetitive and complex scenes. First, a novel 3D descriptor called LP-PPF is constructed with the point and line features from the aircraft fuel tank point clouds, so as to identify the repetitive structures correctly. Then, according to the proposed descriptor, the accurate registration can be achieved between the neighboring point cloud pairs. Finally, based on the results of pairwise registration, the complete aircraft fuel tank point cloud can be obtained via the multi-view registration method. Experiments demonstrate that our method achieves favorable results on both synthetic and raw scanned point cloud data.

Analytical Algorithm for Oxygen Concentration of Aircraft Fuel Tank in Various Inerting Stages

Ullage washing is an efficient inerting method to keep the ullage oxygen concentration under the safe value, thus reducing the hazard and loss of fire and explosion of aircraft fuel tanks. In the conventional model of ullage washing, the initial derivatives of oxygen concentration that are used to solve the differential equations are selected subjectively by researchers and the empirical select influences the accuracy of the result. Therefore, this paper proposes an analytical algorithm that can calculate the ullage oxygen concentration without selecting any initial derivative value. The algorithm is based on a fuel tank ullage washing model regarding various inerting stages. It has been experimentally validated with an average relative error of 5.781%. Moreover, sensitive analyses carried out on the proposed model show that ground-based inerting can effectively reduce the ullage oxygen, concentration in the climb phase. Increasing 5 min of pre-takeoff inerting duration can shorten the time of decreasing the ullage oxygen concentration to 9% after takeoff by 2.1 min.

Eeloscope—Towards a Novel Endoscopic System Enabling Digital Aircraft Fuel Tank Maintenance

In this research article, a novel endoscopic system, which is suited to perform a digital inspection of the aircraft wing fuel tanks, is introduced. The aim of this work is to specifically design and develop an assisting system, called `Eeloscope’, to allow accessing and diving through an aircraft kerosene tank in a minimally invasive matter. Currently, mechanics often suffer from the harsh working environment and the arduous maintenance duties within the tank. To address such challenges and derive a tailored solution, an adapted Design Thinking (DT) process is applied. The resulting system enables a fully digital inspection and generation of 3-dimensional structural inspection data. Consequently, devices such as the Eeloscope will facilitate a more efficient and continuous inspection of fuel tanks to increase the transparency regarding the condition of hardly accessible aircraft structures and provide a work relief for mechanics at the same time.

Lightning Currents on Fastening Assemblies of an Aircraft Fuel Tank—Part III: Validation of the Current Assessment Method With Measurement

This article proposes a new fastener model and validate the stochastic process for the lightning current assessment in the aircraft assemblies proposed in the previous parts. In particular, the stochastic method concerns the finite-difference time domain (FDTD) fastener modeling for which the variability of the contact resistance has to be taken into account. The principle is to merge an electromagnetic fastener model with an uncertainty model. The new fastener model proposed in this article is a wire with a lumped resistor on a low conductive plate. This model is an improvement of the model of Part I, where the fastener is only represented by a wire with a lumped resistor. The proposed model in this article is able to ensure a good shielding effectiveness without current distribution disruptions provided that the conductivity of the plate is weak in contrast to the lumped resistor. Moreover, it has the benefits to be able to represent any fastener without location constraint in the FDTD grid. A log-normal distribution has been previously established as uncertainty model that represents the variability of the resistive parameter. The fastener model is included in the FDTD modeling of a realistic fuel tank with each lumped resistor taking a probabilistic value according to the log-normal law. To take into account, the variability of resistors, several simulations with different sets of resistance values are performed. The aim is to surround current measurements with simulated currents at various locations of the fuel tank for a lightning injection performed directly on a fuel tank fastener. This article demonstrates that a specific attention must be given to the modeling of fasteners close to the lightning injection point for the current assessment. Moreover, the results highlight the relevance of the use of an uncertainty model and its reliability for the lightning current assessment.

Lightning Currents on Fastening Assemblies of an Aircraft Fuel Tank, Part II: FDTD Modeling Merged With a Circuit Model Supplemented by a Statistical Model

This paper presents a fastening assemblies FDTD model based on a lumped element circuit integrated into thin wire formalism. It can be used to quantify current dispersion or extreme current in aircraft fuel tank fasteners and to optimize the lightning protection in hotspot zones. An original method allows the characterization of the fastener lumped resistances. This method dealing with dc measurement and an optimization process is validated provided that 1) the measurements number is greater than the lumped elements number and 2) each node of the circuit is used at least once. Due to the large uncertainties from one fastener to the other one in the same family, the circuit model is supplement with a statistical model using the results about the fastener resistances state after a lightning shot presented in part I. Stochastic distribution values are applied to each lumped resistance of the fastener circuit model. Making a hybridization between a circuit solver and the finite difference time domain (FDTD) method, the circuit model is added in the same three-dimensional FDTD generic fuel tank modeling as presented in part I. Comparing the current distributions of the simple model of the part I and the circuit model, the uncertainties introduced by each model are presented.

Lightning Currents on Fastening Assemblies of an Aircraft Fuel Tank, Part I: Uncertainties Assessment With Statistical Approach

This paper proposes a statistical approach in order to assess the fastening resistances uncertainties in aircraft assemblies. This method relies on the use of the maximum likelihood estimation method, several statistical tests, and/or statistical criteria. Using the Dassault-Aviation measurement database, distribution laws are established in order to characterize uncertainties in the lightning impact on the fasteners. A simple finite-difference time-domain (FDTD) fastener model is proposed with a wire and a resistance. This generic model can represent any fasteners. The statistical model established from the fastener resistances state after a lightning shot is used to define the stochastic distribution values in the fastener electric model. This model is added to a 3-D FDTD parallelepiped generic fuel tank model. In this paper, we compare the current distributions between a composite and metallic fuel tank. The results highlight not only the model uncertainties effects on the statistical approach but also the fuel tank material choice impact.

Safety Assessment of Aircraft Fuel Tank Access Cover under the Impact Load by Tire Fragments

According to relevant airworthiness standards, the aircraft fuel tank access cover must withstand the impact by tire fragments, and minimize the penetration and deformation, which is critical for flight safety. To assess the safety of an aircraft fuel tank access cover subjected to tire fragments, a study of dynamic response was presented in this paper using the Finite element (FE) software ANSYS/LS-DYNA. To obtain the reliable mechanical characteristics of tire tread rubber, a series of material tests have been conducted. Then the proposed rubber material model is validated by comparing the numerical simulations with the experimental results of aluminium alloy plate impact. The simulation results indicate that the rubber fragment and alloy plate will undergo the largest deformation when impact angle is equal to 90°. Finally, the proposed FE model and modelling approaches are extended to the numerical simulation of a full-scale aircraft fuel tank access cover impact. The numerical simulations are carried out with impact velocity of 71.1 m/s and impact angle of 40.5°. The simulation results indicate that the aluminium alloy by precision casting is more likely to rupture, and the middle region of the access cover is vulnerable to fragment impact. This research proposes a reliable rubber model applying to various strain rates. Considering the influence of impact regions, the dynamic response and various failure patterns of fuel tank access cover are acquired. The findings of this paper can be used to improve the future aircraft safety design.

Experimental Comparison of Fuel Scrubbing Inerting Process Using Nitrogen and Carbon Dioxide of Aircraft Fuel Tanks

Fuel scrubbing technology could be used for fuel tank inerting and fuel deoxygenation. Both N2 and CO2 are perfect inert gases, but the solubility of CO2 is nearly 20 times higher than that of N2 in jet fuels, so the scrubbing inerting process varies with the selection of N2 or CO2. A scrubbing test bench is constructed, and the variation of oxygen concentration on ullage or in the fuel is measured under various flow rates, fuel loads and initial oxygen concentrations on ullage. Experimental results reveal that the ullage and dissolved oxygen concentrations of CO2 scrubbing are always higher than that of N2 scrubbing. The inerting time of CO2 scrubbing of a 30%, 50% and 70% fuel load is approximately 1.42, 1.7 and 2.75 times that of N2 scrubbing, respectively. The scrubbing test under 5%, 9% and 14% initial ullage oxygen concentration revels a peak in ullage oxygen concentration of 7.23% and 9.97% for N2 scrubbing and that of 12.63%, 13.4% and 15.4% for CO2 scrubbing, respectively.

Impact of Synthetic Hydrocarbon in Biofuels on Two Polysulfide Aircraft Fuel-Tank Sealants

Abstract The impacts of synthetic hydrocarbon in biofuels on two fuel-tank polysulfide sealants were systematically studied in this research. Synthetic hydrocarbon was derived from waste oils and fats and produced by hydroprocessed esters and fatty acids process (HEFA). The experimental results revealed that the volume of two polysulfide sealants shrunk after being immersed in the pure biofuels for 28 days at 93°C. Furthermore, mechanical properties, such as elongation rate and hardness, failed to satisfy the requirement of the specification. The experimental results also showed that the volume swell of two polysulfide sealants varied from jet reference fuel (JRF) more than 5 % after being immersed in the blended fuels when neat biofuel component was mixed with No. 3 jet fuel in a volume ratio of 50/50. The mechanical properties of elongation and hardness still cannot meet the requirements of the specification. The results demonstrated that synthetic hydrocarbons in biofuels would have a significant impact on the polysulfide sealants of the aircraft fuel tank.

Stress and Deformation Analysis of Aircraft's Fuel Tank under Different Inertia Load Cases in Addition to a Static Test Pressure Using FEA

In the modern era the aerospace technology plays a very significant role in the development of the mankind. The evolution of the light weight aircraft has a special focus in the present industrial trends. Several research organizations are in the process of developing Light Weight Aircraft, which is ideally suited for civil transport, aerial survey, training etc. This Light Weight Aircrafts are to be designed accordance to Federal Aviation Regulations part 23 (FAR-23). This paper deals with the analysis of the Aircraft's Fuel Tank under variable conditions. The analysis of aircraft fuel tank is carried out for different inertia load cases in addition to a test pressure of 3.5psi (24KPa), to validate whether the structure is safe or not. The size of the fuel tank has been taken as per the FAR-23 guidelines. The Finite Element Analysis is carried out to arrive at stresses and displacements in critical components using the Ansys software. The maximum shear stresses included are observed to be much less than the Yield strength of materials.

Aircraft Fuel Tank CATIA Model Pretreatment Method for Quality Property Calculation

According to the requirement of aircraft fuel quality property calculation, this paper studied pretreatment methods for tank CATIA model. Firstly, extract outside surfaces of wing skins, start and end wing ribs, front and back spars and then joint them to create a complete closed surface by additional repairing surfaces gap. Secondly, inside the closed surface, bool operation is utlized to remove actual bodies of fuel tank structures and internal accessories from the model of fuel tank. Direct accurate calculation of fuel quality property in CATIA environment is then achieved. Finally,simulation is carried out with an real aircraft fuel tank, comparison between simulation results and test data shows that relative error of pretreated fuel tank volume model is less than 1%, which satisfies engineering requirements.

Numerical Study of the Influence of Ambient Pressure on the Inerting Effect of an Aircraft Fuel Tank Inerting System

The numerical study of the influence of the ambient pressure of the fuel tank on the inerting effect of an aircraft fuel tank inerting system was carried out. The mathematical model of ullage equilibrium oxygen concentration has been established using the differential time calculation method based on the mass conservation and ideal gas state equations. The variations of ullage oxygen concentration and dissolved oxygen concentration in the fuel with time under different working conditions have been obtained. The results have shown that the as the ambient pressure of the fuel tank became lower, the speed of the decreasing of oxygen concentration of the fuel tank ullge and the dissolved oxygen concentration of the fuel was slower.

Electrochemical Oxygen Separation from Aircraft Fuel Tank Ullage

Combustion of oxygen rich fuel vapors in aircraft fuel tanks can lead to explosions and fires. This was demonstrated unfortunately on July 17, 1996 with a Boeing 747 exploding in mid-air due to heated, highly explosive fumes in the center fuel tank. Sloshing of fuel, lightning and static discharge, and, for military aircraft, enemy ground fire can pose significant risks to the fuel tanks when the oxygen content is greater than 9%.Given the importance of fuel safety for both military and commercial aircraft, improved fuel inerting systems are needed that make these fuel tank ullage vapors non-explosive. This is often done by adding a nitrogen-rich gas stream to the fuel tank to reduce the oxygen content to less than 9%, a level that mitigates combustible explosive mixtures. On-board inert gas generating systems (OBIGGS) have been used on aircraft where engine bleed air is used as a pressurized air source flowing through a zeolite adsorption bed to separate oxygen and nitrogen molecules. The resulting enriched nitrogen stream fills the tank ullage lowering the oxygen content to non-explosive limits, however, this occurs at the expense of engine power.For certain military aircraft such as the V-22, the use of compressed engine bleed air to drive the separation process is not desirable, especially in landing zones that throttle back the compressor. For this reason, an electrochemically driven inerting system was developed by Reactive Innovations using a collection of membrane and electrode assemblies to remove the oxygen from the fuel and air mixture. The operating principle behind the separation process is to electrochemically reduce the oxygen in the fuel-air mixture to a water molecule that migrates via diffusion across a polymer ion-exchange membrane. On the opposing anode side, this water molecule is oxidized releasing protons that migrate to the cathode maintaining the separation process. This process is shown in Figure 1.The separator cell consists of a 5 mil thick Nafion membrane that is catalyzed with platinum on the cathode surface and catalyzed with a platinum/iridium oxide mixture on the anode. Air or a mixture of fuel and air flows over the cathode surface while an imposed voltage is applied to drive the process. The resulting current is measured over time while the cathode and anode outlet streams are sent individually to a gas chromatograph to measure the constituent concentrations.To avoid introducing or using external water with this separator that could affect the fuel quality, the separation process uses the internal hydration state of the membrane to facilitate the electrochemical separation process. This requires that the diffusive water flux from cathode to anode is balanced by the electro-osmotic drag of water from anode to cathode. Operating the separator at too fast of a separation rate causes regions of the membrane separator to dry out lowering the transport rate. This behavior is shown in Figure 2 where an applied voltage of 1 to 2.5 volts was used to drive the process. Stable current profiles were obtained up to about 1.75 volts with higher applied voltages causing the current profiles to decay.Cascaded operation was examined with one or two separators in series showing that the oxygen content in the tank ullage could be reduced to less than 9% as shown in Table 1. This indicates that the separator can be sized accordingly to extract the oxygen from the fuel-air mixtures.Acknowledgment: This work was supported by Navy Contract No. N68335-11-C-0397.

The Oxygen Concentration Measurement of an Aircraft Fuel Tank Inerting System

There are several oxygen concentration measurement methods applied in aircraft fuel tank inerting systems. In this work, an aircraft fuel tank inerting experiment system was built and oxygen concentration of the fuel tank ullage (fuel tank space above the surface of the fuel which is filled with fuel vapor and air) and the dissolved oxygen in the fuel was detected with the methods of light absorption and optical fluorescence. The experiment was conducted through different operating conditions and results has illustrated that the light absorption method as well as the optical fluorescence method has the same accuracy sensing calibration gases, but the suitable condition of the two methods are different. Results have shown that the method of light absorption is more suitable to test oxygen concentration of gas mixture, and the method of optical fluorescence is more suitable to detect the concentration of dissolved oxygen in liquid substance.