SUPERIORITY OF hydrogen fuel IN HIGH ALTITUDE LONG ENDURANCE UNMANNED AERIAL VEHICLES
Abstract – The use of liquid hydrogen fueling in aircraft engines has many advantages over typical gasoline powered engines in an aircraft. This paper will analyze the design, process, and plausibility of the use of liquid hydrogen fueled HALE (high altitude long endurance) UAVs (unmanned aerial vehicle).
As inferred from the name, this aircraft is capable of flying at extremely high altitudes for extended periods of time, which gives the aircraft many benefits over an average hydrocarbon fueled vehicle. Specifically this paper will discuss the processes of hydrogen fuel cell powered engines of UAVs and their effects on the capability for high altitude, long duration flight. This paper is also designed to report on the technical specifications of such an aircraft in regards to the requirements for a hydrogen fuel cell propulsion system. It will focus partially on the lightweight yet stable architecture of HALE UAVs and how it contributes to their ability to achieve longer mission durations. This analysis includes in depth examination of cryogenic hydrogen fuel tanks and the on board equipment used to facilitate the hydrogen fuel cell powered system. It will also discuss the on board conditions that need to be maintained to produce maximum results. Then the paper will also consider favorable properties of hydrogen in comparison to properties of other hydrocarbon fuels in terms of power generation, environmental effects of emissions and cost reduction, further proving conceivable use in aviation. It will examine the environmental impact, as well as the cost advantages of production, of hydrogen fuel versus other hydrocarbon energy sources. Hydrogen fuel is not the perfect answer to the energy dilemma, but it has many advantages over traditional energy sources, especially for use in high altitude, long endurance aircrafts.
The Term Paper on Human Variations In High Altitude Populations
Human Variations in High Altitude PopulationsJessyca Camo 26 november 1996 Thesis: The purpose of this paper is to describe the high altitude stresses and the general adaptations made by the Tibetan population in the Himalayas and the Quechua in the Andes. I Introduction II Background A Quechua People B Tibetan People III General Adaptations A Physical 1 Growth 2 Development 3 Core temperature 4 ...
Key words: hydrogen fuel, HAL UAV, sustainability, renewable energy, environmental protection
IMPORTANCE OF HYDROGEN FUEL POWERED HALE UAVS
Hydrogen fuel powered high altitude long endurance (HALE) unmanned aerial vehicles (UAVs) is a new technology that shows the progress of science and innovative thinking. The new technology will greatly help the military and other private security companies by providing them with valuable surveillance information. As Ted Wierzbanowski, the managing director at AeroVironment, states on the importance of HALE UAVs, “Military planners have articulated that this demand for persistence far exceeds the existing and planned capabilities of conventional airborne and satellite systems.” [3]. In the
past few years Boeing has been finalizing and presenting a HALE UAV model aptly named the Phantom Eye. This is a liquid hydrogen fueled HALE UAV that collects surveillance information essentially unnoticed and can complete missions upwards of a four days without landing or refueling [5].
Aircrafts powered by traditional fuels do not have the ability to travel as far as needed, and satellite surveillance is limited by location [3]. Using hydrogen fuel to power these aircrafts instead kerosene or other fuels allows them to fly for much longer periods of time and at extremely high altitudes without refueling. For a HALE UAV to be effective it must have low power requirements, lightweight construction, and an efficient power propulsion system. Hydrogen fuel has a much higher energy density than tradition fuel sources and can therefore meet these goals [4].
Hydrogen fuel powered aircrafts are also a major
development of the use of alternative energy sources. This scientific advancement is a great example of alternative energy sources being more effective than traditional sources. On the importance of finding new energy sources, Boudries and Dizene, from the Algerian Center for Renewable Energy Development, state that “growing concern over diminishing reserves of fossil fuels and fear of the environmental consequences have led to the active search for new energy sources” [6]. They also report that hydrogen energy is one of the best alternative energy sources to kerosene. In comparison with other renewable energy sources hydrogen is reliable because its obtainment does not depend on uncontrollable conditions For instance, solar power depends on the availability of sunlight, but hydrogen is always obtainable [6].
The Essay on Hydrogen Fuels Powered Vehicle
Introduction This report covers the new advancement in alternative fuels, specifically hydrogen power, and is intended for the general public as it affects everyone in the world. We, as a whole, have become more aware of the ever-increasing problem of pollution and its effect on the environment in the past two decades. We are noticing such effects as global warming, the green house effect, acid ...
Hydrogen fuel could also give developing nations the
potential to be fuel-producing nations. If using hydrogen power becomes a successful endeavor then every nation will be able to produce this fuel, not just the nations that have guaranteed oil reserves. This idea gives rise to the sustainability of hydrogen as a fuel source. If just about any nation in the world has the resources to produce this type of fuel, it could create a worldwide increase in quality of life. For example, an article published in the International Journal of Hydrogen Energy by Boudries and Dizene explores the potential of hydrogen power production in the country of Algeria. Since everyone is dependent on energy, having a country be able to produce their own energy would allow for a very significant source of income. “For Algeria, hydrogen is of paramount importance. It permits the country not only to increase and to diversify its energy mix but also to keep its share of the energy market at the international level and to meet its domestic demand that is becoming more and
University of Pittsburgh,
Swanson School of Engineering 1 2/7/13
more important.” [6]. Thus, it is the responsibility of modern engineering to create sustainable energy technologies and the development of hydrogen fuel powered HALE UAVs can help contribute to the advancement of sustainable energy technologies.
The Essay on Hydrogen Fuel Cell Benefits And Limitations
What are some benefits or limitations of the alternative technology regarding economics? (What will it cost to purchase, re-fuel, launch, educate and distribute?) Benefits. No pollution: A great benefit of using Hydrogen fuel cells is that they give off no pollution, and in fact produce pure water as a byproduct. Even though currently engineers are concentrating on producing hydrogen from natural ...
WHAT IS HYDROGEN FUEL?
Turning Hydrogen Into Fuel
The first step in creating hydrogen fuel is making liquid hydrogen. Liquid hydrogen is obtained in many different ways, each with its own advantages and disadvantages. One technique is steam reformation, which uses natural gas. Hydrocarbons are heated with steam to temperatures of 800 degrees Celsius to 900 degrees Celsius, and they are split usually using a nickel catalyst. Liquid hydrogen can also be isolated using renewable energy sources. Some ways of doing this are photovoltaic cells, solar thermal energy, wind power, hydropower, and biomass. In addition another way to obtain hydrogen is by using electrolysis. When using electrolysis energy is added to an electrolytic cell to make the hydrogen separate from the oxygen; an example cell is demonstrated in Figure 1 below [7].
FIGURE 1
Diagram of hydrogen production by electrolysis [7]
A large amount of these cells are added together, and they release hydrogen gas. The hydrogen gas is kept separate from the oxygen gas using a diaphragm. Then the hydrogen is cooled down into a liquid [7]
Cooling down the hydrogen is one of the more difficult
steps, because there is not a way to do it that does not involve using energy. The best way to liquefy hydrogen would be to do it without using heat, and instead use pressure. There are several ways in theory to do it, but none of them are practical when it comes to being performed on an airplane. This is because the equipment to do so is too large and would take up too much space. Instead, the hydrogen is cooled down gradually, commonly by using liquid nitrogen. This requires about 0.00244 MJ/kg of hydrogen to be done, therefore it needs electricity [7].
At the Massachusetts Institute of Technology, the Cryogenics Engineering Laboratory is studying the possibility of large-scale liquefaction of hydrogen. The model they made converts hydrogen at high pressures, because when hydrogen is generated it often happens at high pressures. This also helps eliminate errors that occur when the hydrogen gets near to the supercritical point. The model has many promising aspects, for instance it is safer then other cycles, can be scaled to a larger size, and is can be upgraded to work with a different catalyst [8]. This is a very promising development, because it shows how the future of hydrogen is being improved.
The Term Paper on Fuel Cell Technology Power Cells Energy
Fuel cell technology 1 Running head: FUEL CELL TECHNOLOGY: TRANSPORTATION AND RESIDENTIAL/ COMMERICAL APPLICATIONS Fuel Cell Technology: Transportation and residential / commercial applications Monique University 2 A fuel cell is an electrochemical energy conversion device. A fuel cell converts the chemicals hydrogen and oxygen into water, and in the process it produces electricity. With a fuel ...
The Power Advantages and Disadvantages of Hydrogen Fuel
By comparing hydrogen with other types of fuels we can see that hydrogen has both advantages and disadvantages. Gravimetric density is the measure of energy per mass unit. This is used to compare fuel sources, because the greater the gravimetric density number the greater the amount of fuel there is that can be carried. Hydrogen’s gravimetric density is 120 MJ/kg where kerosene’s is 43 MJ/kg, methanol’s is
20 MJ/kg, and propane’s is 46 MJ/kg. As you can see
hydrogen has 74 MJ/kg more energy then the next highest fuel, making it a significantly better fuel source. However, the volumetric density is not nearly as efficient. Volumetric density is similar to the gravimetric density except it compares the volume instead of the mass to the energy. Looking at the volume is important, because the fuel with the least volume will allow the plane fit more fuel onboard. Kerosene’s volumetric density is 35 MJ/L, methanol’s is 16 MJ/L, and propane’s is 25 MJ/L, where hydrogen’s is 8.4 MJ/L. The low volumetric density causes an issue, because it requires the tank to be larger for hydrogen then other fuels. Having a larger tank will give the aircraft more weight and a greater surface area, which will make the aircraft less efficient [7]. Different types of tanks will be compared later on in the paper.
HOW DOES THE FUEL CELL WORK?
Basic Description of a Fuel Cell
The power from Hydrogen is obtained by using a hydrogen fuel cell. A hydrogen fuel cell works by reacting liquid hydrogen with oxygen, which makes water. The most difficult consideration of this process is obtaining the liquid hydrogen fuel. The fuel cell converts the fuel directly into electricity, which is why it is so much more efficient than other fuels. The fuel cell works by having half of the cell contain hydrogen gas and the second half contain oxygen. There is an electrolyte, a membrane that only allows positive ions to pass through, between them. The cell also contains a
catalyst, which it uses to split the hydrogen into an H+ ion and an electron. The electrons travel through a circuit and the H+ ions will travel through the electrolyte membrane to the oxygen. They then combine with the oxygen and form water. The electricity is taken from the electrons traveling through the circuit [9].
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History of the Propeller The aircraft propeller looks like a simple mechanism to the uneducated individual. To the educated, an aircraft propeller represents the highest sophistication in aerodynamics, mechanical engineering and structural design. This report will touch on the history of the propeller, from early pioneers/experiments, advancement during/after the war, all the way up to current ...
Solid Oxide Fuel Cell
Research is also being done using a solid oxide fuel cell (SOFC).
The scientists at the Imperial College London designed models of different SOFCs to study their usefulness in HALE UAVs. One of the problems of using a solid oxide fuel is that the pressure needs to remain constant. The compressor required to achieve this would take up too much space on the aircraft. The scientists then looked at multi-stack systems, which combine more than one fuel cell. They discovered that when they put air intercoolers in between them the compressor does not need to be as large, and the efficiency increases. This is very promising research, but other research needs to be done before this can be implemented. Some of the other aspects that need to be looked at are the weight, volume, if it meets the different power requirements, and if the needed amount of liquid hydrogen needed can be stored on the airplane [2].
Combining Fuel Cells and Batteries
An alternative study done by the Korea Science and Engineering Foundation made a system for UAVs powered by both a fuel cell and a lithium battery. The set up for the fuel cell system contained the fuel cell, the hydrogen generator, and the hybrid power management system. The hydrogen generator then consisted of a fuel cartridge, a micropump, a catalytic reactor, a gas-liquid separator, and a dehumidifier. To provide the hydrogen they used sodium borohydride, which through the micropump was inserted into the catalytic reactor, which decomposes the sodium borohydride into hydrogen gas and liquid borate. They are then transferred to the gas-liquid separator where they are separated, and the dehumidifier then purifies the hydrogen. After that the hydrogen is transferred to the fuel cells to create the energy. The energy from this process is used for when the UAV is cruising, since it is good at providing lower amounts of energy for long periods of time. The lithium battery is used during takeoff and landing since it can provide more power but only over a shorter period of time [1].
The Essay on Fuel Gauges Tank Gauge Float
the is cut and pasted off. com to get an account If you " re like me, you like to squeeze every last mile you can out of your tank of fuel. If you could get 20 miles extra from each tank, that could save you two or three trips to the gas station over the course of a year. The main impediment to stretching your mileage is the fuel gauge on your car, which makes you think you have less fuel than you ...
THE PROPULSION SYSTEM
The propulsion system of the HALE UAV usually consists of a motor and a propeller system. The propeller drives usually consist of a power converter, an electrical machine, and occasionally a gearbox. The researchers at the Israel Institute of Technology describe in detail all of the
aspects of the propeller that are analyzed. Since the aircraft is supposed to be as light and efficient as possible, the design of the propeller is considered for its weight and also to see which design allows the aircraft to stay in the air as long as possible. Its diameter, the air density, the velocity of the air, and the effectiveness of the design are all aspects that are looked at to judge the propeller [10]. They analyze the number of propellers, blades, the radius of the propeller, and the rotational speeds are analyzed. They test different combinations of these aspects to see which makes the lightest and most effective propeller. Then the different qualities of the blade that are analyzed are pitch angle, chord, sweep angle, dihedral angle, mass and inertia, structural properties, etc. Then optimization methods are used to figure out the best values. This is done by using different schemes and algorithms, as well as having an engineer adjust the measurements of the different if the algorithms and schemes have not worker quite right. [11].
The Georgia Institute of Technology is going to use the
classic propulsion system consisting of a motor and propeller combination to power their aircraft. To figure out which combination would be the most effective and light they made an analysis code using momentum and blade element theory [12]. A general model of the motor was created, and they used that to help them choose potential motors. They have considered over 30,000 different combinations to find the one with the maximum efficiency, or thrust margin. To compare the different combinations they were tested with flight velocities of 0 ft./s, 46 ft./s, and 60 ft./s. After this comparison they came up with the Hacker C50 13XL being the best model, and purchased one. After purchasing it though they realized that the peak current of the motor would not be the peak current of the overall system, because the fuel cell limits the current. They repeated their analysis with the new parameters and got the comparisons down to in between the Hacker B50 17XL with a 24×24 propeller, the Hacker C50 13XL with a 22×20 propeller, the Hacker B50 14XL with a 22×20 propeller, and the NEU 1515 1.5Y with a 22×20 propeller. As shown in Figure 2 by comparing the airspeed and the percent change in thrust of the motor/propeller combinations we can see that the Hacker C50 13XL is clearly the most consistent and best option [13]. That is how the Georgia Institute of Technology decided on the engine they wanted to use.
FIGURE 2
“Percent Change in Thrust vs. Airspeed for different motors“[13]
UAV ARCHITECTURE
Due to the process of hydrogen fuel cells, they require specific accommodations on board HALE UAVs. Although there is not one set architecture for every aircraft, there are vital components that each must have in order to function as intended. These intensions, as indicated by the acronymic name, are the ability for flight at extremely high altitudes (upwards of 65,000 miles) and extended flight durations [5]. Generally each aircraft needs to have a lightweight frame that can support both the hydrogen fueled propulsion system as well as some type of cryogenic fuel tank. The following section will discuss how these are the key to these capabilities.
Proposed Architecture
In an article published in the International Journal of Hydrogen Energy, researchers propose a prototype UAV based closely on HALE UAVs currently under development. More specifically a HALE UAV is a slow moving aircraft with a low aspect ratio (wing length versus breadth) in order to efficiently provide large enough amounts of lift. These specifications are outlined in Table 1. In this case, the aircraft has an all-electric power system with the intent of hitting a one week mission length at a cruising altitude of 65,000 feet [2].
Parameter | Value |
Cruising altitude | 15–20 km50,000–65,000 ft |
Cruising speed | Mach 0.25–Mach 0.35 |
Maximum take-off mass | 3500 kg |
Payload mass | 300 kg |
Maximum fuel mass | 1575 kg(45% of total mass) |
Wing span | 12 m |
Fuselage length | 2.1 m |
Aspect ratio | 30 |
TABLE 1
Physical characteristics of a prototype UAV [2]
Designing an aircraft with a one-week flight duration in mind we would obviously need a huge change in power.
Hydrogen Storage
By nature of liquid hydrogen fuel (H2), which has a boiling point of -252.8 °C or -423.04 °F, [13] the fuel tanks need to be kept extremely cool in order to reduce boil off and buildup of pressure within the tank [18]. “Soon after research into the use of H2 for aviation started, the feasibility of lightweight, insulated cryogenic tanks was identified as a key technical enabler for hydrogen fueled flights” [14]. Designing a fuel tank that can sustain such cool temperatures is an integral factor to the effectiveness of hydrogen fueling.
Tank Design
Designing a new type of tank is critical because tanks for this particular application do not currently exist within other automotive, space or aeronautical sector. A spacecraft tank is designed for very short term use while an automobile tank has a similar lifecycle to that of our aircraft’s although much less affected by weight restrictions. Developing a light yet highly insulated and durable tank remains one of the biggest challenges in the use of hydrogen fuel in aviation [14]. Hydrogen has high heat content per mass, about three times higher than kerosene, but has a low density giving way to a need for a larger tank volume [14, 18]. Fuel volume requirements for hydrogen are around four times as much as those of kerosene fuel [17]. This fact needs to be considered when discussing size, location and structure of a hydrogen fuel tank.
We can compensate for the increase in volume by
discussing the specific fuel consumption (SFC) of a proposed HALE UAV prototype. We compare the SFC of hydrogen fuel to other types of fuel by using Equation 1, the Breguet range equation, to estimate the necessary specific fuel consumption to achieve the same amount of power [12].
EQUATION 1
Breguet Range Equation [20]
According to researchers from both Imperial College London and University College London “a small Turboprop engine will have an SFC in the region of 0.5–0.7 lb/hp h (pounds per horsepower hour), a small four-stroke internal combustion engine will have an SFC in the region of 0.45–
0.5 lb/hp h and some advanced two-stroke diesel engines
claim SFC values in the region of 0.35 lb/hp h” [12].
Hydrogen fuel has a particularly low SFC, especially for a small aircraft with a SFC of only 0.13 lb/hp h [12].
Although hydrogen can be stored as solid, pressurized gas, a hydride or slush, the liquid form of hydrogen gives us the best opportunity for an efficient tank design because it can be stored in appropriate quantities and kept cool using reasonable heat management. Gaseous hydrogen has far too much volume to be stored on board and slush or solid hydrogen requires costly sub-cooling systems [14].
An ideal tank has the greatest amount of volume with
minimal surface area. Minimizing the surface area is a vital component to a successful tank because the lesser the surface area the less insulation required and the less boil-off of fuel. In the article Hydrogen fuel tanks for subsonic transport aircrafts, the authors decide on a spherical tank for this specific reason.
Another discussion is that of integral versus non-integral
tanks. Non-integral tanks are isolated from other working engine components and exist purely to contain and bear weight of fuel while integral tanks, being part of the actual architecture of the aircraft, must be able to “withstand fuselage axial, bending and shear stresses” [14]. The combination of roles of the integral tank leads to weight savings and is therefore a more ideal choice [14].
Tank material is an important component to tank design because it has one of the biggest effects on weight and therefore performance of a HALE UAV. First we consider a light durable material for the tank; polymer matrix composite (PMC) but soon run into problems. Hydrogen’s ability to permeate through PMC walls is conceivably the most crucial problem in on board hydrogen storage, loss of valuable fuel [18]. Hydrogen permeates much more slowly through metallic tanks than those made of non-metals; therefore metal tanks seem like a solution. This is not true though because now there is an issue with weight. This problem can be reasonably contained with the use of metal lined tanks [18].
In previous applications of LH2, fuel has only been used
for short durations such as takeoff boosts, therefore boil off was not particularly inconvenient, but now that we are looking to use hydrogen in long duration flights, excess boil off of fuel is highly undesirable. If the liquid hydrogen fuel is maintained at a constant absolute pressure of around 170 kPa (25 psia), the boil off will be kept at a reasonable level without an excess weight cost [18].
Another issue involved in storage of liquid hydrogen is
that due to the low temperatures, many nonmetals materials become embrittled, deteriorate and can fail, causing disastrous damage. Resistance to hydrogen embrittlement should be taken into account when considering tank materials [18].
WHY HYDROGEN?
Hydrogen is currently considered one of the cleanest, lightest and cheapest fuels for a number of reasons. It out preforms traditional hydrocarbon and kerosene fuels in a variety of areas. We aim to investigate these properties in order to integrate them into the discussion about sustaining energy in our world. We are living in a delicate world that needs our protection. Engineers have always modified their environment for the purpose of satisfying human need, but in recent decades they are beginning to notice the impact these modifications are having on the quality of our environment. In the following sections we will outline many of the environmental and economic benefits of using hydrogen fuel in aviation. “Engineers represent the bridge between science and society that is essential to sustainable development” [21].
Sustainable engineering is development that uses
resources responsibly, designs with minimal waste in mind, considers lifecycle costing, and plans technological solutions that both eliminate negative environmental and increases social benefits [21]. Using hydrogen fuel works toward the accomplishment of these goals, thus deeming itself a particularly sustainable energy source.
Environmental Effects (vs. Hydrocarbon Fuels)
In a world where global warming and other environmental issues are more forthcoming than ever, finding alternative forms of energy is becoming increasingly popular in the transportation industry. As mentioned above, sustainable energy development aims to eliminate negative environmental effects. “Renewable energy has attracted so much attention due to the ever-growing demands in friendly environment, especially with the increase of population and green-house gas emissions in the world” [16]. We can consider the sustainability of hydrogen use in aviation by exploring research based on the impact hydrogen fuel on our surroundings. Hydrogen fuel is already fairly well known for its lack of harmful effects on the environment, but we can solidify these facts by analyzing specific data.
The aviation industry has been increasing carbon dioxide
emissions by about 2–3% per year and advances in technology has not yet found a way to balance this buildup. Liquid hydrogen fuel has the possibility of being a nearly zero emission fuel, producing only H2O and a barely traceable amount of NOx [17]. This fact alone could convince an audience that hydrogen fuel is at least worth some further research.
Jet fuel burns according to the following stoichiometric equations:
EQUATION 2
CxHy + a(O2 + 3.76 N2) ⇛
xCO2 + 0.5yH2O + 3.76 aN2 + other by products
Equations of jet fuel burning [17]
EQUATION 3
C12H23 + 17.75 O2 + 66.77 N2O2 ⇛
12 CO2 + 11.5 H2O + 66.77 N2
Equations of jet fuel burning [17]
The quality of hydrocarbon fuel burning depends on a number of factors (the variable coefficients in Eq. 2) including viscosity, sulfur content volatility, calorific value and composition. Combusting 1 kg of kerosene produces
3.16 kg of CO2, 1.24 kg of water vapor, 1 g of NOx and between 1 and 2.5 g of CO [17].
In order to produce the same amount of energy using liquid hydrogen fuel would require only 0.36 kg of fuel and produce 3.24 kg of water vapor and trace amounts of NOx [17]. In terms of environmental impact water vapor has zero effect on the atmosphere while CO2 emissions break down the ozone layer and cause a plethora of environmental problems.
In one study Toronto, Montreal, London and Calgary are chosen to determine average fuel consumptions of different durations of flights in an airbus A320, a short to medium range commercial aircraft.
TABLE 2
City | Kerosene (L/km) | LH2 (L/km) |
Montréal | 9 | 4.4 |
Calgary | 6.32 | 4.35 |
London | 6.78 | 4.04 |
Comparison of kerosene and liquid H2 consumption from Toronto to various destinations [17]
Although hydrogen fuel has a 65% lower SFC (specific fuel capacity) than kerosene, the fuel load is significantly lighter and the weight to fly a given distance is much less than it would be with kerosene. These properties are advantageous for a HALE UAV because less weight means more efficiency. Consumption of hydrogen fuel per unit distance is almost 50% less than kerosene. Another benefit of hydrogen fueled engines is low noise due to decreased engine size. Hydrogen fuel also burns at a much lower temperature than kerosene fuel, resulting in a lower engine temperature increasing engine life by 25% as well as lower maintenance frequency [17]. Both of these qualities contribute to the sustainability of hydrogen fuel in aircrafts, particularly the HALE UAV because with a longer engine life and less frequent maintenance we are getting more usage out of the aircraft while putting less labor. An extended engine life also means the aircraft can stay airborne longer accomplishing the long endurance goal of the UAV.
Radiative forcing (RF) “determines how much climate change occurs in response to human disturbances in the earth’s energy balance, with regards to changes in concentrations of greenhouse gases” [17]. Radiative forcing
can be calculated by computing the radiative absorption of each trace gas emitted and the original gas concentration in the atmosphere. The amount of CO2 emitted is an unavoidable factor of using kerosene fuels and can be estimated as 10-7 ppm (parts per million) per one way trip, made three times a day. A liquid hydrogen fueled aircraft emits zero CO2 per trip and therefore has no RF effect (excluding hydrogen production) [17]. Considering the usage of liquid hydrogen fuel produces no harmful emission into the atmosphere, it can be considered a sustainable development under our previously given definition of sustainability.
Cost Analysis
Hydrogen fuel has its advantages in being potentially cost efficient. It can potentially be produced from water and many other easily accessible resources. Hydrogen’s main cost advantage over other fuels is its high-energy efficiency. The graph below shows how hydrogen will in the future be much more cost efficient then any of the other fuels. The graph compares hydrogen from different sources as well as with gasoline and diesel fuels. The H2FCV section contains different methods for obtaining hydrogen fuel, and the ICECV section contains the traditional fuel sources for comparison [20].
FIGURE 3
Well to wheel cost analysis [20]
The graph is split into the sections Future and Base The Future section shows the prospective costs of the fuels in 2015, and the Base section is the current costs of these fuels. The Future section is based on future scenario analysis done by the International Energy Agency. The registration and vehicle costs do not apply to UAVs, but the operation costs will be focused on. The operation costs are the cost of the material, the cost to turn it into energy, and the waste treatment costs. It is calculated using the formula below where IMi is the amount of input material, PMi is the price of the input material, IEj is the amount of inout energy, ECj is the cost of the input energy, AWk is the amount of waste, TCWk is the treatment cost of the waste, ACPl is the amount
of co-product, and RCPl is the revenue of the co-product [20].
EQUATION 4
Operational cost equation [20]
The operation costs for hydrogen are expected to be more than halved, where the operation costs for gasoline and diesel are expected to significantly increase by $15,000-
$20,000 [20].
Hydrogen Fuel Sustainability Overview
The use of hydrogen fuel in high altitude long endurance unmanned aerial vehicles covers all of the previously mentioned goals of sustainability. Resources are used responsibly in the fact that hydrogen can be produced from a number of sources, namely water, an easily renewable resource, therefore making it an easily sustainable source of fuel versus typical hydrocarbons which are only harvested from a limited amount of resources.
HALE UAVs are designed with minimal waste in mind because they are built to be light, yet durable aircrafts that use material wisely. There are also minimally wasteful because their main byproduct is merely harmless water vapor. This fact also covers the idea that they sustain the ability to reduce negative impacts on the environment.
In the future hydrogen fuel’s economic value will
become sustainable. The prices of fossil fuels will have greatly increased, while our increasing ability to turn hydrogen into fuel will make hydrogen fuel more cost efficient. Hydrogen fuel will eventually become more cost sustainable then the traditional fuel sources [20].
FINAL NOTES ON HYDROGEN FUEL
The future is never too far away and environmental, economic, and efficiency difficulties are approaching quickly. Hydrogen fuel has been researched for decades but has lately begun to gain popularity as we are realizing the effects of kerosene and hydrocarbon fuel usage on our environment. HALE UAVs are a beginning to the solutions to these problems. Using liquid hydrogen as a fuel in the aviation industry still requires further research and testing, but as can be inferred from this paper, has a lot of opportunity of becoming a reliable, renewable resource for energy.
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Volume 34, Issue 5
[17] H. Nojoumi, I. Dincer, G.F. Naterer (2009) “Greenhouse gas emissions assessment of hydrogen and kerosene-fueled aircraft propulsion” International Journal of Hydrogen Energy Volume 34, Issue 3
[18] S.K. Mital, J. Z. Gyekenyesi, S.M. Arnold, R.M. Sullivan, J.M. Ma. (2006) “Review of current state of the art and key design issues with potential solutions for liquid hydrogen cryogenic storage tank structures for aircraft applications” NASA
[19] J. Leea, M. Yooa, K. Chaa, T.W. Limb, T. Hura. (2009) “Life cycle cost analysis to examine the economical feasibility of hydrogen as an alternative fuel” International Journal of Hydrogen Energy Volume 34, Issue 10
[20] (2013) “13.3 Aircraft Range: the Breguet Range Equation” Massachusetts Institute of Technology (Online Class Notes) http://mit.edu/16.unified/www/FALL/thermodynamics/notes
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qualities. Amanda would also like to thank her father as well for motivating her to pursue engineering,
We wish to express our gratitude towards Professor Bateman Newborg and Professor Bursic for providing us with all of the tools, information, and direction that made writing this paper possible. We would also like to thank the University of Pittsburgh library staff for informing us about the university’s online library system through which we found several helpful resources. Lastly, We would like to thank everyone who contributed to the sources from which we took our information from for helping make this paper possible.
[21] (2012) “US Engineering Societies’ Statement of Sustainable Development For Rio+20” Online Ethics Center for Engineering – National Academy of Engineering (Online Article) 158.aspx
ACKNOWLEDGMENTS
First Jen would like to acknowledge her father for his input, ideas, and opinions on the topic, challenging her to debate either side of the argument. His interest and enthusiasm gave her inspiration to research the topic and realize how much of a real world possibility it is. On a broader note she would like to thank him for my overall interest in engineering. He has always taught her to problem solve and to be very independent, two vital engineering
