Ammonia A Solution for Airships Demanding Rapid …me.umn.edu/~hork0004/AIAA-2005-7393-913.pdf · Minneapolis, MN 55418 USA, and AIAA Member . [email protected] or [email protected]

American Institute of Aeronautics and Astronautics1

Ammonia – A Solution for Airships Demanding RapidChanges in Net Buoyancy

Donald P. Horkheimer*, BAEMUniversity of Minnesota, Minneapolis, MN, 55414 USA

Nonequilibrium aerostatic flight conditions, caused by the delivery of a large payload,represent a significant engineering challenge to overcome in the design of large scale airshipsand impediments to their overall financial success. Gaseous ammonia, used as a portion ofthe airship’s lifting gas, i.e. “negative ballast” and partly as a fuel or as a means to reduceNOx emissions of typical airship power plants is a relatively safe and practical way to meetthe challenge of nonequilibrium aerostatic flight. Gaseous ammonia used as a secondarylifting gas can be vented quickly to restore the airship to aerostatic equilibrium. Thus the useof ammonia as a lifting gas is primarily used to provide aerostatic lift of the payload only.This concept is contrasted with conventional means of dealing with nonequilibriumaerostatic flight such as exhaust water recovery, vectored thrust, primary lifting gas ventingand aerodynamic lift as well as less conventional means such as primary lifting gascompression or air liquefaction and hot-air or steam ballonets. In order to illustrate theadvantages and disadvantages of the use of ammonia as a secondary lifting gas, system-levelmeasures of performance for the various concepts and generic to airship type, size, andconfiguration are developed for comparison purposes. An airship sizing MATLAB codebased on historical design data is used to compare various concepts to determine whichconcept offers the best performing airship in order to accomplish a mission. The modelmission is based on DARPA’s WALRUS program requirements which are based on thecapabilities of the C-130J-30 cargo airplane.

Nomenclatureβ = power to thrust ratio (kW/N)D = drag force due to aerodynamic lift (N)Fs = factor of safetyg = gravity constant (m/s^2)HHV = higher heating value of fuel per unit mass (water is condensed in the exhaust) (kJ/kg)LHV = lower heating value of fuel per unit mass (water remains as vapor in the exhaust) (kJ/kg)L = lift or payload(N)l = lift per unit volume or buoyancy (N/m^3)λ = efficiency (%)M = mass (kg)P = pressure (kPa)p = power (kW)R = range (km)r = radius (m)ρa = density of air (kg/m^3)ρg = density of lifting gas (kg/m^3)ρm = density of material (kg/m^3)σy = yield strength (MPa)T = absolute temperature or thrust (K) or (N)

* Test Engineer/Analyst, Honeywell - Advance Electronic Systems, 3660 Technology Drive – Rm. 2737,Minneapolis, MN 55418 USA, and AIAA Member. [email protected] or [email protected]://www.me.umn.edu/~hork0004/

AIAA 5th Aviation, Technology, Integration, and Operations Conference (ATIO) <br>26 - 28 September 2005, Arlington, Virginia

AIAA 2005-7393

Copyright © 2005 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.


t = time or thickness (s) or (m)V = volume (m^3)v = velocity (m/s)

H.E. = high efficiencyH.S. = high strengthL.E. = low efficiencyppm = part per million

I. Introductionhe motivation for this paper began with a Defense Advanced Research Projects Agency (DARPA) designprogram solicitation called WALRUS. WALRUS represents the defense community’s interest in developing a

novel Lighter-Than-Air (LTA) strategic airlift capability. The goal of the project is to develop a LTA vehiclecapable of moving an entire Unit of Action (UA) from “Fort-to-Fight”. This means moving both personnel andequipment that are capable of fighting within 6 hours from disembarking the aircraft. The initial Request ForProposal (RFP) requested a design that would eventually be capable of carrying a >500 ton useful payload 6000nautical miles without refueling at above conventional airship speeds. Other requirements include a Vertical Take-Off and Landing (VTOL) capability and an ability to operate without significant infrastructure, such as the

allowance for re-ballasting of the airship that is currently common place, and use of undeveloped landing sites.1,2

The initial development prototype will begin with a design that offers performance comparable to a C-130J-30

airplane.3

One of the most significant obstacles facing the WALRUS program is the difficultly posed by unloading 500 tons ofpayload and the resulting lack of aerostatic equilibrium. DARPA has identified this technical hurdle and isaggressively supporting novel means to deal with this problem. DARPA officials have suggested numerousconceptual solutions to contractors, such as alternative lifting gases and unconventional means to generate ballast torectify the problem.

To date the use of ammonia has not received much attention as a means to solve the aerostatic equilibrium problem.Even though there is a growing community of balloonists that are using ammonia in place of hot-air because it does

not require a burner or in place of helium because it is cheaper,4,5

to the best of the author’s knowledge the availableliterature does not describe any detailed plans at using ammonia as a lifting gas in airships. Ammonia can serve asan easily disposable and cheap secondary lifting gas in an ammonia-helium hybrid airship. The use of ammonia isintended to provide the aerostatic lift sufficient to carry the payload in a WALRUS type vehicle. As such, in whatfollows is a description of the properties of the ammonia, their ramifications for airship design, and their comparisonto other proposed methods for dealing with excess aerostatic lift by means of a MATLAB code. Comparisonsbetween other systems are made in such a way as to model the most significant impacts of utilizing a specific systemwithout modeling every single detail. The results are believed to be accurate in predicting the overall trend of aconcept, without being accurate in specific details if an actual design was manufactured. In other words, once aconcept has been proven inferior to another concept, extreme modeling detail of the inferior concept is not pursued.

II. Consideration and Selection of Possible Lifting GasesThe design of a new airplane often begins with a detailed investigation into finding the optimum wing profile for

the airplane’s intended mission; the search for the right wing requires the exploration of a very large design space ofvarious variables. The conventional airship on the other hand derives its primary source of performance only frombuoyancy, which is practically driven by choice of lifting gas composition and temperature of the same. Equation(1) illustrates the gross lift of a buoyant gas per unit volume where l is the aerostatic lift per unit volume, g is the

gravity constant, and where aρ and gρ are the densities of air and of the lifting gas respectively.

T


)( gagl ρρ −= (1)

Figure 1 is based on empirical gas tables, except in the case of methane which out of convenience is based on anideal gas law treatment.6 Unlike in airplane design, where incremental improvements in the lift of a wing alwaysseem possible, the maximum aerostatic lift is set by the buoyancy generated by a perfect vacuum within an ideallyweightless container. Yet, this does not negate the importance of analyzing the system wide advantages anddisadvantages of different lifting gases. Consideration of only conventional helium in unconventional circumstanceslimits novel possibilities. Ammonia is an unexplored possibility that can expand the design space and give aWALRUS type airship improved capabilities.

III. Ammonia-Helium Hybrid AirshipAmmonia-helium hybrid airship is the best solution for meeting the requirements of the WALRUS program.

Conceptually, helium would be used as the primary lifting gas to carry the deadload of the airship. Ammonia wouldbe stored in separate gas cells and used only to carry the payload. When a WALRUS airship delivers its payload theammonia gas cells would be vented safely by a manner discussed later. The quick venting of ammonia would allowthe airship to remain in aerostatic equilibrium at all times. Aerostatic equilibrium is the most efficient flight regimefor an airship. The ammonia-helium airship offers a compact design over other concepts. For a given mission asmaller airship should offer lower nonrecoverable engineering costs and operating costs. This is especially true ifthe smaller airship is simpler then more complex engineering solutions.

Aerostatic Lift Of Various Gases In Air@ 300K, 1atm, For A Range Of Lifting GasTemperatures

0.00.51.01.52.02.53.03.54.04.55.05.56.06.57.07.58.08.59.09.5

10.010.511.011.512.0

250 300 350 400 450 500 550 600 650 700 750 800

Absolute Temperature, K

Bu

oya

ncy

,N/m

^3

Hot Air Hydrogen Vaccum Helium Ammonia Carbon Monoxide Steam Nitrogen Methane (Ideal Gas)

Figure 1. Aerostatic lift of available lifting gases


A.Sizing of Airships for Different Buoyancy Control Strategies and Results SummaryOne way to evaluate different buoyancy controlling strategies is to develop a means to size airships for missions

that vary in details, but not their basic form. The WALRUS mission is one of an airship flying from point A with apayload, deploying the payload at point B and returning to point A. This mission is inherently different then othermissions. For example a missile defense or anti-submarine warfare type mission would dictate a different overallairship design. Using a historical reference a rudimentary sizing program was created to evaluate different concepts.The original reference utilized design data from actual non-rigid and semi-rigid airships to derive coefficients thatcorrelate details such as envelope weight to overall airship volume and maximum speed. Although there has beenmuch improvement in technology since these coefficients were first calculated, it is believed by the author thattechnological improvements generally favor all concepts equally, hence the use of this reference still presents theoverall trends.

The original method proposed by Col. Crocco7 in his NACA paper from 1922 required the user to initiallyspecify the overall volume of the airship and its maximum speed. From there design details like deadload, payload,and installed horsepower could be calculated. The author’s requirements were different in that it was desired for theuser of the code to specify maximum speed, range, and payload and then iterate to the final volume that allowed forairships sufficient in size to meet the requirements. The code also allowed for the user to specify a primary andsecondary lifting gas as well as force an increase in the deadload because of the mass of buoyancy control hardware.The code was written in MATLAB and is included in the appendix. The code is not particularly elegant, and morerefined versions are in the works. One interesting observation when using the iterative code is that if you specify anunrealistic performance criterion like an extremely high speed, the code will grow the airship indefinitely as it triesto add volume to carry the additional fuel burden caused by the high speed. In hindsight this is obvious, but it alsoserves as a good reminder that it can be difficult to grow designs to deal with problems, whereas realistic designsstrike a precarious balance of opposing requirements.


No effort was made to update Col. Crocco’s coefficients, but some items were omitted. Instead of breaking theresults down in detail like Col. Crocco did, it was decided for brevity’s sake to keep the results at as high a level aspossible. As such, only the total quantities of deadload, total volume, installed horsepower, and fuel will bereported. The payload is assumed to be 16,329 kg, with a maximum velocity of 40m/s and a maximum range of3,148 km. These assumptions are intended to give performance comparable to the C-130J-30 in all but velocity.3

These assumptions also tended to keep the overall airship size within the realm Crocco considered. Particularassumptions pertaining to specific concepts are discussed where appropriate. Table 1 presents a summary of theresults of a purely helium baseline design, an ammonia-helium hybrid design, a hot air-helium hybrid design, asteam-helium hybrid design, a gas compression design, a gas liquefaction design, a vectored thrust design, and aaerodynamic-design. The designs utilizing two lifting gases had an additional deadload term activated in the code torepresent the additional weight of the secondary lifting gas envelope. This additional term is based on Crocco’soriginal term for ballonet mass, but this volume is not iterated as the secondary lifting gas is assumed to be constantand present only to provide payload lift.

IV. Additional Possible Features of Utilizing Ammonia as a Lifting GasAmmonia can provide additional benefits when used on board an airship in addition to being used as a

disposable lifting gas. In the past, ammonia has been used as an alternative fuel for various types of heat enginesand in the present there is growing interest in using ammonia to chemically after treat engine exhaust such that NOxemission levels are reduced. The right level of consumption of ammonia lifting gas by a dual fuel propulsion systemwould allow the airship to maintain aerostatic equilibrium as well as increase the amount of water vapor available

Table 1. Results of airship sizing code showing the advantage of ammonia-helium hybrid airshipsAirship Concept Volume

m^3Rangekm

MaxVelocitym/s

LHVfuelkJ/kg

InstalledPowerHP

TotalFuelMass kg

Deadloadkg

Payloadkg

Pure HeliumBaseline Airship

142,450 3,148 40 5.0E+04 10,055 47,208 127,180 16,329

Ammonia-Helium Airship

209,130 3,148 40 5.0E+04 12,988 60,979 176,230 16,329

Ammonia at400K-HeliumAirship

177,460 3,148 40 5.0E+04 11,641 54,657 153,490 16,329

Air at 400K-Helium Airship

222,790 3,148 40 5.0E+04 15,798 74,175 226,510 16,329

Steam-HeliumAirship

181,960 3,148 40 5.0E+04 11,837 55,578 156,750 16,329

GasCompression-Helium Airship

272,190 3,148 40 5.0E+04 15,483 90,865 259,100 16,329

GasLiquefaction-Helium AirshipH.E.

215,790 3,148 40 5.0E+04 13,262 82,274 200,960 16,329

GasLiquefaction-Helium AirshipL.E.

267,140 3,148 40 5.0E+04 15,291 106,480 254,250 16,329

Vector Thrust-Helium Airship

234,500 3,148 40 5.0E+04 17,303 84,198 219,370 16,329

AerodynamicLift-HeliumAirship

204,220 3,148 40 5.0E+04 12,784 76,545 189,090 16,329


for possible later condensing and recovery as ballast. And although exhaust water recovery is unlikely to provide aquick and robust means of dealing with rapid changes in buoyancy, such as that caused by off loading 500 tons ofpayload, it would seem very plausible that slower changes in aerostatic equilibrium such as that caused byconsuming typical fuels could be dealt with. If conventional airship propulsion became burdened with emissionregulations then conceptually ammonia could be used to meet those regulations without loss of engine performance.

B.Use of Ammonia as a Fuel

Ammonia has always held some appeal as a fuel because of its availability and potential thermodynamicproperties. For reference see Table 2 for comparison of ammonia to other fuels.

Historically, the earliest reference to the limited practical use of ammonia as a fuel appears to belong toAmmonia Casale Limited in 1935.8 The Casale process utilized thermal decomposition prior to introduction into theengine combustion chamber. Thus the ammonia gas was broken down into hydrogen and nitrogen to produce aneasily combustiblefuel for the engine.Although othersources suggest thatthe idea of usingammonia as a fuelgoes as far back as1905, specificreferences are notprovided. DuringWorld War II, withconventional fossil-fuels being in shortsupply, ammoniafound application inseveral nations.9

The bestdocumentedoperational use ofammonia occurred in Belgium from 1943 to 1945.8 Eight buses were outfitted with high pressure tanks of coal-gasand ammonia. The addition of coal-gas helped ignite and burn the ammonia fuel. The bus service covered over10,000 miles in two years without incident. The literature does mention a private car powered by ammonia that wasoverfilled by the owner; the evaporation of the ammonia caused a build up pressure which ruptured the fuel tank,although no loss of life occurred in the incident.

In the early 1960’s the US Army became interested in developing a mobile, in the field, fuel generatingcapability. Observations of military logistical data suggested that fuel for the Army represented a significant amountof the total tonnage transported. During World War II, roughly half of the US Army’s shipping involved petroleumproducts. During the Korean War this number reached 70% of the US Army’s supply tonnage.10 The focus of theresearch became known as the Energy Depot Concept, see Fig. 2.11 Essentially, the goal was to develop a landmobile nuclear reactor that would either regenerate a potassium-mercury fuel cell or produce a fuel derived fromelements only readily available in air, dirt, and water such as ammonia, hydrazine, or hydrogen. 12 From the fieldgenerated energy depot, the full range of Army vehicles would be supplied. For various reasons ammonia receiveda great deal of attention as one of the ideal fuels possible with the Energy Depot Concept.

Table 2. Comparison of ammonia to common fuels

NH3Ammonia

CH4Methane

H2Hydrogen

OctaneC8H18"Gasoline"

n-DodecaneC12H26"Diesel"

Specific Heat ReleaseLower Heating Value@ 25C 1atm [kJ/kg] 17,426 50,016 120,100 44,791 43,000Specific Heat ReleaseHigher Heating Value@ 25C 1atm [kJ/kg] 18,585 55,528 141,900 48,275 45,900Fuel Density Liquid[kg/m^3] 682 554 71 695 808Octane Number >111 130 130+ 100 -Stoichmetric MassAir-Fuel Ratio 6.06 17.20 34.50 15.10 15.00


General Motors13, ContinentalAviation, University ofCalifornia14, and Allis Chalmersperformed extensive research inusing ammonia as a fuel in sparkand compression-ignition enginesand in gas-turbine engines.15 Theinability to burn pure ammoniaeffectively within the engines testedwithout modification wasdiscouraging. In one case the directinjection of liquid ammonia into adiesel engine with a compressionratio of 30:1 was unsuccessful inachieving combustion. Severaldifferent methods were researchedto improve the combustionefficiency as shown below:16

1. Higher compression ratio or mild supercharging2. Introduction of easily combustible fuel additives or pilot injection using a more combustible fuel3. Increased spark energy or multiple spark sources4. Intake charge heating or cylinder head heating5. Thermal decomposition of ammonia to generate readily combustible hydrogen prior to use within

engines

When incorporating these modifications performance was enhanced. For example an ammonia compressionignition engine with diesel fuel pilot injection exhibited a 13% improvement in thermal efficiency and a 32%improvement in Indicated Mean Effective Pressure (IMEP) output.16 The requirement of either a dual-fuel systemor increased engine complexity for complete combustion negated much of the benefit of the overall Energy Depotsystem. Nothing further came of the US Army’s efforts.

In the 1970’s to the present, interest in ammonia as an alternative fuel was generated because of either the OilCrisis or out of more spontaneous interest. At the same time basic research into combustion of nitrogen containingcompounds was on going.17-20 At the present time there appears to be some interest in the use of ammonia as the firststep in moving to a hydrogen based economy rather then oil based economy. Ammonia offers higher chemicalenergy storage density over hydrogen and it production and distribution is well established.

The historical lesson of ammonia as a fuel is that by itself it is a rather poor performer because of combustioninefficiency. There is historical evidence that when ammonia is not the sole fuel used in an engine, there is anadvantage in using ammonia. The airship community is not oblivious to the obvious advantages of dual fuelairships. If one fuel is lighter than air and the second fuel is heavier than air, by mixing the fuels in the rightproportion it is possible to maintain aerostatic equilibrium throughout the mission.47 This is true so long as thepropulsion system can operate on the mixture of fuels. The airship sizing code presented in this paper does not takeadvantage of the use of lifting gases that can also be used as fuels, but this feature is only expected to enhance theuse of ammonia as a secondary lifting gas. One cubic meter of ammonia gas contains the LHV thermal energy of12,059 kJ and can lift 0.485 kg of diesel fuel which contains the thermal energy of 20,855 kJ.

Figure 2. Illustration of the US Army’s Energy Depot Concept13


C.Use of Ammonia as a Means to Limit NOx Emissions through Selective Catalytic Reduction (SCR)

Environmental regulators are increasingly putting pressure on diesel engine manufacturers to reduce bothparticulate and NOx emissions from engines. See Table 3 for typical NOx emissions or stationary power sourcesand European and US regulatory limits.21

Conventional techniques for limiting particulate emissions generally increase NOx emissions and vice-versa.The diesel engine designer is faced with consideringunconventional measures to meet regulatoryconstraints. One method proposed that is attractingserious attention to reduce NOx emissions is SelectiveCatalytic Reduction of diesel engine exhaust. Thebasic chemical reactions are shown below in Figure3.22 Various sources of ammonia for this applicationhave been proposed from on-board ammonia tanks, todecomposition of urea, to catalytic generation ofammonia in the exhaust stream.23,24 The ammoniausing airship could use the secondary lifting gas forSCR.

SCR has been shown to reduce NOx by 65% to80% and allowing engine designers greater freedom indealing with particulate emissions withoutsignificantly affecting overall performance. If airshippropulsion became burdened by NOx emissionregulations or if there was a desirer to achiever agreener airship then a ready supply of ammonia as alifting gas could find use in a SCR system. SCRwould also be expected to improve the yield ofexhaust water recovery system to help maintainaerostatic equilibrium

Table 3. Typical NOx emission of commonstationary power generators21

NOx Emission [g/kW-hr]Type of PowerGenerator

TypicalMinimum

TypicalMaximum

Reformed Natural GasFuel Cell

0 0.0052

Microturbine 0.10 0.46Gas Turbine 0.07 0.97Natural Gas Engine 0.41 6.69SCR Exhaust TreatedDiesel Engine

0.33 0.63

Untreated DieselEngine Exhaust

3.29 7.48

EPA Tier 1 RegulatoryEmission Limit

5.16

TA-Luft EuropeanRegulatory EmissionLimit

0.82

Figure 3. Chemical processes by which ammonia inconjunction with an SCR catalyst reduce NOxemissions22


D.Availability of Ammonia

Because of ammonia’s extreme importance toagriculture, it is safe to say that any country with aminimum level of industrialization and anindigenous agricultural industry manufacturesammonia or at least possesses a distributionnetwork to utilize the gas. The agriculturalindustry in 1997 consumed 85% of ammoniaproduction for the generation of fertilizer.25 Thereexists an extensive ammonia infrastructure.Ammonia can and has been moved by pipeline,ship, rail car, and tanker truck. Ammonia in bulkquantities costs anywhere from $94/ton to$325/ton in the USA and balloonists have foundthe gas to be cheaper than helium.20 Figure 4illustrates the historical growth in both worldpopulation and ammonia production.25 Table 4displays the geographic distribution of ammoniaproduction capacity and utilization.25

V. Ammonia Lifting Gas ShortcomingsAmmonia has not received much attention by the airship industry partly because operational requirements have

not driven its consideration and partly because of regulatory problems. It is important to discuss the specialcircumstances an airship utilizing ammonia would have to face, such as problems of possible corrosion,flammability, and toxicity.

E.Problem of Ammonia Related Corrosion

Unlike most other lifting gases, the use of ammonia will dictate that greater attention be paid to corrosivecompatibility between the lifting gas and materials used aboard the airship. Generally it is assumed that theconventional lifting gases are inert when it comes to reacting with airship structure, and even though hot-air orsteam may present hygrothermal implications for the airship structure, the chemical nature of ammonia makes it theleast inert lifting gas available. Looking at the available corrosion literature and specifically at common aerospaceand airship materials, it appears that material selection will be important. It seems unlikely that it would be possibleto maintain extremely high levels of gas purity in ammonia gas cells and since water vapor is both a commonimpurity and a noninert player in ammonia related corrosion Table 5 includes data on saturated ammonium-hydroxide.26-28 It appears that there are structural and gas cell materials available that would be satisfactory to use in

Figure 4. Historical growth of ammonia supply25

Table 4. Global ammonia capacity and utilization25


an airship. But, at the same time there is very little research available in the literature discussing real worldenvironmental tests. For example there could be serious interactions between a material, UV light, ammoniaimpurities, and atmospheric weathering and pollution.

F.Problem of Ammonia Flammability

Flammability is a serious problem in the selection of lifting gases. This has historically been driven by the earlyuse of hydrogen in airships. Hydrogen is the best performing buoyant gas, but it is also extremely combustible. Afair number of lives have been lost due to this fact. As such, there was a drive early on to locate helium reserves andto develop the means to cost-effectively refine helium which is both nonflammable and the second best performinggas. Because of historical incidents with the use of hydrogen, many government regulatory agencies dictate the useof nonflammable lifting gas. For example, the Civilian Aviation Authority (CAA) of Germany and Netherlands hasin the recently released Transport Airship Regulations (TAR) included the following rule TAR 893.29

Table 5. Corrosion resistance of various common materials

MaterialPure AmmoniaGas

SaturatedAmmoniumHydroxide Material

PureAmmoniaGas

SaturatedAmmoniumHydroxide

Alloy Steels E E to GPolyamide e.g.Nylon R R

Aluminum Alloys S E

Polyester e.g.Terlen, Dacron,Mylar R to U R to U

Aramid e.g. Kevlar N/A N/A

Polyethylene e.g.Spectra,Dyneema R R

Butyl Rubber U UPolyimides e.g.Nomex N/A N/A

Carbon Fiber R R Polyurethane N/A RChlorosulphonatedP.E. e.g. Hypalon R R

PolyvinylChloride R R

Cotton U UPolyvinylFluoride N/A N/A

E-glass S-glassFiber R R PTFE e.g. Teflon R R

Epoxy Polyamide R N/APVDCCopolymer N/A N/A

Epoxy Plastic R to U R Silicone Rubber U R

Magnesium E E Stainless Steels E to G G

Natural Rubber U R Tedlar N/A N/A

Neoprene R R Titanium Alloys E E

Phenolic Resin R UFor MetalsE = < 0.00508 mmPenetration/Year

For MetalsS = < 0.0508 mmPenetration/Year

For MetalsG = < 0.127 mmPenetration/Year

For MetalsU = > 0.127 mmPenetration/Year

ForNonmetals R= Resistant

For NonmetalsU=Unsatisfactory


TAR 893 Lifting GasThe lifting gas must benon-flammable, non-toxic, and non-irritant.

Although, there is goodreason for these specificrules, it is an area thatneeds to be better defined.Yes, ammonia isflammable, but the USDepartment ofTransportation (DOT)classifies ammonia gas asbeing nonflammable.30

There is scientific evidenceto show that ammonia isdifficult to ignite, yet notimpossible. Refer to Table6. Perhaps operationalexperience and sounddesign practices couldbring about changes ingovernment regulations toeliminate such confusion. Ammonia’s use in ballooning does not appear to be burdened with similar regulations.

G. Problem of Ammonia Inhalation and Toxicity

Even though ammonia is commonly used on a massive scale in agriculture, chemical compound productionindustries, steel nitriding, and large-scale refrigeration it still can present a health hazard when mishandled. Table 7shows the physiologicaleffects of the inhalation ofammonia.31

Table 8 describes theeffects of variousconcentrations of carbonmonoxide.32 It is presented notbecause the physiologicalmeans by which bothammonia and carbonmonoxide do harm is similar,but because many people arealready familiar with thedanger of carbon monoxide.The danger posed by ammoniais similar to that of carbon monoxide. When considering that carbon monoxide is both tasteless and odorless, andammonia is not; it is the author’s opinion that carbon monoxide is a more serious threat. Granted carbon monoxideis not at issue here and as such any airship design and operation that involves ammonia should take specialprecautions for personnel safety. Table 7 includes the minimum resolution of various means to detect ammonia.The most promising means to improve safety appears to be the voltammetric microsensor being developed byArgonne National Laboratory.33 The microsensor is robust, simple, accurate, and cheap. Early indications suggestthat the sense element could cost as little as $1 when produced commercially in 1000 part volumes. Byincorporating smart sensor technology and wireless networking into the sensor small leaks anywhere on the airship

Table 6. Flammability properties of ammonia and common fuels

NH3Ammonia

CH4Methane

H2Hydrogen

Iso-OctaneC8H16"Gasoline"

n-DodecaneC12H26"Diesel"

Ignition Temp[deg C] 650 537 570 215 316Ignition Energy[mJ] 8.00 < 0.40 0.18 0.24 0.24ConstantPressureStoichometricAdiabatic FlameTemperature @1atm [deg C] 2,050 1,953 2,318 2,002 2,327StoichiometricPremixedLaminar FlameQuench Distance[mm]46 6.96 2.50 0.64 - -FlammabilityLimits In Air [%] 16-25 5.3-75 4-75 1.3-6 0.6-5.5

Table 7. Ammonia toxicology and detection thresholds inair31

Ultra-violet absorption sensor - Approximate minimumresolution

1-5 ppm

Color-changing card sensors - Approximate minimum resolution 1-5 ppm

Voltammetric microsensor - Approximate minimum resolution 0.1-1 ppm

Human perception - Approximate minimum resolution 0.5-3 ppm

Recommended short term exposure limit (15 min) 35 ppm

Nose, eye, throat irritation 100 ppm

Headache and nausea 200 ppm

Immediate burning sensation in the eyes 700 ppm

Immediate coughing 1000 ppm

Coughing with labored breathing 1700 ppm

Fatal concentration after short exposure 2500-4500 ppm

Fatal concentration by respiratory arrest 5000 ppm


could be detected. Emergency design measures could include a high capacity ventilation system and or crewindependent breathing systems.

The problem of safelyventing ammonia gas could bedealt with by using commonoff the shelf technology knownas flaring. Flaring is theprocess of intentionallyburning off unwanted wastegases such as hydrocarbonsand ammonia, or even moretoxic chemicals.34 Industrialflaring is common to thepetrochemical industry. Whendriving by an oil refinery it iscommon to see flaring stacksthat are continuously burning off waste gases. The technology is a safe means to deal with waste gases and in thecase of the ammonia flame, without any carbon typically present, the amount of thermal radiation directed to thesurrounding structures is very limited. And conceptually it would seem possible to use the airship’s propulsionsystem to do the flaring of ammonia gas as well.

Even with ammonia flaring the designer should develop plans to deal with accidental and or emergency releaseof pure ammonia gas. Loss of life or injury is not the rule in an ammonia accident. It is not unheard of. Any airshipprogram that involvesammonia should pay seriousattention to preventivemaintenance, warningsystems, accident handlingtraining, and medical training.Table 9 shows the effects ofhelium asphyxiation, sincehelium does not react withhuman physiology, it is the displacement of oxygen that causes harm and hence requires greater concentrations ofhelium to generate an effect.35 The author has not come across any ammonia ballooning related fatalities, but therehave been instances of helium asphyxiation recently in the airship industry. Helium unlike ammonia is odorless andtasteless. It should also be pointed out that even though ammonia gas is legally toxic, ammonia gas has also beendirectly injected into the ground to improve agricultural yields36 and also used to treat low grade ruffage37 toincrease livestock yields.

VI. Hot-Air, Steam and Helium-Hybrid Lifting Gas ShortcomingsHot-air has been used in sport blimps as a cheap and simple lifting gas. Steam has been used in balloons, but as

of yet has not been used in blimps, but there is a growing interest in steam aerostatics.38 Both lifting gases offerstrong advantages in that both gases are readily available and easily disposable. Unfortunately both require heat togenerate buoyancy. The requirement of constant thermal input to these lifting gases requires an additional weightpenalty be paid in terms of boiler, burner, heat exchanger installation as well as possibly thermal insulation.

Steam offers superior buoyancy to that of ammonia only if ammonia is not heated to a similar temperature. Botha heated ammonia and unheated ammonia case are treated in the airship sizing code. The code did not include anyadditional mass estimate for fuel or heaters nor any heat transfer between primary and secondary lifting gas cells. Ifammonia gas is heated it results in an airship that is more compact then the use of hot-air or steam as the secondarylifting gas.

Table 8. Carbon Monoxide toxicology thresholds in air32

No effect in healthy adults 35 ppm

Slight headache, fatigue, shortness of breath, errors in judgment 100 ppm

Headache, fatigue, nausea, dizziness 200 ppmSevere headache, fatigue, nausea, dizziness, confusion, lifethreatening after 3 hours of exposure 400 ppm

Headache, confusion, collapse, death if exposure is prolonged 800 ppmHeadache, dizziness, nausea, convulsions, collapse, death within 1hour 1500 ppm

Death within 30 minutes 3000 ppm

Death within 10-15 minutes 6000 ppm

Nearly Instant Death 12000 ppm

Table 9. Helium asphyxiation - Effect of reduced oxygen35 O2 Available

Typical Amount of Oxygen Available in Air by Volume 21% OxygenBreathing/pulse rate increase, muscular coordination slightlydisturbed 12-16% Oxygen

Emotional Upset, abnormal fatigue, disturbed respiration 10-14% Oxygen

Nausea and vomiting, collapse or loss of consciousness 6-10% Oxygen

Convulsive movements, possible respiratory collapse, and death <6% Oxygen


VII. Lifting Gas Compression as a Means of Ballast Generation ShortcomingsC. P. Burgess dismissed the idea of generating ballast by compressing lifting gas or air into high pressure tanks

in his classic text, Airship Design on the grounds that the high pressure storage tanks would be too heavy to bepractical.39 A more recent airship text also dismisses the notion of gas compression, yet the idea reappears oftenwithout much technical backing.40 When new advocates of gas compression schemes appear, their argumentsusually follow the notion that material science has produced such strong new materials that the weight of the storagetanks is no longer a problem. Typically supporting technical documentation does not follow such statements.

It is best to put actual numbers to such concepts. It is a simple matter to calculate the mass of a spherical storagetank and its volume for a given amount of negative ballast and fixed tank material yield strength. To begin withassume an idealized isothermal compression process such that the pressure ratio of the gas being compressed is

equal to the density ratio as shown in Eq. (2) where P and ρ are the pressure and density at states 1 and 2.

1

2

1

2

ρρ=

P

P

(2)

Then find the volume of the compressed gas ballast tank for the amount of negative buoyancy force required asshown in Eq. (3) where V is the volume of the ballast tank and L is the weight of the payload delivered at thelanding site.

−

=

agg

LV

ρρρρ

1

2

(3)

Then use Eq. (4) to solve for the radius of the sphere r .

31

34 πV

r = (4)

Since 12 PP − dictates the net pressure or stress acting on the sphere and using knowledge from deformable

body mechanics, it is possible to calculate the required thickness of the sphere for a given material yield strength

yσ in order to avoid rupturing the sphere. The sphere thickness t is calculated by use of Eq. (5).

( )y

PPrt

σ212 −= (5)

And then given the material’s density mρ , the overall mass vesselpressureM _ of the tank can be calculated by

using Eq. (6).

( )33

433

4_ )( rtrM mvesselpressure ππρ −+= (6)

Shown below in Fig. 5 is a graph assuming a series of different pressure ratios from 2:1 to 15:1 and consequenttank volumes sufficient to generate 16.329 metric tons of ballast.


The spherical tank is hypothetically madeout of a material with a yield strength of

yσ = 1200 MPa and a density of mρ = 4500

kg/m^3, which would be very similar to highstrength titanium alloys in terms ofmechanical and physical properties. Acomposite material would probably offerslightly better weight performance thentitanium. But since composites arenonisotropic materials, meaning their strengthdepends on the direction of mechanicalloading, and the stresses acting on a thinwalled sphere are assumed to be biaxial innature, a composite material is lessadvantageous then a simple strength toweight number would indicate.

Observe that this idealized high pressure tank represents a mass equivalent to almost half of the specified usefulpayload. And this is a highly idealized mass estimate, as it assume a safety factor of one, no structuralreinforcements to the overall airship to deal with a large point load, no compressors, no power system to drive thecompressors, and no fuel to feed the power system. As this is a manned vehicle pressure vessel safety standardsmay dictate a factor of safety of at least 5.2=Fs .41

The airship sizing code was modified such that an additional 7,600 kg*2.5 = 19,000 kg was added onto thedeadload to represent the mass of the idealized gas compression system. No attempt was made to include the poweror fuel requirements of gas compression. Furthermore no effort was made to take into account the volume the highpressure tank itself displaces within the airship. The gas compression scheme results in airship that is larger then anequivalent performing ammonia-helium hybrid airship.

VIII. Gas Liquefaction as a Means of Ballast Generation ShortcomingsLiquefaction of a gas—either lifting gas or air—to generate ballast has been suggested as a means to deal with a

lack of aerostatic equilibrium. Its appeal over gas compression schemes is that it does not require storage tanks thatare as large or as heavy for structural reasons. Gas liquefaction suffers from the burden of large energyrequirements and more sophisticated hardware, all of which represent a significant deadload penalty to the airship.

It was a difficult task to find detailed sizing mass estimates for various liquefaction schemes used in industry thatcould practically be applied to an aircraft. In other words, a means to predict how light weight an aerospace gradeliquefaction system could be over its industrial counterpart with a method based on engineering experience overaggressive and perhaps unrealistic mass budget cutting, is very difficult to find. But, there exists detaileddescription of required energy consumption per liquefied mass of many different cryogenic systems based onobservation of actual cryogenic liquefaction plants. Figure 6 presents the energy requirements of several differentcryogenic processes for liquefying air.42 The liquefaction of air should require less energy and system weight thenliquefying helium and as such air liquefaction was used as the baseline. The most efficient industrial processobserved is the Dual-Pressure Claude system.

Tank Mass Vs Volume forConstant Stress and Constant Negative Ballast of 16.329 Metric Tons

7596

7598

7600

7602

7604

0 2000 4000 6000 8000 10000 12000 14000

Volume of Compressed Air Ballast Tank, m^3

Mas

so

fT

ank

Mad

eo

ut

of

H.S

.Tit

aniu

m,k

g

Figure 5. Relationship between tank mass and volume


Using the knowledge of realistic work requirements it is also possible to estimate the power requirements if thetime allowed to liquefy a given mass can be specified, see Fig. 7. Trade studies would need to be performed to lookat what kind of power requirements would be needed to satisfy mission requirements if a liquefaction system waschosen as the means to generate ballast. The sizing code only estimates additional fuel requirements caused by theliquefaction system and not overall liquefaction system mass. The power source for liquefaction is assumed to havea thermal efficiency of 20%. An airship was sized assuming the high efficiency Dual Pressure Claude system aswell as the lower efficiency Linde-Hampson system. It is debatable as to where an intentionally designed aerospaceliquefaction system would lie in terms of cryogenic yields for a given energy input. It could very well be lessefficient then the industrial systems mentioned.

Observed Energy Requirements of Liquefaction Methods Used Industrially

717.7

27193248 3323 3571

5564

6351

10253

0

2000

4000

6000

8000

10000

12000

Types of Liquefaction Systems

Wo

rko

fth

eL

iqu

efac

tio

no

fA

ir,k

J/kg

Ideal Carnot System Dual Pressure Claude System Cascade System

Heylandt System Claude System Pre-Cooled Linde-Hampson System

Linde Dual-Pressure System Linde-Hampson System

Figure 6. Specific energy requirements for observed liquefaction of air in an industrial setting


Power Requirements of Industrial Liquefaction Processes

0.1

1

10

100

1000

0 5 10 15 20 25 30

Time, minutes

Air

Liq

uef

acti

on

Po

wer

Req

uir

emen

ts,k

W/k

g

Ideal Cascade System Dual Pressure Claude System

Heylandt System Linde Dual Pressure System Linde-Hampson System

Claude System Pre-Cooled Linde-Hampson Systems

Figure 7. Specific power requirements for a given amount of time to produce a kilogram of liquid air


IX. Vectored Thrust, Aerodynamic Lift, and Water Recovery Shortcomings

Vectored thrust can be ameans to restore equilibrium toairships by providing a forceopposite to that of buoyancy.There are several methodscommon to aircraft for generatingthrust. Figure 8 shows the typicalpower requirements to generate aunit amount of thrust for thevarious methods available.43

Based on this efficiencyinformation and missionknowledge, specifically operatingrange, cruising speed, and netbuoyant force to be countered, itis possible to estimate theadditional power and fuelrequirements dictated by use ofthrust vectoring post payloaddelivery. Using the C-130J-30aircraft as a guide, per Walrusprogram plans, along with a fewassumed performance parametersspecifically range R = 3148 km,

flight velocity v = 40 m/s , payload payloadM = 16,329 kg, and the use of high thrust helicopter style rotors it can be

shown what incorporating thrust vectoring means to the design. First, define the amount of power required tocounter the buoyant force acting on the airship as shown in Eq. (7). Then use Eq. (8) to calculate the amount of timethat the thrust vectoring has to be sustained. Equation (9) is then used to calculate the additional mass of fuel

required. The essential equations are shown below where β is the power to thrust ratio, t is time, stVectorThrup is the

power required to generate thrust to counter aerostatic lift, λ is the thermal efficiency of the heat engine, and

fuelLHV is the lower heating value of the fuel utilized in the heat engine.

stVectorThrupayload pgM =β (7)

tv

R =2

(8)

fuelfuel

stVectorThru MLHV

tp =λ

(9)

Buoyancy Control Through Vectored Thrust of the Propulsion System

0.01520.0234

0.0380 0.0400 0.0422

0.1014

0.1267

0.2534

0.0000

0.0500

0.1000

0.1500

0.2000

0.2500

0.3000

Static Thrust Propulsion Concepts

Po

wer

Req

uir

dp

erU

nit

Th

rust

,kW

/N

High Thrust Helicopter Rotor Low Thrust Helicopter Rotor High Thrust Propellor Low Thrust Propellor

High Thrust Ducted Fan Low Thrust Ducted Fan High Thrust By-Pass Turbojet Low Thrust By-Pass Turbojet

Figure 8. Power to thrust ratio for various vector thrust methods43


Burgess discusses the use of lifting surfaces on airships to generate additional aerodynamic lift and suggests thatthis form of lift is rather inefficient. He suggests that a plane surface on an airship could generate 1000 lbs ofaerodynamic lift and an additional 60lbs of drag which represent a lift to drag ratio ( DL / ) of 16.6 just for the

additional aerodynamic surfaces, which is similar to the overall cruise DL / of commercial airplanes. It would

seem unlikely that the overall aerodynamic DL / of an airship, even a lifting body airship would approach DL / of16.6, without the airship looking very much like a conventional aircraft or even a glider as the conventional airshipshape does not favor efficient generation of lift.

Using the information of the mass of the payload payloadM and aerodynamic DL / it is possible to calculate the

additional drag burden on the airship and the fuel penalty incurred by the drag assuming there is sufficient “wing”area and forward velocity to generate the required lift. First the additional drag force D due to aerodynamic lift iscalculated using Eq. (10).

DL

gMD payload

/= (10)

Knowing that drag equals thrust in steady flight and that a force D times a distance R is a unit of work it ispossible to calculate the additional fuel burden because of the additional drag using Eq. (11).

LHV

DRM fuel λ

21

= (11)

The use of aerodynamic lift to deal with excessive buoyancy does appear to be a design concept worthinvestigating, assuming a high enough DL / ratio can be achieved. In order to utilize aerodynamic lift tocompensate for excessive buoyancy the airship has to be moving with some forward velocity, this makes unloadingthe airship extremely difficult as the net buoyancy is increasing as the payload is unloaded, but there is no means tocompensate the net force acting on the airship. The proposed solution to this problem is to utilize some combinationof vectored thrust and aerodynamic lift.44,45 Vectored thrust would only be used to hold the airship to ground when itis stationary offloading its payload and then when returning from its mission it would rely on more efficientaerodynamic lift to keep it in equilibrium. This solution certainly makes it possible to achieve the intended mission,but it seems unlikely to be as efficient as an ammonia-helium hybrid airship in aerostatic equilibrium.

Exhaust water recovery has been used in the past to maintain aerostatic equilibrium in airships as fuel wasconsumed. Exhaust water recovery has several drawbacks. It adds both mass and drag to the airship. It also placesan additional burden on the propulsion system through increased back pressure. Typically the system works bestwith heat engines that utilize a combustion process that does not use a lean air to fuel ratio. In other words exhaustwater recovery works well with spark ignition engines, but not diesels or gas turbine engines. Another fault ofexhaust water recovery is its inability to handle step changes in net aerostatic buoyancy, in other words it could takean exhaust water recovery system many hours to restore equilibrium to the airship after delivering the payload. Ifexhaust water recovery was used on a WALRUS type airship it would most certainly have to be used in conjunctionwith one of the other methods described in this paper. Since exhaust water recover is not a stand alone solution it hasbeen ignored in the airship sizing code simulations. A more detailed study should investigate how exhaust waterrecovery systems could compliment other systems to make them more efficient in terms of overall performance.

X. ConclusionsUse of ammonia as a secondary lifting gas needs to be considered as a viable alternative to other concepts to best

meet the needs of a WALRUS type mission. Ammonia has found its way into balloons, but no progress has beenmade in the use of ammonia within airships. The biggest obstacle to the use of ammonia appears to be regulatorylaws on the grounds of safety. Ammonia is technically both an irritant and flammable, but as an irritant its toxicitythresholds are similar to carbon monoxide, a chemical we are exposed to on a daily basis. Ammonia’s flammabilityis substantially less then other flammable lifting gases. The US Department of Transportation does not treat


ammonia as a flammable substance. An airship utilizing ammonia as a secondary lifting gas should only emit traceamounts of raw ammonia into the environment by utilizing off the shelf technology to safely vent ammonia by useof flare.

Ammonia also has other potential uses which benefit the airship. Ammonia can be used as a fuel and under theright circumstances it can even enhance the performance of conventional engines. Environmental regulatorypressures are also inspiring the development of the use of ammonia to reduce NOx emission in conventional heatengines by the use of Selective Catalytic Reduction (SCR). These secondary features, particular with ammonia offeradditional possibilities over that of other disposable lifting gases such as hot-air and steam.

Using an airship sizing code based upon historical design data it has been shown that an ammonia-helium hybridairship offers superior performance to all other concepts evaluated. The sizing code was written such that anammonia-helium hybrid airship was presented in the most realistic possible manner, given the resources available,along with hot-air helium and steam-helium hybrid airships. The accuracy of the code in predicting the performanceof an airship equipped with gas liquefaction, gas compression, vectored thrust, or aerodynamic lift is sufficient toshow performance problems associated with these systems, but not necessarily predict true performance. In otherwords these other concepts are given more leeway then typical design conservatism would dictate.

AppendixMATLAB Code Used to Estimate Airship Sizes – ‘%’ symbol represents a comment in the MATLAB

programming language

%Donald Horkheimer%Airship Sizing Program Ver 1.0

%This program take a fixed volume for a fixed payload and an initial guess at deadload to iterate to a final volume%to cover both loads.%volume1+volume2 = total volume of the airship. If the airship used two lifting gases, one helium and one%disposable, then the program iterates the helium volume% and keep the disposable volume constant, such that when the payload is dropped off, the disposable lift can be%dumped.%All units are in SI, ie m, kg, s, K, J, except range = km

%payload represents just the tanks and troops and nothing else, in essence the disposable load of the airship%deadload represents envelop weight, gas/air valves and controls, bow hull reinforcements, empennage, engines,%reinforcing structure, pilots cabin, power plant supports, mooring cables, and keel%fuelmass is calculated separately based on mission requirements and added into the dead load as well as fuel tanks%and lines.%I have disregarded crew, gangway, wireless set, generating set, engine spare parts, and ballast masses, contrary to%Corocco's estimation process

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

function airshipsize(Pguess, payload, range, speed, LHV, n, iterations, LD, liq, hybrid, compress, thrust, aero)

%Example function airshipsize(5000, 16329, 3148, 40, 50000000, 10, 800, 0, 0, 1, 0, 0, 0)%The variables liq, hybrid, compress, thrust are on/off switches that add in deadload terms depending on system, set%to 1 or 0.%C-130J-30 Range=1,700nmi or 3148.4561 km, Maximum Normal Payload = 36,000 lbs or 16,329 kg%1nm = 1.1508 statute mile, 1 statute mile = 1609.344m, 1nm = 1852.033 m%1mph = 0.447 m/s

%Density of various gases at 300K Sea Level kg/m^3


%AIR = 1.177 kg/m^3%He = 0.1627 kg/m^3%HotAir = 0.883 %Defined to be air at @400K, so there is a 100K differential%Steam = 0.555 @400K%NH3 = 0.692 @300K or 0.519 @400K

Gas2 =0.1627; %Set gases manually, set gas1 and gas2 for a nonhybrid lifting gas airshipGas1 =0.1627; %kgm^3Air =1.177; %kgm^3eff = 0.2; %thermal efficiency of the engine, measure of ability to convert chemical energy into mechanical energy%or work

endurance_hours = range/(speed*(3600/1000)); % range in km divided by speed in km/hr

%Initial Guess At Volume

volume1 = payload/(Air-Gas2); %This sets a volume of lifting gas just for payloadvolume2(1) = Pguess/(Air-Gas1); %/(Air-Gas2); %This take an initial guessvolumetotal(1) = volume1+volume2; %total hull volumeP(1) = Pguess; %Pguess become initial dead load guess

%System SwitchesPhybrid = hybrid*1.09*volume1^(2/3); %kg mass term of secondary lifting gas cellPcompress = compress*2.5*7600; %kg Mass of compressed air ballast tankPliq = liq*((payload*2719*1000)/(eff*LHV)); %kg Mass of extra fuel to liquefy airPthrust = thrust*((payload*0.5*endurance_hours*0.15*1000*3600)/LHV); %mass of fuel for vector thrustPthrust_HPinstalled = thrust*(payload*0.15*1.341); %Extra installed power for thrust vectoringPaero = aero*(((payload*9.81/LD)*(1000*(range/2)))/(eff*LHV)); %Calculates extra fuel required to overcome%extra drag because of aerodynamic lift generation

%Iterative solver%Solver works by taking the sum of the calculated deadload and required payload and iterating the growth in%volume, until there is sufficient volume to lift, both payload%deadloadfor i = 1:iterations

%Estimation of required cruising horsepower and fuel requirement%Col Crocco assume a 70% propellor efficiencyHP(i) = 0.0000576*(volumetotal(i)^(2/3))*speed^3; %Crocco equation to calculate horsepower requirements for%propulsionHPtotal(i) = HP(i)+Pthrust_HPinstalled; %combines propulsion HP requirements with other system's HP%requirements, specifically vector thrust and aerodynamic liftwork_customary(i) = HP(i)*endurance_hours; %calculates total propulsion work over course of missionwork_SI(i) = work_customary(i)*2544.5*1055.056; %1HP-hr = 2544.5 BTU, 1 BTU = 1055.56 Jfuelmass(i) = (work_SI(i)/(eff*LHV))+Pliq+Pthrust+Paero; %does not include fuel tanks and lines, according to%Corocco this represents about 7% of the total mass of fuel.

%Dead load + fuel load calculations - Dead load include fuel massP(i+1)=(0.1755+0.00002275*(speed^2))*volumetotal(i)+(0.09994*n+3.075)*(volumetotal(i)^(2/3))+0.0019725*(volumetotal(i)^(4/3))+HPtotal(i)*2.15+1.07*fuelmass(i)+Phybrid+Pcompress;

%Logical iterative breakif P(i+1)+payload >= volume2(i)*(Air-Gas1)+volume1*(Air-Gas2); %logic

volume2(i+1) = 1.01*volume2(i); %Volume growth update til logical condition is satisfied, 1% growth in airship%volume per iteration

volumetotal(i+1) = volume1+volume2(i+1); %Future total volume used for the next iteration of the code


elsebreak %logical break acts if there is sufficient displacement to carry both deadloads and payload

endend

save %saves results to MATLAB data file

AcknowledgmentsThe best part of this paper is getting to say thank you. I would like to thank my parents, Ronald and Maureen

Horkheimer for stressing at an early age the importance of education and life long learning. I would also to thankMark Andrews and Mark Claywell for their support and being good friends through the time it took to prepare thispaper. I owe much to Greg Weinand, you helped me make time when it appeared that I didn’t have enough time forimportant things to happen in life. David Harris, Jacob Sirek, Louise and Charles Ewald have also been verysupportive in making this paper happen. I would also like to thank members of John Dziadecki’s email Airship-Listfor a constant discussion of all things airship and then some. Specific thanks go to Airship-List members Jim Smithfor always listening and Marc de Piolenc and Mark Foxwell for feedback. I have also come to appreciate the worldclass library system the University of Minnesota has built for itself and the public that supports it.

References1D.A.R.P.A., Walrus: Heavy Lift Air Vehicle Design Program Phase 1 Solicitation. Arlington, VA.: May, 2004.

http://www.darpa.mil/tto/walrus/Draft_Solicitation_Walrus.pdf2“Walrus—Heavy-Lift Air Vehicle Program”., Airship: Journal of the Airship Association, UK. June 2004 pp. 8-10.3US Air Force, Air Force Link – Fact Sheet: C-130 Hercules. Arlington, VA.: September, 2003.

http://www.af.mil/factsheets/factsheet.asp?fsID=924Eidsness, C., “Ammonia Limits Continue to Expand”. Balloon Life, Vol. 10(11), November 1995.

http://www.balloonlife.com/publications/balloon_life/9511/ammonia.htm5Ruffenach, G., “Compatibility of Balloon Fabrics with Ammonia”. United States Department of Agriculture-Forest Service,

Contract No. 19-50, February 1966.6Cengel, Y. A. and Turner, R. H., Fundamentals of Thermal-Fluid Sciences. New York, NY.: McGraw-Hill. 2001.7Crocco., “The Dead Weight of the Airship and the Number of Passengers That Can be Carried”. NACA 80, January, 1922.8Kroch, E., “Ammonia – A Fuel For Motor Buses” Journal of the Institute of Petroleum, Vol. 31, July 1945, pp. 213-223.9Egloff, G. and Alexander, M., “Combustible Gases as Substitute Motor Fuels”. Petroleum Refiner, Vol. 23(6), June 1944,

pp. 123-128.10“Energy Depot Concept.” Society of Automotive Engineers Publication SP-263, 1965.12Grimes, P. G., “Energy Depot Fuel Production and Utilization”. Society of Automotive Engineers, 650051.13Rosenthal, A. B., “Energy Depot-A Concept for Reducing the Military Supply Burden”. Society of Automotive Engineers,

650050.14Cornelius, W., Huellmantel, L. W., and Mitchell, H. R., “Ammonia as an Engine Fuel”. Society of Automotive Engineers,15Sawyer, R. F., Starkman, E. S., Muzio, L., and Schmidt, W. L., “Oxides of Nitrogen in Combustion Products of Ammonia

Fueled Reciprocating Engine”. Society of Automotive Engineers, 680401.15Verkamp, F. J., Hardin, M. C. and Williams. J. R., “Ammonia Combustion Properties and Performance in Gas Turbines”.

11th Symposium on Combustion, The Combustion Institute, 1967, pp. 985-992.16Pearsall, T. J. and Garabedian, C. G., “Combustion of Anhydrous Ammonia in Diesel Engines”. Society of Automotive

Engineers, 670947.17Bro, K. and Pedersen, P. S., “Alternative Diesel Engine Fuels: An Experimental Investigation of Methanol, Ethanol,

Methane and Ammonia in a D.I. Diesel Engine With Pilot Injection”. Society of Automotive Engineers, 770794.18El-Emam, S. H., and Desoky, A. A., “A Study On the Combustion of Alternative Fuels in Spark Ignition Engines”.International Journal of Hydrogen Energy, Vol. 10(7/8), 1985, pp. 497-504.19Dhall, S. N. and Beans, E. W. “Correlation of Knock with Engine Parameters for Ammonia/Nitrous Oxide Mixtures”.

Society of Automotive Engineers, 912310.20Liu, R., Ting, D. S. K. and Checkel, M. D., “Ammonia as a Fuel for SI Engine”. Society of Automotive Engineers, 2003-01-

3095.21Cler, G., “Diesels Come Clean(er)”. Power, March 2005, pp. 76-82.22Seher, S. H. E., Reichelt, M., Wickert, S., “Control Strategy for NOx –Emission Reduction with SCR”. Society of

Automotive Engineers, 2003-01-3362.23Takiguchi, M. and et. al., “Catalytic Engine” NOx Reduction of Diesel Engines with New Concept Onboard Ammonia

Synthesis System”. Society of Automotive Engineers, 920469.24Ogunwumi, S., Fox, R., Patil, M. D. and He, L., “In-Situ NH3 Generation For SCR NOx Applications”. Society of

Automotive Engineers, 2002-01-2872.


25Appl, M., Ammonia. New York, N.Y.: Wiley-VCH. 1999.26Schweitzer, P. A., Corrosion Resistance Table: 5th Ed. Revised and Expanded. New York, NY: Marcel Dekker Inc. 2004.27Tanner Industries, Inc. “Storage & Handling of Anhydrous Ammonia”. 1995.28Pincha, E. M. W., Heizer, B. L. and McHale, M. P., “Material Compatibility Problems for Ammonia Systems”. Society of

Automotive Engineers, 881087.29Civilian Aviation Authority., “Transport Airship Requirements”. Braunschweig, Germany: Luftfahrt-Bundesamt. March

2000, p. 56.30LaRoche Industries, Inc. “Anhydrous Ammonia Safety”. 199731Nielsen, A., Ammonia Catalysis and Manufacture. New York, N.Y.: Springer-Verlag. 1995.32Washington State Department of Labor and Industries, Carbon Monoxide. Olympia, WA.:

http://www.lni.wa.gov/Safety/Topics/AtoZ/CarbonMonoxide/33Vogt, M. C. and Skubal, L. R., “Flexible Ammonia Detection with Voltammetric Microsensors”. Sensors, February, 2005.34EPA, AP 42, 5th Ed., Washington, D.C.: September, 1991, Chapter 13, Section 5, pp. 1-5.35Air Liquide, “Material Safety Data Sheet-Helium”. Chemical Safety Associates, Inc., June 1998.36Noyes, R., Ammonia and Synthesis Gas. Park Ridge, New Jersey: Noyes Development Corporation. 196737Kuhl, G., and Blasi, D., “Ammonia Treatment of Low Quality Forages”. Kansas Forage Task Force, Kansas State

Univesity Research and Extension.38Goodey, T. J., “Advances in Steam Aerostation”. American Institute of Aeronautics and Astronautics, AIAA-2003-684139Burgess, C. P., Airship Design. Honolulu, Hawaii: University Press of the Pacific. 1927.40Khoury, G. A. and Gillet, J. D., Airship Technology. Cambridge, UK: Cambridge University Press. 1999.41NASA, NASA Medium Weight Pressure Vessel Safety StandardNSS/HP-1740.4. Washington, D.C.: August, 1976. 42Barron, R., Cryogenic Systems. New York, N. Y.: McGraw-Hill. 1966, pp. 110-111.43Stepniewski, W. Z., and Keys, C. N., Rotary-Wing Aerodynamics, Mineola, N.Y.: Dover Publications Inc. 1984, p .44Blake, B., “Why a Behemuth? The Story of the AHA Ltd. Behemuth Heavy Lifter, Buoyant Aircraft”. Aerostation, Vol.

28(1/2), Spring/Summer 2005, pp. 2-3.45de Piolenc, M. F., “Gestation of a “Walrus””. Aerostation, Vol. 28(1/2), Spring/Summer 2005, pp. 4-6.46Turns, S. R., An Introduction to Combustion: Concepts and Application 2nd Edition. New York, N.Y.: McGraw-Hill. 2000.47Gerrish, C. H. and Foster, H. H., “Hydrogen as an Auxiliary Fuel in Compression Ignition Engines”. NACA 535, April

1935.

Documents

Ammonia A Solution for Airships Demanding Rapid …me.umn.edu/~hork0004/AIAA-2005-7393-913.pdf · Minneapolis, MN 55418 USA, and AIAA Member . [email protected] or [email protected]