Conceptual Design of a Space Power System Based on Combustion of Metals

Open AccessTechnical NotesConceptual Design of a Space Power System Based on Combustion MetalsEvgeny ShafirovichEvgeny Shafirovich https://orcid.org/0000-0002-3632-2349The University Texas at El Paso, 79968*Professor, Department Aerospace and Mechanical Engineering. Associate Fellow AIAA.Search for more papers by this authorPublished Online:2 Jan 2023https://doi.org/10.2514/1.B39008SectionsRead Now ToolsAdd to favoritesDownload citationTrack citations ShareShare onFacebookTwitterLinked InRedditEmail AboutI. IntroductionCurrently, there is growing interest in the so-called chemical heat integrated power systems [1], which are based exothermic reactions between solid or liquid reactants. Such could provide electric space missions where use sunlight nuclear energy impractical batteries cannot serve as primary source because their low specific energy, limited storage time, relatively narrow temperature range.One approach development involves combustion lithium with sulfur hexafluoride (SF6). These reactants were used generate Rankine cycle underwater propulsion through reaction that does not produce any gas products [2]. The SF6 was stored saturated (the vapor pressure 21 bar 20°C), whereas (Li) solid, melted before operation melting point 180°C). In Li-SF6 system, can occur either surface phase. For latter, reactor include wick capillary flow molten toward gas-phase zone case, produces fluoride (LIF) sulfide (LI2S): 8Li+SF6→6LiF+Li2S(1)where LiF Li2S (their points 848 938°C, respectively). Because they immiscible several times denser, sink, hence do inhibit reaction.Recently, system has been proposed be Venus [3] Europa [4]. missions, it also situ CO2 oxidizer Li, magnesium (Mg), magnesium/aluminum magnesium/zinc eutectic alloys metal fuels [3]. calculations have shown both Li-CO2 combustors, coupled Stirling engines, would superior energies (per unit mass entire system) compared [3,4]. However, testing reactors revealed efficiency due accumulation condensed metal–gas interface [5].The rather high energy: 3.9 (kW⋅h)/kg (14.1 MJ/kg) comparison, state-of-the-art battery technology provides 0.2–0.3 ( kW⋅h)/kg (0.7–1.1 [1]. Of course, only part generated converted electricity, masses tank, reactor, converter should accounted for. produced per may still high, unconverted useful “cold worlds,” such moon’s polar regions. addition, long life. successful combustors (on other hand) demonstrate importance sinking prevent inhibiting effect combustion. Apparently, mechanism take place microgravity if gravity too low.Here, we evaluate an alternative approach, metals oxygen apparently independent gravity. Specifically, cylindrical filled combustible powder, gaseous fed into from one end. wave propagation initiated ignition same end opposite one. former leads coflow combustion, infiltrates products; latter counterflow regime, initial powder. storage, propose generators (COGs), those aircraft, submarines, stations. They usually contain sodium chlorate (NaClO3) perchlorate (LiClO4) small amounts fuel (typically iron), catalyst, ingredients [6].In present Note, estimate energetic characteristics heat-generating combustor, described earlier COG. We design includes cartridges required two missions. recent experimental studies Mg Li oxygen, make recommendations combustor. Finally, feasibilities using heat/power generation Mars Venus.II. Results DiscussionA. Energetic Mass CharacteristicsIt important identify Obviously, its effective operation, especially formed oxide occupy less than did; i.e., Pilling–Bedworth ratio lower 1. Aluminum, although advantageous energetically, 1.28, makes problematic. magnesium, equal 0.57 0.81, respectively, so suitable.The equations 4Li+O2→2Li2O(2)2Mg+O2→2MgO(3)The Li-O2 Mg-O2 systems, determined enthalpies formation standard conditions, 20.0 14.9 MJ/kg, higher these estimates taken Ref. [7]). values only. comparison necessary know all components, unit, combustor (which serves fuel), transfer (e.g., engine).The COG estimated assuming oxygen-generating mixture contains 90 wt % LiClO4 oxidation ingredient releases decomposition assumption prior study chlorate/metal mixtures [8]). integral (in generator combustor) assumed 8Li+LiClO4→4Li2O+LiCl(4)4Mg+LiClO4→4MgO+LiCl(5)At assumptions, Li- Mg-based 16.0 12.9 mixture.When needs time 14 Earth days lunar night survival mission), consecutively. Figure 1 shows schematic diagram engine conversion power.Table parameters power, remaining maintain desired lander spacecraft. mission A, 157 MJ heat, correspond total requirement [1]: 130 W days. B, 2592 MJ, constant rate 1500 20 commercially available COGs aircraft submarines estimates. Mission A uses (0.45 kg) B much larger (12 (Molecular Products, MPOG®). Table 1, capacities normal (1 atm 20°C). Each analyzed fuels: Mg. capacity, contained cartridge calculated according stoichiometry Eqs. (2) (3). Next, cartridge, number determined; actual multiplying cartridges. (approximately 2.5 MPOG manufacturer) account. starts duration obtained cartridges.Fig. Schematic supplying (black arrow) (red arrows) spacecraft.It seen require 40 capacity 80 liters, need O2 2600 liters. 75%. densities 534 1738 kg/m3, respectively; 3.25 denser Li. Thus, smaller volume. It noted hard structure stage. worth mentioning (Li Mg) comparable tank (15.84 (4.58 [1].Note contents developed. example, designed follows altitude profile descending (after decompression) airplane, unnecessary application. Furthermore, considered NaClO3 but (60 vs 45 %), backup stations [9]. thorough design, released added combustor.It performed 100% efficiency, full during experimentally. next section presents results laboratory experiments samples powders ignited closed chamber gas. goal verify self-sustained propagate over powder bed result extent metal-into-oxide conversion. discussed respect system.B. Experimental Verification Recommendations Combustor DesignThe infiltration reactive self-propagating high-temperature synthesis nitrides hydrides [10,11]. conducted pressures 1000 order sufficient amount reactant pores. will lower, requires rapid oxide.Recently, natural studied experimentally [12,13]. means no pressurized (forced) feed (i.e., sample located quiescent environment), caused difference environment zone. vertical quartz tube access ends top laser beam inside vacuum atmospheric pressure. propagated downward owing open bottom incomplete. Mg, led second up. typically continued upward observed some tests. metals, incomplete after process: up 74% [12] 63±10% [13]. velocities [12].The findings [12,13] allow made forced particles. scheme preferred operate porosity thoroughly sintering ensure oxygen. optimal configuration ends. This followed self-ignition backward. expected increase efficiencies powders.For implementation concept, velocity low. Indeed, front length shorten removal, undesirable. remarkable axial low: 0.1 mm/s. rarely typical [8]. order. allows dimensions estimated. Mg-COG earlier, simplicity complete single COG, around min 75 MPOG. 71% average [12]), following dimensions: diameter 5.8 cm 12 17.2 B. appear reasonable, close commercial generators. Many 5 10–12 cm, MPOG’s 13.3×13.3×40 cm. favorable design.One additional advantage filtration potentially autocontrolled operation. During steady mode, consumption inlet constant, decrease gradient, rate. essentially generator. Therefore, decreases, increase, turn gradient rate; stabilized. Similarly, acceleration front, normally approaching end, hindered decreasing faster oxygen.The challenge concept short generation. mentioned process, Assuming (where used) MPOGs used), rates 3.3 29 kW, respectively. One option cooling alkali metal, sodium- potassium eutectic, coolant feeding electromagnetic pump. used, TOPAZ-II thermal 115 kW [14]. Another pipes working fluid. attractive pump needed. Heat fluid range 4 developed tested [15]. If built, significant advantages realized, ignition. placing pyrophoric near inlet.Table fuel. significantly reduce provided worse section, analyzed.C. Use Situ CO2In Venus, improve performance adding flow. potential improvement evaluated thermochemical calculations. MgO, CO, C via parallel reactions: Mg+CO2→MgO+CO(6)2Mg+CO2→2MgO+C(7)where CO/C depends process conditions availability Eq. (6) [16–18]. 13.1 16.6 MJ/kg Mg), slightly exceed system: MJ/kg.Combustion carbonate (Li2CO3), C, again dependent [5,13,19]. overall certain combination [13]: 2Li+2CO2→Li2CO3+CO(8)4Li+3CO2→2Li2CO3+C(9)The 38.9 45.1 Li), Li-COG MJ/kg.Based considerations, clearly CO2. Unfortunately, CO2, achieved: transport possible help overcome problem. metal-CO2 organized configurations process. powdered laboratory-scale rocket engines demonstrated [20–25]. mixed applications missions.III. ConclusionsLithium promising supplied Thermochemical (Mg Li) recently survival. multiple durations longer night.Based powders, layer resulted products, inlets oxidizer. trigger backward wave.Thermochemical 2.4–2.8 case (by 1.0–1.3 times).J. RoveyAssociate EditorAcknowledgmentsThe material presented work upon supported National Aeronautics Administration under grant no. 80NSSC20K0293. author thanks Sergio Cordova (currently Northrop Grumman) Steven L. Rickman NASA Engineering Safety Center helpful discussions. References [1] Hendricks T. J., Brandon E. Lam R. L., Peterson D. E., Anderson K. 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All rights reserved. requests copying permission reprint submitted CCC www.copyright.com; employ eISSN 1533-3876 initiate your request. See Rights Permissions www.aiaa.org/randp. TopicsCombustionCombustion ChambersCombustorsElectric PowerEnergyEnergy ConversionEnergy FormsEnergy Forms, Production ProductionFuelsHeat EnginesPropulsion PowerRocketryThermophysics Transfer KeywordsPower SystemCombustor DesignMetal FuelsSpace MissionsChemical EnergyCombustion EfficiencyElectric PowerStirling EnginesHeat TransferAcknowledgmentsThe discussions.PDF Received31 August 2022Accepted12 December 2022Published online2 January