Numerical simulation of detonation of an explosive atmosphere of liquefied petroleum gas in a confin

Available online at www.sciencedirect.comDefenceTechnology①ScienceDirectCrossMarkEL SEVIERDefence Technology 10 (2014) 294- -297www.elsevier.com/locate/dtNumerical simulation of detonation of an explosive atmosphere of liquefiedpetroleum gas in a confined spaceNiculae Serban COSTINMilitary Technical Academy, Sector 5, 050141 Bucharest, RomaniaReceived 15 January 2014; revised 21 February 2014; accepted 20 June 2014Available online 22 July 2014AbstractThe detonation of an explosive atmosphere from liquefied petroleum gas disseminated in air in a confined space is studied using numericalmodeling with software product ANSYS AUTODYN.Copyright o 2014, China Ordnance Society. Production and hosting by EIsevier B.V. All rights reserved.Keywords: Liquefied petroleum gas; Overpressure; Confined space; Explosion limit1. Introduction2. The calculation of the characteristics of LPG-airmixture using CEA programthose petroleum products which are made up of mixed vari-CEA program enables the calculation of the characteristicsables of gaseous hydrocarbons (methane, ethane, butane) andof Chapman-Jouguet detonation. Several reports from Zackambient conditions, which are in a state of vapor, but can beand Gordon (1960 and 1968) were intended to compare theeasily liquefied. In Romania, liquefied petroleum gas, namely, .results for the two ways of calculation of chemical equllib-petroleum product, is composed of mixture of butane (min.rium. It came to the conclusion that it comes down to the same90%) and propane (max. 9%) [1].number of equations. However, in the case of free energyThe characteristics of LPG are defined in SR 66:2007,minimization method each chemical species can be treatedcontaining mainly max. 12% C3 and min. 87% C4, and theindependently without having to specify a set of special ef-vapor pressure is max. 7.5 bar [1].fects, as it is required in the case of the equilibrium constantsA mixture of 8% propane and 92% butane was chosen formethod [2,3].numerical simulation in the paper. This mixture of fuel, mixedThus, the program that uses free energy minimizationwith air, will form an explosive atmosphere. The temperaturesmethod for the calculation of equilibrium composition. Thof self-ignition and explosion limits for LPG components aremethod used to obtain the parameters of engine knockingpresented in Table 1Chapman- -Jouguet is described by Zack and Gordon. There10 kg of LPG (LPG vapor) which will be subject to theare three stages in the procedure. The first stage consists indetonation is used to study normal and reflected overpressuresestimating the initial detonation pressure and temperature. Thein a confined spacesecond stage is to use a recurrent formula for improving theparameters obtained in the first stage. During the third stagethe correct valuesare obtained using a ierative New-E-mail address: niculae.costin@ yahoo.com (N.S. COSTIN).ton-Raphson proc中国煤化工Peer review under responsibility of China Ordnance Society.YHCNMH Ghtp:/:.o.o.o/10.016/./.14./6.008 .2214-9147/Copyright◎2014, China Ordnance Society. Production and hosting by Elsevier B.V. All rights reserved.N.S. COSTIN/ Defence Teclmology 10 (2014) 294- -297295Table 1pl1_ P1=0Heat of combustion for various fuels [6].P(7GasFormulaHeat of combustion/(KJ mol ')h"-1h2=0.PropaneC3HgInitial estimated temperature ratio is found by calculatingButaneC4Ho-2877.5the flame temperatures corresponding to enthalpy [9].IsobutaneC.Hno- 2869.0h2= hy :t 3RTi(84MThe program assumes that all gases are ideal processesThe initial estimates for the values (号)o and (号)o .involved, and the interactions between the phases are neglec-corresponding to h2 are improved to give the followingted [8,10]. The equation of state for the gas mixture isrecursive formulas.pV = nRT,1). 1+ Ys.24r5s,2Qk _(9or().-2rs;2QXk(1+ rs2)5 = nRT,2)3R()。where p is pressure (N/m2); V is specific volume (m3/kg); n is(),=()。-4 MrCp,2the number of moles per unit of mass mixture (mol/kg); T isRyY.2 宝一1(10)temperature (K); and R = 8314.51 J/(mol-' K- ).2MICp.2 In+1 (P+)k+1Based on the definition of the gas mixture, n can be written(会)急(11)1=2”，(3)rt+1=an(中)where n is the number of moles; and is the number of moles ofgas per kg of mixture.where M2,Ys.2 and Cp2 are the steady values for (号)。si (语)o.In a conventional manner, an average molecular weight ofAfter running the CEA program, the parameters corre-the mixture issponding to a gaseous LPG-air mixture (Table 2) werecalculated, which will be introduced into the model of materialEji n;M;to be used in AUTODYN. The values were calculated ac-MW=4)2mηjcording to the temperature of 18 °C and a pressure of 1 bar.It can be seen from Table 2 that the maximum overpressureFor iterative purposes, since are valid for the shock equa-corresponds to a volume of 4% LPG vapor into the air. We willtions, it is necessary for these three conservation equations tomake the simulation of detonation for this gaseous mixture.be reduced to two3. The detonation of an explosive atmosphere usingP2i=1-ra2(()5)modeling in Ansys AutodynLPG-air mixture is defined as a material using the char-Rr,T2h2=h+2M2|(2)-1|6)acteristics calculated by C.E.A program. One- dimensionalnumerical model of this new defined material, with a pre-For ease of writing the iterative equations, symbols pl anddefined geometry type“wedge", for a spherical explosivehl" are used to replace the right member of the above equa-cargoes in open space is shown in Fig. 1. Detonation point isions. These equations becomein (0,0).Table 2Characteristics of gaseous LPG-air mixture calculated with CEA program.%vol.LPGinDetonation pressureTemperature ofSpeed of detonationDensity reagent products/initialthe airPD [bar] gasdetonation T/(°K)V/(m.sdensity of gas (RHO/RHO).511.8501954.771457.3| 中国煤化工18.4012786.301777.719.4222814.441830.2MHCNMHG18.7072586.471806.717.6442310.141754.81.745096N.S. COSTIN/ Defence Technology 10 (2014) 294-297Material locationDetonation pointAirVoidGPL8% aer82%6 YGPL-aerFig. 1. One-dimensional numerical model.CONC140MPaThe initial condition is first defined. The internal energy ofthe air has the value of 2.068 * 107 J because the air needs tobe at atmospheric pressure (P= 1 bar) [7].The model has been realized with the Euler multi-materialsolver, specific to problems in which are modeled gases, fAuids .or solids that will undergo large deformations. Having as mainadvantage the fact that the elements of the meshed domain areFig. 3. The domain meshing.not distorted and there is no need of a new grid during thesimulation，the Euler solver is recommended in case ofmodeling the shock waves generated at explosive detonation. .model of an explosive mixture LPG air was used, which wasThus, a domain having 1240 mm in length has been definedoriginally saved as part (part fll-in) and loaded in the two-because the radius of the sphere corresponds to disseminationdimensional model. The origin point of detonation was elec-in air of 10 kg explosive atmosphere, by applying the initialted to be (0.0). The virtual transducers were set to analyze thecondition previously set (P = 1 bar) (Fig. 2).normal and reflected overpressures.In order to create the numerical models, the followingIn order to fulfill the radiation condition, a transmittingmaterials existing in AUTODYN library: AIR, TNT andboundary is defined for the external limits of blast part. TheCONCRETE- 140 MPA [5] have been used.transmitting boundary condition allows the blast wave toCONCRETE-140 MPA material was used for wallscontinue to“go through” the physical boundary withoutmodeling. Hiermaier, Riedel and Thoma have defined thereflection [5]. The transmitting boundary is only active formodel properties “RHT Concrete" to be able to represent theflow-out of a grid. Flow-out (Euler) of air and LPG-air ispressure and deformation of this material [4]. It is alsoimportant to specify that the material is not reinforcedFig.2 shows the layout of the explosive load against theconcrete.wall and the arrangement of the virtual transducers. Fig. 3Concrete is used in the proposed numerical model only topresents domain meshing.evaluate the reflected overpressure and not to study the pres-In Figs. 4 and 5, we can see the evolution of the shock wavesure transmitted through the wall, therefore the equations thatfront at various time intervals, and the overpressures are showndefine this material won't be presented.in Fig. 6.An 2200 mm x 2200 mm Euler ideal gas domain, havingWe can notice that, inside the explosive atmosphere, the221 Ox knots and 221 Oy knots, was defined. This environ-overpressure is approximately constant, lying around 20 bars,ment has been assigned to the AIR material. For each indi-value that is estimated in Ref.[1]. As a result of reflectionsvidual case, the wall was defined by using a Lagrange domain.with walls, it was formed an overpressures 4- -5 times higher.The wall thickness is 200 mm. The one-dimensional numericalThe GPL atmosphere takes up a huge volume compared to a| Material locaPressure/kPa! 940e+034.843e+03! 746e+03| 1.552+0331.164e+030Detonationpoint中国煤化工9.700e+01YHCNMHGFig.2. Layout of LPG- air atmosphere against the wall.Fig. 4. The shock wave front evolution - time 0 msN.S. COSTIN/ Defence Teclmology 10 (2014) 294- -297297PressurekParesulting from the detonation of a quantity of shatteringexplosive, which makes it possible to produce significantdamage.The results from the present study show that the reflectedoverpressure increases in comparison with the incident over-pressure, depending on the wall geometry. The values corre-spond to those obtained experimentally in the study INCD-INSEMEX Petrosani [11].Damages recorded following the detonation of explosiveatmospheres are mainly inside it, a gaseous mixture acting asIn explosive with a much larger volume. To obtain animprovised explosive device using an explosive mixture gasCycle 2200gaseous mixture homogeneity represents an essential condi-Time 2.152E+000mstion in order for the aerosol to be found within the limits ofexplosivity. To achieve this, it is necessary to disseminate theFig. 5. The shock wave front evolution - time 2.152 msaerosol in an enclosed space.- (1) Gauge# 1Acknowledgments3000t一(2) Gauge# 2These researches were conducted in the Military Technical- (3) Gauge# 32 500- (4) Gauge# 4Academy of Bucharest.2 000References1500|[1] Cavaropol DV. Elements of gas dynamics. Plants for LPG and LNG.1000Bucharest: Publisher Ministry of Interior and Administrative Reform;2008. ISBN 978-973-745-057-9.500[2] Sanford G, McBride JB. Computer program for calculation of complexchemical equilibrium compositions and applications, I analysis. NASA1.1.32.0 2.53.0 3.5Reference Publication 1311; 1994.[3] Sanford G, McBride JB. 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Detonation produces overpressures inINSEMEX petrosani, explosives properties of household LPG, Petro-shock wave front of about 20 bars compared with thosesani; 2009.中国煤化工MHCNMH G