Ignition and combustion characteristic of aluminum and magnalium particles in AP/AN composite propellant

Transcription

1 45th AIAA/ASME/SAE/ASEE Joint Propulsion Conferene & Exhibit 2-5 August 2009, Denver, Colorado AIAA Ignition and ombustion harateristi of aluminum and magnalium partiles in AP/AN omposite propellant Takuya MANO 1, Mitsuaki TANABE 2, Takuo KUWAHARA Department of Aerospae Engineering, College of Siene and Tehnology, Nihon University , Narashino-dai, Funabashi, Chiba , Japan and Masafumi TANAKA National Defense Aademy of Japan , Hashirimizu, Yokosuka, Kanagawa, , Japan Abstrat Combustion effiieny of harateristi veloity is important fator that shows reation situation in ombustion hamber. And if a propellant burned ompletely in ombustion hamber, C* ombustion effiieny is 100%. However, metal partiles are mixed in the propellant and metal partiles are hard to ompletely burn. Therefore, there is a possibility that C* ombustion effiieny dereases. It is neessary to evaluate the ignition and ombustion harateristi of the metal partile. There is temperature distribution in the reation zone of propellant. It is diffiult to evaluate the ignition harateristi of the metal partile in reation zone. We measured temperature gradient in the reation zone by thermo ouple of Pt-Pt10%Rh (the diameter is 12.5µm ). In the result, temperature flutuations appeared by ignition of the metal. We obtained the ignition harateristi of the aluminum(al) partile and magnalium(mg-al) partile from the flutuations. And we obtained ombustion time of aluminum partile in air. We alulated C* ombustion effiieny when harateristi length (L*) is hanged. Metal partiles ignite on the burning surfae. And it is onsidered that metals ignite in diffusion flame of AP partiles on the burning surfae. And ombustion effiieny of harateristi veloity, η, of AL7µm ompletely burned when L* is 5m. And η of AL20µm ompletely burned when L* is 0m. Therefore, the smaller diameter of aluminum partile is, the shorter time for omplete burning beomes. C* E L* M P Q R T d m n q r x γ ρ = harateristi veloity = melting heat of aluminum = harateristi length = molar weight = pressure = amount of heat = universal gas onstant = temperature = onstant pressure speifi heat = average diameter of aluminum partile = mass = number = ombustion heat of per unit mass = burning rate = distane = speifi heat ratio = density Nomenlature 1 2 Phone: FAX: Graduate Student Assistant Professor Professor (+ 81) (+ 81) triosu@kvf.biglobe.ne.jp 1 Copyright 2009 by the, In. l rights reserved.

2 η τ h omb gas i ig t liquid melt 0 p pro solid th up = C* ombustion effiieny = time Subsript = aluminum partile = ombustion hamber = ombustion of aluminum partile = hemial ignition delay = ombustion gas of total (gas and aluminum) = ombustion gas (without ombustion aluminum) = ignition point = ignition delay = theoretial value = liquid of aluminum = meriting point = initial = physial ignition delay = solid propellant = solid of aluminum = value of thermo ouple = for inreased temperature Ⅰ. Introdution ombustion effiieny of harateristi veloity, η, is important fator that shows reation situation in C ombustion hamber. And if a propellant burned ompletely in ombustion hamber, C* ombustion effiieny is 100% (it is adiabati state). uminum partiles are mixed in the propellant, beause we improve thrust performane of solid roket. However, aluminum partiles are hard to ompletely burn. Therefore, there is a possibility that C* ombustion effiieny dereases. It is neessary to evaluate the ignition and ombustion harateristi of aluminum partiles. There is temperature distribution in the reation zone of propellant. Length of the reation zone of AP omposite propellant is under 0.2mm in atmosphere pressure [1]. The diameter of luminous flame of aluminum partile is about 0.2mm. Therefore, it is diffiult to evaluate the ignition harateristi of aluminum partiles in reation zone. We derease burning rate and inrease length of reation zone. We measured temperature gradient in the reation zone by thermoouple of Pt-Pt10%Rh (the diameter is 12.5µm ) and obtain the ignition harateristis of aluminum partiles and magnalium partiles. We obtained aluminum ombustion time in air and alulate C* ombustion effiieny of propellant. And we obtained ombustion harateristi. Ⅱ. Theoretial alulation of C* ombustion effiieny C* is obtained from the following equation (1) and η is obtain from the following equation (2) [1]. η = C * (1) C * t ( γ+ 1) 2( γ 1) * R TC 2 C = (2) γ M γ+ 1 Charateristi veloity, C*, is hanged by temperature of ombustion hamber, T, molar weight, M, and speifi heat ratio, γ. Therefore, η shows the ombustion state in the ombustion hamber [2]. We assumed that M and γ are onst. Charateristi veloity, C*, is hanged only by temperature of ombustion hamber, T. Reation rate of gas is very fast. When we obtained T, we onsidered only ombustion status of aluminum partiles in ombustion hamber. 2

3 If imperfet ombustion of aluminum partiles is disharged from the ombustion hamber, T dereases. Imperfet ombustion of aluminum partiles draws heat from ombustion gas when aluminum partiles melt and inreased temperature. Then, T is obtained from the equations (), (4) that are heat energy balane. Q = Q + Q + Q () m( T m omb T 0 ) melt = m up ombomb( Tomb T0) ( T T ) + ( T T ) { E+ } solid melt 0 liquid melt (4) T is funtion of T omb, m omb, m. T omb, m omb ome under the influene of mass of aluminum partiles of inomplete ombustion, m. Mass of aluminum partiles of inomplete ombustion, m, is obtained from the equations (5) - (9). Fig.1 Behavior of the aluminum partile in ombustion hamber. d r 2 ( τ τ ') ig d Before ignition 2 r ( τ τ ') ig Disharge from the ombustion hamber Fig.2 Combustion model of the aluminum partile. Figure1 shows the behavior of the aluminum partile in the ombustion hamber. And Fig 2 shows the model of ombustion of the aluminum partile. Mass of aluminum partiles of inomplete ombustion, m is obtained from the equation (5). 4 d m = πρ n r( τ τ ig ') (5) 2 We assume that burning rate of aluminum partile, r, is onst. Burning rate of aluminum partile, r, is obtained from the equation (6).

4 r d = (6) 2τ And in this study, we used omposition propellant that is AP/AN/Otadeyl alohol/partiles=80/10/10/10. n is obtained from the equation (7) d n= m π ρ (7) And it is onsider that veloity of aluminum partiles equal veloity of ombustion gas. τ is obtained from equation (8) []. ( γ+ 1) ( 2( γ 1) ) L * γ + 1 τ = (8) γrt 2 We substituted expressions (6), (7), (8) into the equations (5). m is obtained from the equation (9) m = m d d 2 m is funtion of τ, τ ig. Therefore, m omes under the influene of ignition and ombustion harateristi. We need to obtain T omb, m omb, for alulating T. m omb is obtained from the equations (10). m = m omb + m (10) d 2τ L * γrt γ + γ 1 ( γ+ 1) ( 2( γ 1) ) τ ig ' (9) Temperature of ombustion gas, T omb, is obtained from the equations (11), (12) Q = Q + Q (11) m omb omb omb gas ( T T ) omb 0 = Q gas + q m 10m (12) = Qgas + q m 110 Temperature of ombustion gas, T omb, is fration of m, so T omb is funtion of τ, τ ig. obtain ignition and ombustion harateristis. It is important that we Ⅲ. Experiment Table 1 shows the omposition of propellants. The oxidizers of the omposite propellants were AP and AN, and the binder was otadeyl alohol. Reation zone of AP omposition propellants was too short to obtain the ignition delay time of metals. Using AN and otadeyl alohol dereased burning rate and inreased the reation zone. The ratio of the omposition that we used AP(diameter is 40µm)/AN(diameter is 200µm)/otadeyl alohol =80/10/10 [wt%], beause, maximal measurable length of the temperature gradient beame 0.7 mm. Therefore, we an obtain ignition delay time of metals from the temperature gradient. The partiles of AL, Mg-AL were used and also oxidized aluminum ( 2 O ) was used. AL partile has generated a large amount of heat, but the AL partile is diffiult to ignite. The Mg-AL partile redues hydrogen hloride gas yield and ignition delay time of the Mg-AL partile is shorter than that of the AL partile. The AL 2 O partile doesn t ignite in the gas phase. Therefore, propellants with AL 2 O partiles are used to ompare the temperature gradient of propellants that is mixed metal partiles. The average partile diameter of metals and AL 2 O are 20µm, when we measured temperature gradient near the burning surfae. When we measured ombustion time of aluminum partile and alulated η, we used aluminum partile that the average partile diameter is 7µm and 20µm. Beause, ombustion time of the aluminum partile is hanged by the partile diameter. Therefore, it is neessary that partile diameter is hanged over double. We used AP/AN/otadeyl alohol/partiles =80/10/10/10. The oxygen onentration near the burning surfae of the propellant is 26wt%. It is about the same oxygen onentration of air. Therefore, ignition delay time of metal partiles in propellant an ompare that in air. And when we alulate η, we an use ombustion time of the aluminum partile in air. 4

5 Prop AP AN Table 1 Composition of propellants 1-otadeyl alohol Compositions [parts] AL Mg/AL AL 2 O Burning rate [mm/s] ( 0.1MPa ) AL AL 2 O AL Mg-AL Ignition delay time Figure shows an experiment of eletroni furnae. We obtained the ignition delay time of metal partiles by the eletroni furnae. The eletroni furnae had an opening at the top. The metal partiles were dropped into the eletroni furnae through the opening. The partiles ignited with a luminous flame. The ignition delay time, τ ig, was defined as the time from the dropping metals to appearing of the luminous flame of the metal partiles. This experiment was repeated 10 times per one ondition. Less than 10 mg of the partiles were dropped eah experiment. The physial ignition delay time, τ p, is the minimum ignition delay time [4] and the hemial ignition delay time, τ h, is time until reah the ignition temperature to appear the luminous flame. The hemial ignition delay time, τ h, is obtained by following equation (1). τ = τ + τ (1) ig h p Fig. Experiment of eletroni furnae. Temperature gradient We obtained temperature gradient near the burning surfae with the thermo ouple. Thermo ouple was inserted in the enter of the propellant. The thermo ouple was a platinum platinum10%rhodium line, and the diameter was 12.5µm. The omposite propellants were ignited by the heated nihrome wire and temperature history was measured. 5

6 Combustion time We used experiment of Fig. to measure τ. Adiabati flame temperature of AL0 is about 2650K, and burning surfae temperature of AL0 is about 600K. Therefore, we measured τ in air at 1600K that is value intermediate between adiabati flame temperature to burning surfae temperature. AL partile diameter is 20µm and 7µm. Less than 10 mg of the partiles were dropped eah experiment. We measured time from ignition of the AL partile to disappearing the luminous flame of the AL partile. This experiment was repeated 10 times per one ondition. And τ is average of that dates. Ⅳ.Result and Disussion 2000 L Temperature, K L2 x,mm x, mm Ignition point of metal Fig.4 Temperature gradient near the burning surfae Figure 4 shows the experimental results for measuring temperature gradient near the burning surfae. X-axe shows the distane from the burning surfae to ignition of metal and y-axe shows the temperature. The blak line is an experimental result without metals and the gray line is an experimental result of ontaining metals. Temperature flutuations (L1, L2) are shown to Fig.4. L1 equals the diameter of the AP partile. L2 is over the diameter of the AP partile. Therefore, L1 appears when the thermo ouple enters in the diffusion flame of the AP partile. L2 appears when the thermo ouple enters in the diffusion flame of the metal partile. AP partiles make diffusion flames on the burning surfae [1][5]. Temperature of the diffusion flames of the AP partile is higher than surrounding temperature, and the diffusion flame temperature is over 2000K. L1 appears when the thermo ouple enters in the diffusion flame of the AP partile. The diffusion flame had been held until omplete ombustion of an AP partile. Therefore, L1 equals the diameter of the AP partile. The metal partiles ignite in the gas phase. The diffusion flame temperature of metal partile is higher than 2000K. L2 appears when the thermo ouple enters in the diffusion flame of the metal partile. Therefore, L2 is over diameter of AP partile. 6

7 Ignition delay time x x1 x2 T1 T2 T Ignition point of metal Fig.5 Temperature gradient near the burning surfae for measuring ignition delay time Figure 5 shows definitions of x i, T i. Ignition delay times of metals in gas phase were obtained from start of large temperature flutuations that length was over 40µm. Metal partiles ignited on the burning surfae, so we obtained ignition delay time by the following equation (14) and ignition temperature by the following equation (15) xi 1 τ th = (14) r n T pro i 1 T n th = i i (15) τ th (AL) τ h (AL) τ ig (AL) τ th (Mg-AL) τ h (Mg-AL) τ ig (Mg-AL) Fig.6 Ignition delay time of AL partiles Fig.7 Ignition delay time of Mg-AL partiles 7

8 Figures 6, 7 show experimental results for hemial ignition delay time, τ h, physial ignition delay time, τ p, and ignition delay time for measuring temperature gradient near the burning surfae, τ th. The ignition delay time of the Mg-AL partiles was shorter than AL partiles in air and gas phase. AL partiles didn t ignite less than 1570K in air and Mg-AL partiles didn t ignite less than 80K in air. Therefore, metal partiles in gas phase ignite at lower temperature than the ignition limit temperature in air. It is onsidered that metals enter the diffusion flames of AP partile and ignite. Temperature of diffusion flame of AP partile was higher than surrounding temperature, and the temperature was over 2000K. Aordingly, the diffusion flame of AP partiles had a suffiient temperature to ignite the metal. Combustion time and C* ombustion effiieny Table and Fig.8 show the alulation ondition for alulating T and η of AL10. We substituted expression (4) into the equations (9), (10), Fig. 8 and Table to obtain T. After that, we substituted expression (1) into the equations (2), T to obtain η. When aluminum partile diameter is 7µm, ombustion time, τ, is 8ms. And aluminum partile diameter is 20µm, ombustion time, τ, is 50ms. uminum partiles ignite on the burning surfae, so we assumed that τ ig is 0ms. And Constant pressure speifi heat of total,, was obtained from equation (16) γr = (16) γ 1 Constant pressure speifi heat of ombustion gas, omb was the about same. We assumed that omb equaled. Table 2 shows alulation ondition for NASA-CEA, when we obtain, T omb from NASA-CEA [6]. Figure 8 shows result of alulating T omb. T omb is hanged by m. Therefore, T omb is hanged by L*. Table 2 Calulation ondition for NASA-CEA T 0 [K] P [MPa] 1 P 0 [MPa] 0.1 Fig. 8 Calulation ondition (T omb ) for T and η. 8

9 Table Calulation ondition for T and η T 0 [K] T melt [K] 9 ρ [kg/m ] 2700 R [J/(K mol)] 8.14 d [µm] 7, 20 M * [mol/g] 26 [J/(K kg]] 6715 liquid [J/(K kg]] 1170 solid [J/(K kg)] 880 E [J/kg] γ * 1.05 τ ig [ms] 0 τ [ms] 8 (d=7µm) 50 (d=20µm) C* th * [m/s] 1565 * obtained with NASA-CEA Fig.9 C* ombustion effiieny and T when L* hange Figure 9 shows alulation result of T and η. Combustion effiieny of harateristi veloity, η, inreases with L* inreases. Combustion effiieny of harateristi veloity, η, of AL7µm was higher than η of AL20µm at the same L*. Combustion effiieny of harateristi veloity, η, of AL7µm ompletely burned when L* was 5m. And η of AL20µm ompletely burned when L* was 0m. Therefore, the smaller diameter of aluminum partiles is, the shorter L* for omplete burning is. 9

10 Ⅴ. Conlusion 1. AL partiles and Mg-AL partiles ignite diffusion flame of AP partiles on the burning surfae. 2. Combustion effiieny of harateristi veloity, η, of AL7µm ompletely burned when L* is 5m. And η of AL20µm ompletely burned when L* is 0m. Therefore, the smaller diameter of metal partile is, the shorter time for omplete burning beomes. Referene 1. Kubota, N., et al, Japan Explosives Soiety, Propellant handbook, pp , pp , Kubota, N., Roket ombustion engineering, Nikkankogyo Shinbunsya, pp.29-1.(1995).. Kubota, N., Introdution to roket engineering, Defense Tehnology Foundation, pp.87-89, Seihiro, K., Combustion, Iwanami Syoten, pp.68-72, Summerfield, M., et al., Burning Mehanism of Ammonium Perhlorate Propellant, Solid Propellant Roket Researh, Aademi Press, New York, pp , Gordon, S, and MBride, B., Computer Program for alulation of Complex Chemial Equilibrium Compositions and Appliations, NASA RP-111 (1994). 10