Similarity solution of fuel mass transfer,port mass flux coupling in hybrid propulsion

Boundary layer combustion is the primary mechanism of hot gas generation in hybrid rockets. The idea of a hybrid rocket is to store the oxidizer as a liquid and the fuel as a solid, producing a design that is less susceptible to chemical explosion than conventional solid and bipropellant liquid designs. The fuel is contained within the rocket combustion chamber in the form of a cylinder, with a circular channel called a port hollowed out along its axis. Upon ignition, a diffusion flame forms over the fuel surface along the length of the port. The combustion is sustained by heat transfer from the flame to the solid fuel causing continuous fuel vaporization until the oxidizer flow is turned off. Theory shows that the fuel mass transfer rate is proportional to the mass flux averaged across the port. The mass flow rate increases with axial distance, leading to coupling between the local fuel regression rate and the local mass flux. For proper design, accurate expressions are needed for both the time-dependent oxidizer-to-fuel ratio at the end of the port and the time at which all the fuel is consumed. As the fuel is depleted, the flame approaches the motor case, at which point the burn must be terminated. The purpose of this paper is to present a similarity solution for the coupled problem and a brief discussion of current practice.     

Thermodynamic Modeling of the Composition and Characteristics of Combustion Products of Overrich Liquid Rocket Fluids in the Quenching Mode

The working process in the regenerative gas generators of liquid rocket engines is analyzed and a method for computer simulation based on the Zel’dovich’s model of “quenching” the composition of the products of high-temperature combustion as a result of rapid cooling on supplying an excess of the low-temperature component and the resulting chemical quasi-nonequilibrium is developed. The method is implemented and tested on the basis of the TERRA software package in calculations of the composition and properties of the propellant produced by regenerative gas generators using oxygen as the oxidizer and methane as the fuel. The vacuum specific impulse of the considered fuel is calculated for the possible conditions of a quasi-nonequilibrium working process.     

Plasma thermochemical preparation for combustion of pulverized coal

A plasma model of thermochemical preparation for the combustion of pulverized coal implemented through the PlasmaKinTherm program for the calculation of plasma-fuel systems has been described. Such systems are used at nonfuel-oil start-up of boilers and the stabilization of the combustion of a pulverized coal torch. The model combines kinetic and thermodynamic methods describing the process of the thermochemical preparation of fuel in the volume of the system. The numerical study of the regime parameters of the plasma-fuel system as a function of plasmatron power providing the ignition of the high-ash coal air-petrol mixture is carried out. Distributions of temperatures and velocities of gas and coal particles and concentrations of products of the thermochemical preparation over the length of the system are obtained. The main regularities of the process of the plasma ignition of fuel are revealed consisting in the displacement of the maxima of temperatures and velocities of products of thermochemical preparation upstream (in the direction of the plasmatron), and the independence of plasmatron power maximal values of temperatures and velocities. The results of calculations are compared with experimental data confirming the validity of assumptions accepted at the development of the model.     

高能复合固体推进剂的研究进展

高能化始终是复合固体推进剂的研究热点.介绍了当今复合固体推进剂高能化研究进程中国内外在氧化剂、金属燃烧剂和含能粘合剂体系方面的主要研究成果.借助先进的技术途径改善氧化剂和金属燃烧剂的燃烧性能是目前国内复合固体推进剂的研究重点.超高能量密度材料(氮原子簇化合物和多异氰基立方烷类化合物)和贮氢类金属燃烧剂三氢化铝以及一些新型的含能粘合剂等新型含能材料的出现,为下一代高能复合固体推进剂的研究指明了方向.     

B/CuO复合燃料的制备及其对Mg/PTFE富燃料推进剂的影响

为了研究纳米氧化铜(CuO)改性硼(B)对镁/聚四氧乙烯(Mg/PTFE)富燃料推进剂的影响,利用球磨法制备了B/CuO复合燃料,将其添加到Mg/PTFE富燃料推进剂中,利用混合模压成型法制备含有不同比例的复合燃料的推进剂药柱。利用扫描电镜、TG-DSC分别测试了B/CuO复合燃料的微观形貌和热反应性能;利用红外测温仪、X射线衍射、TG-DSC分别测试了推进剂的燃烧速度、燃烧温度、反应产物以及热反应性能。结果表明:复合燃料混合较为均匀,局部有团聚;n(B)∶n(CuO)=32∶3的复合燃料的放热量高于B的放热量,燃烧效率最高,为73.1%,点火温度比B低66 ℃。含此复合燃料的推进剂的燃烧速度和质量燃烧速度均高于Mg/PTFE,分别提高了25.6%和3.1%,平均燃烧温度降低了16 ℃,最高燃烧温度则提高了6 ℃,但是相对于含B的Mg/PTFE推进剂,含此复合燃料的推进剂的燃烧速度和质量燃烧速度分别下降2.91%和19.51%,平均燃烧温度下降了94 ℃和121 ℃;复合燃料推进剂一次燃烧的凝聚相产物主要有MgF₂、MgO、C、Cu以及Mg₃F₃（BO₃）;一次燃烧反应过程主要是PTFE的分解以及F₂和Mg的反应,二次燃烧反应过程则主要为C、Mg以及复合燃料的氧化。     

Numerical simulation of power-engineering complex with torrefaction reactor

The paper presents a mathematical model of power-engineering complex implementing a combined technology of production of power, heat, and solid biofuels, namely, torrefied pellets. Torrefaction of fuel pellets is carried out in a thermochemical reactor by heat from exhaust gases of a gas piston power plant. The results of testing the model by experimental data and the results of calculations of the main characteristics of torrefaction, the mass and energy flows are given. The analysis results of efficiency of the power plant with a build-on thermochemical reactor are reported.     

Development of a deterred propellant for a large caliber weapon system

There is a continuing need to increase the velocity and associated terminal performance of kinetic energy ammunition as tougher armor targets are encountered. Application of a deterrent, or burning rate reducer, into the surface of standard propellants, together with appropriate changes in geometry and loading density, has been suggested as a means of increasing velocity by as much as ten percent. The attainment of such a desirable performance gain is critically dependent on the deterrent's satisfying certain requirements: (1) chemical compatability with the base propellant, (2) sufficient penetration of the base propellant, (3) diffusion stability of the deterred region over an extended time, (4) ignitability of the deterred layer, (5) sufficient decrease in burning rate. Unfortunately, there exists only a minuscule data base on the way deterrents behave when applied to various base propellants. The deterred propellants used in small arms and anti-aircraft guns were developed by a cut-and-try technique, and the sort of data required for rational design of large caliber weapons systems, e.g. burning rates in the deterred region, is extremely scarce. Since we lack an appropriate data base we have used thermochemical calculations and burning rate estimates to identify promising deterrent/base propellant combinations. The burning rate estimates were based on empirical fits to available closed bomb and strand burner tests with small arms propellants. Several promising deterrent systems are presented, including five candidates which exhibit a decrease in burning rate with no decrease in propellant energy. On the basis of these theoretical predictions, an experimental deterrent coating and analysis study has been initiated at Radford Army Ammunition Plant.     

Influence of fuels and combustion aids on solution combustion synthesis of bi-phasic calcium phosphates (BCP)

The possibility to obtain biphasic HA/TCP composite by solution combustion synthesis method using urea and glycine as fuels was investigated. Calcium nitrate was taken as a source of calcium, and diammonium hydrogen phosphate served as a source of phosphate ions. Nitric acid and nitrate ions were used as oxidizers. The effect of the nature of fuel (urea and glycine) and fuel to oxidizer ratio on the combustion behavior, as well as, chemical composition and morphology of as-formed powders was investigated. It was found that only monoclinic-TCP was formed in the combustion end-product when glycine was used. In contrast to this, the use of certain amount of urea led to the formation of rhombohedral-TCP. A series of combustion reactions were carried out to study the influence of fuel to oxidizer ratio on HA to TCP ratio in synthesized product.     

缓燃型NLG桥塞火药的性能研究

采用常压燃烧实验、热分析实验以及桥塞工具地面实验等方法,研究了新型NLG缓燃桥塞火药的常压燃烧性能、热分解特性及其在桥塞工具中的燃烧性能。结果表明：缓燃型NLG桥塞火药具有燃速低、燃烧残渣粘附性低的特性;通过调节桥塞火药配方中粘合剂含量、氧化剂粒度和降温剂含量等可改善其燃烧性能;缓燃型NLG桥塞火药在桥塞工具中燃烧稳定,能可靠完成坐封工作,具有很好的应用前景。     

Anatase-brookite mixed phase nano TiO2 catalyzed homolytic decomposition of ammonium nitrate

Compared to the conventional ammonium perchlorate based solid rocket propellants, burning of ammonium nitrate (AN) based propellants produce environmentally innocuous combustion gases. Application of AN as propellant oxidizer is restricted due to low reactivity and low energetics besides its near room temperature polymorphic phase transition. In the present study, anatase-brookite mixed phase TiO₂ nanoparticles (∼10 nm) are synthesized and used as catalyst to enhance the reactivity of the environmental friendly propellant oxidizer ammonium nitrate. The activation energy required for the decomposition reactions, computed by differential and non-linear integral isoconversional methods are used to establish the catalytic activity. Presumably, the removal of NH₃ and H₂O, known inhibitors of ammonium nitrate decomposition reaction, due to the surface reactions on active surface of TiO₂ changes the decomposition pathway and thereby the reactivity.     

Combustion stability of a dispersed fuel in a combustion chamber

A combustion instability criterion and an analogy with the burning of a solid propellant element are established as a result of an analysis of the behavior of the gasdynamic disturbances superimposed on the process of turbulent combustion of an atomized fuel in a one dimensional combustion chamber.     

Kinetic modeling of PM combustion with relative velocity at low-temperature and numerical simulation of continuous regenerating type PM removal device that uses a fluidized bed

The size of particulate matter (PM) generated by combustion has decreased with the improvement of combustion technology. While small PM has a significant negative impact on the human body, it is difficult for a conventional PM removal device to collect small PM. We developed a fluidized bed type PM removal device with a focusing adhesion force. This device collects small PM effectively and can be operated as a continuous regeneration device at low temperature. To further develop this device, it is important to investigate the PM combustion characteristics in this device. The kinetic model constructed in conventional thermogravimetry could not accurately represent the combustion rates of the solid fuel in the fluidized bed. Therefore, a new thermogravimetric apparatus was constructed in this study that generates the direct collision of air with carbon to reproduce the fluidized bed combustion. The influence of the relative velocity between PM and gas on the combustion rate was investigated. The effect of relative velocity was represented as the mass transfer coefficient of kinetic model. It is observed that the combustion rate shows Arrhenius behavior, and kinetic parameters were determined by fitting. The kinetic model was applied to the numerical simulations of the PM removal device. The numerical collection efficiency was in good agreement with the experimental data. PM adhesion and combustion characteristics were investigated in numerical simulations. It is observed that the adhesion rate is high at a low void fraction and that the combustion rate is high at a high relative velocity. The PM combustion amount is high for the high adhesion and combustion rates. The total combustion amount is determined to be 55% of the total amount of PM deposition after 180 min at each set of conditions.     

High strain rate deformation and cracking of AA 2219 aluminium alloy welded propellant tank

Aluminium alloy AA 2219 (Al–6.6Cu–1Mn) is the candidate material for the fabrication of propellant storage tank of launch vehicle. Cold rolled sheets of 6.5 mm thickness are used to make the cylindrical shell, while sheets of 4.5 mm thickness are used for the construction of dome through petal forming technique. Petals, formed through cone rolling, treated to T87 temper condition are welded together by TIG welding to configure the dome. Such domes are joined to the cylindrical shell through a ring by TIG welding.The upper stage consists of two tanks, one oxidizer tank (liq. O₂) and other fuel tank (liq. H₂). After completing various developmental qualification tests, propellant flow rate test of one of the system was carried out. Almost all the liquid oxygen of the tank was removed and only a little quantity remained at the bottom. During one of the subsequent tests; when dry nitrogen gas was purged to evaporate the remaining liquid oxygen, the oxidizer tank dome catastrophically fractured with an audible sound. Fracture of oxidizer tank dome, placed at lower part of the system caused excessive deformation and subsequently it also caused fracture of fuel tank dome placed just over it.Detailed metallurgical investigations were carried out on the failed components and it was found that the tank failed under very high strain rate deformation. This paper brings out the details of the investigation carried out.     

Numerical Simulation of Unsteady Gunpowder Combustion at a Rapid Rise in Pressure on the Basis of a Conjugate Combustion Model

Journal of Engineering Physics and Thermophysics - A physicomathematical model has been presented for solid propellant (gunpowder) combustion, in which account is taken of chemical reactions in the...     

Generalized Volume-Averaged Filtration Combustion Model and Its Application for Calculating Carbon Gasifiers

We have developed a generalized volume-averaged model of filtration combustion of gases taking into account the spatial inhomogeneity of a porous medium and the change in porosity due to the heterogeneous chemical processes. Adequate program codes have been realized. The calculations perfomed have shown that the gasification rate in a continuous reactor is almost proportional to the oxidizer flow rate and depends on the degree and character of inhomogeneity. It has been found that the CO content at the outlet depends on the degree of inhomogeneity. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 4, pp. 8–14, July–August, 2005.     

Stress corrosion cracking of stainless steel bellows of satellite launch vehicle propellant tank assembly

Bellows made of austenitic stainless steel (AISI 304 grade) are being used as a conduit for liquid fuel and oxidizer in the propellant tank of a satellite launch vehicle. A few bellows were found leaky during re-pressure tests after 6 years of storage. A number of cracks were found originating from weld fusion lines. One of the leaking bellows was subjected to detailed metallurgical and chemical analysis. The synergistic effect of chloride ions and thermal stresses from welding was identified as the cause-a typical example of stress corrosion cracking (SCC).     

少烟PBT推进剂制备及性能研究

为获得少烟且高能量的复合固体推进剂，使用含能PBT黏合剂，制备了铝粉质量分数为5%的PBT叠氮三组元推进剂，研究了推进剂的能量、燃烧及力学性能。结果表明，推进剂在固体质量分数78%时能量和工艺性能最优，使用φ118标准发动机测试能量比冲达246.4 s；压强指数随燃速铜铬催化剂RC和增塑剂ATC用量的增加而降低；燃烧速度随RC和超细高氯酸铵AP用量的增加而升高；固化参数或键合剂用量增加后，推进剂抗拉强度升高、伸长率降低。制备的少烟叠氮配方综合性能良好，可供高性能少烟推进剂装药。     

Excitation of acoustic vibrations upon combustion of droplets of liquid fuel at supercritical pressure

Theoretical investigation of the excitation of acoustic vibrations upon combustion of liquid fuel droplets at a supercritical pressure of a gaseous mixture is carried out. The droplets are assumed to be spherical and mono-dispersed. The combustion is assumed to run in the diffusion regime. The binary diffusion coefficients are taken equal and independent of the concentration of the components of the gaseous mixture. The Lewis number is assumed to be unity. The flow is considered to be one-dimensional; the mixing in the transverse direction is assumed to be complete, with no mixing in the longitudinal direction. The rate of combustion at supercritical pressure of the gaseous mixture is calculated on the basis of the modified quasi-stationary theory. Expressions for the frequency and excitation increment of acoustic vibrations are obtained in this paper; the properties of the fuel and the oxidizer are explicitly taken into account.     

Adsorption characteristics of trivalent chromium on palm oil fuel ash

The metal uptake characteristics of ash particles obtained from the combustion of oil palm solid waste (referred to as palm oil fuel ash) are evaluated using trivalent chromium as a model adsorbate. The equilibrium and kinetic properties of Cr(III) are studied in batch stirred-tank experiments. The extent of Cr(III) removal increases with an increase in solution pH. The maximum equilibrium uptake capacity at pH 6 is 0.31 mmol/g of sorbent. A Langmuir isotherm model with pH-dependent parameters accounts very well for the measured equilibrium data. Modeling studies using a second order irreversible reaction model and a pseudo-first order kinetic model indicate that transient profiles obtained experimentally for a range of initial metal concentrations and sorbent dosages are in good agreement with calculated curves of both models. The two kinetic models can be employed for a useful summary of the experimental data so long as their rate coefficients are empirically correlated with the two system variables: initial metal concentration and sorbent dosage. Electronic Publication     

Model of coal combustion in a fluidized bed and its experimental identification

The author has formulated a system of one-dimensional steady-state differential equations for the balance of oxidizer, fuel and energy in the diffusion approximation. The model of coal combustion in a fluidized bed is identified from the experimental data, and the unknown parameters of the model describing the rate of oxidation of fuel and the intensity of gas and fuel transfer in the bed are determined.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 60, No. 6, pp. 913–918, June, 1991.