Linear Burning Rate Research Articles

Burn rate characterization of iso-propyl nitrate – A neglected monopropellant

An experimental investigation was conducted to characterize the combustion of a monopropellant isopropyl nitrate (IPN). Quartz tubes of 3, 5, 7.5, and 9mm inner diameter and 1mm thickness were utilized to create the strands of varying dimensions. The experiments were conducted in a quiescent atmosphere of air and the ambient pressure was varied from atmospheric pressure to 50bar. Ignition of the IPN strands was achieved by using a heated 60μm Nichrome wire dipped in the liquid and was retracted after ignition. The effect of ambient pressure and strand diameter on the linear burning rates of pure IPN was elucidated. The ambient pressure variation was investigated for a diameter of 5mm, while the diameter-variation was studied at 1, 10, 20, and 40bar. The linear burning rate of IPN strands of 5mm diameter was found to exhibit two distinct regimes, where a steep rise in burning rate with pressure was observed after an initial decreasing trend. The values of the burn rates increased with a pressure exponent of 1.54, from approximately 0.2mm/s at atmospheric pressure to 1.6mm/s at 50bar. In the first stage, the burn rates were found to be controlled by diffusion-dominated combustion, characterized by a single bipropellant flame up to a pressure of 10bar, beyond which monopropellant-dominated combustion was found to be dominant in the second stage, with a distinct monopropellant flame and a bipropellant flame. The bipropellant flame was found to exhibit an oscillatory behavior in the second stage of combustion. A semi-empirical model was utilized successfully to predict the experimental burn rates of IPN in both regimes. The burn rates were found to depend on the strand diameters under the conditions applied, with a generalized decreasing trend at high pressures and atmospheric pressures, and an initial decrease followed by an increase at intermediate pressures.

Estudo de sistemas retardantes de Chama sem Bromo para ABS

Este trabalho visa estudar e caracterizar o desempenho de aditivos retardantes de chama não bromados em copolímero de ABS. Foram estudadas combinações de retardantes de chama, como: o polifosfato de amônio (APP), a melamina, nanopartículas de dióxido de titânio e argila organicamente modificada com sal quaternário de fosfônio. Os materiais obtidos foram caracterizados por ensaios mecânicos (resistência ao impacto Izod e resistência à tração), análise termogravimétrica (TG), avaliação da morfologia e ensaio de retardância à chama. Os resultados obtidos indicaram uma redução de cerca de 48% na velocidade de propagação da chama dos compósitos com APP/melamina/TiO2/argila organofílica, em relação ao copolímero de ABS puro.

Properties of wood flour/expanded polystyrene waste composites modified with diammonium phosphate flame retardant

The objective of the study was to evaluate properties of waste plastic composite samples manufactured from expanded polystyrene waste (EPS) and sawdust containing diammonium phosphate (DAP) as flame retardant. Thermal degradation along with dimension stability and mechanical characteristics of the specimens as a function of DAP content were determined. The wood fiber/EPS composite modified with DAP content up to 20 wt% resulted in the best linear burning rate. The rate of thermal degradation of samples also substantially decreased while limiting oxygen index and char residual increased. Overall dimension stability in the form of water absorption and thickness swelling along with flexural characteristics of the samples were found comparable to those of commercial wood plastic composites. The wood fiber/EPS containing DAP showed high potential for use as wood composite products with adequate fire resistance. POLYM. COMPOS., 36:604–612, 2015. © 2014 Society of Plastics Engineers

Effects of nano-scale additives on the linear burning rate of nitromethane

This paper examines the effects of various nanoparticle additives on the combustion behavior of nitromethane, using a pressure-based method recently demonstrated by the authors to measure the linear burning rates of liquid monopropellants and heterogeneous mixtures with high precision. The linear burning rates of these mixtures were measured in a constant-volume system at chamber pressures ranging from 3 to 14 MPa, all without direct observation of the burning front. Nano-scale aluminum was used to increase the overall energy density of the mixture, fumed silica powder was used to increase the mixture thickness and encourage aluminum suspension, and nano-scale titania was also included based on its previous use as a burning rate modifier in solid propellants. The silica loading was varied from 1% to 3% by weight, aluminum was varied from 5% to 13.5% by weight, and titania was added at 1% by weight. The use of fumed silica yielded increased burning rates compared to those of neat nitromethane, and the pressure exponent of the burning rate curve shifted from lower to higher than the nitromethane baseline as more silica was added. This increased pressure sensitivity for mixtures containing 3% silica by weight was previously unobserved in similar studies by other groups and may be an effect of the higher specific surface area of the currently used silica. The subsequent addition of aluminum led to even faster burning rates and higher pressure exponents for all but one mixture. The addition of titania also led to elevated burning rates, with dramatically increased pressure sensitivity and rate inconsistency for chamber pressures above approximately 8 MPa but a decreased pressure sensitivity for the same mixture below 8 MPa. These changes in combustion behavior that accompanied titania were diminished by the presence of aluminum and completely negated in mixtures also containing fumed silica.

Combustion of Frozen Nanoaluminum and Water Mixtures

Steady-state strand burner and laboratory-scale static fire motor experiments were used to determine the relative performance and viability of an environmentally friendly solid propellant composed of only nanoaluminum and frozen water. The nominal size of the nanoaluminum particles was 80 nm. The particles were homogeneously mixed with water to form pastes or colloids and then frozen. The measured parameters include burning rates, slag accumulation, thrust, and pressure. A system scaling study was performed to examine the effect of the size of the small-scale motors. The equivalence ratio was fixed at 0.71 for the strand burner and the laboratory-scale motor experiments. The effect of pressure on the linear burning rate was also examined. For an equivalence ratio of 0.71, the mixture exhibited a linear burning rate of at a pressure of 10.7 MPa and a pressure exponent of 0.79. Three motors of internal diameters in the range of 1.91–7.62 cm were studied. Grain configuration, nozzle throat diameter, and igniter strength were varied. The propellants were successfully ignited and combusted in each laboratory-scale motor, generating thrust levels above 992 N in the 7.62-cm-diam motor with a center-perforated grain configuration (7.62 cm length) and an expansion ratio of 10. For the 7.62 cm motor, combustion efficiency was 69%, whereas the specific impulse efficiency was 64%. Increased combustion efficiency and improved ease of ignition were observed at higher chamber pressures (greater than ).

A comparative study on two explosive acetone peroxides

Two explosive cyclic acetone peroxides, diacetone diperoxide (DADP) and triacetone triperoxide (TATP) have been studied in respect of thermal decomposition, burning behavior, impact sensitivity, and initiating efficiency. Using the glass Bourdon gauge technique, the vapor pressures of TATP and DADP were determined over the temperature range 75–144°C and 67–120°C, respectively. The kinetic parameters of decomposition of the peroxides in the gas phase have been obtained in the temperature interval of 140–200°C. The decomposition of both DADP and TATP followed the first-order reaction to high degrees of decay with close activation energies of 159.2kJ/mol (38.0kcal/mol) and 165.8kJ/mol (39.6kcal/mol), respectively. The decomposition rate constants of DADP were found to be approximately 2 times less than those of TATP. The linear burning rate of DADP measured in a constant-pressure window bomb appeared to be approximately 5 times less than that of TATP. Temperature profiles in the combustion wave were measured at subatmospheric pressures with the help of thin tungsten-rhenium thermocouples. The leading reaction on combustion of both volatile peroxides was assumed to occur in the gas phase. Kinetic parameters of the leading reaction derived from the combustion data showed a good agreement with kinetic parameters of low-temperature thermal decomposition extrapolated to the high-temperature flame zone. In the drop-weight impact test, DADP appeared to be notably less sensitive peroxide than TATP. No deflagration-to-detonation transition was observed when RDX was attempted to explode by using 0.5g of DADP in the standard detonator No. 8 shell. Comparing explosive properties of the studied peroxides, DADP may be considered as a less dangerous, however still unsafe explosive in handling as TATP.

Application of Azido Esters as Energetic Plasticizers for LOVA Propellant Formulations

AbstractThe study of a cyclotrimethylene trinitramine‐based low vulnerable ammunition (LOVA) propellant having cellulose acetate (CA) and nitrocellulose (NC) combinations as binders is described herein. Two propellant compositions (1 and 2) were prepared by replacing the non energetic plasticizer triacetin (TA) with the novel tetraazido ester plasticizers tetraazido malonate and tetraazido glutarate, respectively, and their ballistic, mechanical, and thermal properties were studied. Both compositions 1 and 2 showed thermal stability up to 200 °C with a heat release of 1752.81 and 1774.34 J g−1, respectively. Both compositions have high impact insensitivity (h50: 39 cm), friction insensitivity up to 36 kg, and an ignition temperature greater than 250 °C. The flame temperatures of 1 and 2 are 3164 and 3243 K with linear burn rate coefficients of 0.117 and 0.122 cm s−1 MPa−1, respectively. Similar percentage elongations at three different temperatures (−20 °C, +27 °C, and +55 °C) conditions were recorded for both compositions.

Combustion of micro aluminum–water mixtures

An experimental investigation on the combustion behavior of micro-sized aluminum (μAl)–water mixtures was conducted. It was easily ignited and self-deflagrated on μAl and liquid water when using a paper shell tube. Linear burning rates of quasi-homogeneous mixtures of μAl and liquid water as a function of pressure, mixture composition, density and environment gas medium were measured. Steady-state burning rates were obtained at room temperature using a windowed vessel for a pressure range of 1–80bar in a nitrogen atmosphere, particle size of 0.5×30×30μm and overall mixture equivalence ratios from 0.67 to 2.0. The pressure exponent was obtained as 0.47 at room temperature and compared to the case of nano-sized aluminum (nAl) and liquid water. When a wire was inserted into the sample, for increasing local heat transfer, burning rates were found to be faster.

Palm leave and plastic waste wood composite for out-door structures

The objective of this paper is to produce an environmentally friendly artificial wood for structural application, by recycling mixed plastic waste and date palm leaves waste. Several pretreated wood plastic composites mixtures, using a 1:1 ratio of palm leaves and plastic waste, were designed and developed—namely, polycarbonate (PC-mix), polystyrene (PS-mix), and polyvinyl chloride (PVC-mix). The batch mixture of each type was extruded at different temperature profiles.The density, water absorption, hardness, modulus of elasticity (tensile and flexure), impact strength, and linear burning rate of the WPC samples produced were determined, and the results were compared with the natural hard, soft wood, and medium density fiberboard (MDF) woods. The developed wood plastic composites exhibited less water absorption, linear burning and hardness, higher density than that of natural and MDF wood, and can be used in outdoor structures.

Measurement and Analysis of the Burning Rate of HAN-Based Liquid Propellants

A new device for measuring the linear burning rate of liquid propellants at high pressures is reported. High-pressure environments were generated by the combustion of solid propellants. The coated propellants, which burn progressively, were introduced to maintain the approximate constant-pressure environments. By use of ion probe transducers, measurements were made of the spread velocity of the flame surface, i.e. the apparent linear burning rate of the HAN-based liquid propellant LP1846 (HAN =hydroxylammonium nitrate) was measured quantitatively at pressures from 6 to 28 MPa. The results show that it follows the exponential burning rate law. The burning rate coefficient and exponent were fitted by least-squares methods. Based on the experiment, a simplified model of the linear burning rate of HAN-based liquid propellants at high pressures was developed. The numerical simulation is found to be in good agreement with the experimental data.

BALLISTIC PROPERTIES PREDICTION FOR VARIANT BUTALITES COMPOSITIONS, AN EASY ABSTENTION TECHNIQUE

AbstractBallistic properties for variant Butalites formulations based on Ammonium perchlorate (AP) and hydroxy terminated polybutadiene with some other additives were practically investigated then theoretically predicted. The predictions were investigated for formulations with burning rates ranging from 0.26 to 17.94 mm/sec at 70 bar. The predictions were performed using the developments applied to the basic model of multiple flames, the BDP model. The developments were established over the model equations using an easy abstention technique, without multiple flame standoff distances. The results were verified by considering AP regression as the rate-controlling step in combustion, by introducing the additives to the model equations in a passive technique, by the use of a one-dimensionally limited temperature profile to estimate the propellant surface temperature, and by solving the combustion equations iteratively for the mass flux and surface temperature until they reached the required convergence. A computer program was established for obtaining the linear burning rate, surface temperature and other ballistic properties of the previous formulations. The results showed that the predicted linear burning rates were acceptable and verified the international acceptance margins in this field.

COMBUSTION OF BIMODAL ALUMINUM PARTICLES AND ICE MIXTURES

The combustion of aluminum with ice is studied using various mixtures of nanoand micrometersized aluminum particles as a means to generate high-temperature hydrogen at fast rates for propulsion and power applications. Bimodal distributions are of interest in order to vary mixture packing densities and nascent alumina concentrations in the initial reactant mixture. In addition, the burning rate can be tailored by introducing various particle sizes. The effects of the bimodal distributions and equivalence ratio on ignition, combustion rates, and combustion efficiency are investigated in strand experiments at constant pressure and in small lab-scale [1.91 cm (0.75 in.) diameter] static firedrocket-motor combustion chambers with center-perforated propellant grains. The aluminum particles consisted of nanometer-sized particles with a nominal diameter of 80 nm and micron-sized particles with nominal diameters of 2 and 5 μm. The micron particle addition ranged from 0% to 80% by active mass in the mixture. Burning rates from 1.1 (160 psia) to 14.2 MPa (2060 psia) were determined. From the small scale motor experiments, thrust, C∗, Isp, and C∗ and Isp efficiencies are provided. From these results, mechanistic issues of the combustion process are discussed. In particular, overall lean equivalence ratios that produce flame temperatures near the melting point of alumina resulted in considerably lower experimental C∗ and Isp efficiencies than equivalence ratios closer to stoichiometric. The substitution of micron aluminum for nanometer aluminum had little effect on the linear burning rates of Al/ice mixtures for low-mass substitutions. However, as the mass addition of micron aluminum increased (e.g., beyond 40% 2-μm aluminum in place of 80-nm aluminum), the burning rates decreased. The effects of bimodal aluminum compositions on motor performance were minor, although the experimental results suggest longer combustion times are necessary for complete combustion.

Burning Characteristics of Aminoguanidinium 5,5′-Azobis-1H-Tetrazolate/Ammonium Nitrate Mixture—Effects of Particle Size and Composition Ratio on Burning Rate

Ammonium nitrate has been attracting attention over the years as an oxidizer for clean gas-generating agents. Aminoguanidinium 5,5′-azobis-1H-tetrazolate was mixed with ammonium nitrate to improve its burning performance and the burning behavior of the formulations was studied by measuring the linear burning rate. The effects of particle size and composition ratio on the burning rate were studied. It was found that the mixture containing 50% ammonium nitrate by weight was the most promising composition. The particle sizes of fuel and oxidizer do not influence the burning rate.

Effects of diammonium phosphate on the flammability and mechanical properties of bio-composites

The flammability, thermal stability and mechanical properties of natural fiber-reinforced thermoplastic bio-composites were measured using a horizontal burning test, thermogravimetric analyzer, and universal testing machine, respectively. The composites were fabricated from film resins (Polylactic-acid, PLA and Polypropylene, PP) and natural fibers (coconut filter and jute fiber) by a hot press machine. To improve the flame retardancy of the bio-composites, various diammonium phosphates (DAP) were treated into the fibers. In general, the results indicate that increasing the percentage of DAP used to treat the fibers effectively improves the flame resistant, weight loss rate, and flexural modulus but decreases the flexural and tensile strengths of the bio-composites. Bio-composites with DAP-treated fibers showed a greater flexural modulus than those with untreated fibers, and the flexural modulus was even greater than that of neat polymers (PLA and PP). Also, increasing the percentage of DAP for treatment of the fibers in the composites decreases the temperature required for 5% weight loss and the decomposition rate, but increases the char residual at 500°C. The best linear burning rate and weight loss rate were observed for fiber treatment with 5% DAP. The compressive and wear properties of these bio-composites were also studied.

Burning Characteristics and Sensitivity Characteristics of Some Guanidinium 1,5′‐bis‐1H‐Tetrazolate/Metal Oxide Mixtures as Candidate Gas Generating Agent

AbstractBurning characteristics and sensitivity characteristics of some stoichiometric ratio guanidinium 1,5′‐bis‐1H‐tetrazolate (G15B)/metal oxide mixtures were examined. The linear burning rates of the G15B/CuO mixture were higher compared to other G15B/metal oxide mixtures and 5‐amino‐1H‐tetrazole(5‐ATZ)/Sr(NO3)2 mixture, although the average rate of pressure rise during the closed vessel test was lower compared to 5‐ATZ/Sr(NO3)2 mixture. The temperature rise for both G15B/CuO and G15B/MnO2 mixtures was considerably lower than that of 5‐ATZ/Sr(NO3)2 mixture. G15B/Fe2O3 mixture was the most insensitive among G15B/metal oxide mixtures during the drop hammer test, while G15B/CuO mixture was the second most insensitive. All G15B/metal oxide mixtures were insensitive against friction and electric spark discharge (ESD). Four seconds ignition temperature for G15B/CuO mixture was over 100 K lower than that of 5‐ATZ/Sr(NO3)2 mixture, but the apparent activation energy for ignition was higher. Among the G15B/metal oxide mixtures studied, G15B/CuO mixture showed the fastest burning rate, while it showed a relatively low temperature rise and low sensitivity. G15B/ZnO did not burn at all.

Combustion of alane and aluminum with water for hydrogen and thermal energy generation

The combustion of alane and aluminum with water in its frozen state has been studied experimentally and theoretically. Both nano and micron-sized particles are considered over a broad range of pressure. The linear burning rate and chemical efficiency are obtained using a constant-pressure strand burner and constant-volume cell, respectively. The effect of replacing nano-Al particles by micron-sized Al and alane particles are examined systematically with the additive mass fraction up to 25%. The equivalence ratio is fixed at 0.943. The pressure dependence of the burning rate follows the power law, r b = aP n , with n ranging from 0.41 to 0.51 for all the materials considered. The burning rate decreases with increasing alane concentration, whereas it remains approximately constant with cases containing only Al particles. The chemical efficiency ranged from 32% to 83%, depending on the mixture composition and pressure. Thermo-chemical analyses are conducted to provide insight into underlying causes of the decreased burning rate of the alanized compositions. A theoretical model is also developed to explore the detailed flame structure and burning properties. Reasonably good agreement is achieved with experimental observations.

Exploring the Effects of Nanostructured Particles on Liquid Nitromethane Combustion

Monopropellants consisting of liquid nitromethane and high-surface-area particles of silicon- and aluminum-based oxides were examined to determine the effects of low concentrations of nanostructured materials on deflagration processes. The combustion rates were characterized by measuring linear burning rates in a large pressure vessel filled with argon. Results showed that nitromethane burning rates may be increased at lower pressures with dilute additions of particles. Increases in nitromethane burning rates of greater than 50 % were found with less than 1.0 wt% of particle addition at a nominal pressure of 5.24 MPa. The particle additions were estimated to have only small effects on the equilibrium flame temperatures, density, viscosity, and specific heat. Nitromethane with particle additives displayed a lower burning-rate equation pressure exponent (i.e., reduced pressure sensitivity), which was inversely proportional to particle concentration. Above a pressure of approximately 9 MPa, up to the maximum test pressure (∼14 MPa), the particle additives did not affect the nitromethane burning rate. Condensed-phase temperature profiles of the deflagrating fluid, surface tension, and fluid thermal conductivities were measured in order to elucidate some of the mechanisms causing enhanced burning rates at lower pressures.

Novel burning rate measurement technique for solid propellant by means of ultrasonics

A novel burning rate measurement technique for solid propellants using ultrasonics has been developed. Ultrasound is applied to the burning surface of the end-burning propellant grain from the bulk side, and the reflected wave, which is frequency-shifted by the Doppler effect, is analyzed with a wavelet technique. This method enables us to get the instantaneous linear burning rate and, thus, can be a strong tool for the instability study of solid propellants. The wavelet method is also favorable for the identification of the reflected signal from the burning surface even if the signal intensity becomes very low and indistinguishable from white noise with normal measuring techniques. Efforts have also been paid to eliminate the coupling material between the ultrasonic probe and the propellant grain to simulate the real situation of rocket motors. An oscillation deadener circuit has been successfully employed to reduce strong multi-deflection signals within a metallic plate between the probe and the propellant grain. With these two improvements, it becomes possible to detect and process the signals in longer propellant grains in the actual solid rocket motor situations.

Functionalized Graphene Sheet Colloids for Enhanced Fuel/Propellant Combustion

We have compared the combustion of the monopropellant nitromethane with that of nitromethane containing colloidal particles of functionalized graphene sheets or metal hydroxides. The linear steady-state burning rates of the monopropellant and colloidal suspensions were determined at room temperature, under a range of pressures (3.35-14.4 MPa) using argon as a pressurizing fluid. The ignition temperatures were lowered and burning rates increased for the colloidal suspensions compared to those of the liquid monopropellant alone, with the graphene sheet suspension having significantly greater burning rates (i.e., greater than 175%). The relative change in burning rate from neat nitromethane increased with increasing concentrations of fuel additives and decreased with increasing pressure until at high pressures no enhancement was found.

Erratum to: Combustion Characteristics of a Hydroxylammonium Nitrate Based Liquid Propellant. Combustion Mechanism and Application to Thrusters

A new composition of hydroxylammonium nitrate based solution containing ammonium nitrate, methanol, and water was developed for monopropellant in a reaction control system (RCS) as an alternative to conventional hydrazine. In comparison with hydrazine, this solution has a 20% higher specific impulse, 1.4 times higher density, and lower freezing point and toxicity. The linear burning rate of the solution is moderate at the operating pressures of RCS thrusters. It was found that the linear burning rate had some characteristics whose mechanisms had not been understood. The combustion mechanism of this solution was investigated. The burning behavior was observed using a medium speed camera, and a temperature profile for the combustion wave was measured with a 2.5 µm diameter thermocouple. From these results, the instability of the liquid-gas interface may trigger a sudden increase in the burning rate, and methanol was found to be effective in reducing the bubble growth rate in the solution. The reactivity of several catalysts was evaluated in an open-cup test, and the S405 catalyst for hydrazine showed the best performance among them. Thruster tests were conducted using the S405 catalyst with variation in the propellant mass flow rate, catalyst bed configuration, and length-to-diameter ratio of the combustor. As a result, parameters were determined that ensured long operating time. The model thruster operated stably for up to 100 sec with a specific impulse I sp = 240 sec, which corresponds to a 90% efficiency.