Ignition Of Solid Propellants Research Articles

Controlling the combustion and agglomeration characteristics of solid propellants via new micro-unit composite fuel Al@AP

New micro-unit composite fuels Al@AP with different mass ratios of Al and AP are designed, prepared, and added to solid propellants in place of the original aluminum powder. Through Thermogravimetric Analysis- Differential scanning calorimetry- Mass Spectrometry (TG-DSC-MS), laser ignition experiment, thermocouple temperature measurement, burning rate test, and combustion diagnostic, we study how Al@AP affects the ignition, combustion, and agglomeration properties of solid propellants. The results indicate that the increase of Al content of Al@AP can promote the advance of thermal decomposition of AP. As the AP content increases in Al@AP, the ignition delay time of Al@AP decreases by three times, and the mass burning rate increases by almost five times. At the same time, Al@AP significantly improves the burning rate and temperature gradient. When compare to the baseline propellant, Al@AP-containing propellants present a maximum increase in burning rate of 33% at low pressures and 19% at high pressures. In terms of agglomeration reduction, the number of large-size agglomerates in the CCPs of propellants containing Al@AP is reduced, the average particle size decreases by 78%, and the combustion efficiency increases to 99.34%. A mechanism is proposed to explain how the micro-unit composite fuel Al@AP alters propellant combustion and agglomeration. In summary, Al@AP provides excellent control over ignition, combustion, and agglomeration characteristics. This study provides guidance on the application and development of new aluminum-based composite fuels used in solid propellants.

Double-modified C–MgCo2O4 as a highly active catalytic material for the thermal decomposition of AP and its application for CSPs

The design and development of microscopic surface structures and surface defects of nanomaterials provide infinite possibilities for optimizing their catalytic activity. In this study, the microscopic surface structure of MgCo2O4 was modified while introducing combustible porous defective carbon (PDC) in MgCo2O4 by taking advantage of the incomplete decarbonization during solution combustion after the addition of biotemplates. The double-modified Cx-MgCo2O4 (x denotes the abbreviations of Reed, Cherry, Bougainvillea-spectabilis, Crab-apple-flower and Cotton: Re, Ch, Bs, Cf and Co) exhibited high activity in catalyzing the thermal decomposition of AP. Among them, CCo–MgCo2O4 with the highest carbon defect level (ID/IG = 4.54) significantly optimized the thermal decomposition performance of AP. The addition of CCo–MgCo2O4 ensured both the reduction of the AP thermal decomposition THTD (From 473.48 °C to 258.17 °C) and the increase of the AP heat of decomposition (ΔH, From 888.26 J/g to 3669.38 J/g). The introduction of combustible defective carbon in Cx-MgCo2O4 not only provides favorable conditions for the electron transfer process, but also generates synergistic heat during the thermal decomposition of AP and optimizes its energy release behavior. Compared with MgCo2O4, CCo–MgCo2O4 further accelerates the ignition (From 17 ms to 14 ms) of the composite solid propellants (CSPs) and ensures the energy release during combustion.

Enhancement in ignition and combustion of solid propellants by interfacial modification of Al/AP composites with transition metals

To improve the ignition and combustion behaviors of Al, the strategy of interfacial modification using transition metals (TMs) for the Al/AP composites to produce the multi-layered core-shell structured Al@TMs@AP composite fuels is provided. The relevant Al-based composite fuels are fabricated using spray granulation method and their morphologies are characterized by SEM and TEM techniques. The ignition and combustion of the solid propellants prepared with the core-shell structured composite fuels are evaluated and compared with that of reference propellant formulated with typical compositions using laser ignition setup and combustion diagnostic system. Results indicate that the heats of reaction measured for the Al@TMs@AP contained propellants are increased by as high as 13%, suggesting the completeness in combustion of Al is greatly improved by construction of Al composites with the multi-layered core-shell structure. The ignition delay times are apparently shortened from 421 ms to 373 ms for the propellants with Al@TMs@AP involved, which proves that the promoted ignition of Al is achieved by surface modification with transition metals. Additionally, the significantly increased burning velocity is monitored for the Al@TMs@AP contained propellants at low-pressure regime leading to the corresponding pressure exponents to be reduced by more than 20%, which is beneficial to the stability in operation of solid rocket motors. At last, the higher combustion wave temperature and finer particle size in CCPs are observed for the propellants containing surface modified Al, and the plausible combustion mechanism is proposed based on the phase composition analysis for the CCPs of studied propellants.

Laser ignition of solid propellants using energetic nAl-PVDF optical sensitizers

Laser ignition of propellants could provide better control of the ignition process and improve safety. However, sustained laser ignition of solid propellants is often challenging in practice due to a lack of optical absorptivity at convenient wavelengths. Common optical additives, i.e., opacifiers, improve the absorption characteristics but are typically inert and fail to contribute to the reactivity of the propellant. In this work, ammonium perchlorate (AP)/hydroxyl-terminated polybutadiene (HTPB) composite propellants are optically sensitized by adding reactive nano-aluminum (nAl)/polyvinylidene fluoride (PVDF) particles (ranging from 600 to 1000 µm). These propellants are compared with neat (no additive) AP/HTPB, and other AP/HTPB propellants with carbon black or nano-aluminum (nAl) additives. The nAl/PVDF additives enable sustained ignition with relatively low laser energy levels (< 5 J/cm2) at common wavelengths (1064 nm). Only the propellant with added nAl/PVDF exhibited sustained ignition. The ignition delays of the nAl/PVDF propellant ranged from 2 to 5 ms, depending on the energy density of the laser. We propose that the sustained ignition in nAl/PVDF propellants is due to the lower critical energy needed for nAl/PVDF composites (estimated 0.5 J/cm2 compared to 15 J/cm2 needed for AP/HTPB based propellant). The propellant's calculated critical energy is similar to the reported values of nAl/PVDF composites. The nAl/PVDF based propellant has a faster burning rate and increased pressure dependence due to the PVDF's gas generation and rapid burning of aluminum particles near the surface. Potential applications for this propellant, such as flash ignition and subsurface ignition, are also explored.

Research on the vacuum aging performance of HTPB propellant based on the DSC method

The space environment has extreme conditions such as high vacuum and rapid temperature changes, which will lead to problems such as energy drop, irregular burning rate, and abnormal ignition of solid propellants. To obtain the space aging law of HTPB propellant, the aging performance of HTPB (hydroxyl-terminated polybutadiene) propellant in a vacuum environment was studied and compared with that under the atmosphere. According to the DSC test results of the propellant before and after aging, the behaviors of oxidative crosslinking, chain-scission degradation, and oxidant decomposition during the aging process of solid propellant were investigated. The research showed that the low-temperature endothermic peak and “V-type” high-temperature exothermic peak temperature of HTPB propellant increased after aging, and the high-temperature peak bifurcated into “W-type” double peaks. The right peak caused by the “decarboxylation” reaction was more obvious after atmospheric aging while the left peak caused by AP decomposition was remarkable after vacuum aging. In addition, the oxidative crosslinking reaction occurred after aging, and the activation energy characterized by low-temperature peaks continued to increase. In the later stage of atmospheric aging, chain-scission degradation occurred due to OA moisture absorption, and the activation energy decreased. It firstly increased by 126% within 93 days, and then decreased by 23.4%. No degradation and chain-scission reaction occurred in a vacuum environment, the crosslinking reaction rate was high, and the activation energy increased by 40.4% within 49 days. After the aging of the HTPB propellant, the internal AP decomposed, and the activation energy characterized by the high-temperature exothermic right peak continued to increase. The activation energy increased by 40.5% within 49 days after vacuum aging, and increased by 29.9% within 93 days after atmospheric aging, indicating that the decomposition of AP in the HTPB propellant was more obvious under a vacuum environment.

Photoflash and laser ignition of Al/PVDF films and additively manufactured igniters for solid propellant

Solid propellants are employed in a range of applications from the inflation of airbags to propulsion systems for rockets. The ignition of solid propellants must be carefully controlled and modified on a per-use basis due the specific ignition requirements of each application. Using tailored photoreactive materials as a source of ignition for solid propellants, or other energetic materials, could reduce the added weight and risk of traditional initiators and result in safer, more effective solid rocket motor ignition systems. This study demonstrates the tunability of the ignition delay and propagation properties of optically-sensitive, nearly full density reactive aluminum/polyvinylidene fluoride (Al/PVDF) films and additively manufactured igniters. A single printed layer of pure nano-aluminum (nAl) at ideal stoichiometry in PVDF was found to flash ignite, but frequently yielded delayed transitions in steady propagation from the igniter to the propellant. To improve the continuity and steadiness of the transition, fuel particle size, igniter thickness, and a combination of layers of nAl and micron-sized aluminum (μAl) were investigated. In printed igniters with layers of μAl, only a single layer of nAl was needed to flash ignite the material and propagate to the layers of μAl without delay. For igniters cast onto strands of ammonium perchlorate composite propellant, continuous ignition was achieved with a single layer of nAl printed atop a triple layer of μAl for the flash-activated igniters and a single layer of nAl printed atop a single and triple layer of μAl for laser-driven igniters. The nAl/PVDF layer enabled good flash or laser ignition sensitivity, while the μAl/PVDF produced more sustained heat transfer to produce a reliable ignition process.

Controllable ignition, combustion and extinguishment characteristics of HAN-based solid propellant stimulated by electric energy

Hydroxyl ammonium nitrate (HAN)-based electrically controlled solid propellant (ECSP) is the advanced solid chemical propellant stimulated by electric energy, which has throttleable ability. This characteristic is impossible for traditional solid propellants, and greatly expands the potential applications for solid rocket motors that are fit with the ECSP. In this work, the ignition, combustion and extinguishment characteristics of propellant were studied at different voltages, initial temperatures and pressures. It is concluded that the incremental voltage, initial temperature and pressure enhance the burning rate, mass loss and extinguishment delay time, while reducing the ignition delay time, energy required for ignition and electrolysis mass ratio. Specially, as the initial temperature increases from -15 °C to 45 °C (at 200 V and 0.1 MPa), values of mean ignition delay time decrease from 247.4 ms to 116.2 ms, and values of mean burning rate and extinguishment delay time increase from 0.25 mm/s to 0.47 mm/s and 19.2 ms to 27.6 ms, respectively. Moreover, as the pressure increases from 0.1 MPa to 1.0 MPa (at 200 V and 25 °C), values of mean ignition delay time decrease from 151.6 ms to 74.2 ms, and values of mean burning rate and extinguishment delay time increase from 0.44 mm/s to 0.89 mm/s and 28.0 ms to 55.6 ms, respectively. Based on the experimental results, the processes of propellant from ignition to extinguishment were analyzed, and the ignition mechanism was proposed that the fracture of NOH in NH3OH+ in the electrochemical decomposition is a key step that affects the ignition of ECSP. Overall, those results reveal that the electrolysis reaction rather than the pyrolysis reaction exerts an important role for ECSP on achieving the controllable combustion.

Hot-Spot Ignition of Solid Propellants by a Hot Surface

Hot-Spot Ignition of Solid Propellants by a Hot Surface

Modeling of Ignition and Combustion of Boron-Containing Solid Propellants

Modeling of Ignition and Combustion of Boron-Containing Solid Propellants

Fluid–structure coupled simulation of ignition transient in a dual pulse motor using overset grid method

In this paper, the second pulse ignition transient in a dual pulse solid rocket motor with elastomeric barrier pulse separation device has been conducted numerically. An in-house code has been developed to solve governing equations for unsteady compressible flow, heat conduction and structural dynamic. The solid propellant ignition and burning numerical models have been added. The fluid structure interaction is implemented by using the conventional serial staggered algorithm. The large deformation and expansion of the elastomeric barrier are addressed by the dynamic overset grid technology. The accuracy of the numerical method is validated by the experimental cases. Then, the detailed flow field development, pressure evolution, flame propagation characteristics in the combustion chamber, and the structural response of elastomeric barrier are analyzed carefully. The rupture-time and rupture-pressure of the elastomeric barrier are also obtained. The numerical results show that the elastomeric barrier deformation presents a small displacement at the front part and a large displacement at the rear section. The interaction of the compression waves and expansion waves from the convergent portion of the nozzle and from the motor head-end, as well as the supersonic annular jet flow in the combustion chamber, can induce obvious pressure rises with fluctuations and spikes. The first pulse free volume has a significant effect on the time to reach a steady state.

Mechanism of microwave-initiated ignition of sensitized energetic nanocomposites

One of the challenges in propellant formulation is the inability to moderate the burn rate dynamically. Here, we consider spatially localized remote ignition of additively manufactured composites via microwave absorption. Previous studies demonstrated that a passivating shell on Ti nanoparticles (nTi) enhances microwave absorption. Incorporated within a polyvinylidene fluoride (PVDF) matrix, Ti/PVDF films ignite under microwave irradiation in air. To gain more comprehensive insight into pre-ignition behavior, the ignition delay was studied as a function of applied power and the microwave susceptor loading. Infrared (IR) camera studies were further used to investigate the heating behavior of the films under variable power. We found that ignition delay decreases with increasing power to an apparent heating saturation region, where the ignition sensitivity is limited by the combustion reaction kinetics. Thermogravimetric analysis coupled with differential scanning calorimetry (TGA-DSC) showed that nTi oxidizes with O2 at lower temperatures than fluorination with PVDF and drives combustion. Findings in this work build a pathway for remote and controlled ignition of solid propellants via microwave radiation.

Simulation of Ignition and Combustion of Boron-Containing Solid Propellants

Simulation of Ignition and Combustion of Boron-Containing Solid Propellants

Agglomeration and combustion characteristics of solid composite propellants containing aluminum-based alloys

Agglomeration in solid composite propellants is known to exacerbate two-phase flow losses. In this experimental study, we investigate the substitution of aluminum particles with metallic alloys in order to reduce agglomeration in aluminized propellants. We consider five different aluminum-based alloys: Al-Mg, Al-Ni, Al-Si, Al-B, and Al-Zn. Through thermogravimetric-differential scanning calorimetry measurements, we find that all five alloys can increase the initial oxidation temperature relative to a baseline Al propellant, but that only Al-Si and Al-Zn exhibit lower melting temperatures. Laser ignition experiments show that Al-Mg produces the most balanced combination of a short ignition delay time and a short self-sustaining combustion time. High-pressure experiments at 0.5 to 3 MPa show that Al-Si has a markedly higher burning rate than the baseline Al propellant, while Al-Mg and Al-Ni have the lowest pressure exponents. High-speed microscopic surface imaging at 0.5 and 1 MPa shows that Al-Ni produces the largest reduction in agglomeration, with an average agglomerate size some 30% smaller than the baseline value. By contrast, Al-Zn produces the worst agglomeration, with an average agglomerate size around 15% larger than the baseline value. From these findings, we propose a qualitative phenomenological mechanism for agglomeration in metallic-alloy propellants based on a competition among four distinct effects: the metal melting temperature, the adhesive force of the agglomerates, the propellant burning rate, and micro-explosions. We then analyze the agglomeration of the different alloys using the proposed mechanism. As well as providing new experimental data on the agglomeration, ignition and combustion characteristics of solid composite propellants containing aluminum-based alloys, this study reinforces the notion that the agglomeration and combustion performance of aluminized propellants can be optimized through a judicious choice of alloying elements.

Ignition and Combustion of Composite Solid Propellants Based on a Double Oxidizer and Boron-Based Additives

The use of boron-based powder materials in solid propellant compositions is an effective method for increasing the energy characteristics in the combustion chamber due to increasing the released energy through the combustion of boron particles. In this study, powders of amorphous boron and aluminum borides, obtained by the method of self-propagating high-temperature synthesis—the SHS method, which were added to the composite solid propellant composition based on a double oxidizer and an energy fuel binder, are studied. The paper presents the characteristics of thermal decomposition, ignition, and combustion for solid propellant samples. The tested samples are ignited using a continuous CO2 laser in the air in the heat flux density range of 90 to 200 W/cm2. The combustion of propellant samples is carried out in a manometric bomb in a nitrogen atmosphere at pressures ranging from 0.5 to 7.0 MPa. It is shown that the use of amorphous boron and aluminum boride powders in the solid propellant composition reduce the ignition delay time and increase the burning rate of the samples compared to the aluminum-based propellant composition, due to the increase in temperature near the surface of the reaction layer of the sample and the specific heat release during the oxidation and burning of boron.

Study on Electrical Explosion Mechanism and Ignition Characteristics of Copper and Aluminum Powder Under Ignition Solid Propellant

In order to study the characteristic of the electrical explosion of copper and aluminum powders, a multilayer generator was designed, an experimental system was set up, and the parameters of metal powder electrical explosion were measured and analyzed. The results show that the duration of the electrical explosion process increases significantly due to the addition of metal powder. The duration of aluminum powder electrical explosion jet flow is ~86.36 ms due to its self-sustained combustion, which releases a large amount of energy, and a small fraction of aluminum powder particles is not burned. The duration of copper powder electrical explosion jet flow is ~15.84 ms, and most of the copper powder particles are in the solid state. The current pause process is absent; instead, the first discharge process is connected to the second discharge process. The effect of copper powder on the first discharge process is greater than that of aluminum powder. Furthermore, the ignition ability of copper powder electrical explosion to solid propellant is stronger than that of aluminum powder in a closed bomb experiment. These results are indubitably meaningful for the application of metal powder electrical explosion and ignition of solid propellant in an electrothermal chemical gun.

Firing range optimization of a 155mm uni-modular charge howitzer by ETC technology

Electrothermal-chemical (ETC) launch technology can accurately control and enhance the ignition and combustion of solid propellants to improve the consistency and accuracy of ballistics. In this paper, a calculation model including the transient burning rate formula and six-degree-of-freedom rigid body trajectory equation is established to simulate both interior and exterior ballistics processes for a 155mm uni-modular charge howitzer. The simulation results show that the muzzle velocities are optimized via the ETC technology. The 155mm uni-modular charge ETC howitzer can effectively obtain the minimum range, increase the range overlap and maximum range, and improve the ballistic stability and consistency.

Hierarchical Bulk Nanoporous Aluminum for on-Board Hydrogen and Heat Generation By Hydrolysis in Pure Water

Despite the remarkable key features of hydrogen energy technology such as the high gravimetric energy density of hydrogen, the zero-emissions electricity generated using fuel cells, and the high natural abundance of hydrogen resources (particularly in the form of water), there are still many scientific and engineering challenges that must be addressed before a true sustainable hydrogen economy can be realized. Two of these challenges include sustainable hydrogen generation without CO2 emissions and effective storage of this hydrogen for specific applications. In this presentation, I will present a sustainable method to produce hydrogen on-board, which could be used to overcome the two challenges mentioned above. Our approach involves: (i) Fabrication by selective alloy corrosion of hierarchical bulk nanoporous aluminum characterized by the coexistence of both macroscopic and mesoscopic ligament/pore structures, with the mesoscopic ligaments in the range of 10-20 nm. (ii) Recovery of the sacrificial material simultaneously during selective alloy corrosion, which contributes to sustainability of the process. (iii) Use of this hierarchical bulk nanoporous aluminum to produce hydrogen and heat on-board by hydrolysis with “pure” water, with a yield of ~52-85 % during hydrogen production without incorporation of any catalyst or reaction promoter in the aluminum-water system. Besides hydrogen and heat generations, I will demonstrate the combustion of this bulk nanoporous aluminum in air and under ambient conditions, which implies that this material could be attractive as a combustion fuel catalyst, e.g. to enhance the ignition and combustion of solid propellants. Thanks to a new carbon-free sustainable pathway to extract aluminum by Elysis (https://elysis.com/en), a joint venture composed of high-profile aluminum suppliers including Rio Tinto and Alcoa, and aluminum consumers including Apple, aluminum can be obtained by electrolysis of Al2O3 without CO2 emissions. The inclusion of this carbon-free aluminum in our process will make it possible to produce hydrogen from nanoporous aluminum and pure water without greenhouse gas emissions at any stage of the process.

Research on the Dynamic Model of Plasma Ignition Process of Solid Propellant

In decades, the plasma ignition technology has drawn much attention due to its advantages. However, the numerical research on the plasma ignition of solid propellants is still limited. In this paper, a 1-D transient plasma ignition model of solid propellant is developed. A simplified chemical reaction mechanism of XM39 is employed in the model to explore the solid phase and gas phase chemical reactions and species transportations in the gas phase. The expansion process of the plasma jet is also investigated. The predicted surface pressure and ignition delay are compared to the experimental results. Good agreement with these data provides the necessary validation of the presented model. In the model, the calculated temperature profiles and the mass fraction distribution of the gas hexogen are used to characterize the reaction zone. In addition, the mass fraction distributions of CH2O and HCN are used to estimate the possibilities of different reaction paths.

Dynamic simulation of ignition, combustion, and extinguishment processes of HMX/GAP solid propellant in rocket motor using moving boundary approach

Solid propellant burning rate, gas phase temperature, and condensed phase thickness depend on combustion chamber pressure, laser intensity, and propellant compositions. The ignition and combustion of solid propellants occur in three phases namely solid phase, condensed phase, and gas phase. In this study, moving boundary modeling was applied to each of the phases by coordinate transformation. This research includes modeling and dynamic simulation of the ignition and combustion of HMX/GAP, a high-energy material in the ratio of 8:2, with the gas phase of the combustion model consisting of 50 species and 234 reactions. The mathematical modeling used mass, energy, and momentum conservation equations, as well as constitutive equations for the moving boundary. Parametric studies were run under different operating conditions, with an initial temperature of 300 K, a pressure of 10–100 atm and a laser intensity of 100 W/cm2. A burning rate of 2.2 cm/s and a gas phase temperature of 2700 K were obtained under an operating pressure of 100 atm. Extinguishment of the solid propellant was rigorously analyzed in terms of dynamic simulation with various depressurization rates during combustion. This was carried out by depressurizing the solid propellant from 70 atm to 40 atm. Important factors of the extinguishment were discussed based on the mathematical model and various depressurization rates with parametric studies. At a depressurization rate of −8000 atm/s, the solid propellant was fully extinguished. From this study, one can identify the phenomenon for the extinguishment of HMX/GAP propellant using fast depressurization with rigorous mathematical model used for ignition and combustion.

Three-dimensional multi-physics coupled simulation of ignition transient in a dual pulse solid rocket motor

In this paper, numerical investigation of ignition transient in a dual pulse solid rocket motor has been conducted. An in-house code has been developed in order to solve multi-physics governing equations, including unsteady compressible flow, heat conduction and structural dynamic. The simplified numerical models for solid propellant ignition and combustion have been added. The conventional serial staggered algorithm is adopted to simulate the fluid structure interaction problems in a loosely-coupled manner. The accuracy of the coupling procedure is validated by the behavior of a cantilever panel subjected to a shock wave. Then, the detailed flow field development, flame propagation characteristics, pressure evolution in the combustion chamber, and the structural response of metal diaphragm are analyzed carefully. The burst-time and burst-pressure of the metal diaphragm are also obtained. The individual effects of the igniter's mass flow rate, metal diaphragm thickness and diameter on the ignition transient have been systemically compared. The numerical results show that the evolution of the flow field in the combustion chamber, the temperature distribution on the propellant surface and the pressure loading on the metal diaphragm surface present a strong three-dimensional behavior during the initial ignition stage. The rupture of metal diaphragm is not only related to the magnitude of pressure loading on the diaphragm surface, but also to the history of pressure loading. The metal diaphragm thickness and diameter have a significant effect on the burst-time and burst-pressure of metal diaphragm.