Ignition Of Propellants Research Articles

Denitration and nano-ZnO loading strategies to achieve high combustion progressivity, easy ignition and low ablation of the nitrocellulose-based propellant

Denitration and nano-ZnO loading strategies to achieve high combustion progressivity, easy ignition and low ablation of the nitrocellulose-based propellant

Insights into the Fragmentation of Aluminum Hydride and Its Effect on Combustion and Agglomeration of HTPB Propellant.

AlH3 has gained considerable attention as a fuel additive due to its ability to offer high specific impulse and superior combustion performance. However, few studies have focused on the fragmentation and agglomeration behavior of AlH3. This study investigated the effects of fragmentation of AlH3 and AlH3/PVDF particles on the thermal decomposition, ignition, agglomeration, and combustion of HTPB propellants. Thermal analysis indicated that AlH3 and AlH3/PVDF can accelerate the decomposition of ammonium perchlorate by abundant active sites for the adsorption of the decomposition intermediates. Single-particle combustion uncovered the mechanism behind the directional spray of molten Al from the AlH3 particle and the fragmentation of the AlH3/PVDF particle. The melting of porous Al induces particle shrinkage due to solid-liquid interfacial tension and the structural restoration of the oxide shell, which consequently results in the sealing of cracks in the oxide shell of AlH3. Additionally, the accumulation of internal tensile stress leads to the reopening of these cracks and the directional ejection of the molten Al. The flexible oxide shell contributes to a smaller minimum normalized diameter of the AlH3/PVDF particle, aiding in the generation of internal tensile stress, while the sublimation of AlF3 induced the fragmentation. Synchrotron-based X-ray imaging revealed the formation of aggregates promoted by molten Al, the splitting of AlH3 aggregates due to hydrogen explosion, and the enhanced fragmentation of AlH3/PVDF due to the synergistic effect of hydrogen explosion and the sublimation of AlF3. Compared to raw particles, the CCPs (condensed combustion products) of SP2 propellant display a 48% reduction in average size (D50 = 24.5 μm), whereas there is an over 89% decrease in particle size for the CCPs of SP3 propellant (D50 = 5.14 μm). This study contributes to understanding the fragmentation of AlH3 and AlH3/PVDF upon ignition and combustion, providing valuable insights for the development and optimization of propellants containing AlH3.

Ignition and flow combustion characteristics of hydroxylammonium nitrate - based liquid propellant based on electric method

Hydroxylamine nitrate (HAN)-based liquid propellants are characterized by high energy content and low toxicity ionic monopropellants, offering great potential application prospects in the space engine. This paper proposes an experimental system for electric ignition and combustion of HAN-based liquid propellant. The energy for decomposition, current, and combustion image of HAN-based liquid propellant are measured under different initial voltage, propellant volume, and the initial pressures in Ar and air atmospheres. The results show that the energy for decomposition decreased with an increase in initial voltage, propellant volume, and initial pressure. An increase in the initial voltage accelerates the reaction speed of HAN-based liquid propellant, and the energy for decomposition is approximately 3 J. An increase in the propellant volume decreases the equivalent resistance in the circuit, increasing the current and enhancing the thermal effect of the propellant. The accumulation of decomposition products and heat under high pressure reduced the energy for decomposition; the energy for decomposition is less than 1.5 J for the pressurization condition. Compared with the Ar atmosphere, the energy for decomposition of HAN-based liquid propellant shows better stability in the air atmosphere. The flow combustion device of HAN-based liquid propellant for the flow state is designed. The HAN-based liquid propellant is successfully ignited for different initial voltages and flow rates. The research results provide a reference for the design of space engine for HAN-based liquid propellant based on the electric ignition method.

Experimental Study on the Influence of Microwave Energy Pulse Width and Duty Cycle on Evaporation and Ignition Characteristics of ADN-Based Liquid Propellant Droplets

This study investigates the evaporation and ignition characteristics of a single droplet of ammonium dinitramide (ADN)-based liquid propellant utilizing a waveguide resonant cavity device, in conjunction with a high-speed photographic imaging system and testing system. Experimental methods are employed to analyze the impact of microwave pulse width and duty cycle on the puffing and meicro-explosion phenomena of the droplet, as well as the delay time and duration of ignition. The experimental findings reveal that increasing the duty cycle enhances the ignition success rate and diminishes flame development time. Specifically, elevating the microwave duty cycle from 60% to 80% reduces the ignition delay time of the droplet from 132.8 ms to 88.1 ms, and the ignition duration from 23.1 ms to 19.9 ms. Furthermore, an increase in microwave energy pulse width expedites the combustion process of the flame and influences plasma generation. Increasing the pulse width of microwave energy from 20 µs to 40 µs prolongs the ignition delay time from 140.3 ms to 200.5 ms and extends the ignition duration from 56.7 ms to 77.8 ms. Additionally, it is observed that a higher duty cycle leads to a more pronounced puffing phenomenon that initiates earlier. In contrast, a higher pulse width results in a more pronounced puffing phenomenon that commences later. This study provides a thorough investigation into the microwave ignition mechanism of ADN-based liquid propellants, offering theoretical insights into the ignition and combustion stability of such propellants in microwave-assisted ignition systems.

Electrical ignition of ADN-based green liquid propellant in constant volume combustion chamber and continuous flow

Ammonium dinitramide (ADN) propellant for green space propulsion is perceived as a focal point in space propulsion research. The development of electrical ignition methods to realize the ignition for ADN-based liquid propellant can overcome the technical bottleneck of the catalytic ignition methods currently applied to ADN-based space thrusters. This work presents an experimental investigation of the electrical ignition and combustion characteristics of an ADN-based liquid propellant in a constant volume combustion chamber, considering ignition voltages and initial pressures. It is observed that increasing the ignition voltage and initial pressure reduces the flame retardation period, combustion duration, droplet lifetime, ignition energy, and total energy. Also, the combustion peak pressure decreases with an increase in the ignition voltage but increases with higher initial pressures. The energy consumption is mainly concentrated in the ignition stage, with the ignition energy accounting for approximately 76% to 96% of the total energy. The measurement of the concentrations of the keycombustion products are reported, highlighting that the mole fraction of CO decreases with an increase in ignition voltage and pressure. The ignition and combustion of the ADN-based liquid propellant in continuous flow were achieved for the first time through a combination of resistive ignition and high-temperature arc-assisted combustion. During the testing of the propellant ignition in continuous flow, there is a need for a continuous supply of electrical energy, and the combustion cannot be self-sustaining.

Numerical study on ignition start-up process of an underwater solid rocket motor across a wide depth range

Solid rocket motors have important applications in the propulsion of trans-media vehicles and underwater launched rockets. In this paper, the ignition start-up process of an underwater solid rocket motor across a wide depth range has been numerically studied. A novel multi-domain integrated model has been developed by combining the solid propellant ignition and combustion model with the volume of fluid multiphase model. This integrated model enables the coupled simulation of the propellant combustion and gas flow inside the motor, along with the gas jet evolution in the external water environment. The detailed flow field developments in the combustion chamber, nozzle, and wake field are carefully analyzed. The variation rules of the internal ballistics and thrust performance are also obtained. The effects of environmental medium and operating depth on the ignition start-up process are systematically discussed. The results show that the influence of the operating environment on the internal ballistic characteristics is primarily reflected in the initial period after the nozzle closure opens. The development of the gas jet in water lags significantly compared with that in air. As the water depth increases, the ignition delay time of the motor is shortened, and the morphology evolution of the gas jet is significantly compressed and accelerated. Furthermore, the necking and bulging of the jet boundary near the nozzle outlet and the consequent shock oscillations are intensified, resulting in stronger fluctuations in the wake pressure field and motor thrust.

Novel graphene iron organic nanocomposites for enhancing combustion and safety properties of AP-HTPB propellant

Graphene iron tannate and graphene iron gallate nanocomposites (G-D-Fe and G-M-Fe) were designed, synthesized and characterized to deal with the performance requirement of AP-HTPB propellent. Effects of the G-D-Fe and G-M-Fe on the thermal decomposition of AP, laser ignition, combustion and safety characteristics of AP-HTPB propellant were explored. By taking Catocene as the benchmark (156.80 mJ), the G-D-Fe improves the safety performance of propellant, and the ignition energy (E50) is increased by 17.25 mJ. Besides, the G-D-Fe and G-M-Fe have positive effects on enhancing the burning rate and the reducing the pressure exponent of propellant, and the influence of G-D-Fe is more significant. The burning rate enhances from 13.87 to 16.92 mm·s−1 at 15 MPa and the pressure exponent reduces from 0.47 to 0.32 in 4∼15 MPa after the introduction of G-D-Fe. The catalytic mechanism of G-D-Fe were analyzed on the basis of flame morphology, combustion wave structure, in-situ FTIR and gas-phase FTIR-MS. The outstanding catalytic property of G-D-Fe is due to its promotion effect on AP pyrolysis and the formation of stable products, which is conductive to the intense reactions of gas products and the thermal transmission between burning surface and gas phase, and reflecting in the significant enhanced burning rate.

Ignition and combustion characteristics of micro/nano-Al and Al@Ni alloy powders at elevated pressures

Nanosizing and alloying of aluminum (Al) promisingly improve ignition and combustion performance of Al-based propellants. To aim this, lased-induced ignition and combustion characteristics of micro/nano-Al and aluminum@nickel (Al@Ni) alloy powders at elevated pressures (0.1–3.0 MPa) were investigated and the pressure effect on these characteristics was correspondingly evaluated. Comparative results demonstrate that nanosizing and alloying significantly shorten ignition delay and total burn time at elevated pressures, with ignition delay reduction of 98.04% and 52.28% at 1.0 MPa for nano-Al and Al@Ni alloy compared to micro-Al counterpart. Nanosizing and alloying can decrease crucial pressure values (‘mid-pressure extinction domains’) influencing ignition delay, and promote the transfer from the surface to gaseous combustion mode. Maximum combustion temperatures of nano-Al are higher than micro-Al and Al@Ni alloy. During combustion, the combustion of Al@Ni alloy is further intensified due to the microexplosion, while possibly inhibited at higher pressures.

Effects of ignition voltage and electrode structure on electric ignition and combustion characteristics of Ammonium Dinitramide (ADN)-based liquid propellants in electric ignition mode in inert gas environment

Hydrazine is toxic and carcinogenic, which greatly increases the difficulty of application and no longer meets the needs of green aerospace. As a green propellant, the Ammonium Dinitramide (ADN)-based liquid propellant has the advantages of higher specific impulse, being non-toxic, pollution-free, and easy storage. However, an ADN-based space engine in orbit has exposed the problems of high-temperature deactivation of catalysts and cold-start failure. An active ignition technology—electric ignition technology was explored in this paper to break through the technical bottleneck of catalyst deactivation and the inability to a cold start. An experimental system of a constant-volume combustor for the ADN-based liquid propellant based on the electric ignition method was established. The electric ignition and combustion characteristics of the ADN-based liquid propellant in a volume combustor with an electric ignition method were studied. The influencing mechanisms of the ignition voltage and the electrode structure on the electric ignition characteristics of the ADN-based liquid propellant were investigated. An elevation of the ignition voltage could facilitate the ignition process of the ADN-based liquid propellant, curtail electric energy input and heating effect, while exerting an adverse impact on the combustion process of the propellant. An increase in the ignition voltage enhanced the ignition process of the propellant while simultaneously suppressing its combustion process when utilizing mesh electrodes. Compared to the strip electrodes, the mesh electrodes increased the contact area between the electrodes and the propellant, increased the electric energy input power in the electric ignition process, and reduced the ignition delay time. The mesh electrodes could promote the combustion process of the propellant to a certain extent.

Reduction of agglomeration effect by aluminum trihydride in solid propellant combustion

AbstractAluminum trihydride (AlH3) has gained considerable attention as a substitute fuel for aluminum in solid propellants. In this study, we conducted a systematic investigation to evaluate the effects of AlH3 content, ranging from 0 % to 18 %, on propellant ignition, combustion, and agglomeration. Experimental methods such as thermogravimetry−differential scanning calorimetry (TG‐DSC), laser ignition, high‐speed photography, and collecting condensed combustion products (CCPs) were employed. The results indicate that AlH3 significantly promotes the high‐temperature decomposition of ammonium perchlorate (AP). Meanwhile, the addition of cyclotetramethylene tetranitramine (HMX) in propellant does not affect the hydrogen release reaction of AlH3. As the AlH3 content increases from 0 % to 18 %, the spectral emission intensity of the propellants decreases, and the ignition delay time initially increases from 253 ms to 321 ms, and then decreases to 258 ms. Furthermore, the burning rate increases with increasing the AlH3 content, while the pressure exponent is reduced from 0.551 to 0.460. The inclusion of AlH3 in propellants significantly inhibits aluminum agglomeration near the burning surface. Additionally, as the AlH3 content increases, the mean particle size D43 of the CCPs decreases from 50.95 μm to 8.28 μm at 1 MPa. The agglomeration degree of aluminum is very weak at 7 MPa, especially when the AlH3 content exceeds 9 %. The conclusions drawn from this study can serve as valuable guidance for optimizing propellant formulations.

The effects of Al (111) and Al2O3/Al (111) surfaces on the decomposition of ammonium perchlorate: A DFT-D study

Ammonium perchlorate (AP) is a crucial oxidizing agent in composite solid propellants, where aluminum (Al) is used as an additive to increase the energy density of composite solid propellants. The interaction between AP and Al significantly improves the ignition and combustion performance of propellants, but the mechanism of their interactions still lacks essential understanding, especially the interaction between AP and Al, as well as the Al surface containing aluminum oxide (Al2O3). To solve this problem, the adsorption and decomposition processes of AP and its decomposition products such as perchloric acid (HClO4) and ammonia (NH3) on the pure-Al (111) and Al2O3/Al (111) surfaces were studied by using the density functional theory (DFT). The effects of temperature and pressure on the adsorption and reactions were discussed. AP tends to adsorb on the pure-Al (111) surface with O-termination, while under the influence of Al2O3, AP is more inclined to adsorb on the surface of Al2O3/Al (111). At the low-temperature stage, the Al2O3 molecules on the surface of Al (111) promote the disengagement H of AP decomposition and the adsorption and decomposition of NH3, while at the high-temperature stage, the pure Al surface is more conducive to the AP disengagement H and NH3 decomposition. The increase in the pressure is in favor of NH3 adsorption, but the effect gradually decreases. HClO4 cannot adsorb on the pure-Al (111) and AP (001) surfaces, but it can adsorb on the surface of Al2O3/Al (111). In the gas phase, the decomposition of HClO4 priors to NH3. At the high temperature and pressure, the pure-Al (111) surface can contribute significantly to the adsorption and activation of NH3. The findings are very valuable for regulating the combustion of solid propellants.

Study on dynamic deformation-damage-ignition mechanism of GAP/RDX/TEGDN propellant

ABSTRACT Investigations on high-energy and low-vulnerability propellants can provide a better understanding for improving the operational effectiveness and survivability of strategic and tactical missiles. In the present study, the dynamic compressive mechanical properties and damage-ignition response mechanism of the GAP/RDX/TEGDN (GRT) propellant under high strain rates have been studied using a split Hopkinson pressure bar apparatus and a high-performance high-speed camera. The experimental results suggested that the mechanical properties of the GRT propellant, in terms of yield stress, initial compressive modulus, and ultimate stress, were greatly affected by the loaded strain rate. The true stress-strain curves exhibited an initial linear elasticity region followed by yielding a subsequent strain hardening and strain softening region stage. It has been found that the yield stress and ultimate stress increased with the strain rates. Moreover, at higher strain rates, the impulse increases significantly, leading to earlier and more intense ignition. The critical strain rate and the critical impulse of the GRT propellant are 5000 s−1 and 13.28 N · s, respectively. A judgment basis for GRT propellant ignition is established. Finally, according to the high-speed images and the posttest SEM images, it has been concluded that the dominant ignition mechanism of GRT propellant is flow at the macroscopic level and internal frictional heating at the mesoscopic level.

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.

Ignition response of NEPE-based propellants under drop weight through experiments and numerical simulation

ABSTRACT Experimental and numerical studies were conducted to investigate the effects of drop height on the ignition mechanism of NEPE nitrate ester plasticized polyether-based propellants. A modified drop-weight system was equipped with a high-speed camera to capture the ignition response images during the whole impact process. A macro-mesoscopic thermomechanical model considering the microcrack and viscous shear flow hotspot formation mechanism was established. The experimental results showed that the ignition responses of the propellants heavily depended on drop height, and the main ignition mechanism was viscous shear flow. The whole loading process could be summarized into three stages: radial extension (viscous shear flow), macroscopic crack initiation and ultimate failure (multiple macroscopic cracks or ignition). The ignition threshold was 35 cm. The posttest scanning electron microscopy (SEM) images further revealed that viscous shear flow played an important role in the ignition of propellants. The numerical simulation results indicated that viscous shear flow was the dominant ignition mechanism compared with the microcrack hotspot mechanism. Point A (along L1) was the most dangerous location under the drop-weight experiment. The predicted features of ignition evolution were consistent with the experimental results and prove that the critical drop height of ignition was 35 cm.

Microwave controlled ignition and combustion characteristics of ADN-based ionic liquid propellant with fast response and environmental friendliness

The ADN-based ionic liquid propellants have been successfully implemented in liquid rocket engines, owing to high specific impulse and thrust, low toxicity and environmental friendliness. However, the traditional catalyst ignition of ADN-based propellant suffers from the problems of catalyst deactivation problems in the heating process. Microwaves could interact with the material holistically due to excellent penetration ability. Compared with solid materials, ionic liquids are natural microwave receptors on account of great polarity. To date, the possibility of microwave ignition of ionic liquid materials has not been explored. In this work, two kinds of ionic liquids: ADN and [AMIM][DCA] were used as oxidant and fuel of liquid propellant to achieve the maximum microwave absorption effect. The microwave controlled ignition and combustion of ADN-based liquid propellant was first realized and systematically studied. Compared to single component, the heat release, gas production, conductivity and heating rate of the mixed system was greatly enhanced. The sample (ADN/[AMIM][DCA] 10%) was successfully ignited by microwaves, displaying a decreased ignition delay time at higher power inputs. The ignition was generated in the gas phase and rapidly diffused into the solution, and the extinguishment was highly consistent with the input cessation of microwaves. The ignition delay was significant reduced in repeated ignition, resulted from the faster moving speeds of ions. The successful realization of microwave controlled ignition and combustion of ADN-based IL propellant will broaden the scope of their applications in space fuel and provide a new direction for the reform of liquid engines.

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.

Ignition and Extinction Characteristics of Electrically Controlled Solid Propellants

The ignition and extinction characteristics of perchlorate-based electrically controlled solid propellants (ECSPs) that can achieve multiple ignition and produce controllable thrusts were investigated. We examined the multiple-ignition and combustion behaviors of ECSPs and identified the basic ignition-model parameters for these materials. Single-frame photography and a schlieren imaging system were used to determine the ignition, combustion, and extinction properties of two different ECSP formulations at various voltages, pressures, and initial temperatures. The results revealed that increasing the voltage, pressure, and initial temperature reduced the ignition delay; whereas increasing the number of ignitions decreased the ignition delay and ignition energy but increased the extinction delay and smoldering time. Furthermore, under the same experimental conditions, the voltage, pressure, and initial temperature produced a larger effect on a nonmetallic ECSP than on an ECSP containing 5% aluminum (Al) powder. The nonmetallic ECSP exhibited a longer ignition delay, higher ignition energy, and better extinguishing performance than the Al-containing ECSP. Moreover, four distinct stages of the ECSP ignition process were identified. The findings of this study demonstrated that the electrical energy consumed during condensed phase heating plays a critical role in propellant ignition.