Pressure Exponent Research Articles

Effect of Dual Curing Agent (TDI:DDI) on the Mechanical Properties and Burning Rate of HTPB-Based Solid Propellant

ABSTRACT In this study, the effect of dual curing agent (toluene diisocyanate:dimeryl diisocyanate (TDI:DDI)) on the properties of hydroxyl-terminated polybutadiene (HTPB)-based solid propellant (such as mechanical strength, elongation percentage, elastic modulus, hardness, burning rate and pressure exponent (n)) has been investigated. Thus, five solid propellant formulations with different proportional amounts of TDI and DDI, with same loading rate and constant R value, were prepared, and the mechanical properties and burning rate of the prepared samples were evaluated. Tensile test conducted on the solid propellant cured for 7 days showed that increasing the proportional amount of DDI compared to TDI in the solid propellant formulation increases the elongation percentage and decreases the tensile strength, modulus, burning rate and pressure exponent (n). Considering that DDI also plays the role of a softening agent in the solid propellant formulation, increasing its amount in the solid propellant formulation will decrease the viscosity, causing a higher pot life.

Theoretical and experimental study on combustion response of aluminized solid propellant under acceleration effects

The combustion performance of solid propellants is significantly affected by the external operating parameters of rocket motors. In this paper, the combustion response characteristics of aluminized solid propellant under acceleration conditions have been studied theoretically and experimentally. A theoretical model of unsteady burning for aluminized solid propellant, considering transient heat transfer and acceleration effects, is developed based on the Zel'dovich-Novozhilov solid-phase energy conservation. The pressure-coupled responses of the solid propellant are also measured experimentally under different normal accelerations using the T-burner and centrifuge. The model is well validated by comparison with literature and experimental results. The unsteady burning of propellants is analyzed in detail, and the effects of acceleration and propellant properties on combustion response are investigated. The results show that there is a significant difference between the transient and quasi-steady burning rate under dynamic environments. As normal acceleration increases from 0 g to 1000 g, the fluctuation amplitude of the net heat flux on the burning surface continues to decrease, the magnitude of the pressure-coupled response peak decreases significantly by 69 %, and the frequency of the response peak shifts from 140 Hz to 230 Hz. Moreover, the pressure exponent and thermal conductivity plays a positive role in the pressure-coupled response. The model presented in this paper can be helpful for predicting the differences between flight and ground test performance and evaluating the combustion stability of solid rocket motors.

Control of burning rate pressure sensitivity for solid propellants by changing the interfacial contact of Al/HMX/AP with precisely located graphene-based energetic catalysts

The control of burning rate pressure sensitivity is essential for stable and reliable combustion of solid propellants. It has been proved that the combustion behavior of propellants can be effectively tuned by interfacial control of Al/oxidizers. In this work, core-shell Al-based composites, using oxidizers such as ammonium perchlorate (AP) and cyclotetramethylene tetranitramine (HMX) as the shell layer, have been prepared with a well-controlled location of graphene-based carbohydrazide complexes (GO-CHZ-M, M = Co2+ or Ni2+) as the catalysts. The catalysts can be located inside HMX or embedded on the surface of AP particles. The decomposition of AP and HMX could be greatly promoted with a trace amount of catalyst. Under the synergistic effects of Al/oxidizer interfacial control and GO-CHZ-M, the ignition delay time is shortened by >48 % with increased in flame radiation. More importantly, the burning rate (r) and pressure exponent (n) of the solid propellants are effectively regulated in a wide range. In particular, the use of Al@HMX/Co results in a lowered n of 0.29 within 1∼20 MPa compared to 0.79 for the blank reference sample. The agglomeration of Al particles during combustion was also inhibited due to the micro-explosion effect of Al@HMX composites. Novelty and Significance statementThe innovative approaches of integrating Al/HMX/AP composites and precise catalysis of graphene-based energetic catalysts in solid propellants have successfully achieved, regarding the modulation of the burning rates and pressure sensitivity. Moreover, the effect of catalyst location on the ignition delay and burning rates has also been studied thoroughly and clarified. This paper provides new insight into the regulation of combustion performance of solid propellants, with improved reaction efficiency and maintained energy density.

Numerical investigation of effect of pressure exponent for enhanced Coulomb friction model

The complexity of sheet metal parts has reached a level, that without supporting process planning applications almost impossible to design the process planning. Because technology is sharpened to the limit the slightest disturbance in the production results in a waste product. The lubrication condition used during the sheet metal forming is crucial to the success of production. Therefore, the need to model the resulting tribological system as accurately as possible has become increasingly important. This paper purpose with the physically based measurement of the so-called enhanced Coulomb model material parameter used in AutoForm software and the analysis of its effect.

Optimal permeance ratio, flux direction and layer distribution in composite asymmetric membranes composed of sequences of layers obeying real-power flux laws

In this study, the optimal permeance ratio and layers distribution in multilayer membranes and thin films in which each layer obeys the following real-power law: Flux=πi(P1,ini−P2,ini) are determined for any positive real values of ni. Such an exponent has a physical meaning in several cases, such as: diffusion-controlled permeation of hydrogen in metal membranes i) under infinite-dilution conditions (n = 0.5), and ii) under higher-concentration ones (0.5 < n < 1.5), iii) desorption-limited permeation (n = 1) in the same type of membranes, Knudsen-type diffusional mechanism (n = 1) and viscous flow (n = 2) in microporous membranes. Furthermore, n is equal to 4 in radiation-driven thermal flux. The work considers two generic layers of different thicknesses and exponents, for which it is proven the existence of a general optimal permeance ratio π1/π2 maximising the flux ratio, which is found to be equal to the inverse of the ratio between the respective maximum theoretical driving forces that can be established in each layer. Such an optimal permeance ratio is also proven to be a global optimum. Afterwards, we provide a theoretical generalisation of this optimality to whatever types of driving forces. Then, we provide a demonstration that the highest species permeating flux is always established when feeding it from the layer side with the highest exponent independently of the permeance ratio. As an important consequence, to maximise flux, a multilayer membrane/thin film should be fabricated by depositing the layers in cascade according to the ascending or descending exponents, and should be used in a configuration in which the flux flows from the layer with the highest pressure exponent to the layer with the lowest one. It is also shown that there exists an optimal value of the lower exponent n1 that maximizes the flux ratio keeping constant the other parameters. Finally, we showed that a virial-type linear combination of polynomial driving forces can be approximated by the empirical flux law investigated. Overall, our results are valid not only for whatever type of composite membranes and thin films (metallic, ceramic, polymeric and hybrid ones), but also for any sequential system involving a flux of whatever physical entity obeying the aforementioned law, such as heat transfer in the presence of radiation, non-linear electrical resistances and possible others.

Response characteristics of combustion pressure exponent of propellants: compensation effect of three energetic potassium lead complexes with Co, Cu, Ni

Response characteristics of combustion pressure exponent of propellants: compensation effect of three energetic potassium lead complexes with Co, Cu, Ni

A novel method of internal ballistics identification and performance prediction for SRMs based on genetic algorithm

Improving the identification accuracy of internal ballistic parameters in the solid rocket motor(SRM) is of great significance in guaranteeing that missiles fulfill their intended operational missions. In practice, the internal ballistic performance is according to the inverse calculation burning area obtained by the measured pressure data of the SRM and the measured burning rate, which still has ascending space for optimization in the prediction accuracy. Accordingly, a genetic algorithm-based method for the identification of internal ballistic parameters and performance prediction for SRMs was proposed. Based on the measured, data of limited test runs, the initial identification of the burning rate coefficient, pressure exponent and propellant density was carried out by GA (Genetic Algorithm). The model was updated on the basis of the inverse calculation burning area obtained by identification results. Then the secondary identification was carried out to modify the key parameters. The Φ50mm laboratory-scale test SRM was analyzed as an example. The internal ballistic performance in the SRM was predicted. The calculation results show that the prediction results obtained by the method are in high agreement with the measured pressure data, which verifies the effectiveness of the method in improving the prediction accuracy of the internal ballistic performance.

A Simplified Correlation for Burning Velocity of Gaseous Fuel-Air Mixtures

Using ideas of burning velocity dependence on the adiabatic flame temperature at any mixture ratio (equivalence ratio), and the behavior of pressure and initial temperature dependences, simple correlations have been obtained for hydrocarbons and alcohols, hydrogen air as well as syngas compositions. These exploit simple behavior of the burning velocities with adiabatic flame temperature with equivalence ratio, and for a combination of equivalence ratio and a specific compositional parameter and the pressure dependence is taken with the pressure exponent as −0.3 for hydrocarbon-air and 0 for hydrogen air compositions in a mean sense since the dependence varies slightly over the other parameters like equivalence ratio and initial temperature. Observed behavior also brings out limited universality in the behavior. In the case of syngas compositions, a parameter that depends on the mixture composition that treats even carbon dioxide as an inert seems to provide reasonable predictions for a wide range of compositions. One anomaly that comes up is that methyl alcohol appears distinctly more reactive (by 15%) than methane and deserves examination since the results at higher initial temperatures seem to follow the trend noted in the general correlation.

On‐demand microwave growth of porosity within a granular composite energetic material: Void formation via a dielectric loss phase change binder additive for propellant burning rate control

AbstractThis study demonstrates, for the first time ever, the ability to grow, in an on‐command fashion, porosity within a granular composite energetic material to effect a change in energy output rate. Specifically, the study investigates the change in burning rates of ammonium perchlorate composite propellants as a result of porosity created in situ via microwave field‐driven volatilization of the low boiling point binder additive, ethylene glycol. Theoretical mass densities were measured before and after microwave irradiation finding that the maximum observed %TMD change for tested propellants is 6 %. Propellants were burned at 1.72 MPa to 6.89 MPa pressures, finding that for all propellants, microwave irradiation produced a change in ballistic characteristics. Most propellant formulations demonstrate acceptable burning rate parameters for use within rocket motors; some exhibited a large change in their pressure exponent as well as slope breaks attributed to the onset of convective burning, while microwave irradiation produced no change in burning rate or density in reference propellants without the additive. Microwave heating simulation results are presented to gain insight into the thermal environment of the propellant during microwave irradiation. These results provide valuable insight into propellant formulations that can have their burning rates (and thus the thrust profile for motor grains) altered after casting via microwave irradiation.

Tuning the Ballistic Performance of a Single-Burning-Rate Grain Solid Rocket Motor via New Discontinuous Embedded Metal Wires

This work proposes a new effective method to realize variable thrust through discontinuous embedded metal wires in the solid rocket motor (SRM). We aimed to study the influence of discontinuous embedded metal wires on the performance of an SRM with a single-burning-rate grain. A model based on convection heat transfer, heat conduction, and heat radiation was established to calculate the heat transfer in the discontinuous embedded metal wires in the grain, to then obtain the burning rate ratio. Most importantly, a solid rocket motor was designed to verify the feasibility of variable thrust and of the present model prediction, with the embedded silver–nickel alloy wire divided into two segments in the grain. According to the SRM ignition experiment, the silver–nickel alloy wires raised the burning rate of the grain. The pressure varied regularly with changes in the discontinuous embedded metal wires. The theoretical burning rate ratio matched the experimental result well. Based on the verified model, the effects of the burning rate, pressure exponent, burning rate ratio, and number of wires on thrust were investigated. Burning rate, burning rate ratio, and pressure exponent were found to be positively correlated with thrust ratio. The thrust ratio could reach 12.5 when the burning rate ratio was 5. The ability to adjust thrust tended to increase with an increase in the number of wires. This study also provided a method to assess whether the consecutive embedded metal wires had been broken or not. The method using discontinuous embedded metal wires in the grain was proven to be feasible to realize multi-thrusts of single-burning-rate grain, which is a new idea for the design of a multi-thrust SRM.

Combustion performance modulation and agglomeration inhibition of HTPB propellants by fine Al/oxidizers integration

Modulation of burning rates and inhibition of aluminum agglomeration in solid propellants have generated considerable research interest in the field of energetic materials. In this paper, integrated Al/oxidizer composites have been prepared by a spray-drying technique, which offer intimate contact between the fuel and oxidizers. The morphologies, thermal stability, density, heats of explosion and combustion performance of the resulted solid propellants containing these Al-based composites were systematically investigated, where the condensed combustion products (CCPs) analysis and the agglomeration behavior of Al particles have been focused. After well control of the Al/oxidizers structure, 9 % higher explosion heat, 58 % higher pressurization rate and 65 % stronger flame radiation intensity were achieved in comparison to the conventional solid propellants with the same formulation. The burn rate of the propellants can also be well controlled by using different type of Al/oxidizers composites, in the range of 3.6–5.9 mm s−1 under 0.5 MPa and 9.2–10.9 mm s−1 under 15 MPa. More importantly, very low burn rate pressure exponent of 0.1 within 0.5–15 MPa was obtained. Inspired by decreasing size of CCPs, the evolution of Al on the burning surface was studied and the agglomeration inhibition was observed, whose potential mechanism was then proposed and elucidated.

The significant role of passive oxide layer on reactive metal combustion: insights into composite solid propellant with superior performance

ABSTRACT Passive oxide layer could expose a significant impact on reactive metal combustion. Boron and aluminum experience combustion enthalpy of 59.3 and 31.1 KJ/g and passive oxide layer of 200 and 7 nm, respectively. In this study, surface oxygen of born and aluminum particles (10 µm) was quantified via EDAX analysis. Boron and aluminum demonstrated surface oxygen content of 14.6 and 7.2 wt %, respectively. Reactive particles were integrated into ammonium perchlorate (AP) oxidizer. While boron demonstrated decrease in AP decomposition enthalpy by −14.8%; aluminum offered an increase in AP decomposition enthalpy by 60.8% using DSC. Whereas, aluminum oxide layer could be pealed out more effectively; boron passive oxide layer could melt with the evolution of an insulating barrier. Aluminum particles offered decrease in AP apparent activation energy by 68%, 105%, and 76% using Kissinger, Kissinger-Akahira-Sunose (KAS), and Flyn and Wall (FWO) models, respectively. Solid propellant formulations were developed; ballistic performance was assessed using small-scale rocket motor. Aluminum particles demonstrated stable combustion process with enhanced specific impulse and total pressure impulse compared with boron. Additionally, aluminum particles demonstrated stable burning with pressure exponent of 0.19 compared with 0.4 for boron particles.

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.

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.

Determining flux-limiting mechanism of hydrogen permeation through palladium membrane by n value

Pd film has been endowed with the hydrogen selective permeation capability and widely used for hydrogen separation via a series of complex processes. Clarifying the exact relationship between permeating mechanism and hydrogen pressure exponent (n) is of great significance to optimize the purification performance, adequate exploration toward which is nevertheless insufficient. In this work, Pd membrane-based hydrogen permeation was divided into seven steps according to the “dissociation-diffusion” principle. The effect of each step on permeation flux with and without considering external mass transfer process was quantified by mathematical and physical models, in which the relationship between n value and the flux-limiting mechanism was deeply analyzed. The calculation suggested that desorption-limiting mechanism acting as leading role would result in n value to be 0, while external mass transfer dominating the permeation would make n value to be 1. When n value was between 0 and 0.5, desorption and diffusion processes would impose combined impact on the permeation (ignoring external mass transfer) and desorption might have more weight as n approaching to 0. On the other hand, taking external mass transfer into account, desorption-limiting and external mass transfer-limiting mechanism would work together as 0 < n < 1. The closer n approaching to 1, the more significant of external mass transfer mechanism. In addition, the influences of Pd film thickness, ΔP variation and mass transfer coefficient on n value were also elucidated systematically.

Enhancing the Ignition and Combustion Performances of Solid Propellants Incorporating Al Particles Inside Oxidizers.

The combustion efficiency of Al plays a critical role in the combustion of high-energy aluminum-based solid propellants. For traditional formulations, the Al powders are dispersed in the binder matrix, leading to limited contact with the oxidizers and hence usually insufficient combustion and higher values of the pressure exponent. In this paper, various core-shell structural Al/oxidizer composites such as Al@HMX, Al@AP, and AP@Al have been prepared by a spray-drying technique based on which solid propellants with precise interfacial control between Al particles and oxidizers were realized. Compared to the control sample, the modified propellants have a greater heat of explosion of 5890 J g-1 (15% higher) and a reduced ignition delay time of 58 ms (65% decrease). Without changing the content of components, the burn rates of propellants can be easily modulated by tuning the interfacial contact of Al and oxidizers, where it varies in a wide range of 4.56-5.79 mm s-1 at the same pressure of 1 MPa. After introducing Al/oxidizer composites, the lowest pressure exponent of 0.19 within 1-15 MPa could be achieved by using Al@HMX and AP@Al composites. The agglomeration of Al was also inhibited by using Al/oxidizer composites, and the mechanism can be interpreted by using a classical "pocket" model. Moreover, the improved combustion efficiency of the solid propellants was verified by a noticeable reduction in the unreacted Al content.

Investigation on laminar burning velocity measurements of premixed Ethane-Air mixture at higher pressure and temperature conditions

The externally heated diverging channel (EHDC) method was utilized to evaluate the laminar burning velocity (LBV) of premixed ethane-air flames at higher mixture temperature (350-620 K) and pressure (1-5 atm) conditions over different mixture strengths (ϕ = 0.7-1.3). The maximum LBV was noted at ϕ = 1.1 for all pressure and temperature conditions. The inverted parabolic behavior of the temperature exponent was obtained with the minima at ϕ = 1.1. The pressure exponent (β) exhibits a parabolic variation with its maxima at ϕ = 1.0. The current results are further analyzed and compared with the literature measurements, and the comprehensive kinetic model predictions of USC mech II, San Diego mech, and Aramco mech 1.3. The present LBV measurements match well with the kinetic model predictions of Aramco mech 1.3 at most of the mixture and pressure conditions. The present results propose the variation of pressure exponent (β) as a function of temperature ratio, and temperature exponent (α) as a function of pressure ratio for different mixture conditions (ϕ). A revised power-law correlation for α and β variations is also recommended as, Su=Su0Tu/Tu0∝0+∝11-Pu/Pu0)Pu/Pu0β0+β11-Tu/Tu0. The sensitivity analysis indicates the maximum decrement in the positive sensitivity for the chain branching reaction HCO + M ↔ H + CO + M (R30) across all the stated mixture conditions, owing to an increment in the third body effects along with pressure and temperature. The reaction pathway analysis reveals a maximum net reduction in the elemental flux (∼56 %) for the reaction between the species carbon monoxide (CO) and carbon dioxide (CO2) through different reactions, due to a rise in pressure and temperature.

The regulation of ferrocene-based catalysts on heat transfer in high-pressure combustion of ammonium perchlorate/hydroxyl-terminated polybutadiene/aluminum composite propellants

The regulation of the burning rate pressure exponent for the ammonium perchlorate/hydroxyl-terminated polybutadiene/aluminum (AP/HTPB/Al) composite propellants under high pressures is a crucial step for its application in high-pressure solid rocket motors. In this work, the combustion characteristics of AP/HTPB/Al composite propellants containing ferrocene-based catalysts were investigated, including the burning rate, thermal behavior, the local heat transfer, and temperature profile in the range of 7–28 MPa. The results showed that the exponent breaks were still observed in the propellants after the addition of positive catalysts (Ce-Fc-MOF), the burning rate inhibitor ((Ferrocenylmethyl)trimethylammonium bromide, FcBr) and the mixture of FcBr/catocene (GFP). However, the characteristic pressure has increased, and the exponent decreased from 1.14 to 0.66, 0.55, and 0.48 when the addition of Ce-Fc-MOF, FcBr and FcBr/GFP in the propellants. In addition, the temperature in the first decomposition stage was increased by 7.50 °C and 11.40 °C for the AP/FcBr mixture and the AP/FcBr/GFP mixture, respectively, compared to the pure AP. On the other hand, the temperature in the second decomposition stage decreased by 48.30 °C and 81.70 °C for AP/FcBr and AP/FcBr/GFP mixtures, respectively. It was also found that FcBr might generate ammonia to cover the AP surface. In this case, a reaction between the methyl in FcBr and perchloric acid caused more ammonia to appear at the AP surface, resulting in the suppression of ammonia desorption. In addition, the coarse AP particles on the quenched surface were of a concave shape relative to the binder matrix under low and high pressures when the catalysts were added. In the process, the decline at the AP/HTPB interface was only exhibited in the propellant with the addition of Ce-Fc-MOF. The ratio of the gas-phase temperature gradient of the propellants containing catalysts was reduced significantly below and above the characteristic pressure, rather than 3.6 times of the difference in the blank propellant. Overall, the obtained results demonstrated that the pressure exponent could be effectively regulated and controlled by adjusting the propellant local heat and mass transfer under high and low pressures.

Rheological, Ballistic, and Mechanical Properties of 3D Printed, Photocured Composite Propellants

This study explores the rheological, mechanical, and ballistic properties of printed ammonium perchlorate composite propellant at 82.5% solids loading with binders curable with ultraviolet light of wavelength from 215 to 400 nm (UV). A polybutadiene urethane acrylate and two polyester urethane acrylate propellants are printed by an in-house-fabricated fused deposition molding printer. Propellants are all shear-thinning and have significantly lower viscosity than similar hydroxyl-terminated polybutadiene (HTPB) propellants. Uniaxial stress–strain measurements indicate that ultimate tensile strength and ultimate tensile strain of all photocurable propellants are found to be greater than HTPB propellant. In particular, the ultimate tensile strain of polyester urethane acrylate propellant is six times that of HTPB propellant, demonstrating high compliance. Ballistic properties are measured from combustion of printed propellant articles in a windowed Crawford combustion bomb at inert gas pressures of up to 12.1 MPa. The burning characteristics were found to be relatively planar, though strong burning rate anisotropy, expected as a result of print layer inhomogeneities, was observed in two of the three formulations. Overall, pressure exponents of the propellants were mild and ranged from 0.17 to 0.33. These results are compared and contrasted to those of other printed propellants. These results provide valuable insight into the selection of a safe binder system for printing of photocurable composite propellants.

Mechanistic study of the influence of aluminum nanoparticles on the pressure sensitivity of 1,3,5-trinitro1,3,5-triazinane (RDX) thermal decomposition

The incorporation of Al nanoparticles (Al NPs) into 1,3,5-trinitro1,3,5-triazinane (RDX) can catalyze its thermal decomposition and reduce the pressure exponent (n) of solid propellants. However, the underlying reaction mechanism at a deeper level remains unclear. In this study, the reaction processes of Al NPs catalyzing the thermal decomposition of RDX under different initial pressures were investigated by utilizing the ReaxFF molecular dynamics (ReaxFF-MD) simulations combined with DFT calculations, and the influence mechanism of Al NPs on the pressure sensitivity of RDX thermal decomposition was revealed from various perspectives. In the initial stage of the reaction, unlike the nitro group dissociation observed in pure RDX, the incorporation of Al NPs alters the initial decomposition pathway of RDX, making it more easily adsorbed on the surface of Al and enhancing the early-stage decomposition rate. Furthermore, Al NPs exhibit higher catalytic activity in low-pressure systems. In the later stage, because of the massive adsorption of free radicals generated from RDX decomposition on the surface of Al NPs, the decomposition rate of RDX decreases significantly, especially in high-pressure systems. Consequently, Al NPs synergistically reduce the pressure sensitivity of the RDX thermal decomposition from two different perspectives. Compared to traditional experimental research or single RDX simulation studies, this work further explores the interaction between Al and RDX from a microscopic perspective, addressing the gap in the field of the influence mechanisms of Al NPs on the pressure sensitivity of RDX thermal decomposition. It also establishes a theoretical foundation for the practical application of Al@RDX fuels.