Pressure Exponent Research Articles

Experimental study and kinetic analysis of the laminar burning velocity of NH3/syngas/air, NH3/CO/air and NH3/H2/air premixed flames at elevated pressures

Mixing ammonia with syngas can be a promising way to overcome the low reactivity of ammonia, allowing it to find usage in IGCC (Integrated Gasification Combined Cycle) systems and gas turbines for power generation. However, fundamental experimental data on laminar burning velocity of NH3/syngas/air are rather scarce, especially at elevated pressures. This information is critical for the development and validation of reaction mechanisms and advances in combustor design. In the present work, measurements of the laminar burning velocities (SL) of NH3/syngas/air, NH3/CO/air, and NH3/H2/air premixed flames were performed by the heat flux method at pressures up to 5 atm, equivalence ratios ranging from 0.7 to 1.6, ammonia mole fractions in the fuel mixture from 0.2 to 1.0 in the NH3/syngas/air mixtures and 0.03–1.0 in the NH3/CO/air mixtures. Several recently published ammonia oxidation mechanisms were tested against the present experimental data. The measurements and predictions of SL exhibit discrepancies especially for NH3/H2/air flames at elevated pressures. The pressure exponent factors, β, characterizing burning velocity at elevated pressure via empirical power-law correlation SL/SL0 = (P/P0)β are extracted from the measured SL and compared with the numerical results. The thermal, diffusion, and chemical effects of blending syngas with ammonia on SL of the mixtures are distinguished, and the dominant role of the adiabatic flame temperature on the variation of the pressure exponent β is discussed. Kinetic modeling and sensitivity analyses showed that reactions of NHi to N2Hi (i = 0–4) species affect the predicted SL under rich conditions. At elevated pressures, these reactions also affect the NO formation via third-body collision reactions and NHi + NO reactions. Even for rich flames, the ammonia consumption is favored with the addition of syngas which also promotes NO formation by enriching the H and OH radical pools and increasing the flame temperature. The addition of hydrogen or carbon monoxide has equally promoting effect on the ammonia decomposition and NOx formation although their flame speed differs a lot.

Combustion Properties of Composite Propellants Based on Two Kinds of Polyether Binders and Different Oxidizers

AbstractTwo kinds of solid propellants based on propargyl‐terminated ethylene oxide‐tetrahydrofuran copolyether (PTPET) and ethylene oxide‐tetrahydrofuran copolyether (PET) were prepared with 1,3,5‐trinitro‐1,3,5‐triazacyclohexane (RDX), ammonium perchlorate (AP) and aluminum (Al), respectively. The order of burning rates for PET+RDX, PTPET+RDX and PET+RDX+Cu−B propellants: PTPET+RDX > PET+RDX > PET+RDX+Cu−B. Their pressure exponents are also similar when the pressure is higher than 7 MPa. The combustion residue of PET+RDX and PET+RDX+Cu−B propellants show a loose structure and there are many bright particles distributed in its flame zone. The combustion residue of PTPET+RDX propellant shows a dense structure and its flame is uniform. The burning rates of PET+AP+Cu−B propellant is between the burning rates of PET+AP and PTPET+AP propellants at the same pressure. Their flame shape is similar. The burning rates of PET+AP+Al+Cu−B propellant is also between the burning rates of PET+AP+Al and PTPET+AP+Al propellants at the same pressure. The combustion flame of PET+AP+Al propellant differs greatly in direction and shape at different time. The combustion flame of PTPET+AP+Al and PET+AP+Al+Cu−B become almost identical in shape and direction at different time. These results show that the curing catalyst Cu−B of PTPET propellant plays a catalytic role in combustion.

Anomalies in isothermal compressibility and exponent of pressure in spin-orbit-coupled degenerate Fermi gases

The spin-orbit coupling (SOC) in degenerate Fermi gases can fundamentally change the fate of $s$-wave superfluids. Here we report the anomalous isothermal compressibility ${\ensuremath{\kappa}}_{T}$ in the degenerate Fermi gases with both SOC and Zeeman field. Starting from the Gibbs-Duhem equation, we show that ${\ensuremath{\kappa}}_{T}$ comes from both the explicit contribution of chemical potential and the implicit contribution of the order parameter. In the Bardeen-Cooper-Schrieffer (BCS) limit, ${\ensuremath{\kappa}}_{T}$ is determined by the explicit compressibility, which is proportional to the density of states at the Fermi surface; while in the Bose-Einstein condensate (BEC) regime it is determined by the implicit compressibility, which is uniquely given by the scattering length. Between these two limits, we find a pronouncedly enhanced compressibility in the gapless Weyl phase regime, which is attributed to a remanent effect of the instability of degenerate Fermi gases towards phase separation. This enhanced compressibility also leads to an anomaly in the exponent of pressure. A connection between this exponent and the polytropic index is established. These predictions can be measured from the anomaly in sound velocity, density fluctuation, and collective vibration frequencies.

The potentials of TiO2 nanocatalyst on HMX thermolysis

Even though HMX is one of the most powerful highly explosive materials; HMX-based propellants demonstrated complexity of burning rate control as well as high pressure exponent (n). In addition, HMX is insensitive to common catalyst. TiO2 can offer novel catalyzing ability for HMX. Highly-crystalline, mono-dispersed TiO2 NPs of 5.0 nm particle size with proper surface area (26.87 ± 0. 36 m2/g) were fabricated using hydrothermal processing. TiO2 NPs were re-dispersed in organic solvent and effectively-integrated into HMX via co-precipitation technique; the impact of TiO2 NPs on HMX thermal behavior was investigated using DSC and TGA. TiO2 NPs exposed superior catalytic performance; the endothermic phase change of HMX at 187 °C was decreased by 43.3%. The main exothermic decomposition peak was decreased by 10 °C with enhanced total heat release by 46.7%. The catalytic performance of TiO2 NPs could be ascribed to the release of active surface ȮH radicals that could induce HMX decomposition via hydrogen abstraction. Furthermore, TiO2 NPs could adsorb evolved NO2 on its surface with surge in total heat release in condensed phase.

Improving air leakage prediction of buildings using the fan pressurization method with the Weighted Line of Organic Correlation

In many countries, the fan pressurization method is the most frequently chosen approach for measuring the air leakage of houses. The measurements are usually performed at pressures that far exceed pressures to which buildings are exposed to under normal conditions. A fit of these tests to the power-law formulation allows an extrapolation to data points outside the measured pressure range. With the Ordinary Least Square (OLS) fitting method, the pressure exponent and flow coefficient can be determined. However, the measurement results are highly sensitive to uncertainties induced by external factors like changing wind conditions during the tests, which is neglected by OLS. This may lead to errors in the prediction of flows at lower pressures. The Weighted Line of Organic Correlation (WLOC) is an alternative approach and takes measurement uncertainty into account.In this paper, a statistical analysis of an extensive data set of pressurization measurements has been performed. Both regression techniques have been compared for almost 7500 fan pressurization measurements of six houses in 109 different house leak configurations. The variability in predicting pressure exponent and flow coefficient for both WLOC and OLS regression was analyzed using probability density functions. It was found that the Weighted Line of Organic Correlation significantly decreases the uncertainty in predicting pressure exponent, flow coefficient, and other low-pressure air leakage metrics compared to the Ordinary Least Square fitting. The authors highly recommend the implementation of WLOC in current measurement standards and test equipment.

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.

Combustion behavior of AP/HTPB/Al composite propellant containing hydroborate iron compound

We report a first attempt to investigate the reaction mechanisms of hydroborate iron compound (HIC), a promising candidate for combustion catalyst, in AP/HTPB/Al composite solid propellants using ammonium perchlorate (AP) as the oxidizer and aluminum as the metal fuel. The effects of HIC on the combustion properties of propellants were experimentally examined to determine burning rates, combustion flame structures and flame temperature distribution. The combustion residues were collected and examined; the mechanical sensitivity of propellant samples were tested. It was found that the addition of HIC particles can increase the burning rates with only minor changes of the pressure exponent. When 5.0 wt% of Al is replaced by HIC, the pressure exponent increases from 0.31 to 0.35 over the pressure range 1–12 MPa while the burning rate increases from 33 mm s−1 to 40 mm s−1 at 7 MPa. The combustion flame images of burning propellants surface loaded with HIC at various pressures present multi-flame structures, and the flame brightness increases with increasing the pressure. Many sparks are observed near the burning surface during the propellant combustion, due to burning aluminum particles in gas phase. With 5.0 wt% HIC included, the propellant produces very different condensed combustion products (CCPs) with a variety of morphologies, and the most typical ones are “porous” shape, large alveolate and loose structures. The relative combustion residue mass decreases with increasing pressure (1–5 MPa) and HIC mass fraction in the formulation (0–5%); While HIC powder is insensitive to friction and impact stimuli (0% at height is higher than 125 cm), the tested propellant formulations containing different mass fraction of HIC particles result sensitive to impact and friction a bit more than the reference formulation without HIC particles.

A novel bamboo sheet chair and its influence on sitting comfort.

BackgroundIn today’s economy, workers spend increasingly more time in seated positions, leading to a growing scientific interest in chair design. In this study we used body pressure distribution tests to compare a novel bamboo chair with unique structural features to other commonly-used chairs. We studied the bamboo sheet chair’s physical characteristics and comfort to provide a scientific theoretical basis for common use seat design.MethodsA total of 25 (14 male and 11 female) subjects participated in the study. Subjects were divided into six groups according to their body characteristics parameters included stature, weight, shoulder breadth, hip breadth, waist width, popliteal height, buttocks-popliteal length, and buttock-abdomen depth, with three groups for males and three groups for females. Each subject was required to complete specified body pressure tests for three different experimental chairs for three minutes and subjective comfort evaluations were also administered. The pressure indexes were measured from the seat pan and backrest and calculated with MATLAB 2015b, which mainly included maximum pressure (Pm), average pressure (Pa), pressure exponent (Pe) and contact area index (PAI). Three pressure threshold limits of 0.67 kPa, 4.00 kPa and 9.33 kPa and four contact surface indexes were used in the experiment to reflect the contact area between human and chair.ResultsThe contact areas in the backrest (52.96 ± 32.94 cm2) and seat pan (307.75 ± 90.31 cm2) in the middle-to-high threshold pressure range, and the contact areas of the backrest (4.34 ± 5.95 cm2) in the high threshold pressure range of bamboo sheet chair were smaller than the corresponding indexes of the common office chair (81.430 ± 45.04 cm2, p = 0.00; 394.39 ± 98.99 cm2, p = 0.02; 13.54 ± 12.00 cm2, p = 0.00, respectively). The pressure index (2.68 ± 0.88 kPa), maximum pressure (6.66 ± 2.05 kPa), and average pressure (2.42 ± 0.59 kPa) values of the bamboo sheet chair backrest were also found to be lower than those of the office chair (4.32 ± 1.62 kPa, p = 0.00; 10.50 ± 3.88 kPa, p = 0.00; 3.43 ± 0.97 kPa, p = 0.00, respectively). The average pressure on the seat pan was greater than 4 kPa for all subjects, while the average pressure on the seat pan was greater than 9.33 kPa for male subjects with a body mass index (BMI) of 27.48.DiscussionThe bamboo sheet chair’s contact areas within the middle-to-high and high-pressure threshold ranges of the backrest and seat pan were smaller than those of the office chair, indicating that the bamboo sheet chair is effective at relieving pressure. Human body characteristics must be considered in the design of seat functional size. Buttocks-popliteal length, weight, body mass index, body shape and weight distribution, all have important effects on the distribution of body pressure at the human-chair interface.

Transient flow characteristics and performance of a solid rocket motor with a pintle valve

The pintle valve is currently the most promising technology among all thrust control methods for solid rocket motors. Pintle structure and working condition play a critical role in the successful operation of a pintle motor. Here, 2D transient simulations of a pintle motor using dynamic meshing are performed. Reynolds-averaged Navier–Stokes equations are solved with the implementation of an RNG k–ε turbulence model. In cold flow test, emphasis is placed on the effect of pintle structure, and in hot flow test, emphasis is placed on the effect of propellant pressure exponent. Validation is performed first by comparing the present results with available cold-test experimental data. This shows that the transient simulations can provide good predictions for pintle motors with a relative error of less than 2% in terms of the chamber pressure. It can be found that, when the gas supply system is different, the working principles and conditions of pintle motors are different. The feedback process in propellant combustion has a significant impact on its operation and the effect on the pintle motor performance of different pintle structures is achieved by different variations in the equivalent throat area. Finally, the pressure exponent is an important parameter in hot flow test and changes of thrust in hot flow test are not monotonic, because changes in the flow field and motor performance are asynchronous.

Combustion performance of composite propellants containing core-shell Al@M(IO3)x metastable composites

Aluminum (Al) has been widely used in solid composite propellants (SCPs) to increase the specific impulse. However, Al always subjects to coalescence, sintering to large agglomerations during combustion of SCPs resulting in larger two-phase flow losses. Herein, core-shell μ-Al@M(IO3)x composites have designed and synthesized as a replacement for micron-sized Al (μ-Al) in the Al/AP/RDX/HTPB propellant with tunable combustion behavior. The results show the thermal reactivity and heat releases of SCP are largely enhanced by using these novel metal-based composites. With the inclusion of μ-Al@EGCG@Fe(IO3)3 (EGCG: Epigallocatechin gallate), the major exothermic peak is reduced by 29.1 °C compared to the reference propellant with a heat release increase up to 5475 J g−1, exceeding that of the reference sample (86 J g−1 higher). The burn rates are increased with the inclusion of μ-Al@(MIO3)x, while the pressure exponent is higher. The SCP-1 (0.3), SCP-2 (0.18) and SCP-4 (0.25) that have relatively low pressure exponent and high burn rates are good candidates for future applications. The major condensed combustion products (CCPs) of these SCPs are Al2O3, Al2.81O3.56N0.44, Al4C3, Al2OC, AlN and C7H18ClN. The agglomeration can be reduced with a minor inclusion of μ-Al@M(IO3)x due to the enhanced interfacial reactions, and the average CCP sizes (0.5 μm for SCP-1 and SCP-4) are even smaller than that of initial μ-Al (1.2 μm).

A Promising Fuel for Variable Thrust Motor: HTPB Propellant with High Pressure Exponent

AbstractIn this paper, we developed a HTPB propellant containing energetic compound hydrated‐tetra‐(‐amino‐1,2,4‐triazole) copper perchlorate (ACP) as the fuel for variable thrust motor with the purpose of controlling gas flow. Formulation of the propellant was designed and then various performances of this propellant were investigated. Results show that HTPB propellant containing 2 % ACP has a pressure exponent of 0.57 (static) or 0.56 (dynamic), suggesting an excellent capacity to control the burning rate. Thermal decomposition of ACP and the decomposition of ammonium perchlorate (AP) in high temperature are demonstrated to be sensitive to pressure by PDSC analysis, moreover, decomposition of AP in high temperature (around 400 °C) could be accelerated by ACP, φ 50 mm motors charged with this propellant work stably in the pressure range from 1.18 MPa to 21.72 MPa and less aluminum (Al) deposits in chambers and nozzles. Mechanical performance of the propellant in −40 °C and 20 °C turns out to be excellent with σm≥0.96 MPa and ϵb≥20.92 %, and is better than that in 50 °C. Low impact sensitivity (H50, 72 cm) and friction sensitivity (P, 31 %) of HTPB propellant containing 2 % ACP are found in the security tests, the propellant is also insensitive to shock wave (G50, 23.8 mm).

Fabrication and investigation of 3D-printed gun propellants

Gun propellant is the energy source of barrel weapons. A 3D printed gun propellant based on “Stereolithography (SLA)” was developed to overcome the limitation of traditional extrusion technologies. A demonstration formulation composed of 50 wt% 1,3,5-Trinitro-1,3,5-triazinane (RDX), 25 wt% epoxy acrylate, 12.5 wt% N-n-butyl-N-(2-nitroxyethyl) nitramine (Bu-NENA), 12.5 wt% reactive diluent and additives were fabricated. The 3D-printed propellants were characterized in terms of inner structure, mechanical strength and combustion behavior. Finally, a ballistic assessment of multi-perforated disk (MPD) propellant was carried out using a 30 mm test gun. The results showed that no signs of porosity or defects existed in the propellant printed by the SLA technique. The compression strength and tensile strength were 21.6 MPa and 7.3 MPa, respectively. The 3D-printed propellant exhibited a relatively low linear burn rate and a high pressure exponent value of 1.46. In the gun test, a muzzle velocity of 420 m/s was achieved without crushing the MPD.

Steady detonation propagation in thin channels with strong confinement

We examine asymptotically the dynamics of two-dimensional, steady detonation wave propagation and failure for a strongly confined high explosive (HE), in which the width of the explosive is small relative to the reaction zone length. An energy balance equation is derived, which shows how the longitudinal acceleration of subsonic flow behind the detonation shock is influenced both by chemical reaction and by the effects of HE boundary streamline deflection, specifically via the induced rate of change of mass flux through the detonation wave. The latter serves to either counteract or reinforce the acceleration of longitudinal flow, depending on the sign of the gradient of the boundary streamline deflection at the detonation shock. The analysis is valid for general equations of state and chemical reaction rates in the HE. The asymptotically derived form of the energy equation represents an eigenvalue problem for the determination of the steady detonation propagation speed, solved via a shooting method. We explore specific results for ideal and stiffened equations of state, along with a pressure-dependent reaction rate for which changes in the pressure exponent and reaction order are also studied. We consider the influences of both straight and curved HE boundary streamline shapes. The asymptotic analysis reveals significant physical insights into how detonation propagation and failure are affected by strong confinement.

Unexpected burning rate independence of composite propellants on the pressure by fine interfacial control of fuel/oxidizer

In this paper, micro-spherical Al@PDA@RDX composites with fine interfacial control have been fabricated by spray-drying technique, where poly-dopamine (PDA) is employed as a binding layer. These composites have been applied in HTPB/AP/RDX/Al propellants, which have the same theoretical formulation and hence identical specific impulse (Isp). However, these propellants differ in the interfacial structure due to different ways of assembling the ingredients, resulting in significant changes in their combustion performance. The thermal reactivity, burning rate, flame structure and the morphology of condensed combustion products (CCPs) of the prepared propellants have been investigated comprehensively. It has been shown that the pressure exponent (1–4 MPa) can be decreased from 0.236 to 0.024 (10 times lower) by the fine interfacial control, with more than 500 °C increase in flame temperature and 45.5% drop-off in the flame stand-off distance. In addition, the CCPs size distributions of the propellants have shown the enhanced interfacial interaction from Al@PDA@RDX composites can greatly inhibit the large-sized agglomeration of Al particles during the burning process.

Artificial intelligence approach to estimate discharge of drip tape irrigation based on temperature and pressure

One of the effective factors to ensure the desirable operation of drip irrigation systems is the uniform emitter discharge, which is affected by operating pressure and temperature. Accurate estimation of this parameter is crucial for optimal irrigation system management and operation. In this research, the emitter outflow discharge was simulated through artificial intelligence (AI)-based approaches under a wide range of temperature (13−53 °C) and operating pressures (0–240 kPa) variations. The applied AI models included artificial neural networks (ANN), neuro-fuzzy sub-clustering (NF-SC), neuro-fuzzy c-Means clustering (NF-FCM), and least square support vector machine (LS-SVM). The input parameters matrix consisted of operating pressure, water temperature, discharge coefficient, pressure exponent and nominal discharge, while the ratio of measured discharge to nominal discharge (modified coefficient, M) was the output of the models. The applied models were assessed through the robust k-fold testing data scanning mode. The 5-agent Global Performance Indicator (GPI) was used for the final reliable ranking. The results showed that all the applied AI models with an average mean absolute error (MAE) of 8.8% had acceptable accuracy for estimating the modified M coefficient. According to the GPI, the LS-SVM model had the lowest error, followed by the NF-SC model with a slight difference.

Differences of thermal decomposition behaviors and combustion properties between CL-20-based propellants and HMX-based solid propellants

Differences of thermal decomposition characteristics and combustion properties between CL-20-based propellants and HMX-based propellants were researched by combination of theory and practice. Burning rates and burning rate pressure exponents of CL-20-based propellants were much higher than those of HMX-based propellants, when contents and particle sizes of CL-20 and HMX were identical. The thermal decomposition of CL-20 and CL-20-based propellants was systematically studied by comparison of HMX and HMX-based propellants. HMX melted firstly at 198.53 °C and then decomposed violently at 284.3 °C, while CL-20 only decomposed violently at 246.9 °C without any melting peak, and the heat released from decomposition of CL-20 was much higher than that of HMX. Thermal decomposition of CL-20 or HMX could be greatly enhanced by GAP. CL-20 could accelerate the high-temperature decomposition of AP, whereas the decomposition of HMX was greatly enhanced by AP. Mole ratio of [NO2]/[N2O] in decomposition gas products of CL-20 was 3.07, whereas the result for HMX was 0.43. More oxidative gases were generated for CL-20 or CL-20-based propellants. Molar reaction heat in luminescent flame zone and dark zone for CL-20-based propellants was much higher than that for HMX-based propellants, resulting in a higher burning rate for CL-20-based propellants. Value of [NO2]/[N2O] for gas-phase products of thermal decomposition of CL-20/ammonium perchlorate (AP) mixed system was also much higher than of HMX/AP mixed system, resulting in more oxidative gases, such as NO2, involved in the thermal decomposition and combustion of CL-20-based propellants with ammonium perchlorate, further leading to higher burning rates of CL-20-based propellants.

Tuning the thermal, mechanical, and combustion properties of NC-TEGDN-RDX propellants via incorporation of graphene nanoplates

ABSTRACT Graphene nanoplates (GNPs) were incorporated into a solid composite propellant (NC-TEGDN-RDX) to tune the thermal, mechanical, and combustion properties of the material. Physical, thermal, and combustion properties of NC-TEGDN-RDX with <2 wt% addition of GNPs were characterized using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), tensile/compressive/impact strength testing, and constant volume combustion experiments. Microstructure of the composite propellants examined using SEM demonstrated uniform dispersion of the GNPs at low-weight percent additives (<1 wt%), but began to show large agglomerations of the additives at higher additive content. Decomposition enthalpy of the propellant with 1 wt% GNPs increased by ~130 J/g compared to neat propellants. Moreover, the maximum burning rate was observed for samples containing 1 wt% GNPs, with values of 19 cm/s at 20°C and 17 cm/s at −40°C. Dynamic vivacity of the propellant achieved a maximum upon addition of 1 wt% GNPs. The pressure exponent of the propellant decreased with the addition of GNPs, as well. The mechanical properties including tensile, compressive, and impact strength were improved at 20°C and −40°C. These results demonstrate that the addition of GNPs may offer new methods by which to tune and improve thermal decomposition, thermal conductivity, combustion performance, and mechanical properties of the NC-TEGDN-RDX propellants.

Application and Properties of CL‐20/HMX Cocrystal in Composite Modified Double Base Propellants

AbstractThe composite modified double base (CMDB) propellants containing 2,4,6,8,10,12‐hexanitro‐2,4,6,8,10,12‐hexaazatetracyclo[5.5.0.05,9.03,11] dodecane (CL‐20), 1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocane (HMX) or CL‐20/HMX cocrystal were prepared by the solventless extrusion formation technique. The performances of CMDB propellants were evaluated by means of stability, sensitivity, combustion and mechanical experiments. Raman spectra analysis indicated the stability of CL‐20/HMX cocrystal is partially destroyed in the rolling process under 90 °C, 10 MPa. Methyl violet tests revealed that the colored time of CMDB propellants containing CL‐20/HMX cocrystal, CL‐20 or HMX are 77, 60, and 75 min, respectively. Burning rate tests shown that the burning rates of CMDB propellants containing CL‐20/HMX cocrystal, CL‐20 or HMX in the pressure range of 8 to 18 MPa, increased 1.82, 4.67, and 4.67 mm/s, with the pressure exponents 0.095, 0.306, and 0.346, respectively. Mechanical property tests revealed that the mechanical properties of CMDB propellant containing CL‐20/HMX cocrystal are inconsistent, but the tensile strength has improved compare with CMDB propellant containing CL‐20. These results suggest that CL‐20/HMX cocrystal is a potential material to solve the application problem of the safety performance and stability of the propellants containing CL‐20.

Measurement of laminar burning velocities of methane-air mixtures simultaneously at elevated pressures and elevated temperatures

Externally heated diverging channel method helps accurate and direct measurement of laminar burning velocities at elevated temperatures. In the present work, this method has been extended to higher pressures to evaluate the combined effect of pressure and temperature on the propagation of premixed methane-air flames. The experimental measurements of methane-air mixtures for different equivalence ratios are reported for a pressure range (1–5 atm), and elevated temperatures of 350–650 K. A non-monotonic behaviour for temperature exponent, α is obtained with a minimum value for slightly rich mixtures (ϕ = 1.1). This non-monotonic behaviour of α continues even at higher pressures (2–5 atm) as well. Predictions from three widely used chemical kinetic mechanisms (GRI-Mech 3.0, Aramco 2, FFCM-1) are employed to compare with present experiments. LBV determined using Aramco 2 mechanism matches very well with the present measurements at various elevated pressures and mixture conditions. The variation of pressure exponent, β follows a bell-shaped curve with maximum value for slightly rich mixtures (ϕ = 1.1) and a peculiar non-linear behaviour for very rich mixtures (ϕ ≥ 1.3). Based on the detailed analysis of experimental results, the temperature exponent (α) is proposed as a function of pressure, and pressure exponent (β) as a function of temperature at various equivalence ratios. A modified power-law correlation considering the α,β variations is proposed: Su=Su,oTuTu,oαo+α11-PuPu,oPuPu,oβo+β11-TuTu,o. Analysis of the flame structure at high-pressure conditions indicates that the reaction layer thickness is reduced with an increase in pressure. A decrease in mixture thermal diffusivity with pressure contributes to a reduction in laminar burning velocity at elevated pressures.

Effect of Long-Chain Bonding Agent on the Combustion of Composite Propellant and Modification of Combustion Performance Using Nano Additives

ABSTRACT Novel long-chain bonding agent MST was synthesised and introduced into the bonding agent matrix in order to enhance the mechanical properties of composite propellant by improving the interfacial interactions between the bonding agent and solid particles, in order to withstand stresses produced due to combustion loading conditions, changes in environmental condition, transportation and handling without effecting on the ballistic performance. In this work, the replacement of the long-chain MST bonding agent instead of the most famous reference MAPO bonding agent has improved the mechanical properties especially strain value corresponding to stress value which doubling the maximum strain value with an acceptable value of maximum stress with a good value with Young’s modulus in propellant formulations. Different compositions of composite propellant were carried, in order to measure the linear burning rate and to study the effect of the replacing MST bonding agent instead of tradition bonding agent MAPO. Due to the presence of a bonding agent, the burning process of the composite propellant should become more regular and stable burning but it reduces slightly the burning rate as in formulation F2 in which the pressure exponent (n) value reached .067. It should be modifying the reduction in burning rate due to the presence of MST in order to achieve promising burning properties. By using nano-aluminum it was secured improving performance and achieved a high burning rate of the propellant formulations based on MST bonding agent as well as the composite propellant formulations based on MAPO bonding agent. And by using nano-copper chromite the values of the burning rate of composite propellant formulations became greater than those values of formulations based on nano-aluminum with the same weight ratio and particle size, due to the nature of copper chromite and its effect on the binder and the ammonium perchlorate.