Burning Rate Research Articles

Eco‐friendly chemically crosslinked solid composite propellants via catalyst‐free azide‐alkyne cycloaddition

AbstractWe have innovatively formulated solid propellants by employing a catalyst‐free azide‐alkyne cycloaddition approach, steering away from the conventional urethane curing system reliant on moisture‐sensitive isocyanate compounds. These conventional systems exhibits poor compatibility with the eco‐friendly ionic oxidizers. Azide polymers, including polycaprolactone ether (PCE), polycaprolactone (PCL), and polyethylene glycol (PEG) were incorporated, with their terminal hydroxyl groups strategically modified with azides. Additionally, glycidyl azide polymer (GAP), characterized by an abundance of azides in its side chains, was introduced. For polybutadiene‐based solid propellants, a departure from the norm was pursued. We employed polybutadiene (PB) terminated with electron‐deficient alkynes(propiolate), synthesized through a urethane reaction involving an unsymmetric divalent chain‐linker containing both isocyanate and propiolate functionalities with hydroxyl‐terminated polybutadiene (HTPB). This approach diverged from the common practice of modifying other polymers with azides at the terminal. To ensure the attainment of optical mechanical properties in azide‐terminated polymer‐based solid propellants, trivalent propiolate curatives were judiciously combined with divalent propiolate curatives in an appropriate blend ratio. A meticulously synthesized series of polymeric bonding agents, designed to establish chemical links between solid oxidizers and polymer binder, revealed the idenfication of exceptional bonding agents. These agents played a pivotal role in delivering outstanding mechanical properties in solid propellants based on ammonium perchlorate (AP) and nitramine‐typed oxidizers. GAP‐based solid propellants were meticulously prepared, incorporating both urethane moieties at the terminal and triazole moieties at the side chains. Trivalent azide‐terminal curatives were introduced for crosslinking PB terminated with propiolates. Generally, triazole‐curing system resulted in solid propellants exhibiting notably higher burning rates compared to those crosslinked through urethanes. In summary, this research presents a sophisticated approach to the formulation of solid propellants, emphasizing a departure from conventional systems, strategic polymer modifications, and the meticulous synthesis of bonding agents to achieve superior mechanical properties and burning rates.

The 2024 BBN baryon abundance update

We revisit the state of the light element abundances from big bang nucleosynthesis in early 2024 with particular focus on the derived baryon abundance. We find that the largest differences between the final baryon abundances are typically driven by the assumed Deuterium burning rates, characterized in this work by the underlying code. The rates from theoretical ab-initio calculations favor smaller baryon abundances, while experimentally-determined rates prefer higher abundances. Through robust marginalization over a wide range of nuclear rates, the recently released PRyMordial code allows for a conservative estimate of the baryon abundance at Ω bh 2 = 0.02218 ± 0.00055 (using PDG-recommended light element abundances) in ΛCDM and Ω bh 2 = 0.02196 ± 0.00063 when additional ultra-relativistic relics are considered (ΛCDM + N eff). These additional relics themselves are constrained to ΔN eff = -0.10 ± 0.21 by light element abundances alone.

Cascade computational model for prediction impact of transient depth change on combustion parameters of certain timber species under continuous heating rate

The purpose of this research is to examine the effects of depth variation and exposure duration on the combustion characterization of the Maple wood species (Acer platanoides L.) and Walnut (Juglans regia L.) according to ISO 5660–1 in case of exposing the specimens to a constant heating rate 50 kWm−2. The delivered experimental data by cone calorimeter apparatus is used to train, test, and validate the optimized cascade forward artificial neural network with topology 2–8–8–12–2. This structure is simulated to predict the target parameters: the heat release rate (HRR) and the mass burning rate (MBR). With real systems, it is possible to achieve a reasonable performance and the closest approximations for the cascade model. The experimental combustion parameters: time of flame out, average specific mass burning rate, total heat release, maximum average rate of heat emission, and fire growth index are considered to make a systematic analysis and assessment with change depth. Three regions are considered for investigation of output target curves, thermally thin (d ≤ 1.1 cm), thermally medium (1.1 cm < d< 1.5 cm), thermally thick (d≥ 1.5cm). The findings demonstrate that independent of exposure period, an increase in depth change causes a sizable reduction in the HRR and MBR. Beyond 1.5 cm of depth in thermally thick regions, there is no discernible effect of time instant on changes in target parameters. In contrast, HRR and MBR gradients across depth in thermally thin regions are striking.

Pengaruh Metode Pengarangan dan Ukuran Partikel Terhadap Kualitas Briket Cangkang Kelapa Sawit

One renewable energy source is biomass. Biomass is organic matter that generally comes from plants. Bio charcoal briquettes are solid fuels and come from the remnants of biomass that are charred. This study aims to examine the effect of authoring method and particle size on briquette quality. This study used the method of torrefaction authoring at temperatures of 2000C, 3000C and manual authoring. The particle size of charcoal is varied by 20 and 40 mesh. The parameters tested are moisture content, calorific value, bound carbon content, vapor content, ash content, density and combustion rate. The results showed that the type of torrefaction authoring was able to improve the quality of briquettes through increasing calorific value, bound carbon content and reducing water content and evaporating substances and the production of liquid smoke products by 48.5%. The quality of briquettes from the temperature of 3000C charcoal size 20 mesh briquettes meets the quality I of SNI 01-6235-2000 with calorific values and water content of 6841 Cal/g, 3.52% respectively and the content of bound carbon, vaporizers, ash, density and combustion rate are 50.06%, 37.59%, 8.13%, 1.71 g/cm3, 0.076 g/min.

THE EFFECTS OF NANOPARTICLES AS ADDITIVES TO THE FUEL CHARACTERISTICS PROPERTIES OF THE PALM METHYL ESTER BIODIESEL (PMEB) OIL

This paper presents the effect of nanoparticles as additives on PMEB’s fuel properties. There are three types of nano additives used: Aluminium oxide (Al2 O3), titanium dioxide (TiO2 ), and silicon dioxide (SiO2). In addition, the proportions of each nano additive are 50, 100, and 150 ppm and were tested on 20% of PMEB fuel. Several fuel properties tests, density, viscosity, SEM, XRD, and bomb-calorimeter, were investigated. This study found viscosity and density properties on the B20SiO2 150 nano blend with maximum values of 3.7792 mm2/s and 820.36 kg/m3 compared to the readings on B20, respectively. While in terms of heating value, the maximum value when compared to the B20 fuel is B20Al2 O3 150 (45122 J/g). Furthermore, the properties analysis testing revealed the interrelation of nanoparticle additives enriched B20 fuel properties as it is more effective in improving the biodiesel fuel blend characteristics and reducing the catastrophic gas emissions due to their combustion rate.

An Optical Study on the Ignition and Flame Development Initiated by a Combination of Passive Pre-Chamber and Spark Ignition

ABSTRACT Pre-chamber jet ignition combined with spark ignition in main chamber has advantages in adjusting the combustion phase and improving the burning rate for spark ignition engines. In this study, optical experiments based on a constant volume combustion chamber and high-speed schlieren imaging were conducted to investigate the ignition and flame development under the combined ignition mode with a passive pre-chamber and spark plug using methane fuel. Two modes of flame development were observed with different ignition time interval of pre-chamber ignition and spark ignition (Δt ign). At relatively short Δt ign, the “jet-disturbed flame” mode occurs with a three-stage combustion process: laminar flame; flame acceleration by jet-flame interaction and re-ignition at the jet root; flame deceleration. The maximum global flame speed can be increased from 2 m/s to 9 m/s under λ = 1 and from 1 m/s to 5.5 m/s under λ = 1.3. The ignition delay is relatively short and the heat release shows a slow and multi-stage feature. Moreover, the ignition delay and combustion duration in main chamber are relatively not sensitive to the variation of nozzle diameter. As the spark ignition becomes later (longer Δt ign), the “spark-initiated turbulent flame” mode occurs. In this mode, a rapidly developing turbulent flame is initiated by the spark plug, with a global flame speed up to 16 ~ 18 m/s under λ = 1 and 6 ~ 11 m/s under λ = 1.3. Compared with pre-chamber ignition, a shorter combustion duration is obtained at certain Δt ign and misfire can be avoided because of the synergy of the combined ignition mode.

IMPACTS of SUPERSONIC and SUBSONIC AMMUNITION on GUNSHOT RESIDUE DISTRIBUTION

In incidents where firearms are involved, the determination of the firing distance is one of the basic steps of the analysis aimed at determining the origin of the incident with Forensic Shot Analysis studies. Shot residues consist of partially burned and unburnt powder grains, gunpowder gas, capsule residues and inorganic and organic residues. As a result of determining the presence and density of shot residues on the target, the distance from which the shot was fired can be determined. The pattern and density of shot residues exhibit a direct correlation with the specifications of firearms and ammunition. The intended use and traits of the weapon affect the properties of the ammunition. An instance of specialised ammunition is subsonic cartridges which have lower powder burn rates and amounts compared to supersonic cartridges. To ensure accurate gunshot residue analysis, gunshot residue density and pattern from reference test-fires are necessary. The key factors affecting the GSR analysis are the type of weapon and ammunition used during test-fires, which should closely match those used in the incident. Any variation in these variables can reduce the precision of the residue analysis. In the study, an independent T-test was applied to determine whether there is a significant difference between the gunshot residue density on the target during test firing of 9×19mm diameter and type Supersonic and Subsonic cartridges with semi-automatic pistols at distances of 0cm, 15cm, 30cm, 60cm and 100cm. It was determined that a significant difference existed between supersonic and subsonic cartridges in the density and patterns of gunshot residue on the target resulting from shots fired at the mentioned distances.

Effects of Different Initial Conditions on Combustion Process of Ammonium Dinitramide-Based Energetic Propellant in Straight Nozzle

As a new type of green propellant, ammonium dinitramide (ADN)-based energetic propellants have wide application value and development potential in the field of space propulsion. This paper delves into the intricate impact of varying initial temperatures, pressures, and propellant component ratios on critical parameters, including temperature, combustion rate, and heat release, in the straight nozzle of an ADN-based propellant. The findings indicate that an elevation in both initial temperature and ADN ratio expedites the thermal decomposition rate of ADN, thereby elevating the average temperature in the nozzle. However, the elevation in initial temperature has a negative effect on the overall rise amplitude of average temperature. Furthermore, the initial pressure setting is crucial in determining whether the oxidation reaction of the fuel CH3OH occurs in ADN propellants. When the initial pressure is greater than 10 atm, CH3OH is completely consumed, and the final average temperature is about 2650 K, which increases by 558.89% compared with that at 1 atm. Our work aims to provide theoretical guidance and practical optimization strategies for enhancing propellant performance and optimizing thruster structure design.

VOF based model of numerical simulation for single aluminum droplet evaporation and combustion

ABSTRACT This study investigates the combustion of a single aluminum droplet in a high-temperature convective setting, focusing on the interplay between the environment and droplet evaporation combustion. Using the VOF numerical method, a two-dimensional multiphase flow combustion model for micron-sized aluminum droplets is developed. Experimental validation compares predicted droplet diameter with experimental data. The combustion behavior of aluminum droplets in high-temperature convective environments is analyzed, emphasizing gas-phase combustion during stable stages. Parametric variations in flow velocity and oxygen concentration reveal the formation of vortices around the droplet, influencing aluminum vapor accumulation and evaporation rates. Combustion primarily occurs at the droplet’s windward side, with reaction rates decreasing downstream. Increasing gas velocity from 1.5 m/s to 3 m/s thins the aluminum vapor concentration boundary layer, boosting combustion rates by 35%. Elevating oxygen concentration from 20% to 50% brings the flame closer to the droplet, accelerating combustion rates by 2.7 times, suggesting oxygen concentration’s role in reaction acceleration and combustion duration reduction. This research offers insights for simulating aluminum droplets in propellant applications.

Experimental study on the flame merging and temperature profile produced by two pool fires beneath the curved ceiling

Compared to single-source fires in tunnels, double-source fires may exhibit more intricate flame merging behavior and higher flame burning rates due to their interaction, thereby escalating the risk of fire propagation within the tunnel. In this investigation, a 1:10 scale model of a horseshoe-shaped tunnel test site was deployed to conduct experiments on lateral double-source fires, scrutinizing flame merging behavior, probability prediction models, and temperature characteristics of tunnel ceiling smoke gas by varying the oil pool size and double-source spacing. Findings from the study suggest that flame merging behavior within the tunnel is contingent upon double-source spacing and heat release rate (HRR), manifesting in three distinct forms: complete merging, intermittent merging, and complete separation. Through the introduction of non-dimensional heat release rate and non-dimensional fire source spacing, a piecewise function has been devised to forecast the probability of flame merging for both fire types. Furthermore, a predictive model for the maximum temperature rise along the longitudinal centerline of a horseshoe tunnel was formulated, drawing from established theoretical frameworks.

Numerical investigation of CH4/H2/air micro-mixing combustion flow in a micro gas turbine combustor with different head-end structures

In order to investigate the premixed combustion characteristics of CH4/H2/air in a micro-mixing combustor, the effects of different micro-mixing head-ends (HE1, HE2, HE3) and hydrogen mixing ratios on the temperature distribution, heat transfer process, emission characteristic, flames shape are analyzed. The results show that compared with swirl head-end combustion, the micro-mixing combustion performance is better. Among the three head-ends, HE3 has the best combustion characteristics and stable flames. The temperature distribution in the high-temperature zone is uniform, and low-temperature zone is concentrated near the jet, which can suppress the flashback. The velocity and temperature gradient near the central axis of jet streams show a strong synergistic effect. The flames are plume shaped and flames stability is mainly influenced by the H2 combustion process. Increasing the jet diameter, decreasing the jet spacing and increasing the hydrogen mixing ratio all contribute to the flames stability, but these three methods can stabilize the flames by affecting fluid Reynolds number, interaction between small flames and combustion rate, respectively. Moreover, small jet diameter and high hydrogen mixing ratio can reduce OTDF, which contributes to improve outlet temperature uniformity.

Characteristics of hydrogen enrichment on RNG combustion under various engine speeds in a retrofitted gas engine

Renewable natural gas (RNG) is attractive for energy policy goals in the world. A regional system is designed to explore RNG combustion for power generation in localities. Generally, 50 % methane (CH4) and 50 % carbon dioxide (CO2) in volume are utilized to represent RNG for investigations. However, CO2 reduces the burning rate and narrows the flammability limits, thus decreasing the engine thermal efficiency. Therefore, how to increase the thermal efficiency of RNG combustion through adding H2 or changing engine speed is the main task here. This study investigates a port fuel injection (PFI) engine fueled with hydrogen (H2) blended into the RNG. In order to obtain the higher efficiency, the effect of engine speed on combustion characteristics should be clarified as well as H2 influence demonstrated. Therefore, 1500, 2000 and 2500 revolutions per minute (rpm) of engine speed were tested. When H2 was added, the volume percentage changed from 5 % to 20 % by keeping the volume ratio of CH4 and CO2 at 1:1. Finally, combustion characteristics of CH4, CH4+CO2 and CH4+CO2+H2 were compared and discussed. Results showed that compared with H2, engine speed could only increase the efficiency slightly. “Arched” and “fish-hook” curves are fitted respectively to select the optimal working region. Through cylinder pressure analysis, engine speed could enlarge the Pmax only at some certain but increase coefficient of variation (COV) gradually. However, H2 increases Pmax but decreases COV significantly. Moreover, NOx decreases gradually with engine speed owing to the short reaction duration in combustion. However, NOx increases again with higher H2 concentration. Among the current conditions, for higher efficiency and lower NOx, three conditions are finally selected to be recommended for running.

Atomized Mg-Li spherical alloys: A new strategy for promoting reactivity of Mg

In this study, to improve the reactivity Mg, which is a frequently used fuel, Li was incorporated into it. Mg-Li alloys with 3 and 5 wt% Li, prepared via centrifugal atomization, displayed a high degree of sphericity and consisted of αMg. Thermal behaviors indicated that the initiation oxidization temperature of Mg-Li powders was ∼170–200°C lower than that of pure Mg, owing to the lower melting point of soluble Li than that of Mg. Li passes through oxide shells and initiates the oxidization of metals in the core. The apparent activation energy of Mg decreased significantly from ∼361.2 kJ/mol to ∼141.1 kJ/mol with the incorporation of Li. For combustion in air, the Li content should be 5 wt% to achieve increased combustion intensity compared to Mg powders. When Mg-Li alloys and Mg powders were composited with polytetrafluorethylene (PTFE) serving as an oxidizer, the burn rates of MgLi3/PTFE and MgLi5/PTFE were ∼7.1 and 12.1 m/s, respectively, which were ∼1.8 and 6.8 m/s higher than that of Mg/PTFE. The flame temperature of Mg-Li/PTFE (∼1537–1552℃) of 3–5 µm was slightly lower than that of Mg/PTFE (∼1637℃). Therefore, the prepared Mg-Li alloys are promising candidates for use as fuels for energetic materials.

Flame structure and stability for gradient magnetic field enhanced non-premixed combustion of highly diluted methane with nitrogen

Efficient utilization of low calorific value fuels is challenging due to their limited burning rates and stability. This study explored the use of upward-increasing magnetic fields as a novel approach to enhance flame stability in such conditions, focusing on non-premixed highly diluted methane flames with nitrogen. Employing a vertical burner, magnetic intensities were varied to observe their impact on laminar jet diffusion flames. This research revealed that the gradient magnetic fields significantly modify flame characteristics. At lower magnetic intensities, the influence on flame structure, temperature, and stability was minimal. However, as magnetic intensity increased, notable changes in flame features such as height, shape, and thermal distribution were observed, suggesting a threshold intensity beyond which the magnetic influence becomes pronounced. The research further demonstrated that gradient magnetic fields could enhance the blow-out concentration limit, indicating an effective strategy for managing combustion in diluted fuels. The findings provide valuable insights into magnetic fields' role as a control mechanism, offering potential advancements in combustion technology and contributing to the broader pursuit of energy efficiency and reduced emissions in industrial applications.

In situ synchrotron X-ray diffraction study of synthesis reactions in mechanically activated Ti + Al powder mixture under linear heating conditions

In the present work, we studied the features of phase formation in mechanically activated Ti + Al powder mixture at various heating rates for the first time. The study was carried out using high-resolution diffractometry method which made it possible to study the processes of phase formation in situ at any stage of heating. It was established that ignition of the activated mixture can be initiated in the solid phase with an extremely low content of reaction products formed at the preheating stage. An increase in the heating rate leads to a decrease in the average burning rate and an increase in the ignition temperature. At high heating rates, the ignition is initiated in the presence of a liquid phase when the ignition temperatures are close to the melting temperature of aluminum. In this case, the content of reaction products formed during preheating stage is relatively high. It was found that the all main compounds presented in the equilibrium diagram of Ti-Al system are synthesized in parallel. The content of phases in the reaction products depends on the heating rate.

Innovative coating of cotton textile fabrics for integrating outstanding flame hazard safety, UV protection, tensile strength strengthening and antibacterial properties

A rational green synthesis method was developed to produce sustainable nanocoatings for cotton fabrics that are flame retardant, strengthened, antibacterial, and UV protective. The nanocoatings were created using silica nanoparticles with an average size of 73.2 nm derived from rice husk (RH-SNP). These nanoparticles were adorned with ZnONPs with an average size of 7.6 nm, which were reduced and capped with molokhia extract made from molokhia stems by-products. The ultimate nanocomposite was evenly distributed in a chitosan solution using ultrasonication. The mass ratio of RH-SNP in the nanocoating was adjusted and fine-tuned for optimization. The coated cotton fabrics were analyzed using spectroscopic and microscopic techniques. The flammability of cotton fabrics treated with sustainable coatings was assessed. The coated fabrics exhibited significantly greater flame retardancy, achieving a zero burning rate compared to 110 mm/min for the untreated one. The enhanced flame-retardant properties were a result of the combined flame-retardant effects of RH-SNP and molokhia stem extract, along with decorated ZnONPs, which created a more robust protective char layer. The coated cotton's antibacterial characteristics showed significant inhibition of bacterial growth, resulting in a 10 mm distinct inhibition zone, while pure cotton had no inhibition zone. Additionally, the coated cotton fabrics had exceptional UV shielding properties with a UPF rating of 167.8, which was more than fourth the value of the uncoated fabric. The tensile strength and elongation of the cotton fabrics were enhanced after applying a sustainable nanocoating, indicating a beneficial effect on tensile strength. Furthermore, the coated fabrics exhibited exceptional durability characteristics.

Ignition performance and mechanism of Ti/CuFe2O4 composites with high microwave sensitivity

The microwave ignition holds potential in the ignition of weapons due to its simple structure, non-contact property, and simultaneous ignitions of large area. However, the long ignition delay time of the current ignition agents cannot meet the microwave weaponry advancements. To address the issues, a microwave sensitive oxide-CuFe2O4 (CUFO) which was firstly discovered to be easily ignited by microwaves compared many ferrites, was coupled with Ti nanoparticles (n-Ti) to form Ti/CUFO microwave ignition agents by electrostatic spray granulation. The characterization of microwave ignition, volumetric combustion, burning rate and DSC were used to determine its ignition delay time and the energy release properties. It indicates that the microwave sensitivity, maximum peak pressure and pressure pressurization rate of Ti/CUFO first increases and then decreases with the promoting content of n-Ti. The Ti/CUFO at Φ = 3.5 exhibits the lowest ignition delay time by 79.24 ms compared to the 98.7 ms of n-Ti, meanwhile, its maximum peak pressure and pressurization rate reach the highest by 338.54 kPa and 8.57 kPa/ms, respectively. The DSC results indicate that Ti/CUFO exhibits much lower reaction peak temperature by 320–335 °C compared to 488 °C of n-Ti, which suggests Ti-CUFO reaction maybe much easier be activated. The dielectric loss of n-Ti and CUFO under strong electric field transfer the energy of microwaves to heat, reaching to its reaction temperature. The XPS and XRD results of CUFO after microwave radiation disclosing the crystal transition, formation of divalent iron and oxygen vacancies, as well as the released bright light under microwave radiation, suggest the thermal breakdown mechanism of CUFO. When Ti/CUFO exposes into microwaves, CUFO generates oxygen vacancies due to heat loss and n-Ti is dielectric heated, followed by the generated oxygen reacting with n-Ti, improving the combustion performance of n-Ti. This result provides new insight for the designing of microwave ignition.

Investigation of differential diffusion in lean, premixed, hydrogen-enriched swirl flames

Hydrogen combustion is a promising alternative to fossil fuel combustion in an effort to reduce our carbon footprint. However, hydrogen combustion is prone to thermodiffusive instabilities largely dependent on differential diffusion, a phenomenon that can lead to higher probabilities of flashback in industrial burners, given hydrogen’s high reactivity and diffusivity. This paper evaluates low-swirl flames of methane and air enriched with hydrogen to highlight the onset of differential diffusion. Testing was conducted in a fully controllable swirl burner, where bulk velocity Uav = 13 m/s and swirl number S = 0.6 were kept constant for each hydrogen–methane blend to isolate increases in flame surface area from increases in turbulence intensity. Furthermore, each fuel blend of hydrogen and methane is evaluated at the same laminar flame speed of SLo = 0.267 m/s to isolate flame stretch effects on the turbulent burning rate. Combined hydroxyl (OH) PLIF and stereoscopic PIV at the National Research Council of Canada were used to analyze the OH fluorescence in a 2D-3C velocity field for each flame condition. High-speed PIV at McGill University was used to resolve local flame phenomena, such as local flame displacement velocity and flame stretch rate. Using these techniques, it can be observed that the flame displaces axially in response to turbulent flame speed while exhibiting increases in flamefront wrinkling. This increased corrugation due to flame stretch is highlighted in the PDFs of local curvature and κSf and is further evidenced by a shift towards positive curvatures (κ> 0) for increasing H2 volume fraction. This trend suggests that there is a strong correlation with increases in turbulent burning rate and positive curvature as a result of differential diffusion, but it is not necessarily a control mechanism of the most forward propagating points proposed by the theory of leading points.

A numerical determination of complex solid gun propellant burn rates through closed bomb simulation

AbstractClosed bomb testing is a prominent means of characterizing the combustion behavior of solid gun propellants. This sub‐scale test allows the propellant to burn in a constant volume environment, where the resulting pressure‐time trace can be collected via a pressure transducer. Historically, numerical procedures have been developed to determine the burn rates of the gun propellants from these pressure‐time traces; however, no standardized procedure exists to determine the burn rates of grains with variable surface thermochemistry and ignition criteria. To address this capability gap, a non‐linearly constrained, multivariate optimization algorithm has been developed to decouple propellant grain surfaces and determine surface‐specific burn rates [1]. In this work, the optimization algorithm as well as the legacy Excel‐based Closed Bomb (XLCB) program [2] were used to determine the burn rates of homogeneous, deterred, and layered propellants from experimental data. Closed bomb simulations using these burn rates were then conducted with the two‐phase, multidimensional, interior ballistics solver, iBallistix [3]. The maximum mean error between the simulated and experimental pressure‐time curves was 6.8 % for the optimization algorithm and 23.8 % for XLCB, showing a marked improvement with our new approach. Furthermore, the approach discussed herein improves burn rate predictions of complex solid gun propellants when compared with legacy closed bomb data reduction analysis programs.

Hydroxyl‐terminated polybutadiene(HTPB) propellants cross‐linked by dimer acid diisocyanate (DDI): Cross‐linking network and properties

AbstractConsidering the high toxicity of toluene diisocyanate (TDI) and the low reactivity of isophorone diisocyanate (IPDI), a low‐toxicity curing agent, dimer acid diisocyanate (DDI), was used to cross‐link HTPB elastomers and propellants. The unique long‐chain structure of DDI not only ensures the elastic modulus and tensile strength of the elastomer, but also improves the flexibility to some extent. The long flexible chains promote the segment movement, which is very important for the formation of hydrogen bonds between segments. The chemical cross‐linking network and hydrogen bonding association play a significant role in the mechanical properties of the HTPB/DDI system. The relationship between the mole ratio of ‐NCO to ‐OH (R‐value) and the mechanical properties of HTPB/DDI elastomers were also investigated. In the range of R‐value from 0.85 to 1.2, the elastic modulus and tensile strength first increase and then decrease, and the elongation at break first decreases and then increases. Under the same curing conditions, the elastic modulus and tensile strength of the HTPB/DDI propellant are similar to the HTPB/TDI propellant. For the HTPB/AP/Al propellants and HTPB/AP/RDX/Al propellants, the HTPB/DDI system has lower burning rates in the range of 5–19 MPa than the HTPB/TDI system and HTPB/IPDI system. The application of DDI can reduce the burning rates of the propellant without adding any burning rate modifiers. It is considered that DDI can replace TDI and IPDI as a new curing agent with low toxicity and moderate reactivity for HTPB systems.