Burning Rate Research Articles

Investigating the reaction mechanism of zirconium as a fuel in reactive multilayer films via multimodal analysis

In this report, we examine the intricate details of the mechanism driving Zr/CuO thermite system, shedding new light on the exceptional reactivity of Zr fuel with oxygen. Magnetron-sputtered Zr/CuO reactive multilayers were deposited, and thermo-physical techniques were employed to characterize the progression of the chemical reaction upon heating. Unlike commonly used Al fuel, Zr/CuO exhibited 100% heat release below 500 °C, contrasting with the ∼5% observed for conventional Al/CuO system. This enhanced reactivity at low temperature is attributed to the rapid oxygen consumption behavior of Zr, due to the poor barrier of ZrOx to oxygen diffusion. The oxidizing behavior of Zr was quantitatively analyzed using electron microscopy and spectroscopy. Our observations reveal a three-step process of Zr oxidation facilitated by a rapid reduction of CuO to metallic Cu accompanied by the formation of an intermediate Cu2O phase: (i) a preliminary low-temperature mass transport initiating at 275 °C, (ii) partial Zr oxidation forming ZrO2 and oxygen enriched Zr and finally (iii) complete conversion to zirconia at 450 °C. Finally, Zr/CuO reactive thin-films demonstrated a very high reactivity with an ignition delay time of 0.04 ± 0.016 ms and a burn rate of 3.5 m.s−1, in stark contrast to the same volume of Al/CuO, which failed to ignite and burn altogether. This study not only deepens our comprehension of Zr-based thermite system but also underscores its potential for diverse applications in energetic materials.

Effect of Boric Acid on Electronically Controlled Solid Propellants

Electrically controlled solid propellants (ECSPs) were modified with boric acid (HB). HB affects ECSPs’ combustion performance by changing the volume conductivity. Increasing the HB content can enhance the compressive properties by further increasing the crosslink density of the ECSPs. Based on the calculation results of NASA’s Chemical Equilibrium with Applications program, HB has no apparent effect on the specific impulse and adiabatic flame temperature of the propellant. The volume conductivity of the ECSPs were measured using a three-electrode system. After the addition of HB, the volume conductivity of the ECSPs decreased. In the process of thermal decomposition, the addition of HB can improve the thermal stability of ECSPs as a whole, although this effect is small. The effects of HB on the combustion rate and minimum theoretical ignition voltage of hydroxyammonium nitrate (HAN)-based propellants were studied at 0.1 MPa. The results demonstrate that the combustion rate of HAN-based propellants increases with increasing voltage, and that this characteristic is not affected by HB. However, the combustion rate decreases with increasing HB content, and the minimum theoretical ignition voltage increases accordingly.

New Fire-Retardant Open-Cell Composite Polyurethane Foams Based on Triphenyl Phosphate and Natural Nanoscale Additives.

Despite the mechanical and physical properties of polyurethane foams (PUF), their application is still hindered by high inflammability. The elaboration of effective, low-cost, and environmentally friendly fire retardants remains a pressing issue that must be addressed. This work aims to show the feasibility of the successful application of natural nanomaterials, such as halloysite nanotubes and nanocellulose, as promising additives to the commercial halogen-free, fire-retardant triphenyl phosphate (TPP) to enhance the flame retardance of open-cell polyurethane foams. The nanocomposite foams were synthesized by in situ polymerization. Investigation of the mechanical properties of the nanocomposite PUF revealed that the nanoscale additives led to a notable decrease in the foam's compressibility. The obtained results of the flammability tests clearly indicate that there is a prominent synergetic effect between the fire-retardant and the natural nanoscale additives. The nanocomposite foams containing a mixture of TPP (10 and 20 parts per hundred polyol by weight) and either 10 wt.% of nanocellulose or 20 wt.% of halloysite demonstrated the lowest burning rate without dripping and were rated as HB materials according to UL 94 classification.

Ignition and energy release performance of dual‐oxidant Al/MnO2/CuO ternary thermites under rapid heating conditions

AbstractTailoring the energy release performance of the thermites is crucial for their application in various fields. In this article, dual‐oxidant Al/MnO2/CuO ternary thermites with varying compositions were prepared and systematically evaluated. The ignition delay time, heat of reaction, self‐sustained burning rate, and pressure performance of the thermites were evaluated. As the Al/CuO content increased, the ignition delay time and heat of reaction decreased, while the reaction efficiency, burning rate, pressure peak, and pressurization rate increased. Furthermore, the synergistic addition of the MnO2 and CuO led to enhanced relative flame intensity and maximum flame temperature in the ternary thermite. Our work demonstrates an effective strategy for regulating the energy performance of the thermites by co‐adding of metal oxides. This approach opens avenues for tailoring thermite properties to meet the diverse requirements of various applications.

Prediction and comparison of burning rate of n-heptane pool fire in open space based on BPNN and XGBoost

Pool fires pose a threat to the safety and environmental protection of industrial production. The burning rate is one of the most important burning parameters that determines the behavior of pool fires. Back Propagation Neural Network (BPNN) and Extreme Gradient Boosting Tree (XGBoost) were used to predict the burning rate of n-heptane pool fire with the effect of fuel depth, ullage depth, area and perimeter of pool pans, atmospheric pressure and speed of cross air flow in open spaces. The results show that after optimizing the model parameters using RandomizedSearchCV, both models yielded higher precision evaluation results. Compared with BPNN, the proposed XGBoost model demonstrates better prediction performance, achieving a R2 of 0.9744, RMSE of 4.1068, and MAE of 2.5036 in test set. The impact of different hyperparameters and data normalization on model prediction accuracy was explored. The impact of fuel depth, ullage depth, atmospheric pressure, speed of cross air flow, area, and perimeter on burning rate was determined using SHapley Additive exPlanations (SHAP) sensitivity analysis. This analysis aids in conducting risk analysis for pool fires, and offers early warning and feasible reference for fire safety hazards.

Thermal recombination strategy designed R-CN as active shell to improve catalyst activity

A new recombinant CN material (R-CN) was prepared with g-C3N4 as precursor by hydrothermal method combined with thermal recombination method, which has 2D ultra-thin structure, nanoscale folds, graphite-like texture and some pores, and has richer N and O elements than g-C3N4. R-CN can reduce high temperature decomposition peak of ammonium perchlorate (AP) to 356.06 oC, and its promoting effect is obviously better than that of g-C3N4. Based on specific structural composition and physicochemical properties of R-CN, a novel R-CN@MWO composite with core-shell was designed, which was applied to catalytic decomposition of AP and pressure enlarging effect during combustion process of cyclotrimethylenetrinitramine (RDX)+nitrocellulose (NC). With the introduction of R-CN@MWO, decomposition peak temperature and activation energy of AP are reduced by 104.67oC and 59.24 kJ mol−1, and peak pressure and pressurization rate of RDX+NC constant volume combustion test are increased by 11.33 and 118.54 times, respectively. Moreover, the combustion rate of R-CN@MWO-AP/HTPB propellant is 3.23 times that of AP/HTPB propellant. To sum up, R-CN as a coating layer can significantly enhance catalytic activity of MgWO4 for thermal decomposition of energetic materials.

Prediction of burn rate of ammonium perchlorate–hydroxyl-terminated polybutadiene composite solid propellant using supervised regression machine learning algorithms

Prediction of burn rate of ammonium perchlorate–hydroxyl-terminated polybutadiene composite solid propellant using supervised regression machine learning algorithms

Correction: Effects of intrinsic instabilities in the local burning rate of lean premixed hydrogen/air laminar flames

Correction: Effects of intrinsic instabilities in the local burning rate of lean premixed hydrogen/air laminar flames

Physical and chemical processes during nitriding of chromium ferrosilicon by filtration combustion

In this paper, the nitriding of chromium ferrosilicon is carried out in the combustion mode under the condition of natural nitrogen filtration. The authors studied the effect of the key parameters (pressure of gaseous nitrogen, diameter and dispersity of starting samples) on the maximum temperature and combustion of the starting powder mixture based on chromium ferrosilicon. The combustion synthesis of chromium ferrosilicon proceeds steadily in the stationary mode with formation of a macrohomogeneous nitrided composition which, according to the results of X-ray phase analysis, contains two nitride phases - chromium nitride and silicon nitride. Interaction of the initial powder with gaseous nitrogen in the filtration combustion mode proceeds by the following probable chemical reaction: 3CrSi2 + 3Si + 3FeSi2 + 11.5N2 = 3CrN + 5Si3N4 + 3Fe. Increasing the diameter of the starting samples slightly affects the amount of absorbed nitrogen and slows the propagation of the combustion wave front. An increase in the pressure of gaseous nitrogen increases the amount of absorbed nitrogen and the combustion rate. Increasing the dispersity of the starting powder increases the amount of absorbed nitrogen and the combustion rate. It was found that the combustion reaction is not possible with a dense initial sample. The maximum combustion temperature, depending on the nitriding conditions, varies between 2400 and 2650 °C and increases with increasing gaseous nitrogen pressure, diameter of the initial samples and dispersion of chromium ferrosilicon powder. It is possible to realise nitriding of chrome ferrosilicon in the combustion mode at the pressure of gaseous nitrogen not less than 3 MPa, diameter of initial samples not less than 3.5 cm and size of initial particles not more than 100 μm. Optimal parameters of nitriding are gaseous nitrogen pressure of 5 MPa, diameter of samples 5 cm, size of initial particles less than 100 μm and bulk density of samples (2.23 g/cm3).

A new-proposed triangular- prism flame radiation model of large-scale spilling fire to subsurface convection flow area

The usage of liquid fuel is commonly subjected to a spilling fire due to the accidental leakage. The flame radiation is the primary heat transfer mode in supporting the advancement of large-scale spilling fire. In this work, spilling fires are carried out based on a 6 m × 0.8 m × 0.1 m tray, and the spilling fire performance and flame radiation are examined. The instantaneous flame height and mass burning rate versus fire spread distance are examined. The radiation heat flux of large-scale spilling fire to subsurface flow area is obtained by dividing the flame configuration into a triangular-prism flame and a cuboid flame. The multi-cuboid flame equivalent-division method is proposed to estimate the radiation heat flux of leading triangular-prism flame, finding that the maximal 70 equivalent divisions are sufficiently accurate. The proportion of triangular-prism flame radiation to total heat flux reduces from 100 % to 50 % during spilling fire propagation. The triangular-prism flame radiation plays a dominant role in heat transfer to the subsurface flow area while the cuboid flame radiation plays a secondary role. The current research is of great significance for revealing heat transfer mechanism and predicting rate of spilling fire.

Effect of flame radiation on aluminium particle combustion time

This work proposes a numerical model to estimate the radiant heat feedback from the flame of a burning aluminium particle. The objective is to evaluate its role on the burning time. It rests on a detailed combustion simulation of a single particle coupled with a simple two-flux approximation for the radiant flux emitted from the oxide smoke. Radiated flux from the flame is found to be around 1 MW/m 2 for atmospheric pressures, going up to more than 5 MW/m 2 for higher pressures (30 bar). Parametric simulations show that aluminium size has a small effect while oxygen-rich atmospheres can double the radiated flux. Overall, the role of flame radiation on aluminium burning rate is calculated to lie roughly between 1 and 25%, depending on conditions. This is the first study that clearly evaluates the role of flame radiation on aluminium combustion ; in most configurations, this effect, however, remains limited.

Influence of hydrogen-assisted combustion in compression ignition engines fueled with fuel blends of pine oil and waste cooking oil biodiesel using toroidal combustion chamber

In this research study, fuel blends of pine oil and waste cooking oil biodiesel (P/WCO) were examined for combustion analysis, engine performance, and emission characteristics tests. Improved combustion and engine performance were achieved using a toroidal re-entrant combustion chamber (TCC) and hydrogen supply as a dual fuel. The combustion behavior of fuel blends and hydrogen fuel was examined by varying the engine load at a constant speed. The results revealed that significant reduction in the specific fuel consumption for rich pine oil. Thus, a slightly lesser energy share from the fuel blends and a higher energy share from the hydrogen fuel was required for the engine to maintain the same brake power. Lower viscosity, higher flash point, and presence of oxygen in the pine oil enhance the combustion rate and brake thermal efficiency. Furthermore, hydrogen induction in the engine improves the flame velocity. A lesser crevice volume in the TCC can trap the unburnt fuel which can further increase the combustion efficiency. Thus, rich pine oil with the support of hydrogen induction in TCC causes advanced ignition, improved combustion, and more heat release during the combustion. The investigation results revealed that hydrogen induction increases the heat release rate and peak pressure by 7.4% and 2.67%, respectively. Similarly, the maximum of 24.55% increase in BTE and 18.22% reduction in BSFC was observed due to a constant 10 lpm hydrogen induction. Furthermore, hydrogen fuel significantly reduces the emissions such as CO, HC, CO2, and smoke. However, more NOx was generated due to more heat release rate during combustion. Thus, pine oil and waste cooking oil biodiesel blends with the support of hydrogen induction in TCC improve the engine performance and mitigate the toxic pollutants and can be a suitable alternative to diesel fuel.

A model for the combustion behavior of AP/HTPB propellant containing ultrafine aluminum

AbstractNano‐aluminum, renowned for its remarkable efficacy in augmenting propulsion efficiency and regressive velocity, stands out as a compelling choice for incorporation into heterogeneous propellant compositions. Nevertheless, the considerable expense of this ultrafine aluminum variant, coupled with the inherent hazards associated with conducting propellant trials, may deter extensive allocation of resources and efforts towards the intricate processes of amalgamation, molding, and comprehensive analysis of the combustion characteristics of freshly devised propellant blends. To provide theoretical support for predicting the chemical properties of nano‐Al composite propellant, we establish a numerical framework to study the combustion characteristics under the working environment of a solid rocket motor. A new five‐step kinetic mechanism is developed in this model to describe the reaction process in the gas phase while accounting for heat conduction, radiative effects, and non‐planar moving surfaces. The comparison between our theoretical work and experimental results confirms that making no distinction among Al particle sizes below 3 μm is reasonable. Finally, the effects of nano‐Al on combustion, burning rate variation, and temperature sensitivity are analyzed in detail.

Molecular dynamic simulation on comprehensive performance of ferrocene-based burning rate catalysts in a solid propellent

To determine the compatibility and interaction between ferrocene (Fc) and other components in AP/HTPB/Fc-based BRCs propellant, molecular dynamics simulation (MD simulation) method was used to study the binding energy, cohesive energy density (CED), mean square displacement (MSD) and mechanical properties of mononuclear ferrocenyl compounds (ethyl ferrocene, butyl ferrocene and octyl ferrocene), dinuclear ferrocenyl compounds (2,2′-(ethylferrocene)propane, 2,2′-(butylferrocene)propane) propane and hydroxymethyl bis-ferrocenyl propane), ionic ferrocenyl compounds (three ionic ferrocenes with ferrocene methyl dimethyl ammonium as cation, perchlorate, nitrate and picrate as anions respectively) and cyclic ferrocenyl compounds (1-ferrocenylmethyl-2-ferrocenyl-3-methylbenzimidazolium, binuclear ferrocene bridged by bridged biphenylferrocene and dihydropyrazole).The binding energy results show that alkyl groups, polar groups (such as hydroxyl groups) and cyclic substituents can improve the interaction between Fc and AP/HTPB. Moreover, the electrostatic interaction between ionic ferrocene and AP is strong, but the van der Waals interaction between ionic ferrocene and HTPB is weak. The CED data show that the mixed models based on alkyl mononuclear ferrocene, catocene, cyclic ferrocene and ionic ferrocene all have high cohesive energy with good safety performance. The MSD results show that the order of anti-migration ability is cyclic ferrocene > binuclear alkyl ferrocene > mononuclear alkyl ferrocene > binuclear hydroxyl ferrocene > ionic ferrocene. Regarding to the value of mechanical parameters (K, G, E and K/G), the mixed model of AP/HTPB/ dihydropyrazole bridged binuclear ferrocene possess the best mechanical properties among the 12 models. Based on the comprehensive data, we conclude that dihydropyrazole bridged binuclear ferrocene is the most ideal ferrocene-based burning rate catalyst among 12 ferrocenes.

Experimental investigation on diesel engine performance, combustion, and emissions characteristics with Tucuma and Ungurahui biodiesel blends

The study conducted an experimental investigation of diesel engine performance, emissions, and combustion characteristics using Tucuma and Ungurahui biodiesel blends. Higher yield (greater than 99.4%), lower viscosity than diesel, and higher cetane number of these fuels have motivated a comprehensive investigation of the effect of these fuels on diesel engines. Four blends were tested in the engine by keeping diesel as the benchmarking fuel. The engine was operated at full load conditions, and the results were investigated with respect to brake power (BP). Results indicate that biodiesel blends showed similar combustion behaviour to that of diesel. Next to diesel, TB10 and UB10 showed better brake thermal efficiency (BTE) and lower brake-specific fuel consumption (BSFC). Higher peak pressures and heat release rates (HRR) are observed for the TB10 compared to the diesel operation. Moreover, prolonged combustion was observed for the four biodiesel blends during the diffusion and late combustion phasing. With the increase in BP, slightly higher HC emissions are observed for all the blends except for TB10 compared to diesel. Similarly, a slight increase in CO emissions is also observed for all the blends at higher BP. Higher acid values of both fuels are the likely cause of increased HC and CO emissions at higher BP. NOx emissions are slightly higher for both fuels, among these UB10 has shown lower NOx than other blends. The study concludes that TB10 has demonstrated better performance (near diesel) and combustion rates (better than diesel); however, emissions like CO and NOx are slightly higher than others. The study recommends blending TB10 and UB10 with the alcohols, ethers, and nanoparticles as they can reduce NOx and CO emissions.

Integrated porous self-sustaining combustion of inert pellets and reactive wood lamellae with additives: Dynamic co-production method for heat and hydrogen

Efficient hydrogen production from renewable wood is an important way to solve environmental pollution and optimize energy structure. However, the poor heat efficiency and high emission level of direct combustion limited wood industrial applications. In order to enhance the heat efficiency and hydrogen production of waste wood, a device combining inert porous pellets and reactive wood lamellae was proposed. The effects of additives and porous structure parameters on wood combustion characteristics were investigated under different operating conditions. The results demonstrated that the addition of adhesive improved the combustion temperature and hydrogen production time, and the hydrogen production time increased by 3.6 times after adding two layers of resin. With the increasing of water content, the hydrogen yield increased first and then decreased. Moreover, alkali metals in solution promoted syngas production, which had the lower heating value of up to 3.4 MJ/Nm3. Furthermore, the preheating temperature and inlet air velocity significantly increased the combustion temperature and rate, and achieved efficient combustion at the preheating temperature of 623 K and the air velocity of 4 cm/s. The results provided theoretical guidance for the efficient wood utilization and green hydrogen production.

In situ self-crosslinking binder system − enhances the mechanical performance gain of composite energetic materials

To improve the mechanical properties of microscale composite energetic materials, as well as to investigate their detonation performance, we used Toluene Diisocyanate (TDI) as a self-crosslinking curing agent based on an oil-in-water emulsion binder. We then prepared performance test samples with various microscale morphologies using the Direct Ink Writing (DIW) technique. We compared the mechanical properties of composite energetic materials, such as nanoindentation, quasi-static compression, and adhesion, and examined their infrared spectra, micromorphology, pore distribution, mechanical sensitivity, detonation performance, and combustion performance. The results indicated that with the in situ self-crosslinking binder system, the elastic modulus and hardness of the material were increased to 5.213 GPa and 0.100 GPa, respectively, which corresponds to an increase of approximately 638 % and 370 % compared to the original binder system. In the compressive strength test, the maximum stress increased by 104 %, and the maximum strain increased by 311 %, while the adhesion strength was enhanced by about 37.8 %. The infrared spectroscopy analysis demonstrated changes in the molecular structure due to in situ self-crosslinking. The improved surface morphology and more uniform pore size distribution also led to enhanced detonation performance and safety performance, with a detonation velocity increase of about 7.8 %, an increase in the critical detonation corner by 10°, a reduction in the critical detonation thickness by about 60.8 %, and a decrease in the critical detonation size to 0.3 × 0.3 mm. The impact sensitivity was reduced by 12.5 %, and the friction sensitivity was decreased by 30 %. Additionally, the material exhibited faster burn rates and larger flames. These findings provide significant scientific evidence for the regulation of mechanical properties and detonation performance of microscale composite energetic materials.

Characteristic Property of Combustion and Internal Ballistics of Triple-Based Propellant according to Particle Size of RDX

The important factors in the design of the gun propellant are impetus, flame temperature and pressure. In this paper, we considered a nitrocellulose based propellant composition that replaced sensitive NG(Nitroglycerin) with RDX(Cyclotrimethylenetrinitramine) and DEGDN(Diethylene glycol dinitrate) which high energy and low sensitivity. Particle size and content of RDX are the two main factors that affect the burning stability of RDX-based propellants. Among them, the characteristics of the propellant according to the particle size of RDX were confirmed. The relative combustion rate(R.Q., Relative Quickness) of the propellant changed according to the RDX particle size, and internal ballistics of properties of propellant were also varied. The particle size of RDX can be confirmed as a major factor in the combustion and internal ballistics characteristics of the propellant.

SEM/EDX and FTIR/ATR Behavior of Ammonium Perchlorate Under Accelerated Aging in a New Solid Rocket Motor Fuel Composition with Superior Explosive and Mechanical Performance

Abstract The oxidation potential of perchlorates is high, which makes this material suitable for fuels with high specific impulse. Perchlorates are characterized by a ClO4- moiety/anion in their molecular structure and are crystalline materials used in the formation of solid fuels. Ammonium perchlorate (AP) particle size and shape influence the manufacturing process of fuels and their burning rate. The physical and chemical processes that can occur in the natural degradation process of composite fuels are related to molecular reactions and diffusion phenomena governed by kinetic processes and can be accelerated by increasing the temperature. The paper presents studies carried out by scanning electron microscopy and infrared spectrometry on the behavior of ammonium perchlorate in the new composite material of solid rocket motor fuel under the effect of high temperature, in the range of 65-85οC, at regular time intervals. The self-initiation temperature was also determined, with a temperature rise rate controlled at 5ºC/minute. It is very likely that these accelerated aging studies will show the changes that occur in the stability, sensitivity, mechanical and functional properties of fuels during their lifetime.

Composite combustion behaviors of tubular flame and central jet flame in a reduced-diameter vortex combustor

The characteristics of the tubular flame and the flow field mixing mechanism in a reduced-diameter vortex combustor are investigated by varying the fuel flow rate and equivalence ratio through experiments and numerical simulations. Single-layer tubular flame and double-layer composite tubular flame are found in the combustor under the coupling effect of the cyclone and the central jet. The composite tubular flame will be formed when the air in the combustor is more abundant (Ф>1.00), and the center flame frequency is linearly and positively correlated with the Reynolds number of the central jet air. When the Reynolds number exceeds 2000, the double-layer composite flame tends to stabilize, with the center flame frequency higher than 9 Hz. The turbulence of the central jet air promotes the mixing of reactants by enhancing the recirculation near the nozzle, guaranteeing the central flame's stable combustion. Through analysis of the burn rate of methane at the outlet and the emission species of CO and CO2, it is evident that the double-layer flame achieves the methane burn rate exceeding 95 %, while also exhibiting lower CO emissions compared to the single-layer flame.