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This study aimed to quantitatively analyze the combustion process of a boron/ethanol nanofuel droplet through optical and spectroscopic observations. Boron nanoparticles were added to ethanol at concentrations of 0 %, 2 %, 4 %, and 6 % by weight. Experiments were conducted under atmospheric pressure, and the droplet diameter was controlled at 1.1 ± 0.1 mm. Results indicated that the combustion of the boron nanofuel droplet was similar to that of the 0 wt.% boron nanofuel droplets at the beginning of the experiment, but the former actively combusted as the experiment progressed. Mass ejections, such as puffing and microexplosions, were observed at the late stage of combustion. Spectroscopic measurements revealed that boron oxide emissions were predominant at the late stage of droplet combustion, and this emission trend varied with changes in the boron concentration. Photomultiplier tube data obtained through a bandpass filter of 550 nm demonstrated temporal intensity fluctuations during combustion. The overall signal intensity was enhanced by high boron concentrations. [ABSTRACT FROM AUTHOR]

This study deals with the design of modern environmentally friendly and non-toxic flame retardants based on expandable graphite 25 K + 180 (EG) modified by cellulose ethers (Lovose TS 20, Tylose MH 300, Klucel H) and nanocellulose (CNC) that are biocompatible with wood and, therefore, are a prerequisite for an effective surfactant for connecting EG to wood. The effectiveness of the formulations and surfactants was verified using a radiant heat source test. The cohesion of the coating to the wood surface and the cohesion of the expanded graphite layer were also assessed. The fire efficiency of the surfactants varied greatly. Still, in combination with EG, they were all able to provide sufficient protection—the total relative mass loss was, in all cases, in the range of 7.38–7.83% (for untreated wood it was 88.67 ± 1.33%), and the maximum relative burning rate decreased tenfold compared to untreated wood, i.e., to 0.04–0.05%·s−1. Good results were achieved using Klucel H + EG and CNC + EG formulations. Compared to Klucel H, CNC provides significantly better cohesion of the expanded layer, but its high price increases the cost of the fireproof coating. [ABSTRACT FROM AUTHOR]

This study investigates the feasibility of using an Al-Si eutectic alloy as a reactive fuel in energetic mixtures. Al-Si eutectic alloy powders were obtained from secondary resources and ground to a particle size of less than 100 μm. We examined these powders' burning characteristics and thermal properties compared to pure Al powder. Results showed that the burning rate of energetic mixtures containing Al-Si eutectic alloys was 1.5 to 2.0 mm/s higher than those with pure Al. Additionally, the activation energy of pure PTFE was reduced from 81.29 kJ/mol to 61.75 kJ/mol when the Al-Si alloy was added. The formation of oxides, carbides, and fluorides in the combustion products of Al-Si-based mixtures significantly influenced their thermodynamics. [ABSTRACT FROM AUTHOR]

Nanocellulose (CNC) seems to be a promising surfactant, which, together with expandable graphite (EG), forms the essence of an effective natural-based fire-retardant wood coating. In our research, the most suitable composition of the mixture was tested concerning good solubility, dispersion, and consistency. Favorable results were achieved with the formulation composed of a 4% CNC alkaline solution with 80 wt.% of the selected EG. Subsequently, six different types of EG were used to prepare these wood fire-retardant coatings. The effectiveness of treatments was verified using a test with a radiant heat source, where the test samples' relative weight loss, relative burning rate, and surface temperature during 600 s were evaluated. All prepared formulations can be characterized as more or less equally effective. However, the best results were obtained with the EG of GG 200–100 N, where the mass loss of the sample was 8.10 ± 1.24%. Very good results were also achieved by graphite 25 E + 180 HPH (8.70 ± 0.89%), which is similar to the previous one, even according to the microscopic assessment of the coating as well as the expanded layer. The graphite type 25 K + 180 (8.86 ± 0.65%) shows the expanded layer's best adhesion, coating uniformity, and ease of application. The results of this work confirmed that the CNC coating itself has significant retardation effects. [ABSTRACT FROM AUTHOR]

Burning rate as a function of pressure is one of the primary evaluation metrics of solid propellants. Most solid propellant burning rate measurements are made at a nearly constant pressure using a variety of measurement approaches. This type of burning rate data is highly discretized and requires many tests to accurately determine the burning rate response to pressure. It would be more efficient to measure burning rate dynamically as pressures are varied. Techniques used to make transient burning rate measurements are reviewed briefly and initial results using a microwave interferometry (MI) technique are presented. The MI method used in tandem with a closed bomb enables nearly continuous measurement of burning rates for self‐pressurizing burns, capturing burning rate data over a wide range of pressures. This approach is especially useful for characterization of propellants with complex burning behaviors (e. g., slope breaks or mesa burning). The burning rates of three research propellants were characterized over a pressure range of 0.101–24.14 MPa (14–3500 psi). One research propellant exhibited a slope break at a pressure of 6.63 MPa (960 psi). Using MI in a closed pressure vessel, 14 propellant strand burns resulted in a nearly continuous burning rate curve over a pressure range of 0.41–24.13 MPa (60–3500 psi) that reasonably matched conventional burning rate measurements. The development of this technique provides an opportunity to quickly characterize the burning rate curve of solid propellants with greater fidelity and efficiency than traditional quasi‐static pressure testing techniques. [ABSTRACT FROM AUTHOR]

The results of modeling the accumulation of slag residue in the combustion chamber of a propulsion system on pasty propellant obtained using a multiphase flow evolution model are presented. The influence of composition solutions on the process of slag formation is established; the significance of this process for the quality of such engines is shown. The nature of the influence of the parameters of the burning process for propellants of the type under consideration on the intensity of slag formation is determined. It is shown that the degree of involvement of metallic fuel in the agglomeration process has the greatest influence on slag formation. It has been established that the most effective ''tool'' for suppressing slag formation in the combustion chambers of paste propulsion is to change the regularities of the burning process, mainly associated with the formation of condensed products at the surface of the burning propellant.

Sandwich composite is an important part of engineering products capable of replacing metallic composite. It consists of two types of material, namely polypropylene honeycomb core and skin made from jute fiber-reinforced epoxy composite (JFRP), which are joined with glue. This study presented a unique discussion about adhesives that focused on the burning rate and emission performance of SA-A and SD-E. The burning rate performance was assessed with the UL-94 HB test in accordance with the ASTM D 635 standard. Emission value of both adhesives was also examined in line with the ASTM D 2863 standard using a Gasboard-3100P Syngas analyzer. In addition, FTIR and SEM analyses were used to determine the characteristics of the SA-A and SD-E adhesives. The results showed a significant difference in adhesives rates, with SA-A burning 0.5% faster than SD-E in addition to a 0.58% reduced weight loss. Emission test confirmed that both adhesives have similar LOI values of 22.6% and 22.8%, respectively. SA-A adhesives contained LSD, which is dangerous to human health. In conclusion, SD-E adhesives should be used on sandwich composite due to its epoxy-based potential as a flame retardant because SA-A adhesives has more potential to trigger firing due to the fuel content.

Burning rate plays a crucial role in determining the performance of solid rocket motors (SRMs). In the traditional approach for solid propellant propulsion, technical activities regarding burning rates are developed at three different operational levels: (i) Strand burners or laboratory-scale devices in general; (ii) Small-scale motors (SSMs); And (iii) full-size or end-item rocket motors. While strand burners are extensively used for propellant development (formulation exploration, ingredients screening, performance verification, and production control) and relatively little is done experimentally at the full-size motor level (being large-scale experimentation too expensive and dangerous), a lot is usually carried out at SSM level to obtain burning rate information under motor operating conditions. In the introductory part of this work, burning rate fundamentals are recalled and burning rate measurement devices are quickly summarized. Then, a survey of subscale motors is conducted and several automated procedures to deduce burning rate from SSM testing are analyzed. Data reduction methods commonly used by leading European companies are based on the thickness-over-time (TOT) definition. Attention is dedicated to procedures used in Italy and France for quality control of the European space launchers (solid propellant boosters of Ariane family and core solid rocket motors of VEGA family). In addition, automated data reduction methods based on mass balance (MB) and often used in USA are investigated. Specific features and general trends of the tested industrial procedures are pointed out. Since for any tests the actual burning rates are unknown, results can only be compared based on the statistical quality of the deduced ballistic data. Mainly reproducibility, ease of application, and suitability for automated computer implementation are of interest to industrial users. The effects of test variability, input data quality, and data reduction methods on result reproducibility are discussed with reference to fire tests of the successful Ariane-5 solid boosters. The systematic analysis of industrial data conducted in this work suggests that improving the actual mix reproducibility and quality of experimental data is more important than perfecting the current data reduction methods. Moreover, the international trends suggest that the fundamental TOT procedures are being replaced by MB procedures or advanced TOT procedures with burning times evaluated using pressure integrals.

This study was carried out to assess the fuel pellets produced from wheat straw and sugarcane bagasse. The wheat straw and bagasse were blended into four ratios including; 10:90, 30:70, 70:30 and 90:10 (wheat straw: bagasse) and developed into fuel pellets. The fuel pellets were characterized to determine the moisture content, volatile matter, fixed carbon, ash content, calorific value, bulk density and mechanical durability. The ignition time, burning rate and specific fuel consumption of the wheat straw – bagasse blended fuel pellets were studied at varying blend ratios (10:90, 30:70, 70:30 and 90:10), moisture contents (9.1%, 10.6%, 12.6% and 14.7%) and raw material particle sizes (2 mm, 4 mm, 6 mm and 10 mm). Results indicated that the wheat straw: bagasse blend ratios containing more proportion of bagasse (30:70 and 10:90) recorded a shorter ignition time, higher burning rate and lower specific fuel consumption. Larger raw material particle sizes exhibited shorter ignition time, higher burning rate and specific fuel consumption. Moreso, the fuel pellets with low moisture contents also recorded shorter ignition time, higher burning rate and lower specific fuel consumption. It was concluded that fuel pellets with high quantity of bagasse, large particle sizes and low moisture content demonstrated favorable combustion characteristics. Response surface methodology was used in the optimization so as to determine the optimum combination of blending ratio, moisture content and raw material particle size that would result in the lowest ignition time, highest burning rate and lowest specific fuel consumption. Results indicated that an optimum combination of a wheat straw: bagasse blend ratio of 10:90, moisture content of 14.70% and a particle size of 10.00 mm resulted in the lowest ignition time, highest burning rate and lowest specific fuel consumption.

The energy release process of the Mg-based hydroreactive fuels directly affects the performance of water ramjet engines, and the burning rate is one of the key parameters of the Mg-based hydroreactive fuels. However, there is not enough in-depth understanding of the combustion process of Mg-based hydroreactive fuels within the chamber of water ramjet engines, and there is a lack of effective means of prediction of the burning rate. Therefore, this paper aims to examine the flame structure of Mg-based hydroreactive fuels with a high metal content and analyze the impact of the water injection velocity and droplet diameter on the combustion property. A combustion experiment system was designed to replicate the combustion of Mg-based hydroreactive fuels within water ramjet engines, and the average linear burning rate was calculated through the target line method. On the basis of the experiment, a combustion–flow coupling solution model of Mg-based hydroreactive fuels was formulated, including the reaction mechanism between Mg/H2O and the decomposition products from an oxidizer and binder. The model was validated through experimental results with Mg-based hydroreactive fuels at various pressures and water injection velocities. The mean absolute percentage error (MAPE) in the experimental results was less than 5%, proving the accuracy and validity of the model. The resulting model was employed for simulating the combustion of Mg-based hydroreactive fuels under different water injection parameters. The addition of water injection resulted in the creation of a new high-temperature region, namely the Mg/H2O non-premixed combustion region in addition to improving the radial diffusion of the flame. With the increasing water injection velocity, the characteristic distance of Mg/H2O non-premixed combustion region is decreased, which enhances the heat transfer to burning surface and accelerates the fuel combustion. The impact of droplet parameters was investigated, revealing that larger droplets enhance the penetration of the fuel-rich gas, which is similar to the effect of injection velocity. However, when the droplet size becomes too large, the aqueous droplets do not fully evaporate, resulting in a slight decrease in the burning rate. These findings enhance the understanding of the mechanisms behind the burning rate variation in Mg-based hydroreactive fuels and offer theoretical guidance for the optimal selection of the engine operating parameters. [ABSTRACT FROM AUTHOR]

Sandwich composite is an important part of engineering products capable of replacing metallic composite. It consists of two types of material, namely polypropylene honeycomb core and skin made from jute fiber-reinforced epoxy composite (JFRP), which are joined with glue. This study presented a unique discussion about adhesives that focused on the burning rate and emission performance of SA-A and SD-E. The burning rate performance was assessed with the UL-94 HB test in accordance with the ASTM D 635 standard. Emission value of both adhesives was also examined in line with the ASTM D 2863 standard using a Gasboard-3100P Syngas analyzer. In addition, FTIR and SEM analyses were used to determine the characteristics of the SA-A and SD-E adhesives. The results showed a significant difference in adhesives rates, with SA-A burning 0.5% faster than SD-E in addition to a 0.58% reduced weight loss. Emission test confirmed that both adhesives have similar LOI values of 22.6% and 22.8%, respectively. SA-A adhesives contained LSD, which is dangerous to human health. In conclusion, SD-E adhesives should be used on sandwich composite due to its epoxybased potential as a flame retardant because SA-A adhesives has more potential to trigger firing due to the fuel content. [ABSTRACT FROM AUTHOR]

The formulation fundamentally determines the combustion characteristics and agglomeration behavior of propellants. This study compared the effects of four factors on the combustion, agglomeration, and combustion efficiency of nitramine solid propellants: the aluminum size, the ammonium perchlorate size, the nitramine size, and the mass ratio of ammonium perchlorate to nitramine. The comparison was conducted through a series of experimental methods including burning rate tests, collection of the condensed-phase combustion products, chemical titration, and physicochemical analysis. In terms of burning rate, reducing the particle sizes of aluminum powder and ammonium perchlorate, increasing the nitramine size, and increasing the mass ratio of ammonium perchlorate to nitramine all effectively enhance the burning rate. The influence of these four factors on burning rate, in descending order of impact, is: the mass ratio of ammonium perchlorate to nitramine > the ammonium perchlorate size > the aluminum size > the nitramine size. Regarding agglomeration and combustion efficiency, increasing the particle sizes of aluminum and nitramine, increasing the mass ratio of ammonium perchlorate to nitramine, and decreasing the ammonium perchlorate size can effectively inhibit agglomeration and enhance combustion efficiency. Among these, the ammonium perchlorate size has the greatest effect on enhancing the combustion efficiency, potentially increasing it by 16%. The nitramine size has the weakest impact on combustion efficiency, with a potential increase of 5.5%. The experimental results of this study can provide references for a deeper understanding of the combustion mechanisms of nitramine solid propellants, the establishment of combustion models, and the realization of formula optimization. • Formulation effect on combustion and agglomeration of propellants are studied. • The mass ratio of AP to nitramine has the greatest effect on the burning rate. • The AP size has the greatest effect on enhancing the combustion efficiency. • The comprehensive mechanism of formulation on propellants is proposed. [ABSTRACT FROM AUTHOR]

Pool fire with varying ullage height is a common type of accident that occurs in industrial parks. This paper explores the ullage height effects on the burning rate and heat feedback in pool fires through the experimental and theoretical study. A series of experiments were conducted using heptane with four tray sizes and five ullage heights. The results show that, the burning rate initially decreases, then increases and finally decreases as the ullage height increases. These results are mainly dependent on the change of internal flame behavior and thus heat feedback mechanisms with increasing ullage height. In the small ullage height conditions, the convective heat feedback reduces substantially whereas the radiative one rises slightly. When the ullage height reaches to a certain value, the convective heat feedback suddenly increases because of the flame inside the tray. The radiative heat feedback decreases gradually as the ullage height increase continually, while the convective one becomes nearly constant. Based on these results, three regimes are identified in terms of the burning rate variation with heat feedback: (1) convection controlled, (2) convection-radiation controlled and (3) radiation controlled. The new controlling mechanism of the burning rate variation (with ullage height), as a further extension of the classic scaling model by Blinov and Khudyakov on the burning rate variation (with pool diameter), could lay a solid foundation for future studies of the other key parameters in tank fires.

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.

Background: Spot fires play a significant role in the rapid spread of wildland and wildland–urban interface fires. Aims: This paper presents an experimental and modelling study on the flaming and smouldering burning of wood firebrands under forced convection. Methods: The firebrand burning experiments were conducted with different wind speeds and firebrand sizes. Key results: The burning rate of firebrands under forced convection is quantified by wood pyrolysis rate, char oxidation rate and a convective term. The firebrand projected area is correlated with firebrand diameter, char density, wind speed, and flaming or smouldering burning. A surface temperature model is derived in terms of condensed-phase energy conservation. We finally establish a simplified firebrand transport model based on the burning rate, projected area and surface temperature of firebrands. Conclusion: The mass loss due to wood pyrolysis is much greater than that due to char oxidation in self-sustaining burning. The burning rate is proportional to U 1/2, where U is wind speed. The projected area for flaming firebrands decreases more rapidly than that for smouldering ones. The firebrand surface temperature is mainly determined by radiation. Implications: Knowledge about firebrand burning characteristics is essential for predicting the flight distance and trajectory in firebrand transport. Knowledge about firebrand burning characteristics is essential for predicting the flight distance and trajectory for transport. This work studies the flaming and smouldering burning of firebrands under forced convection. Models are established for burning rate, projected area and surface temperature of firebrands, and applied to predict firebrand transport. [ABSTRACT FROM AUTHOR]

Wood, one of the materials predominantly employed in construction, possesses various advantageous properties alongside certain drawbacks, such as susceptibility to thermal degradation. To enhance wood fire resistance, one approach involves the application of flame retardants. This study compared the fire-retardant effectiveness of expandable graphite, bonded with water glass, as a coating for spruce wood against commercially available fire-retardant treatments. Spruce wood samples (Picea abies (L.) H. Karst) underwent treatment with three distinct retardants: expandable graphite in combination with water glass, Bochemit Antiflash, and Bochemit Pyro. The fire-technical characteristics of the samples were examined by a non-standard test method—a test with a radiant heat source. The experiment evaluated the fire-retardant properties by recording changes in sample mass, burning rate, and temperature difference. The best results among all flame retardants were achieved by expandable graphite in combination with water glass, in all evaluation criteria. Among all the flame retardants used, expandable graphite in combination with water glass achieved the best results in all evaluation criteria. [ABSTRACT FROM AUTHOR]

The process of fluid diffusion and fire dynamics in spill fires at different initial temperatures is unstable and complex, potentially leading to severe consequences. Through a series of experiments, the effects of initial fuel temperature on the combustion mechanism of ethanol spill fire were investigated. The results show that in the liquid-phase control stage, the propagation of the spill fire is greatly affected by the liquid spread, and the increasing rate of combustion area (IRCA) and the maximum combustion area (MCA) gradually increase with the increase in the initial temperature. In the gas-phase control stage, the propagation of spill fire is greatly affected by the combustion of liquid, as initial temperature increase, the IRCA and MCA gradually decrease. The increase in the initial temperature will lead to the attenuation of the pulsation phenomenon during the propagation of the flame, but will lead to the frequency of flame oscillation increases. The prediction equations of burning rate at different initial fuel temperatures are established, which show that there is a significant difference in burning rate in the liquid-phase control stage, the maximum increase in the burning rate was only 2.3%, while in the gas-phase control stage, this value is about 50%. The convective feedback is the main heat feedback mechanism of small spillage fires, and the convective feedback accounts for more than 62.5%. The higher the initial temperature, the stronger the convective feedback mechanism. [ABSTRACT FROM AUTHOR]

The mechanism of erosive combustion of gunpowder and its consideration in solid propellant rocket engines are analyzed. The issues of the influence of erosive combustion of a solid fuel on changes in the thrust of a jet penetrator engine are considered. A mathematical model is presented for calculating changes in parameters of the intra-chamber process over time, taking into account their changes along the length of the charge for an engine with a freely inserted tubular charge. The obtained calculation results confirm the significant influence of the charge temperature on the intra-ballistic parameters of the penetrator. [ABSTRACT FROM AUTHOR]

Ammonium nitrate (AN) is of considerable interest to researchers in developing new types of energetic mixtures due to the release of environmentally benign gaseous products during burning and thermal decomposition. However, poor ignition and a low burning rate require special additives to speed up this process. The advantage of this research is the use of high-energy aluminum-based alloys as fuel to compensate for the disadvantages of AN. In addition, the effect of copper oxide (CuO) on the burning kinetics and thermodynamics of the energetic mixture based on ammonium nitrate–magnesium–aluminum alloys (AN/MgAl) is investigated. Alloys based on aluminum were created through a process of high-temperature diffusion welding, conducted in an environment of argon gas. The structure and thermal characteristics of alloys are determined by X-ray diffraction, scanning electron microscopy, and DTA-TG analyses. It has been found that CuO has significant effects on the thermal decomposition of an AN/MgAl-based energetic mixture by shifting the decomposition temperature from 269.33 °C to 261.34 °C and decreasing the activation energy from 91.41 kJ mol−1 to 89.26 kJ mol−1. Adding CuO reduced the pressure deflagration limit from 2 MPa to 1 MPa, and the linear burning rate of the AN/MgAl energetic mixture increased approximately twice (rb = 6.17 mm/s vs. rb = 15.44 mm/s, at a chamber pressure of P0 = 5 MPa). [ABSTRACT FROM AUTHOR]

The initial part of a hydrogen jet exhausting upward from a mm slot and burning in air is studied. The profiles of the streamwise and transverse velocity are determined by means of particle image velocimetry; the local temperature distribution and the composition of stable substances are obtained by the Raman scattering method with the use of a focusing resonator system. Based on experimental data, the contributions of molecular and convective transfer mechanisms to the heat release intensity is determined. It is shown that the maximum intensity of heat release depends mainly on gas-dynamic and thermophysical characteristics of the gas flow during its macroscopic motion. [ABSTRACT FROM AUTHOR]

This study investigates the feasibility of using an Al-Si eutectic alloy as a reactive fuel in energetic mixtures. Al-Si eutectic alloy powders were obtained from secondary resources and ground to a particle size of less than 100 μm. We examined these powders’ burning characteristics and thermal properties compared to pure Al powder. Results showed that the burning rate of energetic mixtures containing Al-Si eutectic alloys was 1.5 to 2.0 mm/s higher than those with pure Al. Additionally, the activation energy of pure PTFE was reduced from 81.29 kJ/mol to 61.75 kJ/mol when the Al-Si alloy was added. The formation of oxides, carbides, and fluorides in the combustion products of Al-Si-based mixtures significantly influenced their thermodynamics.

Compared to longitudinal ventilation, there are few studies on fire source development under semi-transverse ventilation. This work studied the influence of semi-transverse ventilation on the combustion characteristics of fire sources in a scaled tunnel. The burning rate and heat transfer feedback during pool fire combustion were revealed under different longitudinal and transverse ventilation velocities. The results showed that transverse ventilation had little influence on combustion characteristics, and the burning rate was more obviously affected by longitudinal ventilation. The heat convection feedback increased monotonically with the increase of the longitudinal ventilation, which led to the increase of the total heat feedback on the fuel. The heat radiation feedback changed little, and the heat conduction feedback decreased monotonically with the increase of the longitudinal ventilation velocity. By aid of a Fire Dynamics Simulator, it was found that the flame tilted downstream and was in the flow line of the lower cold air flow coming from upstream and the upper hot smoke flow outgoing in the downstream direction. The transverse ventilation of 2 m/s or lower hardly affected the combustion field of the fire source. Therefore, semi-transverse ventilation is preferable to longitudinal ventilation from the point of view of limiting fire expansion. [ABSTRACT FROM AUTHOR]

The pool fires that occur behind obstructions in a ventilated environment are very different from other wind-blown pool fires. The pool fire formed by fuel leakage in an engine nacelle is a typical example of a pool fire influenced by cross winds and baffles. Mastering the combustion characteristics of this type of fire is of great significance for fire prevention and control. In this study, the burning rate, flame length, and flame tilt angle of heptane pool fires behind a baffle under different cross wind velocities (ranging from 0 to 5 m/s) were experimentally investigated. Square pool fires with dimension of 8 cm and 12 cm with baffle height from 4 to 12 cm and different distances between fire and baffle (0, 20, 30 cm) were tested in a wind tunnel. The experimental results show that the burning rate increases with the increase in cross wind velocity for each baffle height. As wind velocity exceeds 2 m/s, the burning rate first decreases and then increases with the increase in baffle height. The flame length initially increases and then decreases with increasing wind velocity. The upper flame tilt angle is mainly affected by the cross wind, while the bottom flame tilt angle is influenced by the combined effects of cross wind velocity, baffle height, and distance between baffle and flame. The empirical correlations under different distances between baffle and flame, with wind velocity and baffle height accounted for, are then proposed for the dimensionless heat release rate and the flame length of heptane pool fires. [ABSTRACT FROM AUTHOR]

In-situ burning is a fast, cheap, and effective means of cleaning up spilled fuel in the environment. Much in-situ burning takes place at sea and on the ocean surface. Some studies have been conducted which examine the impact of a water sublayer, fuel thickness, pool diameter, and other parameters on the burning rate of a pool fire. Very little research has been conducted which examines the influence of water waves on the burning characteristics of a fuel floating on water. This study analyzes the burning behavior of an 80 cm kerosene pool fire of constant thickness floating on wavy water. A custom modular freshwater wave tank was built to accommodate the experiments. Wave generation and absorption equipment ensure linear wave composition for experimental study. Four different wave profiles with steepness ranging from 0.008 to 0.017 representing a Beaufort Sea state of 1 were used. It is observed that waves increased convective cooling by the water sublayer, decreased flame heat feedback, and lowered regression rates. As the thickness of the fuel is increased the influence of the wave is reduced, with thicker fuels experiencing less dramatic effects than thinner fuels. [ABSTRACT FROM AUTHOR]

Staged combustion of biomass is the most suitable thermo-chemical conversion for achieving lower gaseous emissions and higher fuel conversion rates. In a staged fixed bed combustion of biomass, combustion air is supplied in two stages. In the first stage, primary air is provided below the fuel, whereas in the later stage, secondary air is supplied in the freeboard region. The available literature on the effects of air staging (secondary air location) at a constant primary air flow rate on combustion characteristics in a batch-type fixed bed combustor is limited and hence warrants further investigations. This study resolves the effect of air staging, by varying the location of secondary air in the freeboard at five secondary to total air ratios in a batch-type fixed bed combustor. Results are reported for the effects of these controlled parameters on fuel conversion rate, overall gaseous emissions (CO2, CO and NOx) and temperature distributions. The fuel used throughout was densified hardwood pellets. Results show that a primary freeboard length (distance between fuel bed top and secondary air injection) of 200 mm has higher fuel conversion rates and temperatures as well as lower CO emissions, at a secondary to total air ratio of 0.75 as compared to primary freeboard length of 300 mm. However, NOx emissions were found to be lower for a primary freeboard length of 300 mm as compared to 200 mm. An increase in secondary to total air ratio from 0.33 to 0.75 resulted in higher freeboard temperatures and lower CO as well as NOx emissions. The outcomes of this study will be helpful in the effective design of commercial scale biomass combustors for more efficient and environmentally friendly combustion. [ABSTRACT FROM AUTHOR]

An attempt to understand the relation between the burning characteristics and thermal decomposition in a wide range of pressure is made in the present investigation based on solid propellants with ammonium perchlorate as an oxidizer and 3,3-diazomethylepoxybutane and tetrahydrofuran as a fuel binder. The burning rate measurement is carried out in a wide range of pressure: 1.0, 3.0, 7.0, 13.8, 15.0, and 20.0 MPa. The inflection point of the pressure exponent for ammonium perchlorate with and without oxalate and the flame extinguishing point both appear at 13.8 MPa. Various mechanisms of burning rate reduction by the quaternary ammonium salt and oxalate are analyzed by theoretical analysis, thermogravimetric analysis, and differential scanning calorimetry analysis. The burning rate and decomposition of the oxidizer and fuel binder with combustion modifiers and their overall impact on propellant combustion are studied. Due to modifiers, a transition between kinetically controlled combustion and diffusion controlled combustion is found to occur. [ABSTRACT FROM AUTHOR]

This paper describes a study of the ignition and combustion characteristics of a high-energy material containing ammonium perchlorate, butadiene rubber, and an ultrafine powder mixture of aluminum, titanium, or iron with amorphous boron. An experimental stand based on a CO2 laser and a constant-pressure bomb is used to measure the ignition delay time and burning rate of the high-energy material while varying the heat flux density and the chamber pressure. It is shown that replacing amorphous boron with ultrafine Al/B, Ti/B, or Fe/B in a high-energy material reduces the heating time and the moment at which a flame appears on the propellant surface due to an increase in the reaction rate and a decrease in the oxidation temperature of these mixtures on the surface of the reaction layer. In this case, the burning rate of the high-energy materials with Me/B at excess pressures increases significantly (up to 240% for Al/B-HEM and up to 120% for Ti/B-HEM at a pressure of 5.0 MPa). [ABSTRACT FROM AUTHOR]

This paper describes a study of combustion performance of a Bi2O3/Al nanothermite mixture with the addition of 1-methyl-3-nitro-1,2,4-triazole (1Me-3N) depending on the content of the latter and the component ratio of a base Bi2O3/Al nanothermite pair. Adding 1Me-3N to the mixture increases the explosive force, but the latter begins to decrease as soon as the additive content reaches over a certain limit. Depending on the prescription configuration, it is possible to increase the explosive force by 22–29% relative to Bi2O3/Al nanothermite. Changing the prescription configuration makes it possible to vary the burning rate of Bi2O3/Al/1Me-3N within a range of 400–690 m/s in charges 2 mm in diameter and within a range of 120–430 m/s in a 0.1-mm thick layer. [ABSTRACT FROM AUTHOR]

In this study, the effects of pristine carbon nanotubes (CNTs), sodium dodecylbenzene sulfonate (SDBS), and diesel blends on the ignition delay and burning rate are examined experimentally. For this purpose, single-droplet combustion tests were conducted in a combustion system for 21 days using CNTs at concentrations of 50 ppm and 100 ppm, which were dispersed in Colombian commercial diesel and stabilized by SDBS. Videos of the diesel droplet burning were obtained using a high-speed camera, and the Shadowgraph optical technique was used to observe the development of the droplet size during combustion. Thus, records of the process were collected, and the treatment was carried out using a MATLAB algorithm. The measurements and processing were carried out along with a stability study, which included measurements of dynamic light scattering (DLS), pH, potential Zeta, and properties such as thermal conductivity and surface tension. The results demonstrated that the temporal stability has a direct impact on the single-droplet combustion tests because a concentration of CNTs of 100 ppm showed a higher stability than those achieved by 50 ppm. Consequently, improvements were found with a concentration of 100 ppm—for instance, the thermal conductivity increased by about 20%, the ignition delay time increased by 16.2%, and the burning rate increased by 30.5%. [ABSTRACT FROM AUTHOR]

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There is a dire need to improve our prediction capabilities of wildland fire behavior in a range of conditions from marginal burning to the most extreme. In order to develop a more physically-based operational wildland fire behavior model, we need to improve our understanding of the effect of ventilation on burning rate of fuel beds. In this work, wood cribs are used as a simplified fuel bed. A variety of crib designs were tested with stick sizes ranging from 0.32 cm to 1.27 cm and porosities ranging from densely packed to loosely packed. A pressurized box was built that allowed for a controlled flow rate of air through the cribs from 100 LPM to 1000 LPM. The mass loss rates with forced ventilation were compared to tests conducted outside of the box under unrestricted quiescent conditions. For the flow rates tested here, the burning rate was generally observed to increase with flow. The amount of air naturally induced into a crib while burning was deduced to be best related to the vent area and the square root of the stick spacing (Avs1/2). It was seen that the air-to-fuel ratio inside a fuel bed burning in quiescent conditions is approximately 1.11, indicating that over 75% of the air required to completely combust the pyrolysis gases is entrained in the plume. When the supplied air is less than the amount normally entrained in ambient burning, the crib is under-ventilated and the proportional reduction in the burning rate does not seem to depend on the crib characteristics. When the crib is over-ventilated, however, the relative increase in the burning rate does vary with crib design. Simple physical arguments were used to correlate the data. Future work will include testing at higher flow rates, different moisture contents, and with cribs built with multiple stick thicknesses. [ABSTRACT FROM AUTHOR]

Digital light processing (DLP) or stereolithography is the most promising method of additive manufacturing (3D printing) of products based on high-energy materials due to, first of all, the absence of a high-temperature impact on the material. This paper presents research results of an ultraviolet (UV)-cured urethane methacrylate polymer containing 70 wt.% of high-energy solid powder based on ammonium salts, which is intended for digital light processing. Polymerization of the initial slurry is studied herein. It is shown that the addition of coarse powder transparency for the UV radiation to resin increases its curing depth. The thickness of the layer, which can polymerize, varies from 600 µm to 2 mm when the light power density ranges from 20 to 400 mJ/cm2, respectively. In DLP-based 3D printing, the obtained material density is 92% of the full density, while the compressive strength is 29 ± 3 MPa, and the ultimate tensile strength is 13 ± 1.3 MPa. The thermogravimetric analysis shows the decrease in the thermal decomposition temperature of UV-cured resin with high-energy additives compared to the thermal decomposition temperatures of the initial components separately. Thermal decomposition is accompanied by intensive heat generation. The burning rate of obtained samples grows from 0.74 to 3.68 mm/s, respectively, at the pressure growth from 0.1 to 4 MPa. Based on the results, it can be concluded that DLP-based 3D printing with the proposed UV photocurable resin is rather promising for the fabrication of multicomponent high-energy systems and complex profile parts produced therefrom. [ABSTRACT FROM AUTHOR]

This paper focused on studying the spread radius and burning rate of spill fires on a fine sand substrate. Sand can slow down the spread of spilled oil, but there are still few studies on the effect of sand on spill fires. Ethanol spill fires with leakage rates of 0.04–0.4 L min−1 were carried out on a sand substrate in this experiment. The influence of sand on the spread and heat transfer characteristics of the spill fire was analyzed. The results showed that the spread radius of spill fire on sand is much smaller than that without sand. In the heat transfer process of the spill fire, sand enhanced heat conduction feedback and reduced the proportion of heat loss. Finally, the spread and heat transfer in this experiment were discussed in detail based on the relevant semi-empirical model. This work contributes to the understanding of the effectiveness of sand layer in impeding the spread of spill fire and provides a theoretical basis for extinguishing spill fires. [ABSTRACT FROM AUTHOR]

Our study examined the potential of using activated carbon/nanosized cobalt oxide (AC-Co3O4) as a new catalytic additive to improve the efficiency of the parent ammonium nitrate/magnesium/nitrocellulose (AN/Mg/NC) composite. These findings demonstrate a significant improvement in the thermal characteristics of AN/Mg/NC/AC-Co3O4 compared to the initial AN/Mg/NC. Raman spectra confirmed the multilayered nature of AC. Fourier-transform infrared spectroscopy (FTIR) analysis confirmed the presence of cobalt oxide in the synthesized additive. Differential scanning calorimetry (DSC) revealed the catalytic effect of AC-Co3O4 on the AN/Mg/NC composite, resulting in the reduction in the decomposition peak temperature (Tmax) from 277.4 °C (for AN/Mg/NC) to 215.2 °C (for AN/Mg/NC/AC-Co3O4). Thermal gravimetric analysis (TG) determined the overall mass losses (%) for AN/Mg/NC (70%), AN/Mg/NC/AC (75%), and AN/Mg/NC/AC-Co3O4 (80%). This analysis highlights the significant role of AC-Co3O4 in enhancing the energy release during decomposition. Moreover, the use of the differential thermogravimetric (DTG) technique demonstrated the two-step decomposition pathways attributed to the multi-component system. Finally, the combustion tests under the pressure of 3.5 MPa validated the catalytic efficiency of the AC-Co3O4 additive, which enhanced the burning rate (rb) of the AN/Mg/NC/AC-Co3O4 composite from 10.29 to 19.84 mm/s compared to the initial AN/Mg/NC composite. The advantageous nature of the AN/Mg/NC/AC-Co3O4 composite with a lowered decomposition temperature can be applied in rocket propulsion systems, where the precise control of combustion and ignition processes is crucial. [ABSTRACT FROM AUTHOR]

As a critical factor in tunnel fire safety, previous research on model predictions of the maximum ceiling gas temperature rise under natural ventilation has not demonstrated consistent results. These discrepancies are commonly attributed to variations in tunnel dimensions and materials. To address this issue, an experimental investigation utilizing heptane pool fires with different dimensions was conducted in a model-scale tunnel. The results show that the burning rate increases with an increasing aspect ratio of the fire source for the selected diameter range of 0.078–0.169 m. The flame length was characterized using a modified diameter of the fire source considering the air entrainment, and found that the non-dimensional flame length is 2.4 times the 2/5th power of the non-dimensional heat release rate. Finally, incorporating the concept of flame virtual origin, two different forms of correlations were developed to quantify the maximum ceiling gas temperature rise under different impingement conditions of the fire plume, and the coefficients were determined as 0.065 and 0.215 by numerous experimental results from different studies. The newly proposed models demonstrate good applicability to the fire sources with different dimensions, especially for the rectangular fire source with a large aspect ratio, thus solving the problem of insufficient accuracy of classical models under this condition.

The energy release process of the Mg-based hydroreactive fuels directly affects the performance of water ramjet engines, and the burning rate is one of the key parameters of the Mg-based hydroreactive fuels. However, there is not enough in-depth understanding of the combustion process of Mg-based hydroreactive fuels within the chamber of water ramjet engines, and there is a lack of effective means of prediction of the burning rate. Therefore, this paper aims to examine the flame structure of Mg-based hydroreactive fuels with a high metal content and analyze the impact of the water injection velocity and droplet diameter on the combustion property. A combustion experiment system was designed to replicate the combustion of Mg-based hydroreactive fuels within water ramjet engines, and the average linear burning rate was calculated through the target line method. On the basis of the experiment, a combustion–flow coupling solution model of Mg-based hydroreactive fuels was formulated, including the reaction mechanism between Mg/H2O and the decomposition products from an oxidizer and binder. The model was validated through experimental results with Mg-based hydroreactive fuels at various pressures and water injection velocities. The mean absolute percentage error (MAPE) in the experimental results was less than 5%, proving the accuracy and validity of the model. The resulting model was employed for simulating the combustion of Mg-based hydroreactive fuels under different water injection parameters. The addition of water injection resulted in the creation of a new high-temperature region, namely the Mg/H2O non-premixed combustion region in addition to improving the radial diffusion of the flame. With the increasing water injection velocity, the characteristic distance of Mg/H2O non-premixed combustion region is decreased, which enhances the heat transfer to burning surface and accelerates the fuel combustion. The impact of droplet parameters was investigated, revealing that larger droplets enhance the penetration of the fuel-rich gas, which is similar to the effect of injection velocity. However, when the droplet size becomes too large, the aqueous droplets do not fully evaporate, resulting in a slight decrease in the burning rate. These findings enhance the understanding of the mechanisms behind the burning rate variation in Mg-based hydroreactive fuels and offer theoretical guidance for the optimal selection of the engine operating parameters.

ABSTRAK Penelitian ini bertujuan untuk mengetahui efektivitaf bahan biobriket buah nyamplung terhadap laju pembakaran dan nilai kalor. Proses pembuatan biobriket menggunakan alat tekan manual yang dibuat dengan besi plat, bahan yang digunakan ialah buah nyamplung dan tepung tapioka. Densitas biobriket dihasilkan berkisaran 0,96 g/cm3 – 1,8 g/cm3, densitas terendah didapat pada biobriket dengan perbandingan arang kulit buah nyamplung 90% dan perekat tepung tapioka 10%. Sedangkan densitas tertinggi didapat pada biobriket dengan perbandingan 50% arang isi dan 50% arang kulit buah nyamplung. Kadar air yang paling tinggi terdapat pada biobriket dengan campuran arang kulit buah nyamplung 85% dan perekat 15%. Sedangkan kadar air yang paling rendah terdapat pada biobriket dengan campuran 50% arang isi dan 50% arang kulit buah nyamplung. Kadar air yang didapat pada penelitian ini berkisaran 4,16% - 7,14%. Laju pembakaran yang tertinggi terdapat pada biobriket dengan campuran 50% arang isi dan 50% arang kulit buah nyamplung. Hasil laju pembakaran berkisaran 1,66 g/menit – 8,28 g/menit. Nilai kalor yang tertinggi terdapat pada biobriket dengan campuran 50% arang isi dan 50% arang kulit buah nyampung. Sedangkan nilai kalor yang terendah terdapat pada biobriket dengan campuran 90% arang kulit buah nyamplung dan 10% perekat. Nilai kalor yang dihasilkan berkisaran 2309,88 kalori – 14253,96 kalori. Dari hasil penelitian dapat dilihat bawha laju pembakaran dan nilai kalor yang tertinggi terapat pada biobriket campuran 50% arang isi dan 50% arang kulit buah nyamplung. Kata kunci: biobriket; buah nyamplung; laju pembakaran; nilai kalor ABSTRACT This study aims to determine the effectiveness of nyamplung fruit biobriquette on burning rate and calorific value. The process of making biobriquettes uses a manual press made of plate iron, the materials used are nyamplung fruit and tapioca flour. The density of the resulting biobriquettes ranged from 0,96 g/cm3 – 1,8 g/cm3, the lowest density was found in biobriquettes with a ratio of 90% nyamplung fruit skin charcoal and 10% tapioca flour adhesive. While the highest density was found in biobriquettes with a ratio of 50% filled charcoal and 50% nyamplung fruit shell charcoal. The highest water content was found in biobriquettes with a mixture of 85% nyamplung fruit skin charcoal and 15% adhesive. While the lowest water content was found in biobriquettes with a mixture of 50% filled charcoal and 50% nyamplung fruit shell charcoal. The water content obtained in this study ranged from 4.16% - 7.14%. The highest burning rate was found in biobriquettes with a mixture of 50% filled charcoal and 50% nyamplung fruit skin charcoal. The resulting combustion rate ranges from 1.66 g/minute – 8.28 g/minute. The highest calorific value was found in biobriquettes with a mixture of 50% filled charcoal and 50% nyampang fruit skin charcoal. Meanwhile, the lowest calorific value was found in biobriquettes with a mixture of 90% nyamplung fruit peel charcoal and 10% adhesive. The resulting caloric value ranges from 2309.88 calories to 14253.96 calories. From the results of the study it can be seen that the highest burning rate and calorific value were found in biobriquettes mixed with 50% filled charcoal and 50% nyamplung fruit shell charcoal. Keyword: biobriquettes; nyamplung fruit; burning rate; calorific value

Single-based propellants containing 0.4 wt%, 0.8 wt% and 1.6 wt% nickel powders(NPs) were prepared and investigated in closed bomb tester and transparent combustion chamber, which can provide variable-pressure and constant-pressure conditions for propellant burning, respectively. In closed bomb tester, propellants burned to a pressure above 5–220 MPa. The results showed that burning rate of propellants was increased by 19.0 %, 12.5 % and 11.9 % in 5–8 MPa, 8–16 MPa and 20–200 MPa, when 1.6 wt% NPs used in propellant. Meanwhile, propellants burning in combustion chamber were with a constant pressure of 1.0 MPa, 1.5 MPa, 2.0 MPa, 3.0 MPa and 5.0 MPa. The burning rate of propellants can be increased by NPs in 1.0–5.0 MPa. While the catalytic efficiency(Z) had high dependence on NPs contents and burning pressure. At 5.0 MPa, 0.4 wt%, 0.8 wt% and 1.6 wt% of NPs enhanced burning rate of propellants by 42 %, 44 % and 68 % than that of original propellants. In pressure below 3.0 MPa, burning rate of propellants cannot be increased with 0.4 wt% and 0.8 wt% NPs, but that can be enhanced with 1.6 wt% NPs, suggested that higher NPs content and higher pressure were conducive to catalytic effect, which was significant with the pressure above 5 MPa. Furthermore, after NPs incorporating into propellant, the distance from flame zone to propellant burning surface was significantly reduced. And the potential catalytic mechanism was proposed.

This work provides a series of fire tests in a 1/7 model tunnel to explore the influence of portal-blocking speed on tunnel fire behaviors. Burning rate, ceiling temperature, temperature distribution inside tunnel and thermal characteristic near tunnel portal are obtained and analyzed. Results shown that the comprehensive effect of portal-blocking speed on fire behavior is related to fuel area of fire source. For the fire scenario with small fuel area (Sfuel≤0.18 m2), the effect of blocking speed is not significant. While for the fire scenario with large fuel area (Sfuel≥0.54 m2), burning rate decreases rapidly, due to the blocking of tunnel portals. A critical blocking ratio existed due to the competitive between two action mechanisms of the reduction of air supplement and heat loss. The larger the fuel area is, the smaller the critical blocking ratio is. There is a delay effect on the burning suppression of fire source. For the fire scenario with large fuel area (Sfuel≥0.54 m2), the ceiling temperature distribution was more “uniform”, compared to that of the fire scenario with small fuel area (Sfuel≤0.18 m2). The faster blocking speed can make the ceiling temperature decay to a relatively low level earlier. The larger the fuel area is, the better the suppression effect of blocking strategy is. Earlier and faster blocking operation can effectively suppress the high temperature region, which is beneficial to the protection of tunnel lining.

As a traditional fossil fuel, petroleum fuel is prone to spill fires during storage, transportation, and use, which poses a significant threat to the secure utilization of energy. This research aims to investigate the effect of porous media on the combustion characteristics of spill fire. Quartz sand (diameter is 1.5 mm) is selected as a porous material, and continuous oil spill fire experiments under different oil discharge rates (25–100 mL·min−1) are carried out on both smooth substrate and porous bed. The spread process, burning rate, flame height and spread speed are measured and analyzed. The results show that no burning layer shrinkage occurs during the spread process. There is a significant increase in the stable burning length and in the time required to reach the quasi-steady burning phase. The burning rate of spill fire on a porous bed is negatively correlated with the thickness of the sand layer and positively correlated with the oil discharge rate, but it is still lower than the burning rate of pool fire under the same equivalent diameter. Transformer oil spill fire propagation speed is divided into three stages: acceleration-uniform-deceleration. When the oil discharge rate is 50 mL·min−1, the uniform propagation speed of flame is 0.55, 0.11 and 0.03 cm·s−1 respectively. Flame height is positively correlated with oil discharge rate and negatively correlated with sand thickness. Furthermore, a dimensionless coefficient, d*, is introduced to modify the flame height and burning rate models, and the correctness of the modified model is verified by experimental data. This study is informative for the safe use of liquid fuels. [ABSTRACT FROM AUTHOR]

RP‐3 aviation kerosene is a standard fuel that is used in civil aircraft and is a substitute for Jet‐A fuel. This paper investigates the combustion behaviour of RP‐3 aviation kerosene in an open space in the low‐pressure environment of a plateau. A series of large‐scale pools with diameters ranging from 0.4 m to 2.82 m combustion experiments are performed. Typical combustion characteristic parameters, including combustion rate, flame height and axial plume temperature distribution is measured. Results show that a low‐pressure environment significantly affects pool fires. With combustion rate, there is a linear variation law between oil pool size and combustion rate. The experimental data are fitted as a means of obtaining the large‐scale combustion rate relationship equation at low pressure. Experimental flame height data is compared using classical prediction models. Prediction model coefficients at low pressure are determined. The axial plume temperature distribution is greater than in the literature findings due to flames becoming longer in a low‐pressure environment. The three regimes in McCaffery's model are redefined and correlate well with the vertical temperature profile of the pool centreline. The results of the experimental investigation will help research fire hazards in low‐pressure environments while also contributing to the provision of basic data for the development of firefighting operation strategies. [ABSTRACT FROM AUTHOR]

The burning rate of wildland fuels is a poorly understood yet key fire behavior metric. Previous work has utilized wood cribs; however, it has not yet been addressed whether the burning behavior of a crib, an axisymmetric fire, can be representative of a line fire, a typical configuration in wildfires. In this study, airflow into two sides of the crib was physically blocked and the resulting burning rate was noted. Six crib designs with a range stick thicknesses and porosities were tested both on the ground and with a gap underneath. For most cases, blocking the sides had only a modest effect on the burning rate (up to 22% reduction). In these cases, axisymmetric fire sources may give an acceptable approximation for the burning rate of a segment of a line fire. However, for the cribs built with thinner sticks placed directly on the ground, the reduction was more dramatic (up to 45%) and the use of axisymmetric and line fire sources requires further consideration. Resistances to flow in both the horizontal and vertical directions within the crib were used to understand these trends and to provide a better qualitative picture of how flows govern the burning of cribs in general. [ABSTRACT FROM AUTHOR]

This study investigates the thermophysical and combustion characteristics of ethanol-based nanofuels incorporating aluminum (Al) and nickel-coated aluminum (Ni-Al). The nanofuels are prepared with varying concentrations of Al and Ni-Al nanoparticles. The results reveal that, despite the non-uniform deposition of nickel on Al particles, a sintering reaction occurs between the two materials. Nanofuels containing Al exhibit unburned Al residues after combustion, while nanofuels containing Ni-Al show intense AlO radical emission during combustion termination, indicating enhanced combustion. However, nanofuels containing Ni-Al demonstrate a lower burning rate compared to Al nanofuels, attributed to the lower thermal conductivity of nickel. Overall, the findings suggest that nanofuels containing Ni-Al possess higher energy potential but extended combustion duration. [ABSTRACT FROM AUTHOR]

In staged fixed bed biomass combustion, primary air is supplied beneath the fuel bed with secondary air then provided above in the freeboard region. For fixed bed configurations, the freeboard is further divided into a primary freeboard length (LI), which is upstream of the secondary air and a secondary freeboard length (LII), measured from the secondary air all the way to the exhaust port. Despite extensive research into fixed bed configurations, no work has been successfully completed that resolves the effects of changing LI on fuel conversion, both in the fuel bed and within the freeboard of batch-type biomass combustors. In this study, experiments on a 202 mm diameter and 1500 mm long batch-type combustor have been conducted to determine the effects of changing primary freeboard length over three secondary to total air ratios (Qs/Qt) and two total air flow rates (Qt). The impact of these conditions has been studied on (i) intra-bed fuel conversion, measured through burning rate (kg/m−2 s−1), fuel bed temperature (°C) and ignition front velocity (mm-s−1), as well as (ii) post-bed fuel conversion in the freeboard, expressed through freeboard temperatures and emissions (NOx ppm, CO2%, CO ppm, O2%). The fuel used throughout the above experiments was Australian hardwood pelletised biomass. Results show that changes to primary freeboard length over LI = 200 mm, 300 mm and 550 mm, or LI/D = 1.00, 1.48 and 2.72, respectively, affect both intra-bed and freeboard (post-bed) performance indicators. The highest values of burning rate, ignition front velocity and fuel bed temperature were observed for interim values of LI/D = 1.48 at Qs/Qt = 0.25 and Qt = 0.358 kg/m−2 s−1. Primary freeboard lengths of LI/D = 1.00 and 1.48 were found to have higher freeboard temperatures, NOx and CO2 as well as lower CO and O2 values as compared to LI/D = 2.72 at Qs/Qt = 0.50 and 0.75. Increasing Qs/Qt from 0.25 to 0.50 for LI/D = 1.00 and 1.48 initially increased freeboard temperatures, with an accompanying increase in NOx and CO2 as well as decrease in CO values. However, further increase in Qs/Qt to 0.75 lead to lower freeboard temperatures for all primary freeboard lengths. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Ordnance Equipment Engineering is the property of Chongqing University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Hybrid propulsion, consisting of solid fuel and liquid oxidizer, exhibits major advantage regarding safety, development costs, energetic performance, and controllability. Hence, it has been considered for space and other propulsion programs. One of the characteristic features of hybrid motors, that may be of major disadvantage, is their relatively low thrust due to the characteristic low regression rate of the typical polymeric solid fuels. This research group had revealed that a small fraction of an expandable graphite (EG) additive could double the burning rate and thrust of hybrid motors. EG is an intercalated form of graphite, elongating and swelling, getting a worm‐like string shape at elevated temperatures. In an earlier work it was hypothesized that enhanced heat transfer via conduction through the EG strings protruding from the hot surface, is a significant parameter increasing the burning rate. In the present investigation, thermal analysis revealed that the ignition temperature of polyester fuel containing 5 wt% of EG, is substantially lower than that of the pure polymer, which may promote higher burning rate as well. High‐speed photography of the surface of EG‐containing solid fuels as well as that of individual EG particles during controlled heating, demonstrated the dynamic behavior resulting in the formation of EG strings longer by an order of magnitude compared to the original particles. The different phenomena were related to the observation of enhanced burning rate. [ABSTRACT FROM AUTHOR]