Average Burning Rate Research Articles

The impact of oxygen content in the primary air supply on fuel burning rate and pollutant emissions in a forced-draft biomass stove

Forced-draft biomass stoves have been proposed as a substitute for traditional solid fuel stoves in rural areas. The change in the O2 content of the supply air via flue gas recirculation (FGR) significantly affects the combustion and pollutant emission performances of this household stove type, which has not been thoroughly investigated. In this study, O2 content control system was designed to accurately adjust the O2 content of the primary air supply for a typical household forced-draft biomass stove. Then, six conditions with an O2 content of 16%, 17%, 18%, 19%, 20%, and 21% were tested. The dynamic burning rate and emission rates of carbon monoxide (CO), nitrous oxides (NOx), and particulate matter with an aerodynamic diameter ≤ 2.5 μm (PM2.5) were measured for each O2 content. The results showed that the average burning rate of the six O2 contents ranged from 9.6 to 16.9 g/min. There was a positive linear relationship between the average burning rate and the O2 content in the primary air supply. The CO and PM2.5 emission amounts exhibited the concave and convex quadratic relationships with O2 content, respectively, while trends in NOx emission amount had a negative linear relationship with the O2 content. The real-time burning rate and pollutant emission rates exhibited different trends that influenced the amount of emissions. When FGR was utilized with a constant primary airflow rate, an O2 content of 19.7% may be optimal for household biomass stoves. This study provides basic information on air supply design of household biomass stoves, which is essential for future clean stove design and improvement.

Additive Manufacturing of a Special-Shaped Energetic Grain and Its Performance.

In order to solve the problems of the complicated forming process, poor adaptability, low safety, and high cost of special-shaped energetic grains, light-curing 3D printing technology was applied to the forming field of energetic grains, and the feasibility of 3D printing (additive manufacturing) complex special-shaped energetic grains was explored. A photocurable resin was developed. A demonstration formula of a 3D printing energetic slurry composed of 41 wt% ultra-fine ammonium perchlorate (AP), 11 wt% modified aluminum (Al), and 48 wt% photocurable resin was fabricated. The special-shaped energetic grains were successfully 3D printed based on light-curing 3D printing technology. The optimal printing parameters were obtained. The microstructure, density, thermal decomposition, combustion performance, and mechanical properties of the printed grain were characterized. The microstructure of the grain shows that the surface of the grain is smooth, the internal structure is dense, and there are no defects. The average density is 1.606 g·cm−3, and the grain has good uniformity and stability. The thermal decomposition of the grain shows that it can be divided into three stages: endothermic, exothermic, and secondary exothermic, and the Al of the grain has a significant catalytic effect on the thermal decomposition of AP. The combustion performance of the grain shows that a uniform flame with a one-way jet is produced, and the average burning rate is 5.11 mm·s−1. The peak pressure of the sample is 45.917 KPa, and the pressurization rate is 94.874 KPa·s−1. The analysis of the mechanical properties shows that the compressive strength is 9.83 MPa and the tensile strength is 8.78 MPa.

Thermal Stability and Dynamic Mechanical Analysis of Benzoylation Treated Sugar Palm/Kenaf Fiber Reinforced Polypropylene Hybrid Composites

This research was performed to evaluate the mechanical and thermal properties of sugar palm fiber (SPF)- and kenaf fiber (KF)-reinforced polypropylene (PP) composites. Sugar palm/kenaf was successfully treated by benzoylation treatment. The hybridized bio-composites (PP/SPF/KF) were fabricated with overall 10 weight percentage (wt%) relatively with three different fibers ratios between sugar palm-treated and kenaf-treated (7:3, 5:5, 3:7) and vice versa. The investigations of thermal stability were then carried out by using diffraction scanning calorimetry (DSC) and thermogravimetry analysis (TGA). The result of a flammability test showed that the treated hybrid composite (PP/SPF/KF) was the specimen that exhibited the best flammability properties, having the lowest average burning rate of 28 mm/min. The stiffness storage modulus (E’), loss modulus (E”), and damping factor (Tan δ) were examined by using dynamic mechanical analysis (DMA). The hybrid composite with the best ratio (PP/SPF/KF), T-SP5K5, showed a loss modulus (E”) of 86.2 MPa and a damping factor of 0.058. In addition, thermomechanical analysis (TMA) of the studies of the dimension coefficient (µm) against temperature were successfully recorded, with T-SP5K5 achieving the highest dimensional coefficient of 30.11 µm at 105 °C.

Disproportionate collapse of steel-framed gravity buildings under travelling fires

Observations from realistic fires have revealed that a fire tends to “travel” across the floors rather than burning simultaneously for the duration. However, the collapse mechanism and mitigation measures of structures under travelling fires are still not well understood. This paper investigates the disproportionate collapse behaviour of three-dimensional steel-framed gravity buildings subjected to travelling fires. The effect of fire curves (burning rate) and fire spreading speeds on the collapse behaviour is first studied. The effectiveness of using fire protections and bracing systems in preventing collapse is examined. It is found that the duration of the heating phase has a great effect on whether a building collapses or not, and the building may collapse during the cooling phase. A “long-cool” fire curve (slow burnig rate) is more dangerous than mild (average burning rate) and “short-hot” fire curves (fast burning rate) since the former causes a higher temperature in the structure. The fire travelling speed significantly affects the failure sequence of columns, range of damage and collapse mode of structures. For the structure analysed, a slow travelling fire (e.g. 2.5 mm/s) may lead to a partial collapse mode confined around the fire-affected region, but a global collapse in a wider range may occur in a fast travelling fire (e.g. 10 mm/s). A higher level of fire protection may prevent the collapse of structures, but may also lead to collapse in the cooling phase due to the delayed increment of temperatures in the heated members. The collapse time of a protected structure under a travelling fire is longer than the fire-resistance rating of its components (up to 130 min). Application of bracing systems (horizontal, vertical or combined) can prevent collapse of structures under a slow travelling fire, but not for a fast travelling fire. It is recommended to consider the possible fire scenarios when determining the fire-resistance rating, and increase the fire-resistance rating of components to 3 h to prevent collapse under a travelling fire with a “long-cool” fire curve. The beam-to-column connections should possess a sufficient tension and compression resistance, which may be equal to 100% and 50% of the yielding capacity of beams, respectively.

Kenaf Fiber/Pet Yarn Reinforced Epoxy Hybrid Polymer Composites: Morphological, Tensile, and Flammability Properties.

The application of natural fibers is rapidly growing in many sectors, such as construction, automobile, and furniture. Kenaf fiber (KF) is a natural fiber that is in demand owing to its eco-friendly and renewable nature. Nowadays, there are various new applications for kenaf, such as in absorbents and building materials. It also has commercial applications, such as in the automotive industry. Magnesium hydroxide (Mg(OH)2) is used as a fire retardant as it is low in cost and has good flame retardancy, while polyester yarn (PET) has high tensile strength. The aim of this study was to determine the horizontal burning rate, tensile strength, and surface morphology of kenaf fiber/PET yarn reinforced epoxy fire retardant composites. The composites were prepared by hybridized epoxy and Mg(OH)2 PET with different amounts of KF content (0%, 20%, 35%, and 50%) using the cold press method. The specimen with 35% KF (epoxy/PET/KF-35) displayed better flammability properties and had the lowest average burning rate of 14.55 mm/min, while epoxy/PET/KF-50 with 50% KF had the highest tensile strength of all the samples. This was due to fewer defects being detected on the surface morphology of epoxy/PET/KF-35 compared to the other samples, which influenced the mechanical properties of the composites.

Flammability, Tensile, and Morphological Properties of Oil Palm Empty Fruit Bunches Fiber/Pet Yarn-Reinforced Epoxy Fire Retardant Hybrid Polymer Composites.

Oil palm empty fruit bunches (OPEFB) fiber is a natural fiber that possesses many advantages, such as biodegradability, eco-friendly, and renewable nature. The effect of the OPEFB fiber loading reinforced fire retardant epoxy composites on flammability and tensile properties of the polymer biocomposites were investigated. The tests were carried out with four parameters, which were specimen A (constant), specimen B (20% of fiber), specimen C (35% of fiber), and specimen D (50% of fiber). The PET yarn and magnesium hydroxide were used as the reinforcement material and fire retardant agent, respectively. The results were obtained from several tests, which were the horizontal burning test, tensile test, and scanning electron microscopy (SEM). The result for the burning test showed that specimen B exhibited better flammability properties, which had the lowest average burning rate (11.47 mm/min). From the tensile strength, specimen A revealed the highest value of 10.79 N/mm2. For the SEM morphological test, increasing defects on the surface ruptured were observed that resulted in decreased tensile properties of the composites. It can be summarized that the flammability and tensile properties of OPEFB fiber reinforced fire retardant epoxy composites were reduced when the fiber volume contents were increased at the optimal loading of 20%, with the values of 11.47 mm/min and 4.29 KPa, respectively.

Experimental understanding on combustion and micro-explosion characteristics of mixed droplets of aviation fuel, biodiesel and ethanol

In order to explore the influence of different temperature and oxygen concentration on the combustion and micro-explosion of BD60R10E30 droplets (the ratio of biodiesel, aviation fuel and ethanol was 60:10:30), a set of volume measuring device was designed, and the volume of BD60R10E30 droplets with 1.34 μL was obtained by using this device, and a multi-parameter tube furnace experimental system was established. By adjusting the parameters of temperature and oxygen concentration, the experimental phenomena such as droplet ignition, expansion and micro-explosion were found, and the shape and boundary of discrete flame were firstly observed in mixed fuel. The modified micro-explosion intensity calculation model was established, and the micro-explosion intensity of mixed droplets under different conditions was calculated, and the reasons for the difference of micro-explosion intensity were analyzed. In addition, the concept of volume burning rate of micro-droplets was put forward, and the volume burning rate model based on micro-explosion intensity was established. The average volume burning rate of BD60R10E30 droplets under different micro-explosion intensity conditions was calculated by combining the micro-explosion intensity model with the volume burning rate model.

Assessment of the physical and combustion properties of briquettes produced from banana tree waste

Nepal has an abundance of biomass resources. Heavy dependence on traditional source and waste management resulting from agricultural waste is one of the major problem in our country. Briquetting from agricultural waste can be an option for resource management. This study was undertaken to investigate the physical and combustion properties of briquettes produced from dried banana tree waste (leaves + pseudostem). Altogether four types of briquettes were produced, two from uncharred biomass using screw extruder and hydraulic jack briquetting machine and other two briquettes were produced from uncharred biomass/charcoal using screw extruder and beehive briquetting machine.For charred briquette, the density of screw extruder briquette (1.06 g/cm3) was higher than hydraulic briquette (0.33 g/cm3). For uncharred briquette, the density was higher (0.72 g/cm3) for screw extruder than beehive briquette (0.44 g/cm3). The Moisture content of briquettes varied from 7.23 to 11.04%, Volatile matter varied from 11 to 68.74%, Ash content varied from 4.94 to 49.43% and fixed carbon content varied from 15.27 to 32.34%. The calorific values of the briquettes ranged from 2462.0827 - 3899.193 kcal/kg, while the thermal efficiency ranges between 24.02– 30.71%, other results shows that the average burning rate between 3.55 and 6.41 g/min. Screw extruder briquette from uncharred Banana tree waste and beehive from charred/carbonized banana tree waste biomass was found to be comparatively better from the present study.

Fire incident analysis of a large-scale informal settlement fire based on video imagery

Informal settlements (IS) (also known as slums, shantytowns, ghettos, etc.) regularly experience fires. There has been an increasing interest in understanding fire dynamics in ISs. However, research has tended to focus on theories developed or based on idealized experiments rather than analysing real fire incidents, primarily because of the difficulty in obtaining data from real events. This work describes a recent fire incident that took place in an IS in South Africa. The analysis is based on the recording of a transit CCTV camera that captured the entire fire incident, the Fire & Rescue Service Incident Report and interviews conducted with the firefighters who responded to the incident. The footage provides high quality data allowing for novel analysis and understanding of such events never previously attainable. In a period of 33 min, an estimated 42 dwellings were affected at an average burning rate of 1.2 m/min and 15.45 m2/min. This paper describes (a) the fire spread, (b) the human behaviour, and (c) firefighters’ response and operations. The study of such incidents allows for a detailed understanding and development of policy for safety during urban environment large-scale fires. Additionally, improved interventions, firefighter strategies, community layouts, and response strategies can be developed for low-income communities.

Ignition of nanothermites by a laser diode pulse

Experimental investigation has been carried out for laser ignition and combustion of nanothermites based on aluminum and oxides of copper, bismuth and molybdenum. Ultrasonic mixing of nanosized powders was used to produce compositions. For thermite ignition, initiating laser pulse with a maximum intensity of 770 W/cm2 was generated by a laser diode with a wavelength of 808 nm. The ignition delay times, the minimum initiation energy density, and the average burning rate at various thermite densities and mass fractions of components were determined by recording the emission of radiation of the reaction products using a multichannel pyrometer jointly with a high-speed video camera. The effect of adding carbon black on the threshold parameters of a laser pulse was also studied. Based on the obtained results, certain assumptions were put forward with regard to the mechanism of nanothermites’ ignition by laser radiation and their burning. In particular, the assumptions were made on the two-stage process of the reaction initiation and jet burning mechanism of porous nanothermites.

The effect of the four fire walls to the center pool

According to the characteristics of burning rate of multiple oil pool fire, designing a four fire walls burning model. Influence of the central oil pan height, the fuel volume (oil film thickness) and the distance h between adjacent fire walls on fuel burning rate of central oil pool was studied. The results indicated that: Compared with single oil pool fire, the burning rate of central oil pan is enhanced by the four fire walls and the fire whirls also appears; define three regimes of flame reaction according to the flame shape, including initial state, incline state and merging state; when the gap width between 13cm-16cm, the center pool fire needs the lowest burning time and up to the highest average burning rate.

Combustion characteristics of oxygenated slurry droplets of nano-Al/EtOH and nano-Al/TPGME blends

In this study, two oxygenated slurry fuels were prepared by blending nano-aluminum (Al) particles (5 wt%) with ethanol (EtOH) and tripropylene glycol monomethyl ether (TPGME), respectively. The prepared oxygenated slurries were suspended as droplets on a thermocouple wire, and a laser ignition testing system was used for investigating their combustion characteristics. Snapshots of the combustion process showed that a slurry droplet of nano-Al/EtOH suffered three continuous stages, namely, an ignition delay stage, a droplet combustion stage, and a core combustion stage. In contrast, a slurry droplet of nano-Al/TPGME suffered only the first two stages during its combustion; however, an additional microexplosion phenomenon was also observed. During the droplet combustion stage, nano-Al/EtOH blend displayed higher average burning rate, but lower droplet surface temperature than nano-Al/TPGME blend. Emission spectra indicated the formation of gas-phase intermediate products, namely, Al, AlO, AlO2, and Al2O, via nano-Al oxidation during the combustion of both types of oxygenated slurry fuels. Nano-Al/EtOH and nano-Al/TPGME blends displayed higher emission spectral intensity of AlO and AlO2, respectively. The normalized ignition delay time of nano-Al/EtOH droplets was 41.3% longer than that of nano-Al/TPGME droplets. However, the normalized total combustion time of nano-Al/EtOH droplets was 26.4% shorter than that of nano-Al/TPGME droplets.

Numerical study of preheating primary air on pinewood and corn straw co-combustion in a fixed bed using Eulerian-Eulerian approach

The effect of preheating primary air on the co-combustion characteristics of a 50–50% blend of pinewood and corn straw in a fixed bed. The primary air temperatures were assessed from 20 to 130 °C. The co-combustion characteristics were included the co-combustion behaviors and emissions. In order to reveal the features of the combustion process in the porous bed, a two-dimensional unsteady state model was employed to investigate the combustion process in a fixed bed of blended biomass on the combustion process in a fixed bed reactor. Conservation equations of the bed were implemented to describe the combustion process. The gas phase turbulence was modeled using the k-ε turbulent model and the particle phase was modeled using the kinetic theory of granular flow. Results showed that by increasing primary air temperature the residual mass on bed decreased, while the average burning rates and ignition front propagation velocity increased At the primary air temperature of 85 °C the smallest unburned carbon was left in the ash, and the emissions of nitrogen-compounds were relatively small. In contrast, the primary air temperature of 85 °C was found to be well-operating condition, which can be suggested for industrial boiler during blend co-combustion. The simulation results were then compared with experimental data for different temperature, which shows that the combustion process in the fixed bed is reasonably simulated. The simulation results of solid temperature, gas species and process rate in the bed are accordant with experimental data.

Gas-phase thermography of droplet combustion and its application to characterize nanofuels

An IR thermography-based methodology is proposed to compute the instantaneous burning rate in droplet combustion. Temperature distribution around the droplet surface is measured using an infrared camera with a narrow bandpass filter of 4.25-μm wavelength. The technique holds importance in multicomponent fuels, densely concentrated nanofuels and nanofuels prepared by the addition of surfactant wherein the droplet surface regression rate is not linear due to micro explosions. For such applications, the conventional high-speed videography shows limitations, highlighting the importance of IR thermography. The methodology has first been validated against the results of classical interferometry. Thereafter, it has been applied to characterize the droplet combustion of alumina nanoparticles (AlONPs)-loaded methanol nanofluids. The results of the study showed that burning rates calculated through IR thermography are in good agreement with those determined using the conventional videography approach for the low mass loading of alumina nanoparticles. However, at higher mass loading ratios, the random occurrence of microexplosions towards the end of droplet combustion leads to inherent errors in the computation of the mass burning rate through videography. An increase in the average burning rate of the combusting droplet is observed at higher values of mass loading ratios, an observation that has been explained using IR thermography measurements.

Study on the combustion characteristics of two energetic materials

In order to understand the reaction characteristics of energetic materials after non-impact ignition, the typical energetic material powder was selected as the research object. The combustion phenomena of ZY-1 and ZY-2 energetic material powder were observed by high-speed photography and thermocouple. The combustion models of two energetic materials were preliminarily constructed through analysis. The arrival time of combustion wave was recorded by thermocouple, and the two kinds of energetic material powders were calculated. The average burning rates of energetic material powders are 4.0 mm·s-1 and 0.49 mm·s-1, respectively.

HMX Combustion Mechanism

The mechanism of HMX combustion at pressures of 0.5 to 50 atm is studied. It is shown that HMX burns in the hot-spot mode. The scale of nonuniformity of the burning surface is determined—the characteristic size of hot spots. The dependence of the size of the hot spots on the average burning rate of the sample is obtained. It is shown that this mechanism is similar to the hot-spot’s burning mode of double-base propellants with some peculiarities related to the presence of a molten layer in the k-phase: a significantly higher temperature in the flame zone and the absence of a carbon skeleton on the burning surface.

Fire behavior in multiple burning shrubs separated horizontally and vertically

Fire interactions between multiple 1 m tall, 0.7 m diameter chamise shrubs was studied utilizing the Wildland-Urban Interface Fire Dynamics Simulator (WFDS, Mell et al., 2009). Two shrub arrangements were investigated. First, nine shrubs were placed in a 3×3 horizontal region. The shrub separation distance and wind speed were varied. Two competing interaction mechanisms were identified: heat feedback enhancement, primarily due to thermal radiative heating, and air entrainment restriction. Shrub burning characteristics were examined and a global average burning rate was analyzed. For the no wind condition, the peak mass loss rate of the center shrub is 23% higher than the others, indicating that heat feedback enhancement is dominant. Air entrainment causes the surrounding shrubs to burn less intensely. At an imposed wind speed, air entrainment effects are dominant. Shrubs that are best shielded from the wind burn most intensely. Second, the vertical separation between two shrubs was varied under different wind conditions. With no ambient wind, nearly no interaction between the two shrubs was observed. At a wind speed of 1 m/s, significant interaction between shrubs occurred due to flame-tilting. The downwind shrubs burned the most vigorously for vertical separation distances between 0.2 and 0.8 m.

Melamine-based polyol containing phosphonate and alkynyl groups and its application in rigid polyurethane foam

The rapid depletion of energy resources is the most serious challenge facing humanity today. Energy consumption by buildings is the largest component of energy consumption, and most of it is in the form of heat loss. Therefore, many buildings use rigid polyurethane foam (PUF) as thermal insulation material to effectively reduce heat loss. However, the greatest disadvantage of PUF is its high flammability. In this work, to reduce the risk of fire caused by PUF, melamine-based polyol containing phosphonate and alkynyl groups (MF3.5 and MB3F3) is synthesized and used to improve the flame retardancy of PUF by replacing common polyether polyol. The effects of MF3.5 and MB3F3 on the physical and mechanical properties, cell morphology, thermal stability and flame retardancy of PUF are systematically studied. The research results show that the flame-retardant polyols have no effect on the thermal insulation properties of PUF, but result in a slight decrease in compressive strength. Thermogravimetric analysis proves that MF3.5 and MB3F3 can increase the temperature of the maximum mass loss rate and reduce the maximum mass loss rate, and significantly increase the char yield at 800 °C. The limiting oxygen index (LOI) value is increased to 24.3%. Cone calorimetry experiments show that MB3F3 reduces the peak heat release rate and total heat release by 28.2% and 30.5%, respectively. Vertical combustion tests show that the average burning rate of the flame-retardant PUF is much slower, and melt-dripping behavior is eliminated. The flame retardancy of PUF is improved mainly through a condensed phase mechanism.

Effects of ambient conditions on concurrent-flow flame spread over a wide thin solid in microgravity

Two-dimensional numerical simulations were performed to study concurrent-flow flame spread over a thin solid in microgravity. The main variable is the ambient flow velocity. Results were validated against recent microgravity experiments (Saffire) where samples 41 cm wide were burned in two different flow velocities. The numerical results showed that, when flow velocity increases, the average radiative heat flux out of the solid surface in the pyrolysis region remains constant. The average convective heat flux decreases and the average radiative heat flux into the solid surface increases. The average net heat flux remains approximately constant. Additional simulations using different ambient pressures and oxygen percentages further showed that, while away from extinction conditions, the average net heat flux in the sample pyrolysis region and hence the average solid mass burning rate are insensitive to the ambient conditions (i.e., oxygen percentage, flow speed, pressure). Furthermore, the steady-state flame length is mainly controlled by the rate of oxygen entrainment into the gas-phase reaction zone and the average solid mass burning rate. Based on these observations, analytical model was developed to correlate the flame spread rate and flame length to ambient conditions. It predicts that, for concurrent-flow flame spread at steady state, the flame length and flame spread rate have linear dependency on the ambient pressure and the forced flow velocity, and a second order dependency on the ambient oxygen percentage. The proposed correlations were tested against numerical simulations as well as a collection of data from previous microgravity experiments in a wide range of ambient conditions.

Experimental Investigation on Flame Characterization and Temperature Profile of Single/Multiple Pool Fire in Cross Wind

An experimental study was carried out to investigate the flame characterization and temperature profile for single and multiple pool fire with the influence of cross wind. There were 13 test cases in total, categorized into circle and rectangle fuel pans, with diameter (or equivalent diameter) ranged from 50 mm to 300 mm. Kerosene was used for the fuel of pool fire. Some K-type thermocouples were arranged around the flame to monitor the flame temperature, while the flame tilt angle was measured based on the photograph of flame for different case. Firstly, it can be found that there are three phases, including preheating, steady burning and extinguishing phase, during the flame evolution. The maximum temperature near the fuel surface is ∼1040 K, which is higher than that of flame plume (∼600 K), in the steady burning phase of circle single pool fire (D=300 mm), while the average burning rate is ∼1.525 g/s. In addition, the burning rates of all cases were measured and compared with the current predicted method. Typically, the flame morphology of single/multiple pool fire at different cross wind speed (ranging from 0 to 3.5 m/s) was analyzed, and it is found that the results for single pool fire agree with Thomas model and AGA model well, which are not suitable for multiple pool fire. Finally, the temperature profile of different case was measured with various wind speed.