Flash Flame Research Articles

Measuring thermal conductivity using H2-O2 flame on ceramic films prepared by atmospheric chemical vapor deposition

Uneven micron-sized pores on the surface of the polycrystalline alumina (Al2O3) substrates can affect their performance as electrical insulating plates. In this study, we investigated the sealing of these pores with amorphous Al2O3 films deposited via atmospheric chemical vapor deposition. Furthermore, we conducted annealing treatments on the samples. The color change of the deposited Al2O3 films was investigated using the Commission Internationale de I’Eclairage color space. Notably, the deposited films initially changed the sample color from white to orange or brown. However, increasing the annealing temperature and duration reversed this discoloration effectively and restored the original white (colorless) appearance of the sample. We measured thermal conductivity using the flame flash method with the H2-O2 flame to assess the influence of sealing. While the unsealed substrate exhibited a thermal conductivity of 4.66 W/mK in the range of 400–500 °C, the annealed and flattened Al2O3 film deposited on the substrate maintained a comparable thermal conductivity of 4.67 W/mK within the same temperature range. This finding demonstrates that our sealing method successfully filled the pores while having minimal influence on thermal conductivity, which is a crucial property for electrical insulation applications.

Burns Resulting From Electric Vehicle Manufacturing in Silicon Valley.

The development of electric vehicles (EVs) has introduced novel technologies and manufacturing processes that expose workers to new risks of burn injury. We identified 6 patients who were admitted to our burn center for injuries that occurred while working in EV manufacturing facilities. The burns fell into 3 categories: flash flame burns due to lithium-ion battery explosions, high-voltage electrical injuries, and burns caused by contact with molten metal. Recognizing these recurrent patterns of injury should inform future prevention efforts and prepare health systems to evaluate and treat patients burned in EV manufacturing.

Ignition limit of EPS foam by a hot particle under cross wind

The ignition of the building insulation materials by a hot particle is a typical spot fire phenomenon, but the scientific understanding is still limited. In this work, a hot steel spherical particle (6-16 mm and 800-1200 °C) was dropped onto the low-density expandable polystyrene (EPS) foam with an external airflow velocity of 0-4 m/s to obtain the ignition limit at the flash point and fire point. Airflow provides an alternative shortcut transition of unstable flash flame to a strong fire point and fuel burnout, because airflow increases the oxygen supply and flame heating rather than cooling the particle. As the airflow velocity increases, both flash and fire points first become easier to reach because airflow facilitates the mixing of pyrolysates and oxygen in the Smothering Regime. When the airflow velocity increases to the Thermal Regime, the delay time remains stable. Further increasing the airflow velocity to the Chemical Regime, the ignition delay time slightly increases until the airflow blows off the flash flame by cooling the particle or blowing away the flammable mixture from the hot surface. Such a competitive effect of airflow on hot particle ignition is also qualitatively verified by theoretical analysis. Flame retardants inside EPS foam do not change the flash ignition but inhibit the transition to fire point and burnout, even under the assistance of airflow. This work enhances the comprehension of the complex interactions between flash points and fire points in the spotting or hot-particle ignition of the building facades.

Experimental Study on the Dynamic Combustion Behavior of Thin Fuel Layer Caused by Instantaneous Leakage of Ethanol and Gasoline

ABSTRACT This paper presents an experimental and theoretical research on the instantaneous leakage fire of ethanol and gasoline. A horizontal substrate without vertical boundaries was used, and the leaked fuel could spread freely. The fuel leakage volume was set from 7 mL to 75 mL, and the ignition time was set from 10 s to 40 s. Results showed that the fuel thickness in this study is observed less than 1 mm and decreases continuously throughout the whole process. Different fuels showed different combustion behaviors in same cases. For ethanol, its combustion does not change the surface morphology, and the combustion process includes three stages, namely spreading, quasi-stable and shrinking. The quasi-stable stage is caused by the dynamic balance between flame development and fuel consumption. The quasi-stable burning rate of ethanol leakage fire is about 70–90% to pool fire with same diameter, however, their flame heights are similar. Theoretical analysis was conducted on the heat radiation absorption in the fuel, and found that at longer ignition times, the smaller absorption ratio caused by the lower thickness plays a more important role than the larger radiation feedback from the larger burning area. For gasoline, the soot from insufficient combustion adheres to the substrate impeded the flow of fuel during combustion process, and the burning area includes two parts, i.e. the center constant flame and flash flames intermittently appearing at the edge. The burning area, burning rate and flame height of gasoline decrease continuously during the whole combustion process. In addition, some interesting phenomena are observed before extinguishing, such as the revolved flash flame for gasoline, and the relevant explanations have been attempted.

Use of Flash-Flaming Technology to Improve Seed Handling and Delivery of Winterfat (Krascheninnikovia lanata)

Ecological restoration of rangelands using wild-collected seeds can be challenging due to low seed quality, inconvenient seed anatomy, and poor plant establishment. In North America, the half-shrub winterfat (Krascheninnikovia lanata) is a valuable protein-rich forage for wildlife and livestock. Seeds of this species are contained in one-seeded fruits enclosed in four fluffy, silky bracts. While the seeds can be removed from the bracts, it is not recommended as the bracts are thought to help protect the seed and aid in germination and seedling growth. However, bracts of winterfat make it difficult to incorporate this species within a seed mix because they prevent the seed from flowing through mechanized seeders. The anatomy of winterfat fruit also makes it difficult to treat this species with external seed-coating materials that may aid in direct seeding efforts. We tested the use of a recently developed flash-flaming technique in combination with seed coating to improve the flowability of winterfat fruits. Our results indicate that flash flaming can reduce the appendages on winterfat fruits, which decreased fruit volume by up to 46% without impacting seed germination. Flash flaming also makes it possible to incorporate a polymer seed coating to the exterior of winterfat fruits. We found that flash flaming combined with seed coating improved the flowability of winterfat fruits, as measured with standard laboratory tests and by delivering fruits through a broadcast seeder and a rangeland drill. These results indicate that flash flaming plus seed coating provides a new technology that will allow for the treating and planting of winterfat on degraded rangelands.

Simulation of Low-Temperature Oxidation and Combustion of N-Dodecane Droplets under Microgravity Conditions

Fires are considered among the most dangerous accidents on manned spacecraft. That is why several programs of combustion experiments were implemented at the International Space Station (ISS) since 2008. In the experiments with n-heptane and n-dodecane droplet combustion, a new phenomenon was discovered, namely, the phenomenon of the radiative extinction of a burning droplet with subsequent multiple flashes of flame. In this paper, n-dodecane droplet ignition, combustion, radiative extinction, and subsequent low-temperature oxidation with multiple flashes of cool, blue, and hot flames under microgravity conditions are studied computationally. The mathematical model takes into account multiple elementary chemical reactions in the vicinity of a droplet in combination with heat and mass transfer in liquid and gas, heat release, convection, soot formation, and heat removal by radiation. The model is based on the non-stationary one-dimensional differential equations of the conservation of mass and energy in liquid and gas phases with variable thermophysical properties within the multicomponent diffusion concept in the gas phase. Calculations confirm the important role of the soot shell formed around the droplet and low-temperature reactions in the phenomenon of droplet radiative extinction with multiple flame flashes in the space experiment at the ISS. Calculations reveal the decisive role of the blue flame, arising due to the decomposition of hydrogen peroxide, in the multiple flame flashes. Calculations with forced ignition of the droplet reveal the effect of the ignition procedure on droplet evolution in terms of the timing and the number of cool, blue, and hot flame flashes, as well as in terms of the combustion rate constant of the droplet. Calculations with droplet self-ignition reveal the possible existence of new modes of low-temperature oxidation of droplets with the main reaction zone located very close to the droplet surface and with only partial conversion of fuel vapor in it.

Flash flaming is a valid seed enhancement for a diverse range of species and seed morphologies

Flash flaming has shown promise as a seed enhancement technology that improves the handling properties of bulky or irregularly shaped seed material, which in turn benefits logistical and ecological aspects of large-scale direct seeding. To date, only a small number of grass species, that possess similar morphological characteristics, have been tested. This paper describes the application of flash flaming to diaspores (i.e. the dispersal unit comprising the seed and any surrounding or attached tissues) of 19 diverse dryland species from the Amaranthaceae, Asteraceae, Chenopodiaceae and Poaceae critical to ecological restoration in the mining intensive Pilbara region of Western Australia. Flash flaming parameters for each species were tested to identify and maximise volume and mass reduction, reduce particle cohesiveness and maximise flow through a mechanical seeding device, whilst maximising germination. Flaming of all species resulted in reductions in batch volume and mass, and improvements to flow characteristics. For 17 species, flaming either benefited or did not impact on germinability. For two species in the Amaranthaceae, flaming with the settings tested here resulted in a reduction in germinability; however, flaming enabled the diaspores to pass through a mechanical seeding device enabling mechanical distribution which is critical if the species are to be used in large scale restoration.

Flame Spread Pulsation Characteristics of Transformer Oil Vertical Spill Fire

Abstract To investigate the effects of fuel discharge rate and initial fuel temperature on flame pulsation characteristics of vertical spill fire, a series of experiments under continuous leakage conditions are conducted on a specially designed experimental setup, for which transformer oil is selected as the fuel. Results show that the vertical spill fire burning area can be divided into three parts. Both the main flame and the flash flame are involved in the flame pulsation behavior, and the essence of the flame pulsation of the vertical spill fire is the periodic alternation of the diffusion flame and the premixed flame. Flame pulsation frequency shows a linear negative correlation with the fuel leakage rate, it decreases from 3.56 Hz (4.98 ml m−1s−1) to 2.439 Hz (15.93 ml m−1s−1), and it has a positive correlation with the initial fuel temperature. As the fuel discharge rate increases, the pulsation amplitude increases while the flame transient spread rate decreases, both of them have no significant correlation with the initial fuel temperature. The ratio of the average flame pulsation amplitude to the maximum pulsation amplitude is between 0.57 and 0.76. The flame transient spread rate shows a negative correlation with the fuel discharge rate, the maximum flame spread velocity reaches 3.17 m/s and 2.85 m/s in the growing phase and shrinking phase respectively. Due to the entrainment effect of the flame plume, the flame transient spread rate in the shrinking phase is higher than that in the growing phase. Analyzed the diffusion process of fuel vapor and the heat transfer mechanism of vertical spill fire, the control of fuel leakage rate and initial temperature on the flame pulsation characteristics is mainly manifested in its influence on the fuel evaporation and diffusion process and the length of preheating area. This work provides data supplement on the flame spread of liquid fuel spill fire.

Hysteresis in flame stabilization in a hydrogen fueled supersonic combustor

Hysteresis in flame stabilization mode transitions in a hydrogen-fueled strut-stabilized supersonic combustion test rig was experimentally observed and studied. Air was vitiated using H2–O2 combustion products to stagnation conditions of 8.65 bar and 1350 K and was expanded through a rectangular nozzle to Mach number 2.5. H2 fuel was injected transversely using a strut positioned at the center of the combustor. The equivalence ratio (ER) was changed in time to study its effects on flame stabilization modes. Shadowgraph and wall pressure measurements were used to study the shock system generated by the strut in the supersonic combustor. High-speed OH∗ chemiluminescence and high-speed flame imaging were used to study the heat release zones and flame structure of different combustion modes and transitions between them. Three different combustion modes were observed, namely: divergent section flame (CM1), strut wake stabilized flame (CM2), and jet stabilized flame (CM3). CM1 was observed at a very low ER, where the H2 was ignited by the normal shock positioned in the divergent section. At this point, the weak shock system at the strut is unable to ignite the fuel. At higher ER, CM2 was observed, as a stronger shock system ignites the richer mixture at the wake of the strut. It was observed that the mixture auto-ignites in the strut wake and doesn't flashback from the divergent section. When the ER is further increased, the stronger injection shock reduces the local velocity and increases the static temperature, enhancing the flame speed of the richer mixture. Thus, the flame flashes back to the fuel jet. Two hysteresis were observed in the supersonic combustor based on ER as a time-varying input. The flame stabilization mode has two solutions based on the history of the change in ER, hence indicating hysteresis. The hysteresis between CM1 and CM2 is because of the retention of the temperature and radicals in the recirculation zone at the wake of the strut. The hysteresis between CM3 and CM2 is because of the retention of the temperature and radicals in the horseshoe vortices around the fuel jets. Understanding hysteresis will help design scramjets with wider operability.

Flash Flaming Improves Flow Properties of Mediterranean Grasses Used for Direct Seeding

The demand for native grasses is increasing in restoration and agriculture, though their use is often limited due to seed handling challenges. The external structures surrounding the grass seed (i.e., the floret) possess hairs, awns, and appendages which create blockages in conventional seeding equipment. Flash flaming is a patented technology which allows precision exposure of floret material to flames to singe off hairs and appendages. We used two grasses native to Mediterranean ecosystems of Western Australia (Amphipogon turbinatus R.Br. and Neurachne alopecuoidea R.Br.) to evaluate the effects of different flaming techniques on flow properties and germination. Flaming significantly improved flowability in both species and had both neutral (A. turbinatus) and negative (N. alopecuroidea) effects on germination. Flaming torch size influenced germination, though flaming temperature (low or high) and whether this was kept constant or alternating had no effect. The best evaluation of germination following flaming was achieved by cleaning flamed florets to seed and/or germinating in the presence of karrikinolide (KAR1) or gibberellic acid (GA3). We suggest that flaming settings (particularly torch size) require species-specific evaluation and optimisation. Removing seeds from flamed florets and germination testing this material in the presence of stimulants may be a useful protocol for future flaming evaluations.

A Single Center Review of the Dangers of Recreational Fires in the Pediatric Population.

The increasing trend of admissions due to recreational fires prompted a 5-year review. The retrospective chart review of pediatric burn injuries from campfires or bonfires treated at a single medical center’s burn unit. The study included children within the ages of 0 to 15 admitted or transferred from January 2012 to December 2016 with first, second, and/or third degree burns by bonfires. These patients accrued burns due to active fires as well as postfire ember contact. Two hundred-eighty nine (289) were pediatric admissions out of which 66 (22.8%) were pediatric admissions associated with recreational fires. The mean annual admission for campfire or bonfire burns was 13 ± .98. The mean age was 4 ± 2.47 years. Gender distribution revealed 21 female and 45 male pediatric patients under the age of 15. From the available data, 8 (12%) of these burns occurred at home in the backyard and 16 (24%) at a public camp or park. Injury mechanisms were more commonly a result of direct contact with hot coals and embers (65%). Falls into open flame accounted for 23% (n = 15) of injuries, and flash flames accounted for 12% of injuries (n = 8). The presence of supervision was unknown in 56%; however, lack of supervision was a factor in 14% of our study population. By gaining a better understanding of the type of injury, mechanism of injury, and the demographic of recreational fire burn victims, policy, and awareness campaigns were instituted in an effort to reduce the incidence of recreational fire burns.

Insights into flashback-to-flameholding transition of hydrogen-rich stratified swirl flames

In this study, we investigate the flame stabilization behavior in hydrogen-enriched stratified swirl flames after the flame flashes back into an annular mixing tube with an axial swirler of swirl number 0.9. Two different modes of flame stabilization, namely intermediate stabilization and flameholding, are identified. For 80% or higher hydrogen enrichment of the fuel, the flashback is found to result in flameholding. Acetone-PLIF measurements are used to assess the equivalence ratio distribution in the mixing tube. It is shown that the flow inside the mixing tube has intermittent presence of fuel-rich pockets. Furthermore, high speed laser diagnostic and simultaneous chemiluminescence imaging was carried out to understand the transition of flame propagation from the center-body boundary layer to the outer wall boundary layer. With the help of time-resolved images and simultaneous velocity fields, four different stages of flashback-to-flameholding transition were identified. It was noted that the bright flame kernels formed due to the flame's interaction with fuel-rich pockets, impose significant deflection on the approach flow in the vicinity of the outer wall boundary layer. Acute-tipped narrow flame structures were found to anchor the flame on the outer wall. These flame structures were found to accelerate upstream upon reaching the fuel-rich regions in the outer wall boundary layer.

728 The Faces of Autologous Skin Cell Suspension as Epidermal Grafts

Abstract Introduction Facial burns are frequently severe and are difficult to skin graft, which may lead to increased morbidity including chronic pain, scarring, and psychosocial stigma. The aim of this study was to describe outcomes of patients with facial burns who received autologous skin cell suspension as an epidermal graft. Methods A retrospective chart review of patients with facial burns admitted to an ABA verified Burn Center from January 2019 to August 2019 was performed. Each patient underwent tangential excision of superficial and deep partial-thickness burn wounds followed by autologous skin cell suspension applied as an epidermal autograft. The wounds were covered with a non-adherent dressing along with bismuth-impregnated, petroleum-based gauze. The dressings were secured in place with sutures to prevent disruption. On post-operative day 6 the dressings were removed with transition to an antimicrobial ointment applied to any remaining open wounds or a moisturizing lotion. Results Five patients, aged 41–89 years, were included. Total body surface ranged from 7–50%. Etiology of the burns included: flame from metal fabricating, assault followed by dousing the patient in gasoline and lighting on fire, flash flame from a water heater explosion, hot oil contact, and involvement in a house fire. 3 of the 5 patients had complete healing noted by post-operative day 6 with excellent results. Two patients required a second excision and application of autologous skin to small portions of the lateral face after healing the majority of the face. One patient developed mild microstomia requiring oral splinting. One of the two patients that required a second application developed ectropian to one of her eyes which was treated with temporary tarsorrhaphy. The second patient that required a second application, died during her hospitalization secondary to complications from her burns and underlying medical co-morbidities. Surviving patients reported satisfaction with the cosmetic outcomes. Conclusions Autologous skin cell suspension as an epidermal graft is a viable option for cosmetically important areas such as the face. This case series provides evidence for its validity when treating partial-thickness burns utilizing the above described protocol in conjunction with a multidisciplinary care team within a burn center. Applicability of Research to Practice By sharing our institutions experience with this relatively new technique we hope to share our positive outcomes as an alternative to stand excision and grafting to areas of significant cosmetic outcomes.

329 Prognostic Indicators for Upper and Lower Extremity Amputations in a Verified Burn Center

Patients with burns or necrotizing soft tissue infections are at risk for significant morbidity. Extremities with extensive complex skin defects are at increased jeopardy. This may be increased by co-morbid conditions, yet prognostic indicators are not well defined in the literature. The purpose of this study was to identify and describe those potential prognostic factors found in the burn population patients requiring either upper or lower extremity amputation. This is a retrospective chart review of patients requiring amputation from 2000 - 2017. The co-morbidities of these patients were compared to patients that did not require amputation. Descriptive statistics and the relative risk of amputation for certain co-morbidities were calculated. During the study period there were a total of 110 patients requiring amputation versus 12,997 that did not. For those requiring amputations, burn injury was the most common precipitating event (59%) and flame flash was the most common mechanism (25%). The most frequent level of amputation was at the digit level (39%) followed by the transtibial level (33%). When amputees (AP) were compared to non-amputees (NA) there were significant differences between average (median) age, AP 49.9 (54.1) years vs. NA 34.3 (33.8) years (p < 0.001), TBSA AP 19.9% (6%) vs. NA 8.1% (4%, p=0.003) and length of stay AP 33.4 (26) days vs. NA 11.0 (7) days (p<0.001). Conditions associated with increased risk of amputation included cardiovascular disease (RR 4.3, p<0.001), liver disease (RR 4.8, p<0.001), renal insufficiency (RR 19.1, p<0.001), diabetes (RR 5.0, p <0.001), alcohol abuse (RR4.3, p<0.001) and smoking history (RR 4.1, p<0.001). Several comorbidities are associated with higher risk of amputation. Burn patients at higher risk of amputation are not only systematically different from non-amputees, but more specifically have greater restriction of blood flow from diabetes, cardiovascular disease and end stage renal disease which are the greatest afflictions leading to the need for an amputation. Future studies should investigate the role of circumferential burn injury, escharotomies / fasciotomies, as well as, the differences in amputation level between the upper versus lower extremity. This study gives providers quantified data to identify those patients at higher risk of amputation.

Experimental and Analytical Characterization of Firebrand Ignition of Home Insulation Materials

Wildland firebrands are known to ignite materials in attic spaces of homes. To clarify the effects of choices in attic insulation materials for homes located at the wildland urban interface, this study seeks to characterize the effects of firebrand characteristics on the ignition propensity of several common insulation materials: polyurethane foam, expanded polystyrene (EPS), extruded polystyrene (XPS), flame retarded and non-flame retarded denim, and flame retarded and non-flame retarded loosefill cellulose. An experimental system was developed to explore the effects of firebrand heating, air flow, and firebrand configuration on ignition. For an equal initial mass of wooden material, two firebrand configurations were generated: a single whole firebrand and multiple (five) fragmented firebrands. Relative to whole firebrands, the fragmented firebrands were found to more reliably ignite the insulation materials. Thermoplastic insulation material would only ignite in a temporary flash flame, but did not support sustained burning. Following the flash flame, the firebrands would melt through the synthetic polymer material (XPS and EPS) and cease smoldering. Cellulosic insulation materials would ignite in a sustained fire provided that there was adequate air flow. A simple heat and mass transfer model was developed to describe the ignition process due to firebrand deposition. Traditional lab-scale experiments, thermogravimetric analysis and cone calorimetry, were performed to parameterize the model. Results followed experimentally observed firebrand temperature patterns. There was an average error of approximately 8.5% between firebrand temperature model predictions and experimental measurements. Also, consistent with the experimental results, the model predicted that increasing air flow increased ember temperature and reduced the time to ignition for cases in which ignition occurs.

An experimental study on combustion performance and flame spread characteristics over liquid diesel and ethanol-diesel blended fuel

Ethanol has gradually become a commonly used additive in diesel to reduce the carbon foot print of the combustion products. In the process of production, transportation and storage, once the accidental leaked ethanol-diesel blend fuel is ignited, the flame will spread very fast and cause great threaten to people's lives and properties, the combustion properties of ethanol-diesel blends is thus a matter of great concern to us. A set of experiments was conducted to study the effects of fuel depth and ullage height on liquid flame spread of diesel and 5% ethanol-diesel. Results showed that as the fuel depth increases under ullage effect, the flame spread rate increases first and then maintain constant. For 5% ethanol-diesel, the flame spread rate decreases monotonously and then tends to be unchanged with ullage height due to the higher combustion efficiency and oxygen content of ethanol-diesel. For deep pools, the surface velocity increases with fuel depth. Moreover, the flash flame pulsation frequency is weakly affected by the fuel depth and presents a negative relationship with ullage height. The study on these issues may have the potential to benefit the current safety production, utilization and management of the energy of ethanol-diesel blends.

Characteristics of stoichiometric CH4/O2/CO2 flame up to the pure oxygen condition

To pursue high efficiency in oxy-fuel combustion, usually a stoichiometric mixture with high oxygen content is preferred. However, the oxygen level in industrial operation is restricted by potential hazards of flame flash back, equipment erosion and combustion instability. In this study the stoichiometric CH4/O2/CO2 mixtures are tested in a rapidly mixed tubular flame combustor by varying the oxygen content from 0.21 to 1.0. Based on previous studies, the combustor is optimized to successfully achieve the steady tubular combustion up to the pure oxygen condition; the adiabatic flame temperature can vary between 1750 and 3050 K; in the CH4/O2 tubular flame, the overall mole fraction of active radicals can reach 0.20, and the net heat release rate is much higher than that of CH4/air flame. With three additional burners, this study systematically evaluates the influential factors such as oxygen content, inlet size, burner diameter and flow rate on the flame characteristics; furthermore, the dimensionless Damköhler number and Reynolds number are adopted to quantitatively identify different burning regimes through the Borghi diagram; the results provide a useful guide to the operation of oxy-fuel combustion up to the pure oxygen condition.

Rapidly mixed combustion of hydrogen/oxygen diluted by N2 and CO2 in a tubular flame combustor

In this study hydrogen flames have been attempted in a rapidly mixed tubular flame combustor for the first time, in which fuel and oxidizer are individually and tangentially injected into a cylindrical combustor to avoid flame flash back. Three different cases were designed to examine the effects of fuel and oxidizer feeding method, diluent property, oxygen content and equivalence ratio on the characteristics of hydrogen flame, including the flame structure, lean extinction limit, flame stability and temperature. The results show that by enhancing mixing rate through feeding system, the range of equivalence ratio for steady tubular flame can be much expanded for the N2 diluted mixture, however, at the oxygen content of 0.21 (hydrogen/air) the steady tubular flame is achieved only up to equivalence ratio of 0.5; by decreasing oxygen content, the lean extinction limit slightly increases, and the upper limit for steady tubular flame establishment increases significantly, resulting in an expanded tubular flame range. For CO2 diluted mixture, the stoichiometric combustion has been achieved within oxygen content of 0.1 and 0.25, for which the burned gas temperature is uniformly distributed inside the flame front; as oxygen content is below 0.21, a steady tubular flame can be obtained from the lean to rich limits; and the lean extinction limit increases from 0.17 to 0.4 as oxygen content decreases from 0.21 to 0.1, resulting in a shrunk tubular flame range. Laminar burning velocity, temperature and Damköhler number are calculated to examine the differences between N2 and CO2 diluted combustion as well as the requirement for hydrogen-fueled tubular flame establishment.

Experimental study on characteristics of flame spread over diesel and n-butanol pool fires in tunnel

Comparative tests were conducted to investigate the flame spread characteristics of a typical hydrocarbon fuel mixture (0# diesel) and a typical pure alcohol fuel (n-butanol) in a reduced-scale (1:10) tunnel model. Experimental data with regard to flame spread appearance, flame spread rate, temperature profile, and subsurface convection flow were obtained and discussed in this study. Results showed that: (1) The diffusion flame of n-butanol propagated in a forward-stop-forward pattern, while diesel fuel pulsated in a forward-back-forward manner with less stability. The flash flame of diesel appeared periodically with significant higher spreading velocity than the enduring flash flame of n-butanol. (2) The average main flame spread rate of n-butanol was faster than that of diesel fuel, whereas the transient flame spread rate showed an opposite trend. (3) No sensitive difference was found in surface temperature profile between two fuels, but n-butanol retained higher vertical temperature due to its higher flame height than diesel. The infrared images discovered that the subsurface convection flow of diesel had a larger size and noticeable temperature gradient. Diesel burned with more luminous flame and denser soot than n-butanol, owing to its more complex fuel components.

Low-Temperature Flameless Combustion of a Large Drop of n-Dodecane under Microgravity Conditions

The forced ignition, combustion, and spontaneous ignition of a drop of n-dodecane in an atmosphere of air at a normal pressure under microgravity conditions were studied based on a physicomathematical model of drop combustion and a detailed kinetic mechanism of the oxidation and combustion of n-dodecane C12H26. The selection of n-dodecane was related to the Russian–American experiment CFI (Cool Flame Investigation) Zarevo performed in 2017 aboard the International Space Station with the use of the large drops of this hydrocarbon. The analysis carried out deepens our knowledge about the flameless combustion of a large drop under the conditions of microgravity. The calculations showed that, after the radiation extinction of a hot flame, the drop can continue to evaporate because of the exothermic low-temperature oxidation of fuel vapor with repeated blue flame flashes at a characteristic temperature of 980–1000 K. A detailed analysis of the calculation results showed that the regular splashes of temperature resulted from the thermal decomposition of hydrogen peroxide—branching with the release of hydroxyl radicals.