Liquid Combustion Research Articles

Development and Characterization of Thermal Protection Gels for Steel Pipelines Transporting Combustible Materials

Due to low costs, pipelines are commonly used for transporting hazardous substances such as combustible liquids and gasses. Currently, chemical industrial parks and gas production stations have dense pipeline networks. In the case of a pipeline leakage and subsequent fire accident, the adjacent pipelines could be directly impinged by the flame or engulfed in hot smoke, with the potential to result in a chain of accidents and catastrophic consequences. It is thus of practical importance to develop an efficient thermal protection material for pipelines. In this study, a new type of bio-based gel material was prepared for pipeline thermal protection, using guar gum (GG) as the gelling agent, sodium tetraborate (B) as the crosslinking agent and magnesium chloride (MgCl2) as the fire retardant. Firstly, orthogonal experiments were conducted to examine the gelling time of the gel and determine the optimal formulations that meet the protection requirements. Subsequently, water retention, thermal stability and the microstructure of these formulations were analyzed. Finally, the thermal protection performance of the gel formulations was evaluated under the direct impingement of flames or high-temperature smoke. The results indicated that the best performance was achieved by the formulation with GG, B and MgCl2 mass fractions of 2.5, 0.6 and 0.5 wt%, respectively. This formulation also exhibited the best water retention capacity and thermal stability. In the pipeline thermal protection experiments, this formulation achieved effective protection times of 216 s (for a 90 mm diameter) and 312 s (for a 120 mm diameter) for the lower part of the pipeline under direct flame impingement. Under high-temperature smoke impingement, this formulation also showed excellent performance. These research and findings can provide an important foundation for the further development of thermal protection materials for pipelines under fire conditions.

Investigation the Thermal Behavior of Lemon and Orange Peels Composite Fuel Diesel

Background: The aim of this research is to investigate the thermal behavior of a composite fuel prepared by mixing diesel fuel with citrus peel powder in the presence of activators and combustion accelerators. The study focused on utilizing abundant citrus waste, such as lemon and orange peels, as sustainable bioresources to reduce environmental pollution and optimize fuel efficiency. The research explored the thermal properties of the composite fuel and compared it with pure diesel through combustion experiments conducted at atmospheric pressure and combustion pressure in the engine. Methods: The study set the limits of the investigation to various proportions of lemon and orange peel powder mixed with diesel, ranging from 5% to 15% by mass of the total fuel composite. Two catalysts, sodium hydroxide (NaOH) and sulfuric acid (H2SO4), along with calcium oxide (CaO) powder were incorporated into the mixtures as activators to enhance combustion efficiency. The composite fuel characterization included thermogravimetric analysis (TGA) and thermographmetric station experiments to observe the combustion processes and assess the thermal behavior of the composite fuel. Results: The results revealed four distinct phases of combustion during the burning time of 60 seconds: volatile combustion, liquid combustion, combustion of solid materials, and the interaction of active substances with combustion residues. Using activators and catalysts significantly enhanced combustion efficiency and minimized the amount of residue produced during the process, resulting in thermal behavior that is more similar to that of pure diesel. Lemon peel powder with activators demonstrates better thermal behavior compared to orange peel powder. Conclusions: Based on the findings, some recommendations are proposed for further development such as the optimization of activator ratios, exploration of different proportions of lemon and orange peel powder, and investigation of other catalysts. Real-world engine performance tests and emission profile analysis can validate the thermal behavior results obtained from combustion experiments.

Genomic analysis and biodesulfurization potential of a new carbon-sulfur bond cleaving Tsukamurella sp. 3OW.

Direct combustion of sulfur-enriched liquid fuel oil causes sulfur oxide emission, which is one of the main contributors to air pollution. Biodesulfurization is a promising and eco-friendly method to desulfurize a wide range of thiophenic compounds present in fuel oil. Previously, numerous bacterial strains from genera such as Rhodococcus, Corynebacterium, Gordonia, Nocardia, Mycobacterium, Mycolicibacterium, Paenibacillus, Shewanella, Sphingomonas, Halothiobacillus, and Bacillus have been reported to be capable of desulfurizing model thiophenic compounds or fossil fuels. In the present study, we report a new desulfurizing bacterium, Tsukamurella sp. 3OW, capable of desulfurization of dibenzothiophene through the carbon-sulfur bond cleavage 4S pathway. The bacterium showed a high affinity for the hydrocarbon phase and broad substrate specificity towards various thiophenic compounds. The overall genome-related index analysis revealed that the bacterium is closely related to Tsukamurella paurometabola species. The genomic pool of strain 3OW contains 57 genes related to sulfur metabolism, including the key dszABC genes responsible for dibenzothiophene desulfurization. The DBT-adapted cells of the strain 3OW displayed significant resilience and viability in elevated concentrations of crude oil. The bacterium showed a 19 and 37% reduction in the total sulfur present in crude and diesel oil, respectively. Furthermore, FTIR analysis indicates that the oil's overall chemistry remained unaltered following biodesulfurization. This study implies that Tsukamurella paurometabola species, previously undocumented in the context of biodesulfurization, has good potential for application in the biodesulfurization of petroleum oils.

Diethylenetriaminepentaacetic Acid-based Conducting Solid Polymer Electrolytes Impede Lithium Dendrites and Impart Antioxidant Capacity in Lithium-Ion Batteries.

In the development of lithium-ion batteries (LIBs), cheaper and safer solid polymer electrolytes are expected to replace combustible organic liquid electrolytes to meet the larger market demand. However, low ionic conductivity and inadequate cycling stability impede their commercial viability. Herein, a novel flexible conducting solid polymer electrolytes (CSPEs) based on polyvinyl alcohol (PVA) and ion-polarized diethylenetriaminepentaacetic acid (P-DETP) is developed for the first time and applied in LIBs. PVA and P-DETP form a compact polymer network through hydrogen bonding, enhancing the thermomechanical stability of CSPE while restricting the migration of larger anions. Furthermore, density functional theory calculations confirm that P-DETP can facilitate the dissociation of Li+-TFSI- via electrostatic attraction, resulting in increased mobility of lithium ions. Additionally, P-DETP contributes to the formation of a stable electrode-electrolyte interface layer, effectively suppressing the growth of lithium dendrites and improving antioxidant capacity. These synergistic effects enable CSPE to exhibit remarkable properties including high ionic conductivity (2.8 × 10-4 S cm-1), elevated electrochemical potential (5.1V), and excellent lithium transference number (0.869). Notably, the P-DETP/LiTFSI CSPE demonstrates stable performance not only in LiFePO4 batteries but also adapts to high-nickel ternary LiNi0.88Co0.06Mn0.06O2 cathode, highlighting its immense potential for application in high energy density LIBs.

Building a model of heating an oil tank under the thermal influence of a spill fire

The object of this study is the process of liquid combustion in a spill, and the subject of research is the distribution of temperature along the wall and roof of a vertical steel tank that is heated under the thermal influence of a spill fire. The heat balance equation for the wall and roof of the tank with oil product was constructed. The assumption of a small thickness of the wall and roof of the tank relative to its linear dimensions makes it possible to move to two-dimensional differential equations of the parabolic type. The equations take into account the radiative heat exchange with the flame, the environment, the internal space of the tank, as well as the convective heat exchange with the surrounding air, the vapor-air mixture, and the liquid inside the tank. Using the methods of similarity theory, estimates of the coefficients of convection heat exchange of the outer surface of the tank with the surrounding air and the inner surface with the vapor-air mixture and liquid in the tank in the conditions of free convection were constructed. The application of the finite difference method for solving the heat balance equations has made it possible to derive the temperature distribution on the surface of the tank at an arbitrary moment in time. It is shown that the value of the coefficient of convection heat exchange of the liquid exceeds the corresponding value for the air-vapor mixture by (1÷2) orders of magnitude. As a result, the part of the wall located below the oil product level is heated to a temperature of (80÷230) °C depending on the viscosity of the liquid. This occurs despite the fact that the value of the mutual radiation coefficient reaches its maximum value at the lower part of the wall. From a practical point of view, this means that the part of the wall above the level of the oil product in the tank can reach dangerous temperature values, and it should be cooled first. The constructed model of tank heating also enables determining the limit time for the start of cooling of the tank.

ANALYSIS AND CREATION OF NEW ENERGY-SAVING DESIGNS OF INSTALLATIONS FOR ENVIRONMENTALLY COMBUSTION OF LIQUID FUEL IN OIL FACTORY FURNACES USING THE HEAT OF OUTLET COMBUSTION PRODUCTS

The article analyzes the installations and methods used at oil refineries for recycling the heat of exhaust flue gases in order to increase the efficiency of fuel use in tube furnaces and accompanying reduction in pollutant emission into the air basin. Recommendations on rational type selection of waste heaters for furnace units of oil refining industries are given.The authors present fundamentally new installations for burning liquid fuel in the form of oil-water emulsions using the heat recovery of emitted combustion products of furnace installations for heating the oil-water emulsion and its further environmentally friendly combustion, i.e. reduction of harmful emissions. The proposedoriginal installations differ from well-known analogues in the novelty of their design, a fairly high environmental effect and relatively low material costs.

DETERMINATION OF THE CLASS B FIRE EXTINGUISHING PARAMETERS USING SPRAYED WATER

Sprayed water is a versatile tool for localising and extinguishing fires of various types. When water evaporates, its volume increases by 1700 times, resulting in the dilution of combustible components with non-combustible water vapour. The study aims to determine the parameters of extinguishing class B fires using sprayed water by obtaining analytical dependencies for these parameters. The paper derives an expression for the extinguishing temperature of class B fires when extinguished with sprayed water, using Semenov’s conditions. The process of liquid combustion is considered as diffusion. The study shows that the extinguishing temperature of this type of fire is a function of the activation energy of the burning liquid and the initial temperature (at the time of sprayed water supply) of the flame. A parameter of this function is the universal gas constant. The authors constructed a graph showing the area of change in the fire extinguishing temperature. The difference between the initial flame temperature and the fire extinguishing temperature belongs to the range of (80÷120) °C. Using the transition function of class B fire, the study derives an expression for its extinguishing time, which depends on the initial flame temperature, activation energy, and the multiplicative component in the form of a fire time constant. For the relative extinguishing time, the authors constructed the area of change in this parameter depending on the activation energy and the initial temperature. It shows that the value of the extinguishing time of such a fire is (0.28÷0.32) of the value of the constant fire time. The paper presents an expression for the minimum value of the intensity of the sprayed water supply, which ensures extinguishing a class B fire. This intensity of the supply of sprayed water, reduced to the value of the fire transmission coefficient, is determined by the initial temperature of the flame and the activation energy of the liquid that burns. The authors constructed the area of change of this fire extinguishing parameter. It shows that the minimum value of the intensity of the supply of sprayed water belongs to the range (3.8÷7.8) per unit of the fire transmission coefficient. Keywords: fire, fire parameters, sprayed water.

Spray combustion characteristics and soot formation potential of Nano-Al2O3 diesel at low ambient temperatures

Nanoparticle additives have the potential to enhance combustion efficiency and reduce emissions in liquid combustion processes. This study thoroughly investigates the spray evaporation, ignition, and combustion characteristics of nanoparticle/fuel blends, especially under challenging environmental conditions, to improve combustion efficiency and reduce emissions. Employing diffused background illumination, shadowgraph, Mie scattering, high-speed natural luminosity, and two-color method, the spray combustion dynamics of thermally stable nano-Al2O3/diesel (NAD) blends were examined within a constant volume combustion chamber. Diesel, a prevalent primary or auxiliary fuel, represents other highly volatile renewable fuels, while Al2O3, a significant component in combustion fly ash, is noted for its specific catalytic properties and ability to re-burn, eliminating organic toxic elements. The results indicated that NAD blends exhibit a faster evolution rate for both liquid and vapor sprays compared to pure diesel, attributed to the increased kinetic energy of breakup droplets. Under most experimental conditions, incorporation of nano-Al2O3 slightly reduced the ignition delay time due to enhanced heat transfer. Notably, nano-Al2O3 altered the ignition mechanism of the diesel spray, transitioning it from partially premixed to diffusion combustion and relocating the ignition point nearer to the injector. The combustion flame of NAD blends demonstrated increased luminosity, a shorter flame lift-off length, and variations in start-of-injection and total-injection-nozzle-lift-off. However, due to a high equivalence ratio mixture between the liquid phase spray and combustion region, the soot concentration in NAD blends was higher than that in diesel. Additionally, the elevated flame temperature in NAD blends significantly increased the soot concentration. Overall, nano-Al2O3 markedly enhances diesel combustion, especially in low ambient temperatures, suggesting its impressive potential for the high-efficiency and low-emission utilization of renewable fuels or the combustion of recycled waste solvents.

Burning behavior and fire hazards of petroleum liquid combustible spills

In July 2019, an arson using motor gasoline occurred in Kyoto. After the incident, the Fire Services Law in Japan was revised to regulate the sale of motor gasoline in portable cans to prevent similar incidents. However, other petroleum combustible liquids, such as white gasoline and lighter oil, remain easily accessible. Hence, the burning behavior when petroleum combustible liquids and motor gasoline are spilled should be elucidated. Although the burning behavior of spilled motor gasoline on a floor has been studied, the burning behavior of other petroleum combustible liquids has not yet been reported. Therefore, this study aims to investigate the burning behavior of eight types of petroleum combustible liquids, including motor gasoline. Gas chromatography–mass spectrometry analyses were performed to determine the sample compositions. The flashpoints were estimated from the measured saturated vapor pressures. A circular bank with a diameter of 1.6 m was created on a calcium silicate floor, and 4 L sample liquid was spilled inside the bank. From the results of the burning experiments, the flame temperature, surrounding heat flux, flame height, and burning duration of the petroleum combustible liquids were determined. Additionally, we attempted to predict the potential burn injuries to the human body around the flame based on the flux data. The results of this study can be applied to the fire risk assessment caused by petroleum combustible liquids and help predict burn injuries to victims.

Thermodynamic Reactivity Study during Deflagration of Light Alcohol Fuel-Air Mixtures with Water

In this paper, a thermodynamic and reactivity study of light alcohol fuels was performed, based on experimental and numerical results. We also tested the influence of water addition on fundamental properties of the combustion reactivity dynamics in closed vessels, like the maximum explosion pressure, maximum rate of pressure rise and the explosion delay time of alcohol–air mixtures. The substances that we investigated were as follows: methanol, ethanol, n-propanol and iso-propanol. All experiments were conducted at initial conditions of 323.15 K and 1 bar in a 20 dm3 closed testing vessel. We investigated the reactivity and thermodynamic properties during the combustion of liquid fuel–air mixtures with equivalence ratios between 0.3 and 0.7 as well as some admixtures with water, to observe water mitigation effects. All light alcohol samples were prepared at the same initial conditions on a volumetric basis by mixing the pure components. The volumetric water content of the admixtures varied from 10 to 60 vol%. The aim of water addition was to investigate the influence of thermodynamic properties of light alcohols and to discover to which extent a water addition may accomplish mitigation of combustion dynamics and thermodynamic reactivity.

Ignition of Aircraft Combustible Fluids by Hot Surface Under Ventilation

Abstract Flight-fire is a crucial factor that affects the safety of aircraft. It mainly results from combustible fluids leakages on hot surfaces. Hence, this study investigates the ignition probability of a droplet on a hot surface under ventilation through experiments. Specifically, two types of widely used combustible fluids, No.3 Jet Fuel and Mobile Jet Oil II, were investigated at varying surface temperatures ranging from 500°C to 700°C. This range covers the non-ignition to sure-ignition temperatures for the two fluids. The experiments were carried out considering the actual ventilation conditions of an aircraft, wherein the air flow rate ranged from 0 m/s to 3 m/s, and the air flow temperature ranged from room temperature to 380°C. The experimental results indicates that environmental factors have significant influence on droplet ignition probability, ignition probability corresponds with the air flow temperature but is opposite to the air flow rate. Furthermore, the degree of influence on ignition probability varies with the type of combustible liquid. The critical temperatures for non-ignition and sure-ignition on hot surface for No. 3 Jet Fuel and Mobile Jet Oil II under ventilation conditions have been acquired. Additionally, an empirical model is established to determine the ignition probability of No. 3 Jet Fuel under ventilation. The results of this work have instructional significance for aircraft fire protection design and airworthiness certificate of aircraft fire safety.

One disaster two traumas: Being under rubble and burn injuries in the 2023 Maraş, Turkey earthquakes

IntroductionOn February 6, 2023, two separate destructive earthquakes with magnitudes of 7.7 and 7.5 occurred in Kahramanmaraş, Türkiye. More than 50,000 people lost their lives, and over 100,000 were reported injured. In this study, patients referred to hospitals with burn diagnosis and management of burn wounds following the disaster were evaluated. Material and methodsInformation on burn injury admissions related to the earthquake was collected from all burn facilities in the country within 15 days after the earthquake. The patients' demographics, being under rubble, rescue times, burn causes, grafting procedures, and deaths were recorded. ResultsFollowing the earthquake, burn victims were transferred to the 13 Burn Treatment Centers located in 10 provinces. A total of 191 patients were burned. Among the burn patients, 101 (52.9%) were rescued from the rubble 2–60 h after the earthquake. Eight patients who were hospitalized at the burn centers died. Scalding and flame burns were the most common etiologies. Burned total body surface area, concomitant crush injury, hospitalization, and mortality was higher among the patients trapped under rubble (p < 0.001, p < 0.001, p < 0.001, and p < 0.001, respectively). Victims who stayed longer time under the rubble required significantly more grafting procedures (p < 0.001). ConclusionIn a literature review, it was observed that there are a limited number of publications reporting earthquake-related burns. In the February, 6 Türkiye earthquake, flame burns were seen due to small fires that occurred in collapsed buildings during the earthquake. And also contact burns and hot liquid burns were seen in earthquake victims trapped under rubble. Bursting hot water pipes, overturned stoves, contact with hot central heating radiators, and heated construction irons caused scalding and contact burns. It is believed that prolonged entrapment may cause delays in burn treatment or lead to deeper burns due to prolonged contact with the burning agent, increasing hospitalization rates. This earthquake once again drew attention to burn injuries that could occur during and after earthquakes, including those that may occur under rubble.

EXTINGUISHING TIME OF OIL PRODUCT TANK FIRES WITH SELF-EXPANDING GAS-AEROSOL-FILLED FOAM

EXTINGUISHING TIME OF OIL PRODUCT TANK FIRES WITH SELF-EXPANDING GAS-AEROSOL-FILLED FOAM

Effect of preparation method of pyrolysis liquid mixed with coal on its ignition and combustion characteristics

Relevance. The need to develop technological solutions to increase the competitiveness of pyrolysis processing of various wastes. Combustion of pyrolysis liquid in a mixture with coal is one of these solutions, which makes it possible to stabilize the properties of the obtained fuel and use in standard energy equipment. Aim. To determine the influence of the method of preparing a mixture of pyrolysis liquid and low-grade coal on its ignition and combustion characteristics, as well as on composition of the released gas-phase products, depending on the temperature of heating medium and concentration of the additive. Methods. Pyrolysis and oxidation characteristics were studied using thermogravimetric analysis, and formal kinetic constants were calculated using the Coates–Radfern method. Samples of mixed fuels were prepared by the methods of homogeneous mixing and surface wetting of pyrolysis liquid of rubber processing and low-grade coal. Ignition and combustion characteristics were determined using an experimental stand, and composition of gas-phase combustion products was determined using once-through gas analyzer. Results. The authors have determined the features of pyrolysis and oxidation of the pyrolysis liquid as well as the values of formal kinetics constants, indicating the physical nature of the factors that defining the rate of these processes. It was found that at 600 °C the ignition of the studied mixtures weakly depended on concentration of the additive, while at 700 and 800 °C the dependence was linear, and the differences between the samples prepared using different methods were insignificant. For samples obtained by the method of surface wetting, combustion of the additive occurred in the gas phase near the surface of the sample. For the samples obtained by the method of uniform mixing, it occurred predominantly in the bulk of the backfill. This led to more intense and complete coal combustion in these compositions due to more uniform releasing of heat and initiation of coal particles. The concentration curves of the NO, CO and CO2 release demonstrated, that behavior of the fuel mixture components was additive in terms of released gas-phase combustion products, as well as the absence of significant nonlinear effects over the entire studied range of temperatures and additive concentrations.

Measurement report: Method for evaluating CO2 emissions from a cement plant using atmospheric δ(O2 ∕ N2) and CO2 measurements and its implication for future detection of CO2 capture signals

Abstract. Continuous observations of atmospheric δ(O2/N2) and CO2 amount fractions have been carried out at Ryori (RYO), Japan, since August 2017. In these observations, the O2 : CO2 exchange ratio (ER, -Δy(O2)Δy(CO2)-1) has frequently been lower than expected from short-term variations in emissions from terrestrial biospheric activities and combustion of liquid, gas, and solid fuels. This finding suggests a substantial effect of CO2 emissions from a cement plant located about 6 km northwest of RYO. To evaluate this effect quantitatively, we simulated CO2 amount fractions in the area around RYO by using a fine-scale atmospheric transport model that incorporated CO2 fluxes from terrestrial biospheric activities, fossil fuel combustion, and cement production. The simulated CO2 amount fractions were converted to O2 amount fractions by using the respective ER values of 1.1, 1.4, and 0 for the terrestrial biospheric activities, fossil fuel combustion, and cement production. Thus obtained O2 and CO2 amount fraction changes were used to derive a simulated ER for comparison with the observed ER. To extract the contribution of CO2 emissions from the cement plant, we used y(CO2∗) as an indicator variable, where y(CO2∗) is a conservative variable for terrestrial biospheric activities and fossil fuel combustion obtained by simultaneous analysis of observed δ(O2/N2) and CO2 amount fractions and simulated ERs. We confirmed that the observed and simulated ER values and also the y(CO2∗) values and simulated CO2 amount fractions due only to cement production were generally consistent. These results suggest that combined measurements of δ(O2/N2) and CO2 amount fractions will be useful for evaluating CO2 capture from flue gas at carbon capture and storage (CCS) plants, which, similar to a cement plant, change CO2 amount fractions without changing O2 values, although CCS plants differ from cement plants in the direction of CO2 exchange with the atmosphere.

METHODOLOGY FOR STUDYING THE COMBUSTION OF SOLID AND LIQUID SUBSTANCES A CLOSED VOLUME

The development of new methods for testing substances and materials is a relevant area that allows to assess the fire hazard of substances, including modern materials, the composition of which is constantly improving and changing. There are and are created special conditions in the premises, under which combustion acquires a completely different character. An example of such conditions can be combustion in a closed volume, when there is no oxygen access and no energy exchange with the environment. We present a technique that allows us to study the combustion of solids and liquids in a closed volume and to control the parameters of the gas medium. The purpose of the technique is to study the kinetics of combustion of solids and liquids in a closed volume by controlling the parameters and investigating their influence on each other (temperature of the gas medium, reduction of light transmission of combustion products, total oxygen concentration, mass loss of samples). A description of the three stages and the order of their realization is given. The laboratory bench developed by the author is briefly described. The results of the research are supposed to be used to expand the understanding of the nature and kinetics of combustion of substances and materials in a closed volume, as well as to assess the fire hazard of substances whose combustion can occur in a closed volume.

Методы и технические средства управления пожарной безопасностью производственных аспирационных систем

Purpose. For enterprises where flows containing flammable gases, vapors of flammable and combustible liquids, and combustible dust are generated and circulated, an industrial aspiration system is a key element in ensuring fire safety. As a result of studying the regularities of the cleaning process in dust filters, methods and technical means have been developed to reduce hazards in industrial aspiration systems. Methods. Experimental studies of the total pressure drop on filtering partitions of dust filters of various types have been conducted, the obtained data have been analyzed and summarized. Common patterns have been derived. Findings. The results of the studies are the identified patterns describing the kinetics of pressure drops on the filter during different periods of its operation, which made it possible to develop methods for monitoring this process and the design of industrial aspiration system filters. Research application field. The results can be used in organizing activities in the field of fire safety of industrial enterprises. Conclusions. The use of filters to clean flows from combustible dust is the most effective method to reduce fire risks in production with circulating combustible dust, but the lack of data on the specifics of operation in emergency modes becomes a prerequisite for potential risks. The result of the study is the development of a method for determining filter operation modes in case of fire or explosion, and the designs developed on the basis of this method make it possible to reduce fire risk of the process by regulating filter operation modes.

Strut-assisted injection of liquid fuel in a supersonic combustor

This paper investigates mixing and combustion of liquid fuel in a model scramjet combustor with strut-assisted injection adjacent to a cavity flame holder. Fuel/air mixing in a Mach 2.2 cross-flow and stagnation temperature of 1300 K was studied using filtered IR imaging. The insight gained by this method is discussed along with the method limitations. The impact of the strut assisted injection on the mixing of the liquid fuel was seen by the shorter vaporization distance, as the fuel vaporized upstream of the cavity, in contract to a liquid jet that expanded above most of the cavity when the strut was absent. Moreover, the fuel jet was seen to propagate laterally to the tip of the strut, which lead to lateral dispersion of the fuel up the strut height. The combustion experiments were conducted by piloting the cavity with ethylene and were imaged using CH* chemiluminescence. At stagnation temperature of 1300 K thermal choking and stable combustion occurred at equivalence ratio of 0.43, with the flame stabilizing at the strut wake, above the cavity. Intermittent thermal choking occurred at leaner condition. The flame stabilized on the cavity shear layer when the shock train moved downstream of the cavity and the flame stabilized at the strut wake when the shock train moved upstream. Thermal choking with the strut guided injection relative to a combustion only in the cavity without the strut is the result of the observed higher mixing efficiency, that enabled flame spreading into the supersonic flow and higher heat release. At a higher stagnation temperature of 1500 K the shock train moved downstream of the cavity, and the flame stabilized on the cavity shear layer. Finally, it is shown that the combustion efficiency could be further improved by injecting the fuel from the strut side walls.

Deformation and aerobreakup of RP-2 droplets from hypersonic shock waves

The shock-induced atomization and burning of liquid fuel droplets are paramount for hypersonic propulsion and detonation-based combustion systems. The present work experimentally explores the atomization and aerobreakup of liquid RP-2 droplets in a hypersonic shock tube. The shock tube is operated with normal shocks propagating between Mach 5–10 interacting with RP-2 droplets with diameters between 200 and 300 µm. The droplet deformation and breakup dynamics are characterized by ultra-high-speed 5 MHz shadowgraph imaging diagnostics. For all hypersonic shock-droplet interactions, the droplets first undergo structural deformations with subsequent breakup occurring from a shear-stripping mechanism along the periphery of the droplet. The structural changes and droplet deformation rate are found to be self-similar among all cases, and the rate of deformation collapsed to a unified non-dimensional timescale. The complete breakup time of the fuel droplets were analyzed, and theoretical scaling arguments were used to quantify the effects of the Mach number, Weber number, and Ohnesorge number. The experimental data is then used to develop a modified boundary layer stripping model to estimate the breakup time of liquid drops. The model leverages the concept of displacement and momentum thickness to provide a numerical solution to estimate droplet breakup times when exposed to a high-speed gas stream. The model is compared to the experimental RP-2 data and water data available in the literature. The model predicts the breakup time for a range of droplet sizes between 200 and 2000 µm within a reasonable accuracy. The results can be used to optimize liquid fuel injection for hypersonic and detonation-based combustion systems.

Determining the dynamic characteristics of a class B fire in the case of extinguishing by water spray

The object of this study is a class B fire, which is extinguished with sprayed water. The subject of the study is the characteristics of class B fires when they are extinguished with sprayed water. Diffusion burning of a flammable liquid is considered as such a fire, and its extinguishing is carried out by cooling the flame. Heat and oxygen balance equations are used to build a mathematical model describing the fire extinguishing process. The components of the heat balance equation are the power of heat during heat release due to the chemical reaction of liquid combustion and the power of heat dissipated to the environment. The second component takes into account heat removal due to radiation, convection, and evaporation. The component of removed heat due to evaporation takes into account the Sreznevsky constant. The mathematical model that describes the process of extinguishing a class B fire is built in the class of models belonging to differential equations with constant coefficients. Analytical expressions were obtained for these static and dynamic coefficients, which include thermophysical, kinematic, and geometric parameters of the flame and fire extinguishing agent. To determine these characteristics, the constructed mathematical fire model was transformed using the integral Laplace transform. The dynamic characteristics of the fire were obtained in the time domain – the transient function of the fire, and in the frequency domain – the amplitude-frequency and phase-frequency characteristics of the fire. It is shown that the parameters of these dynamic characteristics should be determined experimentally. Experimental methods for determining parameters of dynamic fire characteristics have been devised. The presence of dynamic characteristics of class B fire makes it possible to spread the proven methods of the theory of control systems to design effective fire extinguishing systems