Search

Hydrogen can be adopted as a clean alternative to hydrocarbons fuels in the marine sector. Liquid hydrogen (LH2) is an efficient solution to transport and store hydrogen onboard of large ships. LH2 will be implemented in the maritime field in the near future. Additional safety knowledge is required since this is a new application and emerging risk might arise. Recently, a series of LH2 large-scale release tests was carried out in an outdoor facility as well as in a closed room to simulate spills during a bunkering procedure and inside the ship's tank connection space, respectively (Aaneby et al., 2021). The extremely low boiling point of hydrogen (-253°C (NIST, 2019)) can cause condensation or even solidification of oxygen and nitrogen contained in air, and thus enrich with oxygen the flammable mixture. This can represent a safety concern since it was demonstrated that a burning mixture of LH2 and solid oxygen may transition to detonation (Litchfield and Perlee, 1965). In this study, the experimental data of an LH2 release test series recently carried out were analysed by means of an advanced machine learning approach. The aim of this study was to provide critical insights on the oxygen condensation and solidification during an LH2 accidental release. In particular, a model was developed to predict the possibility and the location of the oxygen phase change depending on the operative conditions during the bunkering operation (e.g. LH2 flowrate). The model demonstrated accurate and reliable predicting capabilities. The outcomes of the model can be exploited to select effective safety barriers such as a water deluge system to prevent the oxygen change phase. [ABSTRACT FROM AUTHOR]

Thermal decomposition of biomass mixtures has been experimentally studied to assess the potential for more intensive use of local bioenergy resources (straw) in heat production by co-firing straw with wood or peat pellets and for process control using microwave (MW) pre-treatment of straw pellets. It was found that microwave pre-treatment of straw pellets provides modification of their structure, elemental and chemical composition, increases the porosity of pellets and the heating values of the pellets with partial decomposition of the main components of lignocellulosic pellets, i.e., hemicelluloses, cellulose and lignin. Besides, microwave pre-treatment of straw pellets activates the thermal interaction between the activated pellets of straw and unpre-treated pellets of the mixture that results in faster thermal decomposition and faster release of combustible volatiles (CO, H2, CxHy). The time required for thermal decomposition of biomass mixtures decreases by about 300 s, the average weight loss rate of activated mixtures increases by about 17-20 %, increasing the yield of combustible volatiles by about 24 %. [ABSTRACT FROM AUTHOR]

Biorefinery represents an innovative approach for waste management, where products at the end of their service life are seen as valuable resources for the production of high added value bio-products or bio-fuels. In this context, acidogenic fermentation is gaining scientific and commercial interest, since it allows to improve waste/wastewater treatability as well as additional recovery of volatile fatty acids (VFA), the building blocks for the chemical industry or precursors of reduced chemicals in conventional organic chemistry. This work illustrates the results of a study aimed at highlighting the effects of different inputs (feedstock composition and pre-treatment; temperature) on process performance and safety. The fermentation process was applied on a mixture of food waste and sewage sludge (FWs-SS) within the contest of Treviso municipality (northeast Italy). The VFA production and relative ratio respect to soluble chemical oxygen demand (CODSOL) were evaluated, as well as the variation of lower flammability limit (LFL) of flammable gaseous mixture, produced during the acidogenic fermentation. Thermal pre-treatment (72°C, 48 h) enhanced the solubilization of the organic matter, which was converted into VFA in batch mode under mesophilic conditions (37°C). The VFA level increased up to 30 ± 3 g COD/L, with high CODVFA/CODSOL ratio (0.86 ± 0.05). This condition was also characterized by the lowest level in volumetric percentage of flammable gases such as H2, CH4 and H2S. Variation of LFL of gaseous mixture as function of fermenter operating parameters has been investigated by Le Chatelier's Law. The high concentration of CO2 (greater than 80% v/v) increased the LFL and therefore the flammable mixture was considered poorly hazardous. In practice, the variation of fermenter operating parameters to the final optimized protocol caused a continuous LFL growth, up to 29.3%, corresponding to a safer operation of fermentation reactor. [ABSTRACT FROM AUTHOR]

This article presents an experimental quantification of the ignition risk of flammable mixtures in conditions relevant to industry and aviation environment. More specifically, the effect of resistive material on ignition of flammable mixtures was investigated by applying a 500-ns duration high-voltage pulse between pin-to-pin electrodes located across a jet flow of ethylene and air, at atmospheric pressure. Fuel-rich, stoichiometric, and fuel-lean equivalence ratios were considered. A parametric study of the effect of the applied voltage and electrode material was performed. The electrical energy deposited in the discharges was determined from current and voltage measurements. Direct visualization of the sparks and the ignition kernel was performed in order to better understand the early stages of the ignition process. The results showed that the use of highly resistive electrodes compared to metallic electrodes: 1) could significantly reduce the energy deposition in the interelectrode area; and 2) could increase the minimum ignition energy. Therefore, the use of highly resistive material wires instead of metallic wires could offer safer conditions with respect to the ignition hazard in flammable environments. [ABSTRACT FROM AUTHOR]

The article demonstrates the uncertainty in securing an arbitrarily sized area around the location of hot work. It presents case studies in which a flammable mixture was released, ignited and caused an accident. It compares modeled release profiles of vapor leaks from vessels, and evaluates complex geometries that make detection of flammable ambient atmospheres difficult. The article also compares the calculated safety zones to rules of thumb and common guidance.

A flammable gas could be ignited only if its concentration in air is over a threshold concentration, which is known as the lower flammability limit (LFL). Therefore, predicting LFLs of flammable gases is indispensable for safely handling such flammable gases. The Le Chatelier’s mixing rule for the LFL is the prevailing method for estimating the LFLs of mixtures with multiple flammable components. In this work, a novel derivation for this rule is proposed based on the threshold temperature concept. It is found that the important assumption required to reach this mixing rule is that the adiabatic flame temperature rises at LFL are approximately the same for each flammable component. As the adiabatic flame temperature rise is in a sense the required energy gap to initiate a combustion, it should not change while adding/removing inert gas into/from the system. Therefore, it is also the required perquisite to predict the LFLs of inertized mixture or the LFLs in oxygen atmosphere. [ABSTRACT FROM AUTHOR]

Aqueous-organic solutions can flash only over a limited composition range. This manuscript proposes a model to estimate the two critical parameters, maximum flammable content not to flash and the maximum flash point temperature, in judging whether an aqueous-organic solution is flammable or not. The results are applicable to flammability elimination and flammability hazard assessment of liquid solutions. Validation of this model was performed with measurements for 14 aqueous-organic miscible and partially miscible mixtures. Various mixtures were tested including alcohols, ketones, and esters in aqueous solutions. Overall, the estimation of the maximum flash point value and maximum flammable content not to flash were acceptable when using the proposed model. The termination of the flash for aqueous solutions was clarified to be the nonflammability of the vapor phase resulting from the high-steam concentration when the temperature of such solutions is greater than the maximum flash point. © 2017 American Institute of Chemical Engineers AIChE J, 63: 263-271, 2018 [ABSTRACT FROM AUTHOR]

Fire development is influenced by many factors, such as oxygen concentration, external radiation, and the inclination angle of the combustible material. This article examines the effect of these factors on flame spread over a charring solid using a series of experimental studies. The results show that the flame spread can be divided into three regimes based on oxygen concentration: an unsustained flame spread regime (Yo = 0.8), a stable combustion regime (0.8 < Yo < 1.3), and an accelerating flame spread regime (Yo = 1.3), where Yo is the oxygen concentration ratio in mole fraction. The critical angle for the transition from the stable combustion regime to the accelerating combustion regime is between 10° and 20°, measured from the horizontal. When the fuel is exposed to external radiation, the flame propagation velocity generally increases. At reduced oxygen concentrations, the increase in flame spread rate is greater with external radiation, whereas at a higher oxygen concentration level, the oxygen concentration, rather than the external radiation, dominates the increased flame spread rate. [ABSTRACT FROM AUTHOR]

Explosive incidents with harmful consequences continue to occur in boilers and furnaces (heaters) where fossil fuels are burned. Proper designs, proper maintenance, and proper operating procedures have been developed, backed by standards, codes, guidelines, and recommended practices. However, process knowledge (education) and appropriate operating and maintenance procedures (training) remain the essential tools for personnel to understand the circumstances leading to catastrophic consequences and thus be able to enhance the safety conditions of combustion processes. Tackling the root of this problem requires visualizing the associated concepts, rules, and cautions to fully understand the nature of combustion, foresee its hazards, and prevent incident outcomes and consequences. This article is intended to provide colleagues in the field, engineers, technicians, and operators-who, on a daily basis, live in close proximity to the risks of fossil-fired boilers, furnaces, gas turbines, heaters, and processes with flammable mixtures-three basic tools to allow them to visualize, and thus, find it easier to remember, the concepts associated with the hazards of combustion processes by reviewing the knowledge available to prevent explosive incidents. © 2017 American Institute of Chemical Engineers Process Saf Prog 36: 221-236, 2017 [ABSTRACT FROM AUTHOR]

Outwardly propagating spherical flames are well suitable for measurements of Laminar Flame Speed which is a very important thermochemical property of flammable mixtures. There are several facilities, approaches and methods applied to measure Laminar Flame Speed. Due this variety of measurements, consistency and accuracy of the results are mandatory for useful comparisons. Confined premixed flames were assessed using a customized spherical stainless steel vessel, equiped with a Schlieren setup and a dynamic pressure transducer, allowing the comparison between the syncronized results obtained using both approaches. The thermodynamic method presented in this paper uses experimental pressure traces as input to a FORTRAN code that calculates temporal profiles of flame radius, flame surface area, burning velocity, the scalar laminar flame speed and some additional quantities. The proposed algorithm processes the raw pressure trace, controls flow data to an external code to calculate chemical equilibrium and thermodynamic properties and calculates the rate of reactants burned by the flame propagation. The strategy allows to obtain the laminar flame speed without the need to model heat transfer from the flame, diminishing uncertainties in the calculations. The calculations of the proposed FORTRAN code enables to obtain the Laminar Flame Speed at initial datum and the flame behavior for higher pressures and temperatures, maximizing the results for each experiment. Measurements were carried out for air mixtures with methane, iso-octane, n-heptane, Jet A and Jet A-1. The laminar flame speed is the highest for Jet fuels at Ti = 408 K and lowest for iso-octane at Ti = 300 K, about 50% higher for stoichiometric mixtures. The faster flames for Jet fuels presented the highest exergy destruction, about 30%. The joint analyses of the results of flame radius, Laminar Flame Speed, exergetic assessment of the flame propagation and the calculated equilibrium composition of the burned gases showed the consistency and good accuracy of the thermodynamic approach here presented. [ABSTRACT FROM AUTHOR]

The presence of liquid fuel droplets in a flammable mixture causes cellular instabilities on the flame surface, which significantly enhances the flame speed when compared to the fully vaporized case. The prediction of the mechanisms responsible for the onset of cellularity for two-phase mixtures is essential to better understand spray combustion. The present study considers an innovative experimental strategy to isolate and investigate any potential mechanisms. The fuel droplets were replaced by inert water droplets in order to amplify the thermal sink effect, characterized by the absorption of part of the heat released by the flame, and to suppress the local enrichment of fuel formed around droplets. Spherical expanding flames with narrow-size distribution droplets were used and qualitative comparisons of the flame structure were performed with a shadowgraph system. The results have shown that the heat sink has no significant effect, whereas the local enrichment of fuel appears as a key phenomenon, which suggests that in the case of fuel droplet aerosols the onset of cellularities is triggered in the inhomogeneous part of the gaseous phase. [ABSTRACT FROM AUTHOR]

Explosion venting is commonly used in the process industries as a prevention solution to protect equipment or buildings against excessive internal pressure caused by an internal explosion. In practical cases, for instance in the presence of complex 3D obstructions or for stratified flammable mixtures, analytical engineering models fail. At the opposite, for simple situations, engineering models are sufficient and could give an immediate estimation of the overpressure generated. As a consequence, CFD and engineering are two complementary solutions but they have to be carefully validated. This article is dedicated to the validation of FLACS CFD code and an engineering tool for the modeling of vented explosions by comparison with recent published experimental results. Recommendations and good practices are suggested for the applications of both FLACS CFD and engineering models. [ABSTRACT FROM AUTHOR]

An experimental investigation is conducted to analyze hot-surface ignition of n -hexane-air mixtures. The experimental setup, equipped with temperature diagnostics and schlieren imaging, utilizes a glow plug to initiate ignition in a flammable mixture. The hot-surface temperature at the point of ignition is measured for equivalence ratios ranging from 0.6 to 3 and chamber pressures varying from 25 to 100 kPa. The hot-surface temperature resulting in ignition is found to be weakly sensitive to equivalence ratio with a mean value of 980 K for mixtures with equivalence ratios between 0.75 and 3 at 100 kPa. Chamber pressure has a stronger influence with ignition temperature increasing to about 1140 K at 25 kPa. The experimental trends were reproduced in numerical simulations utilizing detailed chemistry of n -heptane as a surrogate for n -hexane given their similar ignition and flame propagation characteristics. The simulations further predict a two-stage ignition process resulting from an initial breakdown of the fuel with a small increase in temperature followed by a main ignition event accompanied by fuel depletion. Reaction rate analysis of the sequence of events leading to ignition conducted using a reduced order kinetic model suggests that the second-stage ignition event is caused primarily by the decomposition of hydrogen peroxide which occurs at temperatures above 900 K. The two-stage ignition process observed here is significantly different from that observed in previous studies due to the presence of convective and diffusive processes as well as the continuous increase in hot-surface temperature. These arguments are used to explain the insensitivity of ignition temperature to equivalence ratio, its decrease with increasing chamber pressure, and the location of the ignition kernel observed in experiments and simulations. [ABSTRACT FROM AUTHOR]

Conductive heat losses from the base of a lean methane-air inverted flame stabilized behind the trailing edge of a thin rod have been experimentally evaluated. The results favor the view that the heat losses to the flame holder play a crucial role in the inverted flame stabilization and blow-off. Simple estimations have been performed, which indicate that the well-established correlation between the mixture composition and the boundary velocity gradient at the flame holder, usually considered as a proof of the flame stretch theory of blow-off, can be explained without involving the flame stretch concept. The suggested explanation of this correlation is based on the assumption that the heat loss to the flame holder is the main factor that determines the inverted flame blow-off behavior and on the similarity between the mechanisms of energy and momentum diffusion in gases (Pr≈ 1). [ABSTRACT FROM AUTHOR]

This work presents an experimental analysis of a non-flammable R1234ze(E)/R134a mixture (R450A) as R134a drop-in replacement. While R134a has a high GWP value (1430), the R450A GWP is only 547. The experimental tests are carried out in a vapour compression plant equipped with a variable-speed compressor. The replacement suitability has been studied combining different operating conditions: evaporation temperature, condensation temperature and the use of an internal heat exchanger (IHX). The drop-in cooling capacity of R450A compared with R134a is 6% lower as average. R450A COP is even higher to those resulting with R134a (approximately 1%). The discharge temperature of R450A is lower than that of R134a, 2K as average. The IHX has a similar positive influence on the energy performance of both fluids. In conclusion, R450A can be considered as a good candidate to replace R134a. [ABSTRACT FROM AUTHOR]

Inorder to understand gas explosion phenomena in industrial buildings,a reduced-scale vented combustion chamber is investigated numerically.In this configuration, a flame is ignited in an initially quiescentflammable mixture and propagates past solid obstacles, generatinga strong pressure increase. The aim of this numerical study is twofold:The first objective is to show how large eddy simulation manages toreproduce the parameters of critical relevance for this multiscaleproblem, in particular the overpressure generated during the flamepropagation. The second objective is to highlight that, even if large-to small-scale turbulence effects play a crucial role in the flamedevelopment and the resulting overpressure, it is also needed to correctlyaccount for thermo-diffusive scale phenomena. [ABSTRACT FROM AUTHOR]

Abstract: This work focuses on the performance analysis of an industrial vegetable oil refinery. Using a commercial process simulator, a process model was developed and validated against actual vegetable oil refinery field data. The simulator allowed investigating both energy and safety aspects related to the presence of residual extraction solvent (extraction grade hexane) in the processed crude vegetable oil. The critical nodes for hexane accumulation in the process were evaluated, both considering ordinary operative conditions and undesired process deviations due to increase of the hexane content. In this latter case, the control actions able to restore the normal operation were simulated, in terms of increased utility consumption (e.g., motive steam for ejectors and cooling water) or by modifying and optimizing equipment operating conditions. Finally, the possibility of flammable mixtures formation inside process vent pipes, caused by the entrainment of air due strong vacuum conditions, was also investigated. [Copyright &y& Elsevier]

Abstract: The mechanism that produces an explosion from the vapor of gasoline in a small leisure boat is elucidated by using a small-scale combustion chamber and a mock-up boat. The study reveals that the explosion is caused by: (i) leakage of gasoline vapor from a fuel tank, (ii) diffusion and accumulation of gasoline vapor in a battery compartment, and (iii) ignition of premixed gas and flame propagation between linked compartments. The leakage of gasoline vapor from the fuel tank is successfully visualized by the schlieren method. The process of diffusion of the gasoline vapor from the fuel-tank compartment to the battery compartment is demonstrated in the mock-up boat. A flammable mixture of gasoline vapor in the battery compartment has been estimated to be maintained from the 1.7th day to the 175th day after placement of the filled and leaking fuel tank. Ignition of the premixed gas and the flame propagation process are verified by using the small-scale combustion chamber. A high-speed camera visualizes the behaviors of ignition and flame propagation during the course of explosions in linked compartments. Finally, in order to confirm the presumed mechanism, a reproducibility test is carried out by using the mock-up boat to simulate the situation in the actual accident. The actual explosion is successfully reproduced in the mock-up boat. [Copyright &y& Elsevier]

Abstract: Flammability limits are one of the most important characteristics to evaluate fire hazards associated with fuels. Currently, numerous correlations, based on either chemistry (stoichiometric oxygen number) or energy (heat of combustion), have been proposed to estimate flammability limits. In this study, a thermal model is proposed to incorporate the dual role (quenching and heating) of each component in a mixture. The energy term plays a vital role in Excess Heating Potential (EHP) and Quenching/Heating Ratio (QHR) and hence an association between flammability limits and energy terms can be established. In addition, oxygen calorimetry bridges chemistry formula with energy release of a certain fuel, thus all existing correlations are unified under the principle of energy conservation. Since this methodology is universal, it can be applied to estimate the flammability limits of any mixtures or guide future correlations with improved precision. Advantages and limitations for this methodology are also discussed. [Copyright &y& Elsevier]

Abstract: An analysis is presented of flame acceleration in a tube filled with flammable mixture, closed at one end and open to the atmosphere at its second end. Ignition takes place near the closed end; experiments then show that the flame accelerates, slows down and moves back, accelerates again, and may eventually reach considerable speeds. The one-dimensional analysis is based upon the assumption that the flame front propagates at a speed that is small compared to the speed of sound, and that depends upon the temperature and pressure perturbation due to acoustics that it encounters. A complete unsteady solution is constructed. The tube acoustics are set in motion by the expansion of the fluid due to ignition at the closed end. Subsequently, both spectrum and amplitude evolve because of the motion of the temperature interface, and because of forcing by the flame front, which itself depends upon the effect of acoustics on the state of the fluid that it encounters. Oscillations in the front position are stronger than in a previous study in which the flame propagation speed was taken to be constant. With the additional feedback now included, it is strong enough to result in strong flow reversal. [Copyright &y& Elsevier]

An experimental study is made of the flow of solutions of cellulose nitrates in a stationary tube and a tube rotating about its own axis. Comparison of the results obtained from experimental and theoretical studies shows that they agree well with one another. [ABSTRACT FROM AUTHOR]

Abstract: Because it is difficult to treat the contributions of diluents explicitly using Le Chatelier''s rule, a methodology based on thermal balance is proposed for estimating the flammability limits of a mixture. This method converts the flammability information of a mixture into a binary domain of heating/quenching potentials and, after some simple manipulations, converts them back into the flammability domain. The advantage of this conversion is the separation of the heating and quenching potential sums. The dual contribution (heating and quenching) of each species is stressed, while the simplicity of hand calculation is preserved. This method is equivalent to Le Chatelier''s rule but has increased flexibility in dealing with various fuel/oxygen/diluents combinations. It will help safety engineers gain more confidence in the hazard analysis of flammable mixtures involving diluents. [Copyright &y& Elsevier]

Abstract: International regulatory representatives have proposed the performance-based test methodology for hydrogen fuel cell vehicle (HFCV) fuel system integrity certification in a new global technical regulation (GTR). For this test method, vehicle certification depends on system performance during barrier/rollover crash tests. The GTR proposal specifies that the test is failed if within 1 h post-crash, hydrogen leakage rates exceed 118 L/min or flammable mixtures develop within the passenger cabin or trunk. An analysis of the capabilities necessary to detect the second failure mode was performed through exploratory in-vehicle leakage tests at SRI International’s Corral Hallow Experimental Site. Hydrogen concentrations were primarily derived from oxygen depletion sensor measurements, and were compared to directly measured concentrations from co-located hydrogen sensors. Close agreement between the two sensor technologies was observed. Since oxygen depletion measurements have the additional advantage that nonflammable gases can be used, helium was investigated as a surrogate due to its similar diffusion and jet spreading characteristics. The good agreement in overall dispersion trends for both gases highlights the flexibility of the indirect sensor method. While hydrogen mixture fractions strongly depended on release characteristics (e.g., rate, location, type), the results of an analytic examination indicated that pinhole leaks from moderate source pressures likely would produce unacceptably high in-vehicle hydrogen concentrations. The optimum sensor location for leak detection was determined to be high above the release point. Accordingly, sensor placement for crash tests involving vehicle rollovers must account for the final vehicle orientation. [Copyright &y& Elsevier]

Abstract: This work presents a methodology for the assessment of hazards due to the formation of flammable mixtures in edible oil refineries, with particular focus on storage tanks. Safety issues in these plants are due to the presence of residual volatile flammable solvents deriving from the extraction processes, which may accumulate in the storage tanks and generate flammable vapour mixtures. The methodology, based on the application of a thermodynamic model for the estimation of vapour phase composition in oil storage tanks as a function of operating conditions (i.e. temperature and residual solvent content), allows the identification of potential hazards due to formation of flammable mixtures inside the tanks. The model was first validated using available experimental data and then extended to case-studies representative of state-of-the-art industrial storage applications. The results of the case-studies were then used to calculate specific hazard indexes, providing a quick tool for preliminary assessment of hazards due to the formation of flammable mixtures in edible oil storage plants. [Copyright &y& Elsevier]

Abstract: Dynamics of the dispersion of a fixed mass of cryogenic natural gas (NG) vapour produced from LNG (liquefied natural gas) boil off is examined. The vapour is considered to have been suddenly exposed to an overlaying atmosphere within open vertical cylindrical enclosures with a negligible pressure difference. A 2-D axis-symmetric CFD model was used to resolve the resulting complex temporal changes of the concentration and temperature fields. Focus was made on the features of the flammable regions, from their formation to dissipation, both inside and immediate outside of the enclosure. It was observed that with adiabatic walls, the structure of the flow changes from diffusion driven to buoyancy driven as methane warms up on mixing with the air to the atmospheric temperature. The effect of heat transfer from the walls on the evolution of the flammable cloud is discussed. The associated potential fire hazard is assessed based on the propagation rate of the lower flammability limit of the NG vapour cloud. [ABSTRACT FROM AUTHOR]

Abstract: An experimental study on pressure evolution during closed vessel explosions of propane–air mixtures was performed, for systems with various initial concentrations and pressures ([C3H8]=2.50–6.20vol.%, p 0 =0.3–1.2bar). The explosion pressures and explosion times were measured in a spherical vessel (Φ =10cm), at various initial temperatures (T 0 =298–423K) and in a cylindrical vessel (Φ =10cm; h =15cm), at ambient initial temperature. The experimental values of explosion pressures are examined against literature values and compared to adiabatic explosion pressures, computed by assuming chemical equilibrium within the flame front. The influence of initial pressure, initial temperature and fuel concentration on explosion pressures and explosion times are discussed. At constant temperature and fuel/oxygen ratio, the explosion pressures are linear functions of total initial pressure, as reported for other fuel–air mixtures. At constant initial pressure and composition, both the measured and calculated (adiabatic) explosion pressures are linear functions of reciprocal value of initial temperature. Such correlations are extremely useful for predicting the explosion pressures of flammable mixtures at elevated temperatures and/or pressures, when direct measurements are not available. [Copyright &y& Elsevier]

An experimental study on maximum explosion pressure in closed vessel deflagration of stoichiometric gaseous mixtures, for various initial pressures within 0.3 - 1.2 bar and ambient initial temperature is reported. Explosion pressures and explosion times of stoichiometric methane-, ethane- and propane-air mixtures were measured in a spherical vessel and in two cylindrical vessels with different diameter/height ratios. The measured explosion pressures are examined in comparison with the adiabatic explosion pressures, computed by assuming chemical equilibrium within the flame front. The influence of initial pressure and heat losses during propagation on explosion pressures and explosion times are discussed for the examined systems. Both measured and calculated explosion pressures are linear functions of total initial pressure, at constant initial temperature and fuel concentration. [ABSTRACT FROM AUTHOR]

The dynamics of the dispersion of a fixed mass of the buoyant fuel, methane, when exposed with a negligible pressure difference to overlaying air within vertical cylindrical enclosures open to the atmosphere is investigated. Features of the formation and dispersion of flammable mixtures created by the gas dissipation were examined using a 3D CFD model. For the cases considered, the lean-flammable mixture boundary appears to travel mainly at a near constant rate while the rich limit front shows a more chaotic behaviour. The corresponding simulation using an axis-symmetrical 2D model tended to under-predict the dynamics of the lean and rich boundaries, for the cases considered. [Copyright &y& Elsevier]

Abstract: The dynamics of the dispersion of a fixed mass of the highly buoyant hydrogen when exposed to overlaying atmosphere with a negligible pressure difference from open vertical cylindrical enclosures are examined. Features of the rapid formation and dispersion of flammable mixtures both inside and immediate outside of the enclosure and their corresponding propagation rates were examined using a 3-D CFD model. For the cases considered, the puffs of the fuel–air mixture appear to produce lean flammable boundaries that move mainly at a near constant rate for much of the time. A similar simulation that used an axis-symmetrical 2-D model tended to under-predict the dynamics of the lean and rich mixture boundaries. Hydrogen plume characteristics were compared with that of the less buoyant methane and helium release. Unlike methane, helium propagation rate was found fairly close to that of hydrogen. [Copyright &y& Elsevier]

To date no commercial fiber coupled laser systems have reached the irradiance and pulse energy required for flammable mixtures ignition. In this work we report preliminary results on the ignition of two-phase mixtures promoted by a laser delivering pulses through optical fiber. Experiments undertaken on free beam path configurations have allowed identification of the optical parameters required for laser ignition. The fiber coupled system used is based on a Q-switched nanosecond laser operating at 1064 nm. The fiber input angle and the focal length have been identified as the most important parameters. We demonstrated the possibility of delivering nanosecond pulses of 30 mJ focused onto a spot of 200 μm through a solid core optical fiber, and to promote ignition of n-heptane/air and JP4/air mixtures. [ABSTRACT FROM AUTHOR]

Many fuel installations and industrial operations often are associated with the release, whether deliberately or inadvertently, of fuel vapors into the surrounding atmosphere. Most of these releases may be considered to be relatively small on a thermal basis, but they do represent collectively a serious source of unburned hydrocarbon emissions into the atmosphere. Moreover, the emissions of methane from various sources of natural gas contribute significantly to green house gas emissions. The paper presents computed results of the transient dissipation of a fixed mass of methane when released within vertical cylindrical vessels containing air, which are open to the outside atmosphere under ambient conditions. Particular attention is given to the rates of emission of gas into the outside atmosphere and how it is affected by the composition and mass of the fuel released and the size and configuration of the fuel retaining cylindrical tank. The corresponding transient formation, growth and subsidence of flammable zones within such a vessel are also described. Some guidelines for reducing the hazards associated with such releases are presented. [ABSTRACT FROM AUTHOR]

An experimental study of laser-induced spark ignition of flammable, gaseous premixtures is reported, with theoretical interpretations. Ignition was in an explosion bomb, equipped with four variable-speed fans that facilitated the study of quiescent and isotropic turbulent conditions. Good optical access enabled the progress of plasma fronts, shock waves, igniting kernels, and propagating flames to be recorded with high-speed schlieren photography. A focused beam from a Q-switched Nd:YAG laser initiated electrical breakdown, with plasma energies between 85 and 200 mJ. Probabilities of breakdown were found for air and isooctane–air mixtures over ranges of pressures and temperatures. Blast-wave theory applied to shock-wave trajectories enabled initial plasma conditions to be inferred. This suggested electron temperatures of over 105 K and very high pressures. Calculated values of the absorption coefficient for the laser beam energy show these plasma properties to be commensurate with the observed energy and size. The ensuing rarefaction wave creates toroidal rings at the leading and trailing edges of the plasma. The former decays more rapidly and a third lobe of the kernel is generated that moves towards the laser. In flammable mixtures this enhances the flame spread. Laminar flame speeds are overdriven by this gasdynamic effect, as well as by the high energy of the plasma, to such an extent that the flame speed decays from elevated values as the flame stretch decreases, contrary to the increases that occur with normal flames with positive Markstein numbers. The extent to which turbulence narrows the ignition limits is found experimentally. For mixtures close to the lean flammability limit, strong gasdynamic flows induced by laser ignition can stretch the flames to extinction and narrow the ignition limits. If a flame becomes established, eventually the third lobe disappears as the initial gas dynamic effects decay and are overwhelmed by the imposed flow fields. Nevertheless, the overdrive effects persist for some time and overdriven flames were observed in regimes where normal flames would have quenched. [Copyright &y& Elsevier]

The limiting oxygen concentration (LOC) of fuel–air–inert premixed gaseous systems are usually determined from measurements of explosion limits at progressive dilution with inert gas of fuel–air mixtures, which is a long and cumbersome procedure. An alternative procedure to evaluate LOC would be of great interest for all fields of activity involving the use of flammable mixtures, especially when less characterized fuels are used. The paper describes a new procedure (algorithm) meant to estimate the LOC of fuel–air–inert premixed systems, using the values of lower explosion limit (LEL) of the fuel–air mixture and the calculated adiabatic flame temperature (CAFT) both at LOC and LEL when nitrogen is used as an inert gas. It is based on an empirical correlation established between the CAFT computed for fuel–air–nitrogen mixtures at LOC and CAFT at LEL, for a large number of flammable gases and vapors. This requires only the measurement of LEL. The correlation was derived from flammability data taken from literature sources (German and American recommended values). The method is based upon the assumption that mixtures at LOC have an equivalence ratio ϕ=1.250, which is close to the equivalence ratio of the most reactive fuel–air systems. Inverse calculations made with this new algorithm for nine fuel–air–nitrogen mixtures allowed the determination of LOC with a relative deviation of 2–22%. [Copyright &y& Elsevier]

Investigates the combined effects of mass, energy and momentum transfer with variable transport and thermodynamic properties on the formation of the fuel vapor-air mixtures above a stagnant liquid surface within the confines of a vertical cylindrical vessel. Overview of the analytical formula used in the study; How the temperature around the base of the fuel tank changes with time; Conclusions.

Butanol is considered as the more promising alternative fuel candidate because of its favorable chemical and physical properties over ethanol and methanol. In this study, the performance and emissions of a port fuel injected spark ignition engine fueled with butanol‐gasoline blends (0–60 vol % butanol blended with gasoline referred as G100‐B60), including brake thermal efficiency (BTE), brake specific fuel consumption (BSFC) and carbon monoxide (CO), unburned hydrocarbon (UHC), nitrogen oxide (NOx), were investigated under various equivalence ratio. Among the butanol‐gasoline blends, B30 performs well in engine performance and emissions due to its CO (2.3%–8.7%), UHC (12.4%–27.5%), and NOx (2.8%–19.6%) emissions compared to those of gasoline. Butanol can be a good alternative fuel to gasoline for its potential to reduce pollutant emissions. It is well known that engine tests are hard, time consuming, and high cost. Therefore, support vector regression (SVR) was used to predict the performance and emissions of the engine, where equivalence ratio and blend ratio were used as the input parameters, and BTE, BSFC, CO, UHC, and NOx were used as the output parameters. It was observed that the correlation coefficients and mean relative error were in the range of 0.9940–0.9998 and 0.1901–10.2570%, respectively. The SVR predictions of BTE, BSFC, CO, UHC, and NOx yielded the root‐mean‐squared‐errors of 0.0511%, 4.6058 g/kW h, 0.9995% vol, 7.7503 ppm vol and 38.5861 ppm, respectively. It could be indicated that the SVR provided an accurate and simple approach to analyze performance and exhaust emissions of spark ignition engine. © 2018 American Institute of Chemical Engineers Environ Prog, 38:e13042, 2019 [ABSTRACT FROM AUTHOR]

The article discusses the demise and use of ether and cyclopropane flammable inhalation agents. It states that ether serves as one of the first anesthetics used in early 1840s as a cardiac stimulant and potent bronchodilator. It mentions the disadvantages of ether, such as the agent's unpleasant smell and bronchial irritant effects. It adds that the increasing diathermy usage contributes in the unsafety effect of ether and cyclopropane.