Propane-air Flames Research Articles

Experimental investigation of the confinement effect on a flame impinging a ceiling in an enclosure

This experimental study highlights the confinement effect on a flame impinging a ceiling in confined or semi-confined environment. The enclosure used in this study represents a 1:10 scale model of a student compartment with two possible openings: a door and a window. It is developed based on the conservation of the Froude number in scaling law. The objective of this work is to provide explanations in terms of fire safety on thermal phenomena that can occur during fires in closed environments, for example in a room of a university residence, regarding eight heat rates release of fuel and five confinement levels. A flame oscillation modelling of propane-air flame is proposed and is verified by the experimental results. It is shown both by theoretical modeling and experimental results that the confinement of a compartment has an effect on period time of flame oscillation. Moreover, experimental results show that the confinement level of compartment is a key parameter to characterize vertical temperature evolution both in the center (impinging zone) and near the wall in the enclosure. The correlations for normalized gas temperature rise near the wall are proposed and these temperature evolutions are bounded by the ventilation conditions of the five configurations. Indeed, under condition of equivalence ratio greater than 1, the maximum gas temperature near the wall of a certain heat release rate decreases dramatically with the increasing of configurations' confinement levels, which is associated to the decrease in flame intensity by lack of oxygen with a great criterion of under ventilation.

Lattice-Boltzmann modeling of a turbulent bluff-body stabilized flame

This Letter reports the first large eddy simulation of a turbulent flame using a lattice-Boltzmann model. To that end, simulation of a bluff-body stabilized propane–air flame is carried out, showing an agreement similar to those available in the literature. Computational costs are also reported, indicating that lattice-Boltzmann modeling of reactive flows is competitive, with around 1000cpuh required to simulate one residence time in the 1.5 m burner.

Toward Better Halon Substitutes: Theoretical and Experimental Studies on the Pyrolysis Mechanism and Fire-Suppressing Performance of C5F10O (Perfluoro-3-methyl-2-butanone)

The urgent desire for Halon substitution has propelled the exploration of potential alternatives because of the severe damage of Halon to the stratospheric ozone layer. As a perfluoroketone substance, C₅F₁₀O has a similar chemical structure and comparable environmental friendliness to that of the widely utilized Novec-1230 (C₆F₁₂O) extinguishant. Both theoretical calculations and experimental measurements are utilized to unveil the thermal decomposition and fire-extinguishing mechanisms of C₅F₁₀O in this study. It was found that the C₅F₁₀O pyrolysis generates perfluoroolefins, perfluoroalkanes, and highly active free radicals that can efficiently capture H· and OH· radicals in the flame to interrupt the chain reactions of combustion. Apart from the chemical exhaustion of radicals, the endothermic pyrolysis of C₅F₁₀O imposes a prominent cooling effect upon high-temperature fires. Moreover, the release of incombustible CO₂ and perfluoroalkanes effectively dilutes the combustible fuel–air mixture in the combustion region. The synergistic chemical and physical suppression effects endow C₅F₁₀O with desirable fire-extinguishing effectiveness (6.83 and 6.04 vol % for suppressing methane-air and propane-air flames, respectively). Notably, compared with C₆F₁₂O, the less poisonous (CF₃)₂C═CF₂ is emitted at high temperatures (700–800 °C) by C₅F₁₀O decomposition, indicating the biosafety of C₅F₁₀O in confined and human-exposed regions. These findings suggest the promising applicability of C₅F₁₀O in practical Halon replacement and the necessity of its further evaluation.

Aluminum-propane-air hybrid flames in a Hele-Shaw cell

This paper introduces a novel Hele-Shaw cell apparatus to be used for the study of propagation and stability phenomena in heterogeneous flames. In particular, the apparatus is used to experimentally examine the coupling/decoupling of dual-front flames propagating in suspensions of micron-size aluminum particles in propane-air gas mixtures at varying gas equivalence ratios and aluminum concentrations. The results show that the thermal coupling that exists between the primary propane-air flame front and the secondary aluminum flame front is a strong function of the rate of reaction, and of the temperature, of the secondary front and much less dependent on the reaction rate or temperature of the primary front. It is also shown that flame instabilities in hybrid aluminum-propane-air flames significantly increase the flame surface area, enhance the propagation rate, and can also exhibit complex interactions with front coupling.

Numerical simulation of the influence of pipe length on explosion flame propagation in open-ended and close-ended pipes.

The pipeline length exerts great influence on flame propagation characteristics, Realizable model and Premixed combustion model were used to study the influence of pipe length on propane-air explosion flame in open-ended and close-ended pipes. Using the numerical model verified by experiments, the changes of flame structure and flame propagation speed are studied. The result showed that the Realizable model was in good agreement with the experimental results. It also proved that the reflected wave produced a strong interference on the flame front, which promoted the formation of tulip flame. Besides, some obvious vortices were usually generated in the burned gas after the tulip flame formed, which will affect the flow field around the flame front and thus exert influence on the flame structure. The formation mechanism of tulip flame as well as the flame self-acceleration is different in open-ended and close-ended pipes. In close-ended pipes, the reflection wave at the pipe end and the reflection-induced countercurrent both promote the formation of tulip flame. As the flame propagates to the pipe end, the flame propagation is inhibited by the compression wave formed by the rapid expansion of combustion products under high temperature. While, in open-ended pipes, the turbulence induced by the opening at the pipe end is the main cause of tulip flame formation. The flame acceleration depends on the combustion reaction of unburned gas, so the velocity of flame propagation continues to increase. Generally, the maximum flame propagation velocity in the open-ended pipe is larger than that in the close-ended pipe.

Analyzing OH*, CH*, and C2* chemiluminescence of bifurcating FREI propane-air flames in a micro flow reactor

An experimental investigation of spontaneous flame chemiluminescence of OH*, CH*, and C2* radicals was conducted for premixed propane-air flames in a micro flow reactor. Equivalence ratios from 0.7 to 1.4 were examined and correlated well to the ratio of OH*/CH* and C2*/CH* (R2 > 0.999 for C2*/CH* power fit). The OH*/CH* ratio better correlated with equivalence ratio for lean flames, while the C2*/CH* ratio better correlated with rich flames. The equivalence ratio model was used to calculate the axial local equivalence ratio for a rich propane-air flame (ϕ of 1.5) exhibiting strong bifurcating FREI behavior, resulting in three visible flame fronts. The measured intensities of OH*, CH*, and C2* chemiluminescence, as well as the calculated local equivalence ratio along the reactor axis support the numerical model explanations of the observed bifurcating FREI flames available in the literature. This work highlights the novel application of this diagnostic technique in the context of micro flow reactors.

Analysis of Gaseous and Gaseous-Dusty, Premixed Flame Propagation in Obstructed Passages with Tightly Placed Obstacles

A recent predictive scenario of premixed flame propagation in unobstructed passages is extended to account for obstructions that can be encountered in facilities dealing with explosive materials such as in coalmines. Specifically, the theory of globally-spherical, self-accelerating premixed expanding flames and that of flame acceleration in obstructed conduits are combined to form a new analytical formulation. The coalmining configuration is imitated by two-dimensional and cylindrical passages of high aspect ratio, with a comb-shaped array of tightly placed obstacles attached to the walls. It is assumed that the spacing between the obstacles is much less or, at least, does not exceed the obstacle height. The passage has one extreme open end such that a flame is ignited at a closed end and propagates to an exit. The key stages of the flame evolution such as the velocity of the flame front and the run-up distance are scrutinized for variety of the flame and mining parameters. Starting with gaseous methane-air and propane-air flames, the analysis is subsequently extended to gaseous-dusty environments. Specifically, the coal (combustible, i.e., facilitating the fire) and inert (such as sand, moderating the process) dust and their combinations are considered, and the impact of the size and concentration of the dust particles on flame acceleration is quantified. Overall, the influence of both the obstacles and the combustion instability on the fire scenario is substantial, and it gets stronger with the blockage ratio.

Numerical simulation of hemispherical hydrogen–air flame propagation with heat losses

The article presents numerical simulation of the propagation of hydrogen–air flame in adiabatic conditions and with the heat absorbtion on the wall. The results of experiments in a cylindrical shell of 4.5 m3 are compared with the results of numerical simulation. The quantitative agreement between the experimental and numerical results is achieved. It is shown that the numerical model of the combustion with the heat losses under the conditions of the experiment may account the heat losses as an integral effect of the heat absorbtion.

A study on two-dimensional temperature and concentration distribution of Propane-Air premixed flame using CT-TDLAS

To use supplying gases and energy resources efficiently, accurate measurement of irregular gas is necessary. The TDLAS (Tunable laser absorption spectroscopy) technique can be used to control and monitor the supplying gas conditions and combustion of industrial processes. Recently, CT-TDLAS (Computed tomography-tunable diode laser absorption spectroscopy) has been developed to measure the temperature and concentration field of gases. In this study, the 2-dimensional temperature distribution of the Propane-Air premixed flame in several mixing conditions of fuel has been measured by the constructed CT-TDLAS system. 2-Dimensional temperature distributions are measured by 16 path cells. Further, the third-order polynomial regression analysis was applied to resolve the absorption spectra from the incident and transmitted light for a particular gas. The SMART (simultaneous multiplicative algebraic reconstruction technique) algorithm has been adopted for reconstructing the absorption coefficients on the detecting area. As a result of comparing the temperature for the 2-dimensional detecting area using the thermocouple and CT-TDLAS technique, it has been verified that the relative error for the temperatures measured by the thermocouples and calculated by the CT-TDLAS was up to 8%.

Flammability and Gravity Effect of Horizontal and Vertical Propagating Flames in Tube

In the current research, experimental work is investigated for vertically and horizontally downward propagating flames in an open-ended tube. The objective was to study and compare the influence of flammability limits, gravity, and the flame speed in the different tube configuration for two different fuels. The experimental facility included a 20 mm inner diameter tube, 1200 mm in length and an optical access quartz tube made centrally of 700 mm in length. Methane-air and propane-air fuel were compared for both vertically and horizontally downward propagating flames. The flame speed at each equivalence ratios for both fuels was lower for the flame that propagates downward compared to the flame that propagates horizontally. For both fuels, the flammability limits tend to rise for the vertically downward flame. The influence of gravity was seen as the flames become leaner and richer in methane-air and propane-air flames that propagate vertically downwards, causing a transformation in the contour of the flame from a steady curved flame to a vibrating corrugated flame.

Flammability and Gravity Effect of Horizontal and Vertical Propagating Flames in Tube

In the current research, experimental work is investigated for vertically and horizontally downward propagating flames in an open-ended tube. The objective was to study and compare the influence of flammability limits, gravity, and the flame speed in the different tube configuration for two different fuels. The experimental facility included a 20 mm inner diameter tube, 1200 mm in length and an optical access quartz tube made centrally of 700 mm in length. Methane-air and propane-air fuel were compared for both vertically and horizontally downward propagating flames. The flame speed at each equivalence ratios for both fuels was lower for the flame that propagates downward compared to the flame that propagates horizontally. For both fuels, the flammability limits tend to rise for the vertically downward flame. The influence of gravity was seen as the flames become leaner and richer in methane-air and propane-air flames that propagate vertically downwards, causing a transformation in the contour of the flame from a steady curved flame to a vibrating corrugated flame.

Recovery of the Temperature Field in the Case of Combustion of Premixed Propane-Air Mixtures by Methods of the Hilbert Optics

Jet combustion of premixed propane-air mixtures is frequently encountered in various devices. In the present study, the flame is investigated by methods of the Hilbert optics. The diagnostic technique adapted to studying combustion products is based on visualization of phase perturbations induced in the probing light field by the examined medium with the use of polychromatic Hilbert and Foucault-Hilbert transforms combined with pixel-by-pixel processing of the dynamic structure of the recorded images. The diagnostic setup is based on the standard IAB-463M device with modified systems of optical filtration, source, and data processing. The dynamic phase structure of the propane-air flame is visualized. The temperature at reference points of the burning jet is measured by thermocouples. On axisymmetric segments, the phase function is recovered from the Hilbert curves, and the temperature field of the flame is retrieved by using the inverse Abel transform.

Flowfield impact on distributed combustion in a swirl assisted burner

Colorless distributed combustion (CDC) is a novel method to enhance flame stability and thermal field uniformity, increase combustion efficiency and reduce pollutants emission, including noise. CDC is achieved through the use of a carefully prepared oxidizer mixture of reduced oxygen concentration through added high temperature reactive species. In this study, a partially premixed, swirl assisted cylindrical combustor utilized a propane-air flame with either nitrogen or carbon dioxide gas in order to reduce the oxygen concentration of the oxidizer. OH* chemiluminescence signatures were used to determine transition to distributed combustion condition. The results showed transition to CDC at approximately 15% using N2, and 17% using CO2 dilution. Emission of NO and CO were determined under conditions approaching CDC. NO levels of only 2 or 1 ppm were achieved using N2 or CO2 dilution, respectively under CDC condition. In order to determine how the flow velocity structure and eddy size effect the stability and emissions a high speed (3 kHz) particle image velocimetry (PIV) system was used. Increase in dilution enhanced both the radial and axial mean and fluctuating velocities under CDC that foster mixing. Additionally, the Kolmogorov length decreased with increase in dilution resulting in smaller eddy size particularly in the swirl lobe region, which enhanced turbulent dissipation that resulted in lower peak temperatures and reduced thermal NOx emission. Investigation of Reynolds stress showed that dilution with CO2 provided stronger impact on stress than N2 due to the increased density and reduced viscosity of CO2.

Numerical Simulation of Coaxial Swirled Lifted Propane-Air Flame under Buoyancy Conditions

Numerical simulation of gas dynamics and combustion in coaxial swirled lifted propane-air jets under buoyancy conditions is performed. Dependences of dimensionless flame length L/d0, lift-off height h/d0 as well as flame front surface area Sfl and mass rate of burn-out U on orientation angle θ are obtained. The results of numerical simulation and experiment for different values of θ are compared. It is confirmed that in the angle range of 30° < θ < 60° flame has the smallest surface area that provides the highest value of the mass rate of burn-out. The numerical solution closest to an experiment data can be obtained by using an additional differential transport equation for the ignition time or setting a delay time in the range of 0.05..0.25 s.

On the turbulent flow and pollutant emission characteristics of disk stabilized propane-air flames, under inlet mixture stratification and preheat

The reacting, time averaged and fluctuating flow field characteristics of bluff-body stabilized, stratified, propane-air flames have been systematically investigated for a range of conditions, under a combination of inlet mixture stratification and preheat. The burner consists of three concentric disks that form two premixing cavities. Fuel is injected in the first cavity and is partially premixed with air flowing through this cavity system, resulting in a radially stratified equivalence ratio profile at the inlet of the stabilization region. Investigations have been carried out at four levels of preheat temperatures, of the incoming reactants, ranging from 300 to 743 K, for lean and ultra-lean mixtures. The burner set up is capable of anchoring flames of sub-limit mixtures, down to global equivalence ratio values of about 0.13 at 743 K. The time averaged and fluctuating reacting velocity fields, developing in the downstream near wake, have been evaluated with Particle Image Velocimetry (PIV) analysis, indicating a proportionate decrease of the recirculation zone length with increasing fuel levels. OH∗ chemiluminescence emissions revealed a progressive alignment of the reacting front with the flame axis at weaker mixtures, while exhaust gas measurements have been obtained to evaluate the impact of preheat on emissions performance and combustion efficiency.

Exhaust CO emissions of a laminar premixed propane–air flame interacting with cold gas jets

This study investigates a laminar premixed flame interacting with cold gas jets, at different cooling jet mass flow fractions (m˙jet*) and diluent types, namely air and N2. A novel burner and wall configuration is used to experimentally induce flame-cooling-air interaction (FCAI). Flame chemiluminescence imaging, exhaust temperature (Texh) and exhaust CO emissions ([CO]exh) measurements are conducted to characterise the flame shape and [CO]exh response to the cooling jets. Flame imaging reveals that the cooling jets greatly affect the flame shape. Measurements of [CO]exh demonstrate a direct correlation with Texh, as decreasing Texh is observed to occur with decreasing [CO]exh. Additionally, the air diluent case shows consistently lower [CO]exh values, relative to the N2 diluent case.Using a novel modelling approach, the cooling jets are simulated using one-dimensional (1D) fully resolved simulations (FRS). The effect of jet dilution, jet cooling and exhaust gas cooling are independently and jointly investigated in these simulations. The FRS results support the experimentally observed behaviour, and show that exhaust gas cooling and exhaust gas oxygenation produce decreased CO concentrations. Using a chemical reactor network (CRN), the jet mixing process is modelled by a perfectly stirred reactor (PSR), while the exhaust gas cooling process is modelled by a plug flow reactor (PFR). The CRN modelling shows that the jet mass flow rates dictated by m˙jet*, the dilution time (tdil) assumed for cooling jet mixing, and the exhaust gas cooling residence time (tcool), play an important role in determining the [CO]exh. An equilibrium analysis illustrates that the relationship between [CO]exh, Texh and exhaust O2, is due to the thermodynamically favoured equilibrium states. Timescale analyses demonstrate that appropriate modelling of jet mixing, and accounting for the rate of exhaust gas cooling, are important for estimations of [CO]exh.

A Numerical Study of Lean Propane-Air Flame Acceleration at the Early Stages of Burning in Cold and Hot Isothermal Walled Small-Size Tubes

In this study, the problem of lean propane-air premixed flame acceleration from closed to open end during the early stages of burning in small-size tubes with isothermal walls was considered. In particular, the effects of tube radius, slip/non-slip wall conditions, and the wall temperature on the flame propagation and shape were investigated numerically. Five stages of flame propagation are identified: 1) spherical expansion of the flame front; 2) finger shape expansion of the flame front before touching the wall; 3) flame propagation in the tube subjected to flame-wall interactions; 4) transformation of the flame shape into tulip form; 5) conversion of the tulip shape flame to finger. Our results show that the tube radius, wall condition and its temperature significantly affect flame propagation regimes even in the first instance of the flame propagation in the tubes. We find that increasing tube radius has, overall, the effect of increasing the flame propagation speed in isothermal tubes. Also, depending on tube radius and wall condition, the wall temperature can increase or decrease the flame propagation speed in the isothermal tubes. Furthermore, the results demonstrate that imposing either slip or non-slip condition on the tube’s walls impressively affects flame acceleration and its configuration in the early stages. We observe that, unlike flame propagation forms in the tubes with slip walls, the early exponential flame propagation phase in the tubes was generally followed by a linear flame propagation phase in the tubes with a non-slip wall condition. We obtain that flame propagation in tubes with slip wall conditions are more sensitive to variations in tube radius and wall temperature compared to non-slip conditions. We also see that, contrary to the exponential flame propagation phase, increasing the non-slip wall temperature reduces the flame propagation speed in the linear part of the flame propagation, while such an increase in temperature leads to oscillations in the flame propagation speed in the tubes with slip walls.

Experimental measurement of atomic composition in sooting luminous flame by Laser-Induced Breakdown Spectroscopy

In the present study, Laser-Induced Breakdown Spectroscopy (LIBS) was applied to the measurement of fuel-rich propane-air luminous flame in a counter-flow configuration to investigate the applicability of LIBS to measure local chemical composition in sooting field. H656nm/O777nm intensity ratio was chosen as the indicator of atomic number ratio H/O which gives direct information on equivalence ratio and is important for analyzing not only blue flame but also sooting flame. Measurement was conducted in the first place on propane-air/air counter-flow flame with the range of local equivalence ratio 0–4, in which the intensity ratio showed a good linear correlation with calculated H/O atomic number ratio as it had been observed in non-sooting conditions. LIBS technique was also applied to uniformly sooting flame supplying the same mixture at equivalence ratio of 2.2 from both nozzles to produce predefined homogeneous atomic composition. The measured intensity ratio was a good agreement with the linear relationship obtained in the propane-air/air diffusion flame experiment. Therefore, robustness of LIBS measurement of atomic/molecular composition in sooting flame was reasonably elucidated.

Effect of propagation speed on the quenching of methane, propane and ethylene premixed flames between parallel flat plates

This paper reports on an experimental investigation of the effect of flame speed on the quenching distance. In a rectangular section channel, the quenching distance of methane-air, propane-air and ethylene-air flames, arriving on the quenching element with different speeds, is investigated. The experiments are performed in a constant volume combustion chamber comprising two volumes separated by the quenching section. The quenching tests are performed at pressure close to atmospheric, with an initial temperature of the walls and flammable mixture of 293 K. Flame quenching is assessed from pressure measurements, while the apparent flame speed is determined from fast schlieren imaging. The results show a similar trend for the three fuels considered: the quenching distance for laminar propagating flames is about twice smaller than when the flow becomes turbulent, close to the entrance of the channel. In the case of laminar flames, the quenching distance is almost constant at 1.3–1.5 mm for the conditions considered, while for turbulent flames, depending on the fuel and equivalence ratio, the quenching distance is in the range 2–2.5 mm. Starting from the quenching theory, the results are analyzed and the effects of flame curvature and turbulence are discussed.

Effect of Obstacle Type on Methane–Air Flame Propagation in a Closed Duct: An Experimental Study

The combustion in a closed environment was the subject of many works in the past century due to its importance and complex nature compared with the combustion in an open environment. Most research works in this field have investigated different types of gas mixtures, the governing boundary conditions and their effect on the flame propagation structure. Additionally, several investigations have been performed on creating disturbance through obstacles in the flow path as well as the process of deflagration to detonation transition. This paper, for the first time, investigates the effect of porous and solid obstacles on the propagation and the structure of premixed methane–air flame in a closed duct with dimensions of 50 × 11 × 8 cm. The blockage created in the duct by obstacles is in such a way that the detonation process does not occur. The results for the unconstrained duct correctly represent the process of forming the classical tulip flame inside the closed duct. The location of the obstacles is changed in four different distance of 5, 10, 15, and 20 cm from the spark plug, and its effect on combustion characteristics has been evaluated. The results show that the obstacles create fundamental changes in the structure and flame propagation. A significant difference between solid and porous obstacles is that the porous obstacle, in proportion to the solid obstacle, creates less disturbance in the flow field and also does not cause excessive acceleration in the flame propagation. Porous obstacles also reduce the maximum pressure in the chamber during the process, more than the solid obstacles.