Burning Rate Characteristics Research Articles

Statistical variation of the burning rate and extinction characteristics of engineered timber products

Understanding the burning rate (mass loss rate, MLR) of timber products is essential in characterizing the ignition characteristics, fire size, and extinction phenomena experienced by timber. Key parameters for timber, such as self-extinction criteria, are presented throughout literature. These parameters are often determined using bench-scale experiments in relatively low trial quantities (e.g., n = 3). This study investigates the influence of trial quantity on the observed statistical variation in key burning rate metrics for timber products (e.g., peak MLR, MLR at extinction). Experiments were performed using a conical heater to conduct 100 repeat trials at incident heat fluxes of 20 kW/m2, 40 kW/m2, and 50 kW/m2 on 12.7 mm (0.5 in.) thick ACX cross laminated plywood samples. Significant variability was observed in trials conducted at 40 kW/m2 due to bimodal behavior where 39% of samples experienced self-extinction and the remaining 61% of samples sustained combustion until burnout (i.e., complete pyrolysis of the material). The MLR at extinction for the trials at 40 kW/m2 displayed nearly double the magnitude compared to trials conducted at 20 kW/m2 due to the breakdown of the semi-infinite solid condition. The results from this work illustrate the significance of large trial quantities when investigating complex phenomena.

Experimental study and new-proposed characterization of burning rate and flame geometry of gasoline pool fires with different aspect ratios

This study investigated the burning rate and the flame geometry of gasoline pool fires under crosswinds in the context of bridge vehicle fires. A 1:4 scale bridge fire platform was established. A total of 45 fire experiments were conducted on 9 gasoline pool with 1–2.2 aspect ratios under 0–2 m/s cross-wind. The influence mechanism of aspect ratio n on the characteristic parameters of pool fires was investigated. The results showed that the burning rate of gasoline pool ranges from 0.028 kg‧m−2‧s−1 to 0.064 kg‧m−2‧s−1, which increases with wind speed and pool size. When the wind speed exceeds 1 m/s, the title angle of the flame on the windward side is greater than 45° and is less affected by pool size. The wall heat conduction at wind downstream increases with aspect ratio when placing the longer side facing to cross flow. The correction factor Fr·n can be used to describe the competition between the air entrainment and the buoyancy in gasoline pool fire. A general model based on aspect ratio is proposed to quantify the burning rate and flame tilt characteristics of gasoline fires. The reliability and applicability of the model are compared with the existing experimental data.

Numerical investigation and experimental validation of aluminized propellant combustion under high pressures: Critical effects of heat feedback

Aluminum is a common metal fuel in propellants, but its effects on the burning rate and the underlying mechanism are still unclear. Numerical calculations and temperature measurement experiments were carried out within the pressure range of 0.1–9 MPa, and the effects of the pressure and the ammonium perchlorate (AP) particle size on the combustion characteristics of aluminized propellants were studied. First, based on a two-dimensional micro-scale combustion model of an AP/hydroxyl‑terminated polybutadiene (HTPB) propellant, by considering the “heat sink” effect of aluminum on the burning surface and the chemical reaction of aluminum in the gas phase, a numerical calculation model of heat flux coupled with the steady-state combustion of an aluminized propellant was established. The flame structure of an aluminized propellant obtained by this model conformed to the multi-flame structure and could correctly reflect the influence of the AP particle size and pressure on the burning rate and other combustion characteristics. Subsequently, the influence of radiation heat feedback was further introduced into the model, which greatly improved its accuracy in predicting the burning rate at low pressures of 1–3 MPa. More importantly, the temperature distributions of the propellants were measured using embedded tungsten–rhenium thermocouples, and the flame temperature was obtained by further processing the temperature measurement data according to the thermocouple response characteristics. The temperature measurement results showed that with the increase in the pressure and the decrease in the size of the AP particles, the temperature gradient increased significantly, the flame temperature increased slightly, and the burning rate of the propellant increased. By analyzing how the temperature gradient and the burning rate changed with pressure, it was found that the conduction heat feedback was important to determine the burning rate.

Burning characteristics of ammonium nitrate propellant containing fine ammonium perchlorate – influence of porosity of ammonium perchlorate**

AbstractFine porous ammonium perchlorate (PAP) has small holes in its crust, and the voids in the particles are connected to the outside. The porosity of PAP results in fine bubble contamination in a propellant because the voids in PAP cannot be completely charged with a binder. Fine bubble contamination can improve the burning rate characteristics of an ammonium perchlorate (AP) propellant. The influence of the porosity of PAP on the burning characteristics of an ammonium nitrate (AN)/AP propellant and the effect of Fe2O3 as a catalyst on them were investigated in this study. The void fraction of the propellant increased with increasing mass ratio between AP and all oxidizers (ξ) and ranged from 1.3 % to 3.2 %. The porosity of PAP increased the burning rate of AN/AP propellants. This effect increased with decreasing pressure and was independent of ξ. However, porosity had minimal influence on the burning rate of AN/AP propellants with Fe2O3. The effect of the catalyst on the increase in the burning rate due to the porosity of PAP was influenced by pressure and ξ. The effect on the AN/AP propellant was greatest when ξ was in the 0.5–0.6 range.

Effects of Eugenol and Cineol Compound on Diffusion Burning Rate Characteristics of Crude Coconut Oil Droplet

The burning rate of coconut oil droplets has been investigated experimentally by adding bio-additives of clove oil and eucalyptus oil. Tests were carried out with single droplets suspended on thermocouples at room atmospheric pressure, and room temperature and ignited with a hot wire. The addition of clove oil and eucalyptus oil as bio-additives into coconut oil was 100 ppm and 300 ppm, respectively. The droplet combustion method was chosen to increase the contact area between the air and fuel so that the reactivity of the fuel molecules increases. The results showed that the eugenol compounds contained in clove oil and cineol compounds in eucalyptus oil were both aromatic, and had an unsymmetrical carbon chain geometry structure. Furthermore, this factor can potentially accelerate the occurrence of effective collisions between fuel molecules. Therefore the fuel is combustible, as evidenced by the increased burning rate, where the results show that without bio-additives, the burning rate of crude coconut oil (CCO) is about 0.7 seconds. These results are 0.15 to 0.2 seconds slower than CCO with bio-additive, which is around 0.55 to 0.6 seconds. Moreover, from the observations, it was found that the highest burning rate was achieved in both bio-additives with a concentration of 300 ppm.

Forecasting the influence of the guided flame on the combustibility of timber species using artificial intelligence

This paper anticipates the burning rate and optical obscuration characteristics of a 10 mm thick timber species often used in buildings under the influence of a guided flame condition with heat fluxes of 25 kW/m2 and 50 kW/m2. The smoke density chamber was used to test the wood species Pinus strobus, Pinus kesiya, Quercus alba, and Faqus sylvatica. The experimental data: time, specific gravity, mass loss, and heat flow were used as input variables to an artificial neural network (ANN) model. ANN with structure of 4-64-32-2 was built and validated, the results revealed that, the correctness of the established simulation was proven by a high value of R2 (0.99292 for validation) and highest validation performance (MSE = 17.809 at epoch 12). When the heat flow was reduced from 50 kW/m2 to 25 kW/m2, Quercus had the greatest drop in mass optical density (MOD). In the case of 25 kW/m2, the average charring rate was roughly 0.57 mm/min, compared to 0.96 mm/min in the case of 50 kW/m2. The MOD declines asymptotically for all species regardless of heat flux. The findings give statistical support and theoretical reference for fire-related construction norms and standards.

Experimental study on the combustion characteristics of aluminized nitrate ester plasticized polyether solid propellant under high pressure

Aluminized Nitrate Ester Plasticized Polyether high-energy solid propellant demonstrates bright application prospects due to its high-density specific impulse and satisfactory mechanical properties. The high-pressure experiment study were conducted on aluminized Nitrate Ester Plasticized Polyether to quantitatively investigate the burning rate characteristics at 1–7 MPa, and qualitatively analyse the agglomeration characteristics at 7 MPa. The burning rate experiment results indicate that the relationship between burning rate and pressure basically conforms to Vielle's burning rate law. When the ammonium perchlorate partice size decreases from 298 to 142 μm, the burning rate coefficient increases by 9.1% and the pressure index decreases by 7.6%. With the octogen particle size increasing from 15 to 150 μm, the burning rate coefficient and pressure index increases by 15.0% and 9.8%, respectively. When the aluminum particle size decreases from 30 to 16 μm, the burning rate parameters remain unchanged. While the aluminum particle size decreases from 16 to 2 μm, the burning rate coefficient increases by 20.5% and the pressure index decreases by 18.6%. The burning rate is significantly affected by octogen particle size and aluminum particle size has the vital influence on burning rate coefficient and pressure index. The agglomeration process and second mergence phenomenon at 7 MPa were observed for the first time and the agglomeration process mainly happens on the burning surface and above the burning surface under high pressure. Qualitative analysis shows that high pressure reduces the retention time of agglomerates on the burning surface and intensifies the combustion process of agglomerates, and coarse octogen can effectively reduce the agglomeration particle size at 7 MPa. The conclusions can provide insights into the influence of Nitrate Ester Plasticized Polyether composition on burning rate and the effect of high pressure on the agglomeration process in the motor.

Experimental study on the effect of canyon cross wind yaw angle on airflow and flame characteristics in a tunnel

The effect of canyon cross wind yaw angle on airflow and flame characteristics of ethanol pool fires in a tunnel was investigated. The fire source location and canyon cross wind speed were studied as factors. The wind yaw angle was ranged in 45°–135° with an interval of 15°. The results showed that the flow field in the tunnel presented three different conditions with the boundaries of wind yaw angles 60° and 90°. The mass burning rate and flame tilt characteristics were affected by the flow field near the fire source. The mass burning rate decreased with the increasing wind yaw angle when the wind yaw angle was in 45°–90°, but remained steady when the angle was in 90°–135°. Additionally, a normalized mass burning rate model considering normalized distance to the upstream portal and the wind yaw angle was developed. The flame close to the upstream portal wiggled, rotated and oscillated irregularly due to the influence of turbulence induced by the external canyon cross wind. This made mean flame length and flame tilt angle in turbulence zone different from those in other zones. A prediction correlation between the flame tilt angle and the canyon cross wind speed and yaw angle was established.

Uncontrollable combustion characteristics of energy storage oil pool: Modelling of mass loss rate and flame merging time of annular pools

Hydrocarbon energy storage has a wide range of applications in modern production and life. Regarded as an important form of energy dissipation, combustion plays an important role in energy storage failure. Energy burning rate and flame shape are the key factors of the combustion system. The classic theories of uncontrollable combustion characteristics for energy storage oil pool will be unable to apply to the cases with annular oil pool burning calculation directly, which never been revealed before. The study of oil energy storage burning rate and flame shape characteristics is of great significance to predict and control the energy storage pool transfer between the fuel surface and the unburned area during the combustion process. Experiments were carried out using an annular pool with an outer diameter that used heptane as fuel. Based on dimensionless theoretical derivation, a non-dimensional correlation is proposed the flame merging time. The received energy heat feedback at the center of pool can explain the change of energy mass loss rate, and a dimensional analysis model with Spalding number was developed to interpret the energy mass loss rate in the energy storage annular pool. Experiments show that the characteristic diameter can be well correlated non-dimensionally with all flame height, indicating that the proposed correlation is applicable not only for annular pools but also for solid burners. The study on these issues have the benefit the current utilization and management of the energy storage oil pool.

An experimental study on mechanical and ballistic characteristics of different HTPB composite propellant formulations

The main goal of this paper is to investigate the changing in the tensile behavior and the burning rate characteristics of hydroxyl-terminated polybutadiene (HTPB) propellantunder the variations of the crosslinking density, which was predominantly determined by the equivalent ratio of diisocyanate to total hydroxyl (NCO/OH ratio), which known as the curing ratio. Four variousbatches with different curing ratios (NCO/OH) percentage were produced in which the production processes were fixed. Uniaxial tensile tests were conducted at different temperatures (-40, 20 and 55°C), and different strain rates (0.000656 1/s, 0.0328 1/s) using a Zwick universal test machine. In order to measure the burning rate, cured solid propellant strands were tested using the acoustic wave emission method under different pressure ranging from 4 to 10 MPa. The experimental results indicate that the tensile behavior of HTPB propellant is remarkably influenced by curing ratio, strain rate, and temperature. It was observed that a great change on stress-strain curves affected various curing ratios and temperatures on the mechanical behavior of propellant composition. The results showed that high curing ratio leads to increase theultimatestress and decrease the strainat maximum stress, but higher temperatures lead to decrease theultimate stress and the strain at maximum stress.The curing ratios (NCO/OH) have an intense impact on mechanical characteristics, but slightly impact on ballistic characteristics for propellant. Furthermore, careful measurements of these parameters are important to control the production quality and to provide a reliable comparison between different propellant batches.

Study of burning rate characteristics of propellants containing Al–Mg alloy nanopowder

Nanopowder of Al–Mg alloy was synthesized using the method of electrical explosion of thin wires of hypo-eutectic Al–Mg alloy. Thin wires of hypo-eutectic Al–Mg alloy were cut by electrical discharge machining and exploded electrically. The nanopowder obtained is examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) for studying the morphology of the particles. TEM and SEM images substantiate the spherical structure of the nanoparticles and the diameter of particles ranges from 20 nm to 95 nm. Solid propellants were prepared by adding the alloy nanopowder as an energetic additive element with bimodal ammonium perchlorate (AP) and Hydroxyl Terminated Polybutadiene (HTPB) propellant formulations. Burning rates of the propellant with nano Al–Mg alloy powder are compared with micro aluminised propellants and propellants with micro Al–Mg powder with the same composition. Mean burn rate of 22.03 mm s−1 was obtained at a pressure level of 9 MPa with nano Al–Mg powder and 20.4 mm s−1 with micro Al–Mg powder compared to mean burning rate of 10.03 mm s−1 at 8 MPa pressure for aluminised propellants. The improved mean burn rate of propellants containing Al–Mg alloy nanoparticles could be accounted for the reduction in the size of the alloy particle and selective melting of eutectic phases along with magnesium. In the process, it gives heat feedback to the high-temperature reaction zone, which results in augmenting further reaction of metal particles.

Investigation of sidewall height effect on the burning rate and flame tilt characteristics of pool fire in cross wind

In the current study the combining effect of sidewall height and cross air flow on the mass burning rate, flame height and flame tilt behavior of pool fire has been experimentally investigated. The mass burning rate increases as the cross wind velocity increases. The presence of sidewalls also influences the mass burning rate, as it is increased at lower cross wind velocities and decreased as this velocity further increases. A dimensionless parameter is introduced to illustrate the sidewall height effect on the mass burning rate. The effect of sidewall height on burning rate, flame height, and flame tilt angle of pool fire is further investigated. The flame height is an exponential function of a new dimensionless parameter Fr˜. Based on the experimental results, new empirical correlations are proposed to predict flame height and flame tilt angle α in relation to the combining effects of sidewall height and cross wind.

Study on Friction Sensitivity of Passive and Active Binder based Composite Solid Propellants and Correlation with Burning Rate


 Friction sensitivity of composite propellants and their ingredients is of significant interest to mitigate the risk associated with the accidental initiation while processing, handling, and transportation. In this work, attempts were made to examine the friction sensitivity of passive binder: Hydroxy Terminated Polybutadiene/Aluminium/Ammonium Perchlorate and active binder: (Polymer + Nitrate Esters)/Ammonium Perchlorate/Aluminium/Nitramine based composite propellants by using BAM Friction Apparatus. As per the recommendation of NATO standard STANAG–4487, the friction sensitivity was assessed by two methods: Limiting Frictional load and Frictional load for 50% probability of initiation (F50). The test results showed that the active binder based formulations were more vulnerable to frictional load as compared to the formulations with passive binders. Examination of a comprehensive set of propellant compositions revealed that the particle size distribution of Ammonium Perchlorate and burn rate catalysts were the most influential factors in dictating the friction sensitivity for HTPB/Al/AP composite propellants. For active binder/AP/Al/Nitramine composite propellants, the formulation with RDX was found more friction sensitive with a sensitivity value of 44 N as compared to its HMX analog (61 N). The correlation studies of friction sensitivity, burning rate, and thermal decomposition characteristics of HTPB/Al/AP composite propellants is described.

Effect of n-butanol addition on the burning rate and soot characteristics during combustion of single droplets of diesel–biodiesel blends

The effect of n-butanol addition on the burning rate and soot characteristics of single droplets of diesel–biodiesel blends was systematically studied. A single droplet of a diesel–biodiesel-n-butanol mixture of approximately 1 mm in diameter was suspended on a silicon carbide fibre and burned in air at 973 K in an electrically heated tube furnace. The droplet size during combustion was continuously recorded using a colour CCD camera and the burning rate based on the d2 law was determined. The soot intensity as indicated by theKLfactor and flame temperature were estimated from the CCD camera spectrum data using a two-colour pyrometry technique. Soot particles were also sampled using a thermophoreric deposition probe and characterised using a high resolution transmission electron microscope (TEM) for particle size and morphology. The results showed that n-butanol addition increased the burning rate of diesel–biodiesel blends, reduced the KL factor, being more profound with increasing n-butanol addition. The temperatures of the flames surrounding the fuel droplets with and without n-butanol addition showed little differences. The mean diameter of primary soot particles decreased and the particle size distribution shifted towards a smaller size range with n-butanol addition. At low levels of n-butanol addition the soot particles consisted of predominantly amorphous carbon, however, became progressively more graphitic in the inner structure with increasing n-butanol addition.

Combustion performance studies of aluminum and boron based composite solid propellants in sub-atmospheric pressure regimes

The aim of present study is to investigate the burning rate, ignition delay, and flame characteristics of ammonium perchlorate (AP)-hydroxyl terminated poly-butadiene (HTPB) [AP/HTPB] based composite propellants (CSP's) in sub-atmospheric pressure regimes (13 kPa–100 kPa). Several fuels and catalyzed were used to evaluate their effects on the combustion characteristics of AP based propellants in sub-atmospheric pressure regimes. In fuels, aluminum (Al) and boron (B) were selected as metallic and non-metallic fuel respectively. While in catalyst, butyl ferrocene (B.F.) and ferric oxide (F.O.) were selected as liquid and solid catalyst respectively. Apart from these, other ingredients that were used are di-octyl adipate (DOA), toluene di-isocyanate (TDI), and glycerol. The article throws some light on the burning rate and ignition delay properties for these new classes of prepared propellant samples. At sub-atmospheric pressures, all propellants are susceptible to irregular burning with the ejection of soot's, fumes, and unburned particles. F.O. based catalyzed propellants can sustain its combustion up to the lowest pressure.

Mathematical simulation of transient combustion of melted energetic materials

The computer code is elaborated for numerical simulation of transient combustion of energetic materials (EM) subjected to the action of time-dependent heat flux and under transient pressure conditions. It allows studying combustion response upon interrupted irradiation (transient pressure) and under action of periodically varied heat flux (pressure) in order to determine stability of ignition transients and parameters of transient combustion. The originally solid EM melts and then evaporates at the surface. It is assumed that chemical transformations occur both in the condensed and gas phases. At the burning surface, the phase transition condition in the form of Clapeyron-Clausius law for equilibrium evaporation is formulated that corresponds to the case of combustion of sublimated or melted EM. The paper contains description of transient combustion problem formulation and several examples of transient combustion modeling. At present time a precise prediction of transient burning rate characteristics is impossible because of the lack of information about magnitude of EM parameters at high temperatures. However, the simulation results bring valuable qualitative information about burning rate behavior at variations in time of external conditions – radiant flux and pressure.

An alternative approach to improve burning rate characteristics and processing parameters of composite propellant

Modification in burn rate of composite solid propellant has become a necessity of a mission. Burn rate can be modified by various mean viz. (i) tailoring the ammonium perchlorate (AP) particle size, (ii) use of nano-sized particles and (iii) incorporating burn rate modifiers. Literature discusses about various burn rate modifiers. Out of these, Iron oxide (Fe2O3)/IO is the well known burn rate enhancer. Here a systematic study was carried out by undertaking experiments at varying levels of IO in composite propellant compositions. This paper attempts to understand the effect of IO content and its specific surface area on burn rate characteristics of composite propellant. This study also attempts to find out alternative to ultrafine AP and nano burn rate enhancer to account for high burning rate of composite propellant along with reduced slurry viscosity and longer pot life for easy processing. As ultrafine AP and nano burn rate enhancers have their limitations in terms of (i) high end of mix (EOM) propellant slurry viscosity, (ii) difficulty in propellant processing, (iii) less reproducibility in attaining the similar particle size in each batch results in lesser repeatability in ballistic properties of propellant, (iv) hazards involved in size reduction, (v) limitations in handling, storage and shelf life and also (vi) the higher cost of nano particles. Therefore an extensive experimental study was performed to achieve this objective. In this study, we incorporated two different grades of IO(A) and IO (B) in composite propellant compositions. The average particle size of both grades of IO i.e., A and B are of ∼1 µm. But the specific surface area of IO (B) was about 15 times more than IO (A). The large difference in specific surface area of both IO was due to difference in the manufacturing process. During the manufacturing of IO, the calcination temperature plays very important role in deciding the specific surface area. High specific surface area is obtained if calcination is done at very high temperature (>1773 K). Burning rate measurements were carried out. It was observed that IO is a good burn rate enhancer. Initially, the burn rate increased with the increase in % of IO. But after that only a marginal enhancement in burn rate was observed. It was noticed that though both grades of IO are effective burn rate enhancer but IO(B) was 30% more effective than IO(A). Also it was found that IO(B) is an alternative to ultrafine AP and nano burn rate modifiers. This IO(B) was further used to develop the propellant compositions with high burn rate without incorporating ultrafine AP and nano particles. Viscosity measurement and mechanical properties determination revealed that both the IOs did not much adversely alter the processing characteristics and mechanical properties of propellant.

Comparison of burn rate and thermal decomposition of AP as oxidizer and PVC and HTPB as fuel binder based composite solid propellants

Abstract In the present investigation an effort has been made to understand the thermal decomposition and burn rate characteristics of AP as oxidizer and PVC and HTPB as fuel binder in composite solid propellant. The burning rate study has been carried out at ambient and different pressures of 2.068Mpa, 4.760Mpa, 6.895Mpa. The mechanism of thermal decomposition of each composition have also been determined by NETZSCH simultaneous thermal analyser, comprising differential scanning calorimeter (DSC) and thermo-gravimetric analyser (TGA). An effort has been made to study the burn rate and decomposition of fuel binder and oxidizer in presence of Fe2O3 and also their overall impact on combustion of propellant.

An experimental study on the burning rates of interacting fires in tunnels

Multiple fires may occur in close proximity in process industries, power generation and fuel storage facilities and confinement conditions such as tunnels, which can lead to a considerable alteration in fire characteristics and safety design. The topic is of significant importance to the fire safety research because there is little work in the literature that investigates the case of interacting fires, which have a destructive potential. In this work, we study the effects of an adjacent fire source on the burning rate and heat release rate characteristics of tunnel fires. Square ethanol pools of 10 and 15 cm in size and 0.22–1 cm in depth were used as fire sources in a reduced scale tunnel model. Ventilation to the tunnel was varied between 0 and 1.5 m/s. Pool fires were configured in single and dual pool orientations. Variations in the pool fire burning rates were discussed as being functions of pool size and depth, and a result of the interaction with the secondary fire. The maximum burning rate enhancement factor, defined as the ratio of the parameter for interacting fires to non-interacting ones, was shown to be 2.3. This was due to the enhancing effect of the secondary fire on the heat feedback to the fuel, and the increased combustion mass transfer. Tests with relatively larger pool sizes burned faster, with an advanced onset of the transition to a bulk boiling phase, which was attributed to the controlling heat feedback mechanism associated with the pool size.

An experimental investigation of burning rate and flame tilt of the boilover fire under cross air flows

This paper presents an experimental investigation on mass burning rate and flame geometry characteristics of crude oil boilover fire under cross air flows. Three circular steel trays with different diameters, filled with crude oil with different initial layer thickness were used in this experiment. The cross air flow speed ranges from 0 to 1.5 m/s. The mass burning rates, flame length and tilt angle in the steady stage and boilover stage were recorded. The results show that the response of steady mass burning rate to cross air flow speed showed a non-monotonic trend, which firstly decreased and then increased with the critical cross air flow speed of 1.0 m/s. The boilover mass burning rate also shows a similar non-monotonic response to the cross air flow speed, with a critical value of 0.5 m/s. Such change trends are discussed based on the physical change of the dominant controlling mechanism in the heat feedback. An improved Thomas model was developed for the correlation of flame length in boilover stage to account for the initial fuel layer thickness effects. The flame tilt angles in steady stage and boilover stage are correlated well based on the tangent value of the angle.