Deflagration Index Research Articles

Impacts of hydrogen fraction and equivalence ratio on the explosion characteristics of ethanol/hydrogen mixtures

With the anticipated widespread integration of biofuels and hydrogen fuels within the future energy landscape, the potential explosion hazards after their release within confined spaces under the atmospheric are deserving of heightened attention. The present work takes the mixtures of ethanol and hydrogen as the objects and experimentally studies the impacts of hydrogen fraction and equivalence ratio on the explosion characteristics in a constant-volume explosion vessel at 0.10 MPa and 400 K. The data reveals that an increase in the hydrogen fraction leads to a rise in the maximum explosion pressure during lean explosions but causes a decrease during rich explosions. Nonetheless, the duration of the explosion decreases with the increase of hydrogen fraction in all the explosions. In consideration of explosion pressure, the maximum pressure rise is found to be exponential in relation to the maximum explosion pressure. However, the confidence level diminishes significantly with an increase in the hydrogen fraction. Conversely, the maximum rate of pressure rise during an explosion appears to be a function of the duration of the explosion, suggesting that the reaction rate plays a more pivotal role in determining the hazardous level. Meanwhile, the duration of fast combustion steadily occupies approximately 83 % of the explosion duration. Furthermore, the deflagration index is no more than 30 MPa*m/s, namely, ethanol/hydrogen mixture is a promising fuel with mild hazardous potential.

Deflagration Dynamics of Methane–Air Mixtures in Closed Vessels at Elevated Temperatures

In this paper, we explore the deflagration combustion of methane–air mixtures through both experimental and numerical analyses. The key parameters defining deflagration combustion dynamics include maximum explosion pressure (Pmax), maximum rate of explosion pressure rise (dP/dt)max, deflagration index (KG), and laminar burning velocity (SU). Understanding these parameters enhances the process of safety design across the energy sector, where light-emissive fuels play a crucial role in energy transformation. However, most knowledge on these parameters comes from experiments under standard conditions (P = 1 bar, T = 293.15 K), with limited data on light hydrocarbon fuels at elevated temperatures. Our study provides new insights into methane–air mixture deflagration dynamics at temperatures ranging from 293 to 348 K, addressing a gap in the current process industry knowledge, especially in gas and chemical engineering. We also conduct a comparative analysis of predictive models for the laminar burning velocity of methane mixtures in air, including the Manton, Lewis, and von Elbe, Bradley and Mitcheson, and Dahoe models, alongside various chemical kinetic mechanisms based on experimental findings. Notably, despite their simplicity, the Bradley and Dahoe models exhibit a satisfactory predictive accuracy when compared with numerical simulations from three chemical kinetic models using Cantera v. 3.0.0 code. The findings of this study enrich the fundamental combustion data for methane mixtures at elevated temperatures, vital for advancing research on natural gas as an efficient “bridge fuel” in energy transition.

Effect of hydrogen fraction and initial pressure on the inhibition of methane/hydrogen/air explosions by NaHCO3

To explore the effects of the hydrogen fraction and initial pressure on the inhibition of methane/hydrogen/air explosions, the inhibition of stoichiometric methane/hydrogen/air explosions (hydrogen fraction ranging from 0 to 0.8) by NaHCO3 at various initial pressures (0.8 atm, 1.0 atm, 1.4 atm) was investigated in a 36 L spherical vessel. The experimental findings indicate that the effectiveness of NaHCO3 in suppressing methane/hydrogen/air explosions is significantly influenced by the hydrogen fraction and initial pressure. For a given hydrogen fraction, higher initial pressures weaken the inhibitory effect of a given NaHCO3 concentration on explosions. The drop ratios in the maximum explosion pressure for initial pressures of 0.8 atm, 1.0 atm, and 1.4 atm are 41.2 %, 19.7 %, and 15 %, respectively, at a hydrogen fraction of 0.8 and a NaHCO3 concentration of 400 g/m3. Additionally, the inhibitory impact of a given NaHCO3 concentration diminishes as the hydrogen fraction increases at the given initial pressure. An increasing hydrogen fraction decreases the drop ratio of the maximum explosion pressure while simultaneously increasing the maximum pressure rise rate and deflagration index. A thermodynamic equilibrium model for the endothermic decomposition of NaHCO3 particles was built to explore the impact of the hydrogen fraction and initial pressure on the decomposition characteristics of NaHCO3 particles of different sizes. The laminar burning velocity was derived using a theoretical model through the experimental pressure history and was calculated through detailed chemical kinetic modeling. The effect of the hydrogen fraction on the suppression mechanisms of NaHCO3 was evaluated by using the normalized laminar burning velocity. The dominant inhibition mechanism of NaHCO3 on the laminar burning velocity changes from physical inhibition to chemical inhibition with increasing hydrogen fraction.

Measuring dust burning velocity for deflagration vent design

Deflagration vent design should be based on the burning velocity in the pressure range below 3 bara, where vent relief devices normally operate, rather than the KSt deflagration index, which is typically measured at pressures >50% of the maximum deflagration pressure, Pmax. Tests using a standardized 1000-L vessel showed that in the pressure range below about 3 bara, niacin and lycopodium burned faster than cornstarch, despite its larger KSt index. We attribute this behavior to the endothermic dehydration of cornstarch during the early stages of deflagration. Deflagration vents for cornstarch and other milled grains may have been oversized while vents for some other dusts may have been undersized. Burning velocities are most relevant in the region of the 2-bara midpoint overpressure and can theoretically be found from the “isothermal pressure rate gradient”, or IPRG, which we define as the gradient of (dP/dt) plotted against P (1-1/P)2/3. However, owing to irregular combustion caused primarily by two 5 kJ igniters, the IPRG is found indirectly from the “pressure rate gradient” or PRG, which we define as the gradient of (dP/dt) plotted against P. The PRG was found to be adequately linear for measurement at 2 bara and the experimental curves passed through the "origin". It was shown mathematically that at 2 bara the PRG is 1.05 times larger than IPRG, permitting the IPRG and turbulent burning velocity to be calculated. Since the calculation of burning velocity from the IPRG requires Pmax, a general extrapolation technique was developed for correcting Pmax values obtained in vessels smaller than 1000-L. We propose that, owing to the greater turbulence in the 20-L vessel, a calibration be made using methane. This would establish the turbulence factors for each vessel at 2 bara, allowing the underlying “reference” burning velocities to be calculated and compared. However, to measure turbulent dust burning velocities in 20-L vessels a smaller and more efficient igniter must be used. Two 5 kJ igniters not only obscure the pressure history but wastefully expend energy far from the vessel core, depleting the unburned mixture and depressing the subsequent pressure rate. An observed “double sigmoid” dependence of dust deflagration rate on particle diameter suggests that routine explosibility testing of organic dusts is usually carried out in a region where pressure rates are relatively insensitive to particle size.

Suppressive effects of alkali metal salt modified dry water material on methane-air explosion

As an abundant and efficient energy source, methane has a wide range of applications and development prospects, but it has a high explosion risk. In order to prevent the occurrence of methane explosion accidents, a new type of dry water material (DW) was used to suppress explosion, and alkali metal salts were added to improve the suppression effect. In this work, the optimal DW with complete monomer and uniform structure can be prepared by stirring nano-silica and deionized water at a mass ratio of 1:10 at a speed of 10000 rpm for 60S. The suppression effect of dry water was analyzed by performing methane-air explosion experiments with different powder concentrations in 20L explosion vessel. The results show that under the action of alkali metal modified DW, the Pmax and the deflagration index KG of methane-air explosion were significantly reduced. The improvement effect of potassium salt-dry water (PS-DW) ranked as KCl＞ K2CO3＞ K2C2O4·H2O＞CH3COOK, and the improvement effect of sodium salt-dry water (SS-DW) ranked as Na2CO3>NaCl > NaHCO3>NaH2PO4. Moreover, the explosion suppression mechanism of alkali metal salt modified DW was analyzed from four aspects: heat insulation, cooling, dilution and interruption of chain reaction. The study confirmed the important application potential of DW in preventing natural gas leakage explosion and coal mine gas explosion accidents. The optimal selection of modified additives in alkali metal salts holds significant importance for the widespread application of novel dry water composite materials.

Quantitative investigation of explosion behavior and spectral radiant characteristics of free radicals for syngas/air mixtures

The combustion characteristics and explosive hazard of syngas (H2/CO)/air mixtures are affected by its exact composition and equivalence ratios. In this paper, the explosion pressure and spectral radiant intensity of free radicals were quantitatively examined for syngas with different H2 proportions ([H2 in syngas] = 0, 30, 50, 70, 100 vol%) and equivalence ratios (φ = 0.8, 1.0, 1.2, 1.4, 1.6, 2.0, 2.5). The results show that the explosion process of syngas/air mixtures can be separated into the initial slow combustion stage, the violent deflagration stage and the deflagration ending stage. The peaks of explosion pressure, pressure rise rate, OH*spectral intensity and rise rate of spectral intensity first increase and then decrease with increasing the equivalence ratio, and they reduce gradually with the decrease of H2 proportion in syngas. The H2 content in syngas greatly affects the heat release and the concentration of excited state OH*, especially for the syngas/air mixtures with smaller proportion of H2. Additionally, the presence of H2 greatly increases the deflagration index and spectral radiant index of OH* for syngas/air mixtures. The average rise rates of explosion pressure and spectral intensity of free radicals are introduced and the coupling model between them is established based on the first law of thermodynamics and the principle of chain reaction. The established model is furthermore verified by the experimental results. It is indicated that there is a linear relationship between average rise rates of explosion pressure and spectral intensity (OH*). The results can be used to improve the combustion efficiency of syngas and to guide theoretically the prevention, mitigation and control of syngas explosions.

Investigations on methyl pentanoate-air mixtures confined explosion and cellularity

Combustible fuels like methyl pentanoate (MPe) could cause accidental explosions and fire. Therefore, MPe explosion characteristics have to be well characterized and understood for its safe and reliable use in industries and combustion devices. Considering this, MPe’s explosion pressure, maximum explosion pressure, rate of pressure rise, maximum rate of pressure rise, heat release rate, etc., were investigated in this study at the initial conditions of 1, 2, and 4 bar and 423 K, 453 K, and 483 K using the equivalence ratios of 0.7–1.4. The maximum explosion pressures and maximum rate of pressure rise of MPe increased as the initial pressures increased but the maximum rate of pressure rise was insignificantly affected by the initial temperature. The explosion duration decreased with a decrease in the initial pressure. The maximum heat release rate and deflagration index increased with increasing initial pressure. The MPe maximum deflagration index was 224.8 bar•m/s, which occurred at a higher initial pressure and fuel-rich mixture. Therefore, the explosion severity of MPe was enhanced at higher initial pressures and fuel-rich mixtures. Moreover, the flame cellularity study showed that MPe unstable flame crack length and cell number were more affected by increments in the initial pressure and equivalence ratio. Therefore, flame instability and cellularity would significantly influence explosion severity at higher pressures and equivalence ratios. This study’s findings provide first-hand data that could be used to further investigate and characterize MPe’s explosion risk.

Experimental and reaction kinetics studies on deflagration characteristics of liquefied petroleum gas-air mixture with different compositions in confined space

To assess the hazardous impact of liquefied petroleum gas (LPG), this study investigated its macro–micro deflagration characteristics under various compositions and equivalence ratios using a 20 L spherical experimental apparatus and CHEMKIN-Pro kinetic software. The findings are as follows: when the equivalence ratio was 1.2, the LPG exhibited peak values for the maximum explosion pressure (pmax), maximum explosion pressure rise rate ((dp/dt)max), deflagration index (KG), and average flame propagation velocity (v). Furthermore, the (dp/dt)max, KG, and v increased with increasing the proportion of C3H8. In the LPG chain reaction, the most influential steps in terms of promotion and inhibition were R1: H + O2 = O + OH and R104: 2CH3(+M) = C2H6(+M), respectively. C2H4 gradually accumulated during the chain initiation phase and rapidly depleted as the temperature sharply increased. Hence, to effectively inhibit LPG explosion, it is recommended to develop inhibitors capable of eliminating reactive radicals (such as H*, O*, and OH*) and targeted inhibitors that specifically inhibit the reaction involving C2H4. Additionally, augmenting the C3H8 proportion in LPG can mitigate the emission of toxic and harmful gases, such as CO and CO2. This study has significant theoretical and practical implications for the safe, environmentally friendly, and efficient use of LPG.

Investigation of the length-to-diameter ratio of ducts effect on the oscillation propagation behavior and vented characteristics for propane-air vented explosions

The effects of length-to-diameter (L/D) ratio on oscillation propagation behavior and vented characteristics of propane explosions have been explored in a rectangular explosion duct. The results show that as the L/D ratio increased, the turbulence of the internal flame was enhanced, and the flame area and gas reaction rate increased sharply, which promoted the appearance of the Mach diamond structure in the vented flame. Due to heat and energy loss, the maximum reduced pressure (Pred) decreased with the increase of L/D ratio, but the maximum pressure rise rate ((dp/dt)max) and the deflagration index (KG) still increased significantly. Besides, the venting diameter (Dv) where the maximum external pressure was obtained increased with the L/D ratio, and the critical venting diameters of the vented propane-air explosions to reach the equilibrium venting state under different L/D ratios were determined. An empirically modified model of Pred was established by introducing the L/D ratio and vent coefficient KV, and the maximum relative error of this model is 137% lower than that of the international standard model. The excellent performance of the results would provide a new idea for the venting safety design of the large L/D ratio duct in process industry applications.

Evolution characteristics of ethyl ether spray explosion process in 20L near-spherical vessel

As a biofuel with a wide range of uses, ethyl ether leakage may cause serious spray explosion accidents during storage and transportation, however, the evolution characteristics and process mechanism of ethyl ether spray explosion have not been thoroughly studied. Therefore, the effects of material temperature and ambient temperature on ethyl ether spray explosion at different concentrations are studied by means of spray explosion experiment system. In this paper, the development of ethyl ether spray explosion with a mass concentration range of 107.1–392.7 g/m3 was studied at different ambient temperature and material temperature. Where the ambient temperature range is 298.15–323.15 K, and the material temperature range is 298.15–323.15 K. Moreover, in this paper, the risk of spray explosion is more clearly understood through the classification of deflagration index, and the explosion characteristics of spray explosion are analyzed comprehensively according to the boiling point as the dividing line. The maximum explosion pressure and its arrival time, the rate of rise of the maximum explosion pressure and its arrival time are used as the basis to evaluate the effect of the explosion process of ethyl ether spray. The results show that when the ambient temperature is lower than the boiling point temperature of ethyl ether, the increase of ambient temperature has little effect on the explosion characteristics of ethyl ether spray. When the ambient temperature is higher than 308.15 K, the maximum explosion pressure and maximum rate of pressure rise of ethyl ether spray explosion increase. At medium and low concentrations(107.1 g/m3, 178.5–249.9 g/m3), the increase of ambient temperature is conducive to the rapid development of spray explosion, and the arrival time of maximum explosion pressure and pressure rise rate both show a decreasing trend. However, under the influence of incomplete combustion at high concentration, the explosion development rate is reduced. At lower material temperature, the maximum explosion pressure and the maximum rate of pressure rise increase with the increase of material temperature. When the material temperature is higher than 303.15 K, the ethyl ether droplet temperature is higher than the ambient temperature, and the heat loss of the droplet has a certain inhibition effect on spray explosion. Especially when the material temperature is high, the inhibition effect is more significant, so when the material temperature rises to 323.15 K, the maximum rate of pressure rise decreases. The effect of ambient temperature on the explosion grade is more obvious than that of the material temperature, and the effect on the explosion characteristics of ethyl ether spray is also greater.

Experimental study on the explosion characteristics of NH3/DME/air mixtures

Co-firing ammonia (NH3) fuel with dimethyl ether (DME) is a promising approach of achieving clean combustion. However, the fundamental explosion characteristics of NH3/DME blends have not been well understood. This paper presents an experimental study of the explosion characteristics of NH3/DME blends using a spherical constant-volume combustion chamber. The effects of equivalence ratio (ϕ = 0.7–1.5), initial pressure (Pu = 0.05–0.5 MPa), and DME fraction (XDME = 0–100%) on the explosions were examined. The results show that peak explosion pressure Pmax, maximum pressure rise rate (dP/dt)max, and deflagration index KG, vary non-monotonically with equivalence ratio, and reach peak values at around ϕ = 1.1–1.2. DME addition has a positive effect on explosion intensity. Both (dP/dt)max and KG show a linear increase trend with increasing DME, while the growth rate of Pmax decreases with DME fraction. The relatively higher increase in Pmax between 0 %DME and 20 %DME is mainly due to greater heat release. Pmax increases with increasing initial pressure, and this is because of the increase in mixture mass promoting the heat release, and the enhanced possibility of effective collision between molecules of gas mixtures. The influence of initial pressure on (dP/dt)max and KG depends on the equivalence ratio. Both (dP/dt)max and KG show a linear increase with increasing initial pressure at ϕ = 1.0 and 1.5, whereas they are insensitive to initial pressure at ϕ = 0.7. This is because the decrease in laminar burning velocity leads to a significant increase in explosion time at ϕ = 0.7 compared to ϕ = 1.0 and 1.5. In addition, the actual explosion pressure is closely associated with non-negligible heat loss during flame propagation, and the heat loss decreases with the addition of DME, but increases with increasing initial pressure.

Re-explosion hazard potential of solid residues and gaseous products of coal dust explosion

In the present work, solid residues and gaseous products after the initial explosion of coal dust were collected by self-made devices, respectively, and their explosiveness was further studied to assess the re-explosion hazard. The results show that the solid residue can explode again, and its explosion pressure (Pex) and pressure rise rate ((dP/dt)ex) both increase gradually as dust concentration and ignition energy increase, but decrease with the larger particle size. Solid residue is characterized by a lower deflagration index (Kst) than raw lignite dust, but it can produce greater severity than some raw high-rank coal dust in some cases. The gaseous products of coal dust explosion are mainly composed of CO, H2 and CH4, and some trace gases. The volume fraction of CO and H2 in the gaseous products rises in proportion to the concentration of coal dust. For coal dust explosion with a concentration >200 g/m3, the gaseous products collected are flammable and have a wider explosion limit and a lower limited oxygen content. This research provides valuable information and reference for future prevention and control of secondary explosion disasters in coal mines.

Effect of palm-based soap noodles dust concentration on dust explosion severity in a spherical vessel

The dust explosion propagation of palm-based soap noodles was experimentally studied in a 20-L spherical vessel. Understanding the effect of concentration on this metric is a prerequisite to characterizing the severity of the explosion. This study focused on the link between concentration and overpressure (Pmax), rate of pressure rise (dP/dt), and deflagration index (KST). The highest Pmax, dP/dt, and KST were recorded at 400 g/m3, corresponding to a class St-2 dust with a strong explosion. The agglomeration process evidently controlled the mass burning rate, which affected the dust explosion propagation. This data can help design preventive measures related to palm-based soap noodle dust explosions.

Making hybrid mixture explosions a common case

Explosions of gas-dust hybrid mixtures have long been considered as particular cases encountered in specific industrial contexts. However, it should be reminded that during the explosion of an organic powder, the presence of a hybrid mixture composed of the dust itself and its pyrolysis gases is compulsory. On these premises, an experimental study to determine the role of cellulose pyrolysis products (gaseous, condensable and solid) on the global phenomenon is presented. Hybrid mixture explosion tests were exploited to carry out the investigation. The G-G furnace and the 20 L sphere were employed. Several experimental strategies were chosen to demonstrate the impact of pyrolysis reaction on the explosion of organic powders: i) the fuel equivalence ratio of the reactive mixture (case 1), or ii) the mass of reactants (case 2) were respectively kept constant, iii) the effects of water vapor, char and tar were tested. They were next compared to identify the most suitable one. The two first experimental approaches lead to significantly different results: only case 2 keeps the maximum explosion pressure almost constant, but maximum rate of pressure rises and deflagration index greatly decrease when the pyrolysis gases concentration decreases, which highlights the importance of the pyrolysis reaction on the explosion kinetics. It should also be stressed that the maximum explosion severity is not obtained for the pure gases but when a small dust content is added. The same evolution is observed when a small amount of char is introduced to pyrolysis gases, which underlines the influence of the radiative transfer. Adding small amounts of tar to cellulose tends to increase its explosion severity. However, this impact is less than that generated by the addition of pyrolysis gases.

Combustion and Explosion Characteristics of Pulverised Wood, Valorized with Mild Pyrolysis in Pilot Scale Installation, Using the Modified ISO 1 m3 Dust Explosion Vessel

Biomass is a renewable energy source with great potential worldwide and in the European Union. However, valorization is necessary to turn many types of waste biomass into a tradable commodity that has the potential to replace coal in power plants without significant modifications to firing systems. Mild pyrolysis, also known as torrefaction, is a thermal valorization process of low-quality biomass that could be suitable for such a purpose. In this work, typical Spruce-Pine-Fir residues from a sawmill were tested in terms of the explosion and flame propagation properties. The ISO 1 m3 dust explosion vessel was used, with a modified and calibrated dust dispersion system that could cope with very coarse particles. The deflagration index, Kst, was higher for the torrefied sample, with a peak at 36 bar m/s compared with 27 for the raw biomass. The peak flame speeds were similar for both samples, reaching 1 m/s. The peak Pmax/Pi was between 7.3 and 7.4 bar for both untreated and torrefied biomass. The mechanism for coarse particle combustion is considered to be influenced by the explosion-induced wind blowing the finer fractions ahead of the flame, which burns first, subsequently devolatilizing the coarser fractions.

Influence of change in obstacle blocking rate gradient on LPG explosion behavior

The aim of this study was to examine the propagation characteristics of liquified petroleum gas (LPG)/air explosion. As such, the flame propagation process and pressure parameters of LPG explosion with an equivalent ratio of 1 were obtained using horizontal, long straight pipes and a high-speed camera. The large eddy simulation and power-law flame model were used to reproduce the simulation results, and the morphological evolution of the flame front during the explosion process was analyzed. The results showed that as the blockage ratio gradient increased, the time required for the flame to propagate from the electrode to the end of the pipe increased. Meanwhile, a flocculent flame formed at the end of the pipeline with a blockage ratio of 91%. Additionally, the maximum flame propagation speed changed in the same way as the blockage ratio. The gradient change of the barrier blockage ratio considerably influenced the pressure kinetics characteristics of LPG explosion: the maximum explosion pressure increased first and then decreased, the time to reach the maximum explosion pressure increased, and the deflagration index increased first and then decreased. The chemical kinetics analysis of premixed gas showed that when propane, n-butane, and isobutane were present in the premixed system, some of the elemental reactions that promote n-butane consumption inhibited propane and isobutane consumption. Meanwhile, the formation and consumption rate of H*, O*, and OH* from LPG during the explosion process was less than that of single-component combustible gas except propane.

Study on flame propagation of H2/LPG premixed gas in a tube

This work aims to is to study the flame propagation characteristics of the hydrogen/liquefied petroleum gas (LPG) premixed gas in a closed tube. With the aid of a self-developed square glass explosion tube and a high-speed camera, the characteristic parameters (i.e., flame structure, flame tip speed, maximum explosion overpressure, maximum rate of explosion pressure rise, deflagration index) were obtained and analyzed the explosion characteristics of the premixed gas. The results show that the time for the flame to reach the end of the pipe decreased, and the maximum explosion overpressure increases as the hydrogen addition ratio increases. However, the explosion overpressure and flame propagation velocity increased slowly when the hydrogen addition ratio was less than 40%, While the explosion overpressure and flame propagation velocity increased drastically in the range of hydrogen addition ratio 40–80%. Therefore, the key turning point for LPG hydrogenation is when the hydrogen volume fraction is 40%. The peak explosion flame propagation velocity and the peak explosion pressure showed the change law of increasing first and then decreasing with the equivalent ratio increasing. The Pmax and Vmax are 6.4 bar and 71.2 m/s respectively. The explosive flame structure of the premixed gas formed a "multiple tulip" structure after the typical tulip flame structure due to the influence of hydrodynamic. In addition, the propagation law of H2-LPG-Air premixed flame in the pipeline was influenced by the interaction of pressure wave and flame front velocity, and Pmax trajectory and Vmax curve showed similar oscillation law. Hence, the study provides crucial data for the prevention and control of H2-LPG-Air gas mixture combustion and explosion accidents.

Theoretical and Experimental Investigation of Explosion Characteristics of Hydrogen Explosion in a Closed Vessel

A simplified model that calculates the deflagration pressure–time curves of a hydrogen explosion was proposed. The deflagration parameters (pressure peak, duration, deflagration index, and impulse) of hydrogen–air mixtures with different hydrogen concentrations were experimentally investigated. The results show that the pressure curves calculated by the model are consistent with experimental data pertaining to a methane and hydrogen explosion. By comparison, the pressure peak and deflagration index are found to be influenced by the aspect ratio and surface area of vessels. The impulse and explosion times at fuel-lean hydrogen concentrations are greater than those at fuel-rich concentrations. When the hydrogen concentration is between 34 vol.% and 18 vol.%, the greatest explosion damage effect is formed by both the overpressure and the impulse, which should be considered for hydrogen explosion safety design in industrial production.

Laminar burning characteristics of bio-aviation fuel candidate derived from lignocellulosic biomass

This study investigated the laminar burning characteristics of bio-aviation fuel candidate produced from corn stover lignin via catalytic hydrodeoxygenation (HDO). The experiments were conducted at equivalence ratios of 0.7–1.4, initial pressures of 1 bar, 2 bar, and 4 bar, and initial temperatures of 443 K and 473 K. The laminar burning velocity (LBV), explosion pressure, maximum pressure-rise rate, and combustion duration were studied. The LBV was studied using the constant volume (CVM) and constant pressure (CPM) methods. The CVM results were significantly higher than that of CPM in the presence of cellular flame. In other cases, the deviations of both were within 10 %. The analysis indicated that the LBV of the bio-aviation fuel candidate at certain equivalence ratios was lower than that of Jet A-1, RP-3, and n-decane. However, the LBV of the bio-aviation fuel candidate was greater than that of n-decane in fuel rich mixtures. A 12-term power-law correlation was determined to quantify the relationship between the LBV of the bio-aviation fuel candidate and the equivalence ratio, initial temperature, and initial pressure. The maximum deviation between the experimental data and the correlation was 11.85 %, and the average deviation was 2.95 %. Finally, the effects of the initial conditions on the explosion characteristics of the bio-aviation fuel candidate were analyzed. The explosion pressure, maximum pressure-rise rate, and deflagration index were linearly and positively correlated with the initial pressure; however, the latter two were insensitive to the initial temperature. Furthermore, a quantitative correlation between the explosion characteristics and the equivalence ratio and initial pressure was determined.

On the smoothing explosion pressure curves using Savitzky-Golay method

This study reports the optimal range of window width of Savitzky–Golay method for smoothing the raw oscillating explosion evolution curves obtained in methane-air mixtures. The experiments were carried out in a closed vessel of 3.375 L at various equivalence ratios (φ=0.8−1.2) and initial pressures (P0=1.0−2.5bar). All experiments were conducted at room temperature (293 K). The optimal range of window width and the corresponding explosion characteristics (the maximum explosion pressure Pmax, maximum pressure rise rate (dp/dt)max and deflagration index KG) of each initial condition were determined. The results show that (dp/dt)max is influenced markedly by the window width, and some similar behaviors (three characteristic segments) of (dp/dt)max-window width curves are found. Besides, the optimal range of window width depends not only on the equivalence ratio but also on the initial pressure, and the representative median of each range shows a downward trend with the initial pressure. And the median is stable at 1251 points when P0 is greater than 2.0 bar at φ=0.8, while it shows a linear decrease at φ=1.0 and φ=1.2, and maybe also tends to a stable value at a higher initial pressure. Furthermore, Pmax, (dp/dt)max and KG corresponding to the optimal range of window width have perfect linear correlations with P0, verifying convincingly the correctness of the range we determined.