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With the growth and development of Construction 4.0, new technologies such as BIM, Big Data, and the Internet of Things are commonly used. These digital technologies play a critical role in fostering firm innovation and also have a major impact on firm performance. Based on panel data of 33 listed construction firms in China’s construction industry from 2015 to 2020, this paper uses regression analysis and mediation analysis methods to empirically examine the relationship between Construction 4.0, technological innovation capabilities, and firm performance. The results demonstrate that Construction 4.0 has a significant positive promotional effect on the firm performance, while technological innovation capabilities mediate between Construction 4.0 and the firm performance. Based on these findings, it is suggested that construction firms should pay attention to the new technologies brought by Construction 4.0, increase investment in research and development, actively cultivate technological innovation capabilities, and build technological innovation networks, so as to promote digital transformation of construction firms.

Gaseous inhibitors are used in many industries for the explosion prevention of combustible dusts, mitigating the potential hazard to humans, properties and environments. This work experimentally and theoretically studied the inerting effect of gaseous inhibitors on the ignition process of dust clouds in O2/N2/CO2 atmospheres, with an emphasis on the role of the CO2/N2 ratio. 10 different combustible carbonaceous dusts were selected, including grain dust, biomass dust and coal dust. Experimental results showed that the inhibition effect of CO2/N2 is closely related to the ignition mechanism of dust clouds. Specifically, a higher ratio of CO2/N2 yields a stronger inhibition effect on the ignition process of dust samples with relatively low volatile matter contents predominated by heterogeneous ignition. In addition, two novel steady-state ignition mechanism models were developed to interpret the experimental observations. Maxwell-Stefan equations were used to describe the diffusivity in the ternary O2/N2/CO2 gas mixtures. The analytical results were in good agreement with the experimental data of the minimum ignition temperature of dust cloud (MITC) in oxygen-lean atmospheres. The mechanism modelling can be used to estimate the critical ignition temperature of all carbonaceous dust clouds with a wide range of volatile matter content under different inert atmospheres, which will provide a reference for the explosion hazard assessment of dust posed by a hot surface in the process industries.

The data center needs more and more electricity due to the explosive growth of IT servers and it could cause electricity power shortage and huge carbon emission. It is an attractive and promising solution to power the data center with hydrogen energy source. The present work aims to conduct an economic analysis on the hydrogen-powered data center. Configurations of hydrogen-powered and traditional data centers are compared and the differences focus on backup power system, converter/inverter, fuel cell subsystem, carbon emission, hydrogen and electricity consumptions. Economic analysis is conducted to evaluate the feasibility to power the data center with hydrogen energy source. Results show that electricity price increasing rate and hydrogen cost are the main factors to influence economic feasibility of hydrogen-powered data center. When the electricity price keeps constant in the coming two decades, the critical hydrogen price is about 2.8 U.S. dollar per kilogram. If the electricity price could increase 5% annually due to explosive growth of electric vehicles and economy, critical hydrogen price will become 6.4 U.S. dollar per kilogram. Hydrogen sources and transportation determine the hydrogen price together. Hydrogen production cost varies greatly with hydrogen sources and production technologies. Hydrogen transport cost is greatly influenced by distances and H2 consumptions to consumers. It could be summarized that the hydrogen-powered data center is economic if hydrogen could be produced from natural gas or H2-rich industrial waste streams in chemical plant and data center could not be built too far away from hydrogen sources. In addition, large-scale hydrogen-powered data center is more likely to be economic. Solar hydrogen powered data center has entered into a critical stage in the economic feasibility. Solar hydrogen production cost has restrained the H2 utilization in data center power systems now, since it could be competitive only when more strict carbon emission regulation is employed, hydrogen production cost reduces greatly and electricity price is increasing greatly in the future. However, it could be expected solar hydrogen-powered system will be adopted as the power source of data centers in the next few years.

Dust explosions have been often reported in many industries that handle or process combustible dusts, with great losses to life and property. This explosion risk could be amplified under some extreme conditions like high-temperature environments. In this work, we develop a 2D numerical method to investigate explosion characteristics of corn starch cloud with an emphasis on the roles of high-temperature environments. The particle tracking trajectories and devolatilization evolution at high-temperature environments are described. The dust explosion severity characteristics including maximum explosion pressure (Pex) and maximum rate of pressure rise (dp/dt)max, are also investigated. In addition, the characterized devolatilization and explosion time are applied to analyze dust explosion behavior and flame propagation. The devolatilization evolution of dust cloud and flame propagation modes are found to vary with ambient temperature. And three ignition modes are observed after ignition. The simulation also provides a satisfactory prediction for dust explosion behavior at high-temperature environments.

The space heating system accounts for 20%~50% of building energy consumption, and may lead to energy waste due to unreasonable controls. In this study, an energy-efficient floor heating system with intelligent control was proposed to improve energy efficiency of the system. In order to validate the concept of the proposed intelligent control, an experimental system was designed and constructed in Chengdu, China. Temperature, control cycle and energy consumption were then studied under different control strategies. The result shows that a larger flow rate of supply water will result in a longer control cycle and a lower control frequency, i.e., the average control cycle at 7 L min−1 is 1.7 h during the test day, while it is 1.5 h at 5 L min−1. Moreover, adopting water with a higher temperature and flow rate could achieve a higher efficiency of the system. The energy consumptions in case 1 (5 L min−1, 50 °C), case 2 (5 L min−1, 55 °C), case 5 (7 L min−1, 55 °C) and case 6 (7 L min−1, 60 °C) are 4746 kJ, 3534 kJ, 3093 kJ and 3028 kJ, respectively. Based on the experimental data, the supply water temperature is suggested to set lower than 60 °C considering human comfort.

Experiments were performed to study the explosion characteristics of DME-blended LPG mixtures with different DME contents and equivalence ratios using a closed vessel. The maximum explosion pressure (Pmax), the maximum rate of pressure rise (dP/dt)max and the propagation velocity of shock wave (v) were investigated. The results indicated that both the peak overpressure and peak rate of pressure rise were raised with increasing DME content, reaching peak values at the equivalence ratio of 1.2. Furthermore, it was found that slight incorporation of DME had a small effect on the explosion hazard, but as the ratio of DME to LPG/DME mixture exceeded 30%, the explosion hazard would increase dramatically. The propagation of the shock wave behind the obstacle was divided into three stages in this paper: initial acceleration, stable acceleration and decaying. In the propagation process, Pmax, (dP/dt)max and v first increased and then decreased along the pipeline, and the peak values often appeared in the stable acceleration stage. The peak overpressure and the maximum value of v also appeared in the same location approximately, indicating that the occurrence of maximum overpressure risk was often accompanied with the appearance of the most severe dynamic evolution.

Smouldering fires and explosions arising from self-ignition of coal dust deposits represent a serious hazard for human beings, environment and industry. It is essential for plant operators to know the conditions (temperature, duration and quantities) at which storage will be safe. In this work, self-ignition behaviour of three bituminous coal dusts in large scales are theoretically studied, based on the experimental data obtained via a standardized hot-basket apparatus. A comprehensive 2-D transient model is developed, using a 2nd-order reaction kinetics considering both coal and oxygen consumptions, to investigate self-ignition parameters of coal dust accumulations. The numerical model shows a less conservative prediction compared with the steady-state methods. The computed self-ignition temperature and ignition delay time show a satisfaction agreement with lab-scale experimental results. In addition, the influences of ambient temperature and moisture content are analysed. The result shows that the moisture content delays the ignition and a small variation of the ambient temperature nearby the critical condition will lead to a large difference in the ignition delay time.

Hydrogen peroxide with the presence of catalytic metal ions or incompatible organic matters has caused some fire and explosion accidents in recent years. This work further studied the effect of inorganic salt and organic acid on the thermal runaway behaviour of hydrogen peroxide via rapid screening device (RSD), accelerating rate calorimeter (ARC) and a batch reactor. Experimental results revealed that both the metal ions and their corresponding inorganic acid ions have significant influences on the thermal runaway of H2O2: the catalytic effect of metal ion followed Fe2+ > Fe3+ > Cu2+, and the synergistic effect of inorganic acid ion followed Cl− > SO42−. No explosion was detected under RSD and ARC test conditions. In addition, a one-step global reaction kinetic model characterized as adiabatic temperature increase and final exothermic temperature was briefly described to estimate the kinetic parameters of the mixture of H2O2 with/without organic acid. The analysis showed that the runaway reaction of H2O2 with formic acid or acetic acid is a first order reaction at a low temperature range ( H2O2/CH3COOH, along with the decreasing apparent activation energy and pre-exponential factor.

To reveal and improve our understanding of the ignition behavior and mechanism, G-G furnace experiments of three typical organic dusts were performed to investigate the minimum ignition temperature (MIT) in O

Minimum ignition temperature of dust clouds (MITC) was studied experimentally and theoretically in different atmospheres. Three carbonaceous dusts were tested in both air and O

A series of experiments were conducted in a 10L closed and vented tube with L/D = 10.0, and effects of initial fuel volume concentration, inert gas dilutions (diluted by N2 and CO2), inert gas–water mist twin fluid medium dilutions (diluted by N2-H2O twin fluid medium, CO2-H2O twin fluid medium) and end boundary conditions on overpressure transients of hydrocarbon fuel–air mixtures explosion were revealed. Results show that the overpressure-time profiles consistent with the dynamic evolution law of ‘approximately zero-1st overpressure rising stage-2nd overpressure rising stage-descending stage’, and ‘rate of overpressure rise-time’ curves exhibit the characteristics of multi-stages and multi-peaks, such as (dp/dt)(1,max), (dp/dt)(1,min), (dp/dt)(2,max) and (dp/dt)(2,min). Specifically, as the fuel volume concentration increased, both the maximum overpressures (pmax), and the maximum rates of overpressure rise ((dp/dt)(1,max) and (dp/dt)(2,max)) show a variation trend of increasing firstly and then decreasing, while the corresponding times (tmax, θ(1,max) , θ(2,max)) show a total different variation trend. Moreover, when YCH is lower than 1.88%, the value of (dp/dt)(1,max) is greater than (dp/dt)(2,max), while the value of (dp/dt)(1,max) was less than (dp/dt)(2,max), and when YCH was higher than 1.88%. The addition of N2 and CO2 can obviously inhibit the explosion intensity of hydrocarbon fuel, and the inhibition effect of CO2 is better than that of N2. Due to the synergy inhibition effect of the inert gas and ultrafine water mist, all the values of pmax, (dp/dt)(1,max) and (dp/dt)(2,max) diluted by inert gas-ultrafine water mist twin fluid medium were smaller than those diluted by sole inert gases. In addition, there are significant differences in the overpressure-time and the rate of overpressure rise-time profiles between closed and end venting explosions. The values of maximum overpressure and the rates of overpressure rise of the closed explosion were higher than those of the venting explosion, but the minimum rate of overpressure rise is a smaller one.

Grewer oven tests with a constant heating rate are conducted to investigate the self-heating characteristics of coal dusts under air and O2/CO2 mixtures with O2 mole fractions ranging from 21% to 50%. Experimental results reveal that the crossing point temperature (CPT) decreases with increasing O2 mole fraction and coal maturity. The inhibiting effect of CO2 is found to be comparatively small for the self-heating process. In addition, a numerical method is developed to study the self-heating behaviour of coal dusts with an emphasis on the roles of moisture content, gas conditions, mass flow and heating rate. The kinetic parameters are estimated by a modified 2nd-order kinetic steady-state CPT method. The computational CPTs related to gas atmospheres show a good agreement with experimental results. Parameter analysis shows that the heating rate has a comparatively pronounced effect on CPTs compared to moisture content and gas flow rate.

Hydrogen peroxide, as a very versatile reagent for many industrial processes, has caused many accidents in recent years. Therefore, understanding the thermal hazards of hydrogen peroxide with or without impurities is essential for the prevention of fire and explosion accidents. In this work, batch reactor tests were conducted to study the thermal runaway behavior of hydrogen peroxide under the contaminations of Fe3+ ion, formic/acetic acid and ethanol/acetone. Experimental results revealed that the thermal runaway risk of H2O2 increased significantly with increasing initial temperature and Fe3+ ion concentration. Comparatively, the potential risk of organic impurities on the thermal stability of hydrogen peroxide was found to be much larger, because several violent explosions were measured resulting from a series of rapid and complicated decomposition reactions. The explosion severity of H2O2 with organic matters followed acetone > ethanol > formic acid > acetic acid. In addition, a modified runaway scenario characterized as adiabatic temperature increase and time to maximum rate was briefly described to theoretically evaluate the thermal risk of H2O2 decomposition. This scenario was found to be valid to estimate thermal runaway hazards. These results improve our understanding of thermal runaway behavior and explosion risk of H2O2 with incompatible impurities.

Hydrogen leakage of vehicles in the tunnel is a great threat to the safety operation of the tunnel and longitudinal ventilation strategies have always been utilized to control the fire and smoke movement of rail transit, electric and fossil-fueled vehicles in the engineering field. It is in doubt whether the longitudinal ventilation strategy could still help to reduce the jet fire hazard of transportation with H2 power in the tunnel, considering the rapid development of the hydrogen energy. In present work, a numerical research on effects of longitudinal ventilation strategies on hydrogen jet flames in the tunnel is conducted. The results illustrate that longitudinal ventilation could affect the flame characteristics of jet flames greatly in the tunnel. The critical ventilation velocity increases firstly with the increase of hydrogen leakage rates and then changes little after a critical value. The predicted theoretical model of pool fires could well predict the critical ventilation velocity for hydrogen jet fires. With the increase of longitudinal ventilation velocity, maximum ceiling temperatures are decreased greatly. According to the heat releases, jet speeds and ventilation velocities, three kinds of flame bending characteristics of hydrogen jet fire could be observed due to different effects of the inertial force. At last, the stable thermal stratification could also be destroyed by large ventilation velocities but the corresponding ventilation velocity is far larger than the critical ventilation one. With the increase of longitudinal ventilation velocities, the height of thermal layer is reduced firstly and then maintained at a constant value.

Thermoelectric generator (TEG) has been proved as a promising technology for directly converting heat into electricity based on Seebeck effect. On the contrary, this electricity can trigger a solid-state cooling based on conventional Peltier effect. However, these two effects induce a coupling between heat and electric flux, especially for the quantitative relationship still remaining a mystery. Here, we show experimental evidence and theoretical calculation for the coupling by monitoring transient response of fluid temperature and output power. The experimental maximum heat flow in open circuit is 1162 W at cold fluid flow rate V c = 0.3 m3/h and fluid temperature difference ΔTf = 70 °C, enhanced by 13% owing to heat compensation from intrinsic coupling in closed-loop circuit. Meanwhile, the measured maximum output power of TEG is 18.2 W, and subsequently decreases to 15.4 W due to the objective existence of coupling. This double-edged sword in coupling vigorously inspires the potential applications in heat-dissipation situation such as spacecraft, electronic components, photovoltaic, refrigerator and etc. Present findings open a novel avenue for manipulating heat-electricity conversion in practical engineering.

The explosion characteristics of anthracite coal dust with/without small amount of CH4 (1.14 vol %) were investigated by using a 20 L spherical explosion apparatus with an emphasis on the roles of oxygen mole fraction and inert gas. Two methods based on overpressure and combustion duration time were used to determine the minimum explosion concentration (MEC) or the lower explosion limit (LEL) of the pure anthracite coal dust and the hybrid coal-methane mixtures, respectively. The experiment results showed that increasing oxygen mole fraction increases the explosion risk of coal dust: with increasing oxygen mole fraction, the explosion pressure (Pex) and the rate of explosion pressure rise ((dp/dt)ex)) increase, while MEC decreases. The explosion risk of anthracite dust was found to be lower after replacing N2 with CO2, suggesting that CO2 has a better inhibition effect on explosion mainly due to its higher specific heat. However, the addition of 1.14% CH4 moderates the inhibition effect of CO2 and the promotion effect of O2 on anthracite dust explosion for some extent, increasing explosion severity and reducing the MEC of anthracite dust. For hybrid anthracite/CH4 mixture explosions, Barknecht's curve was found to be more accurate and conservative than Chatelier's line, but neither are sufficient from the safety considerations. The experimental results provide a certain help for the explosion prevention and suppression in carbonaceous dust industries.

To reveal and improve our understanding of the ignition behavior and mechanism, G-G furnace experiments of three typical organic dusts were performed to investigate the minimum ignition temperature (MIT) in O2/N2, O2/Ar and O2/CO2 atmospheres with oxygen mole fraction from 8.4% to 50%. The experimental results were presented in oxygen-lean and oxy-fuel atmospheres to evaluate the ignition sensitivity of dusts in different atmospheres. It was found that CO2 is the strongest in terms of lowing the ignition sensitivity of the three dusts, and the dust explosion risk increases significantly with increasing O2 mole fraction for the three dusts through a logarithmically and significantly reducing MIT. However, for different dusts, inert gases show different suppression effects. In addition, a modified steady-state homogeneous ignition model was proposed and successfully applied to oxygen-lean atmospheres, and in oxy-fuel atmospheres, this model has also been improved to estimate the ignition mechanism. This ignition mechanism model could be used to successfully predict the minimum ignition temperature of high volatile dust under different inert atmospheres controlled by homogeneous ignition, which will provide a reference for the ignition hazard assessment of dust on hot surfaces.

Aging is accompanied by deficits in cognitive function and neuronal degeneration or loss. Quercetin is a flavonoid that exhibits powerful antioxidant activity. This study evaluated the protective effects and mechanisms of quercetin in d -galactose-induced neurotoxicity in mice. Quercetin was administered daily at doses of 20 or 50 mg/kg in d -galactose-injected (50 mg/kg/subcutaneous (s.c.)) mice for eight weeks. Morris water maze tests demonstrated that quercetin significantly improved learning and memory compared to d -galactose-treated control mice. Quercetin also prevented changes in the neuronal cell morphology and apoptosis in the hippocampus as well as increased the expression of Nrf2, HO-1 and SOD in d -galactose-treated mice. Treatment with the Nrf2 inhibitor Brusatol reversed the effects of quercetin on HO-1 and SOD expression as well as neuronal cell protection. In conclusion, quercetin protected mice from d -galactose-induced cognitive functional impairment and neuronal cell apoptosis via activation of the Nrf2-ARE signaling pathway.

The self-ignition of coal dust deposits and its subsequent smoldering combustion pose a high fire hazard to oxy-fuel power systems which burn fuels using pure oxygen for the sake of carbon capture and storage. The increasing risk of explosion in the gas-phase and self-ignition in the solid-phase for an oxygen enhanced combustion environment has not been well studied yet. In this work, the heterogeneous reactions of a bituminous coal dust are investigated by using a novel hot-basket apparatus with an emphasis on the roles of O2 and diluent gas in chemisorption and smoldering. Experiments show that increasing O2 mole fraction accelerates both self-ignition and the following smoldering combustion. On the other hand, the presence of CO2 increases the ignition temperature and reduces the maximum smoldering temperature. However, the promotion in the fire and explosion risk by elevating O2 mole fraction is substantially stronger than the retardation effected by presence of CO2. The emission-gas measurements show that the CO to CO2 ratio increases significantly after self-ignition, and CH4 counts for 1–8% of the total carbon emission. This research may help improve the understanding of heterogeneous coal combustion and the fire safety in oxy-fuel power systems.

Self-ignition of coal dust deposits poses a higher risk of fires in oxygen-enriched oxy-fuel combustion systems. In this work, we develop a numerical method, using the commercial software COMSOL Multiphysics, to investigate self-ignition behaviour of coal dust accumulations with a main emphasis on the roles of oxygen, diluent gas and dust volume. A one-step 2nd-order reaction kinetic model considering both coal density and oxygen density is used to estimate reaction rate using the kinetic parameters from previously conducted hot-oven tests. This model is validated to predict the transient temperature and concentration profiles of South African coal dusts until ignition. The computed self-ignition temperatures of dust volumes show a good agreement with experimental results. In addition, it is found that the inhibiting effect of carbon dioxide is comparatively small and oxygen consumption increases dramatically after ignition. Parameter analysis shows that the heating value and kinetic parameters have a comparatively pronounced effect on self-ignition temperature. The model provides a satisfactory explanation for the dependence of self-ignition behaviour on gas atmospheres, thus helping to further understand the fire risk of self-ignition in oxy-fuel combustion systems.

Metal hydrides (MHs) are promising materials for thermochemical heat storage. However, poor heat transfer limits the hydrogen absorption/desorption processes in MH reactors. In this study, a modified multilayer MH bed configuration with graded content of expanded natural graphite (ENG) was proposed. A mathematical model was established to obtain the distributions of temperature and reacted fraction within the MH beds during hydrogen absorption. Two comprehensive indices, gravimetric heat storage rate (GHSR) and gravimetric exergy-output rate (GEOR), were adopted to evaluate the heat discharging performance of the MH reactors. The simulation results show that a configuration in which the direction of the ENG content gradient (β) is consistent with the direction of heat flow can improve the performance of the MH reactors. Furthermore, increasing steepness of the ENG content gradient can increase both of the GHSR and the GEOR. The configuration with the squared graded ENG contents (C5-7, β = 3.5 wt%) exhibits the highest GHSR and GEOR values (16.98 and 16.16 W kg−1, respectively), whereas the configuration C1 which employs a uniform ENG content exhibits much lower values of these parameters.

Minimum ignition temperature of dust clouds (MITC) was studied experimentally and theoretically in different atmospheres. Three carbonaceous dusts were tested in both air and O2/CO2 atmospheres with CH4 mole fraction from 0% to 2%. Results showed that the ignition risk of the three dusts significantly increases (decrease of MITC by ~100 ℃) with increasing XO2 from 21% to 50%, but significantly decreases replacing N2 in air with CO2. The inhibition effect of CO2 on MITCs could be diminished by increasing XO2 or adding CH4. The addition of small amount of CH4 has different effects on the MITCs of different dust samples, following the opposite order of volatile matter content: anthracite>bituminous coal>starch. Two modified steady-state ignition models, considering the density of mixture gas and dust cloud, XO2 and its diffusivity, were developed to interpret the experimental observations. The analysis revealed that the global heterogeneous ignition model suits well for the hybrid mixtures of anthracite or bituminous coal dusts. In contrast, the proposed global homogeneous ignition model was found to be only valid for the pure starch dust, and the extra CH4 addition could strongly affect the ignition process of starch, particularly in O2/CO2 atmospheres with higher XO2.

Experiments were conducted in a semi-confined pipe to investigate the effects of obstacle location and gasoline vapor concentration on gasoline-air fuel explosions. The variations of internal overpressure, external overpressure, flame propagation and flame-overpressure coupling relationship were analyzed. The results showed that the internal overpressure histories existed three obvious peaks, and when the obstacle location was set at 0.4 m, the maximum absolute values of overpressure (pmax and pneg), overpressure rise rates ((dp/dt)ave and (dp/dt)max) and the deflagration index (KG) were obtained. Additionally, more than two positive overpressure peaks were observed in the external overpressure histories. The maximum values of external overpressures and overpressure rise rates were obtained at the obstacle location of 0.4 m. For the fuel concentrations of 1.3%, 1.7% and 2.1%, the shortest time to reach pmax appeared at the obstacle location of 0.4 m, 0.2 m and 0.6 m, respectively, while the shortest time to reach (dp/dt)max and the maximum flame propagation speed were obtained for all the fuel concentrations at the obstacle location of 0.2 m. Moreover, a coupling relationship between overpressure and flame propagation was found. It could be deduced that the formation of the positive overpressure peak of the external overpressure might be directly related to the gas explosion inside the pipe and the flow jet caused by the high-speed flame propagation, rather than the external explosion (or secondary explosion) out of the pipe. These results improve our understanding on gas explosion dynamics in a semi-confined space.

Understanding the fundamental basis of coal dust layers ignition behavior is of interest for the mitigation of industrial fires and explosions. This paper develops a 2D numerical method to investigate the self-ignition of coal dust layers with an emphasis on the roles of the oxygen mole fraction and diluent gas. A global one-step 2nd-order reaction kinetic model considering both coal density and oxygen density is used to estimate the reaction rate of self-heating process until ignition. In addition, the overall heat transfer coefficient is evaluated based on a steady state method and the kinetic parameters are estimated by fitting experimental and numerical temperature evolution figures. This model has been found to be valid to predict the transient temperature and concentration profiles until ignition. The numerical results of the minimum ignition temperature of dust layers (MITL) are in close agreement with experimental observations. The ignition delay time and the most sensitive ignition position (MSIP) of dust layer are found to vary with varying ambient gas conditions, hot plate temperatures and ambient temperatures using the verified model. The model provides a satisfactory explanation for the dependence of ignition characteristics of coal dust layer in oxygen-enriched oxy-fuel atmospheres.

BAM furnace apparatus tests were conducted to investigate the minimum ignition temperature of coal dusts (MITC) in O2/CO2 atmospheres with an O2 mole fraction from 20 to 50%. Three coal dusts: Indonesian Sebuku coal, Pittsburgh No.8 coal and South African coal were tested. Experimental results showed that the dust explosion risk increases significantly with increasing O2 mole fraction by reducing the minimum ignition temperature for the three tested coal dust clouds dramatically (even by 100°C). Compared with conventional combustion, the inhibiting effect of CO2 was found to be comparatively large in dust clouds, particularly for the coal dusts with high volatile content. The retardation effect of the moisture content on the ignition of dust clouds was also found to be pronounced. In addition, a modified steady-state mathematical model based on heterogeneous reaction was proposed to interpret the observed experimental phenomena and to estimate the ignition mechanism of coal dust clouds under minimum ignition temperature conditions. The analysis revealed that heterogeneous ignition dominates the ignition mechanism for sub-/bituminous coal dusts under minimum ignition temperature conditions, but the decrease of coal maturity facilitates homogeneous ignition. These results improve our understanding of the ignition behaviour and the explosion risk of coal dust clouds in oxy-fuel combustion atmospheres.

In order to recognize and reveal the explosion characteristics and hazards of LPG blended fuel with active fuel additions, flame dynamics of liquefied petroleum (LPG)/dimethyl ether (DME) blended fuel in the tail space of a closed pipeline was experimentally investigated. A high-speed camera and a pressure transducer were used to acquire the flame structure and explosion overpressure, and the displacement and speed were further calculated by MATLAB programming. The research results show that the flame under the conditions of stoichiometric and lean-fuel concentration presents a more remarkable local suppressive propagation compared with the rich-fuel condition. In the vicinity of stoichiometric concentration, the increase of equivalence ratio leads to the increase of flame front temperature, meanwhile, the process also improves the molecular diffusion coefficient and heat transfer efficiency. The reverse propagation of flame brings obvious temperature loss to fuel system. The existence of reflected reverse flow makes it difficult for the flame to propagate to the end of the closed space. The increase of equivalence ratio and DME blended ratio is helpful for the improvement of flame suppressive mechanism and flame acceleration mechanism, and the effect of the latter is more obvious. The knowledge obtained about flame dynamic characteristics can improve the assessment and recognition of explosion hazards of blended fuel.

Experimental study on premixed fuel–air mixture venting explosion process with various gas volume concentrations and vent sizes was conducted in a 20 L cylinder vessel. The results showed that both overpressure dynamic process and flame evolution process could be divided into 4 stages, including 2 positive and 2 negative overpressure peaks. Specifically, the 1st and 2nd positive overpressure peaks were respectively induced by flame venting and external explosion, while the 1st and 2nd negative overpressure peaks were respectively caused by expansion wave after the external explosion and external large-scale vortex. Both the overpressure and flame parameters were related to initial gas volume concentrations. As the gas volume concentration increased from 1.00% to 2.99%, both the positive overpressure peaks, flame velocity and flame propagation distance presented a first increasing and then decreasing trend, but the negative overpressure peaks and the time corresponding to each overpressure peak presented a first decreasing and then increasing trend. Moreover, as the vent coefficient Kv increased from 1.16 to 10.44, the maximum positive overpressure peaks increased from 2.32 to 60.54 mbar, and the maximum axial flame velocity increased from 9.21 m·s−1 to 53.85 m·s−1. However, as the Kv increased, the minimum negative overpressure peak and the maximum radial flame velocity changed non-monotonically.

The overpressure peaks and flame propagation characteristics of hydrocarbon fuel-air mixtures vented deflagration in a 20-L cylindrical vessel with a slight static activation overpressure (PST = 2.5 kPa) and five vent opening ratio were studied by a series of experiments. The experiments focused on the effect of vent opening ratio on the overpressure peaks and flame propagation characteristics of hydrocarbon fuel-air mixture vented deflagration. The internal overpressure-time profiles and high-speed photographs of flame propagation processes were obtained. The results showed that three overpressure peaks were distinguished in the internal overpressure-time profiles, caused by the burst vent cover (pburst), the acceleration of burnt gas (pfv), and the fierce external deflagration of vented unburned fuel (pext), respectively. The changing of the vent opening ratio had almost no effect on the value of pburst and (dpburst/dt). With increasing vent opening ratio, the values of pfv, pext, (dpfv/dt) and (dpext/dt) showed a decreasing trend while the values of pburst and (dpburst/dt) were nearly constant. The flame presented a hemispherical shape before the vent cover ruptured then developed as a mushroom shape after accelerated to external field. There were three flame speed peaks during flame propagation process, resulted from venting flow acceleration, external deflagration, and axial heat flux formed by internal combustion. With the increase of vent opening ratio, all of the maximum flame speed, external average flame speed, maximum flame distance and external flame duration showed a downward trend, excepting for the internal average flame speed almost remained constant.

Godbert-Greenwald furnace was used to investigate the minimum ignition temperature of dust clouds (MITC) in air with the presence of flammable gas which is lower than its lower explosion limit (LEL). Three flammable gases (CH4, H2 and CO) and three carbonaceous dusts (anthracite coal, bituminous coal and sweet potato starch) were tested. Results showed that all flammable gases have distinct effects on the MITC of the dust samples and volatile matter content of dust plays an important role during the ignition process. Specifically, the MITC of anthracite coal dust decreased from 610 °C to 560 °C, 580 °C and 570 °C with 3% CH4, 3% CO and 2.5% H2, respectively. Moreover, a heterogeneous ignition mechanism model was proposed to verify the equally global ignition characteristic between hybrid anthracite coal-CxHy mixture and bituminous coal. All three gases had an ignorable effect on the MITC of starch dust considering the experimental error. The presence of CO and H2 slightly promoted the ignition of bituminous coal dust, but the addition of CH4 showed a distinct concentration effect on the MITC of bituminous coal: the MITC decreased with 1% CH4 while increased with 2% and 3% CH4. This negative-effect of flammable gases at such low concentrations on ignition temperature of bituminous coal dusts was found for the first time. Furthermore, the presence of the 2nd flammable gas had a smaller effect on the MITC of dust samples with a higher volatile content, resulted from the competition of heterogeneous and homogeneous ignition mechanisms.

A 20-L spherical explosion chamber was used to investigate the minimum explosion concentration (MEC) of coal dusts with small amount of flammable gas which is lower than its lower explosion limit (LEL). Two dust samples (anthracite coal and bituminous coal) and three flammable gases (CH4, H2 and CO) were tested. Two methods respectively based on overpressure and combustion duration time were used to determine the MEC of the hybrid mixtures. Experimental results show that the explosion of hybrid mixtures occurs when both dust and gas concentrations are lower than the LEL or MEC of the single substances. As flammable gas concentration increases, either explosion pressure (Pex) and explosion pressure rise (dp/dt)ex) increase or the MEC decreases for all the hybrid gas-dust mixtures as a general trend, showing a strong concentration effect. At the same concentration of coal dusts, the addition of CH4 poses a higher explosion risk than the other two flammable gases. Moreover, it was found that the results of MEC determined by both methods agree each other well, suggesting that both methods are valid to determine MEC of hybrid mixture in the synergic explosion region. The distribution of experimental data in the explosion regimes shows that the restricted areas defined by empirical formulas are insufficient from safety considerations.

Experiments were conducted in a 907.5-L fuel tank to investigate the effects of concentration, temperature, ignition energy, and humidity on the explosion overpressure transients of gasoline-air mixture explosions. The results show that the overpressure-time profiles can be roughly divided into four stages: incubation stage, slow acceleration stage, abrupt acceleration stage, descending stage. During the explosion process, intense overpressure oscillation occurred in the fuel tank. Specifically, both the maximum overpressure (pmax) and the maximum rate of overpressure rise ((dp/dt)max) increased firstly and then decreased as the gasoline concentration increased, and the correction between overpressure parameters and gasoline concentration is approximately cubic polynomial. The peak values of pmax and (dp/dt)max were obtained at the concentration of 1.71%.The influence of temperature on pmax and (dp/dt)max was relatively complex, which may result from the vessel volume and the initial gas concentration. Moreover, with the increase of ignition energy, pmax and (dp/dt)max according to a linear increase trend and a logarithmical increase trend, respectively. With the increase of initial humidity, both pmax and (dp/dt)max showed a linear decrease trend. These results are useful for understanding the explosion characteristics of fuel-air mixtures under various initial conditions in medium-scale fuel tanks.

For the oxy-coal combustion, the accumulation of coal dust in the system has a fire risk of self-ignition. Therefore, understanding the ignition dynamics of coal dust deposits in oxygen-enriched environment is essential for the prevention of fire and dust explosion. In this work, both hot-oven and hot-plate tests were conducted to study the self-ignition behaviour of coal dusts in O2/CO2 ambient with O2 mole fraction from 21% to 50%. Three coal dusts: Indonesian Sebuku coal, Pittsburgh No. 8 coal and South African coal were tested with different sizes. Experimental results revealed that the self-ignition risk increased significantly with the increasing O2 mole fraction: reducing both the critical ignition temperature (10 °C in hot-oven test and 40 °C in hot-plate test) and the ignition delay time. Comparatively, the inhibiting effect of CO2 was found to be small for self-ignition. In addition, a modified Frank-Kamenetzkii analysis was proposed to explain all measured critical ignition temperatures, and the genetic algorithm was used to determine kinetic parameters of the one-step global reaction. The analysis showed that as the coal maturity/rank increased, both the self-ignition risk and the sensitivity to oxidation decreased, along with the decreasing apparent activation energy and pre-exponential factor. Such trend did not change with the ambient oxygen condition for all three coal dusts. These results improve our understanding of the self-ignition behaviour and the fire risk of coal dust in the oxy-fuel combustion system.