Spontaneous ignition of corrugated cardboard under dynamic high radiant flux

Understanding the response of solid combustibles under high radiant fluxes is critical in predicting the thermal damage from extreme scenarios.Unlike the more moderate radiant fluxes in conventional hydrocarbon fires,extreme events such as strong explosion,concentrated sunlight and directed energy can generate dynamic radiant fluxes at the MW/m^(2) level,creating a unique threat to materials.This study investigates the pyrolysis and spontaneous ignition behaviors of corrugated cardboard by using both experimental and numerical methods,under 10-cm dynamic high radiant fluxes ranging from 0.2 to 1.25 MW/m^(2) for 10 s.The spontaneous ignition process at dynamic high radiant fluxes was recorded and quantified.Two ignition modes were found at the critical radiant flux of 0.4 MW/m^(2),namely hot-gas spontaneous ignition and hot-residue piloted ignition.The latter is not the focus of this paper due to its extremely small probability of occurrence.The research reveals that the increase in flux intensity induces shorter delay times for both pyrolysis and ignition,lower ignition energy density,along with a corresponding rise in the critical mass flux and surface temperature at ignition moment.The simulation results are generally aligned with the experimental findings,despite some divergences may be attributed to model simplifications and parameter assumptions.The work contributes to a deeper insight into material behavior under extreme radiation,with valuable implications for fire safety and hazard assessment.

Evaluation of the Ignition Temperature in Thermal Explosion Synthesis of TiAl_3 by Differential Scanning Calorimetry

Application of the Semenov theory of spontaneous ignition to evaluation of the critical temperature (Tc) in thermal explosion (TE) synthesis was conducted with the Ti-75at pct Al binary system using nonisothermal differential scanning calorimetry (DSC) at different heating rates. And the critical temperature for isothermal TE is predicted to be 728.9癈 by the multiple linear regression of Tcs evaluated according to Semenov theory, which is close to the range of 740~745癈 obtained from the isothermal DSC observation. This result proves that Semenov theory of spontaneous ignition is also feasible for TE synthesis in binary metallic systems like Ti-75 at. pct Al system.

Effects of Ce concentrations on ignition temperature and surface tension of Mg-9wt.%Al alloy

Magnesium alloys are well known for their excellent properties, but the potential issues with oxidation and burning during melting and casting largely limit its industrial applications. The addition of Ce in magnesium alloys can significantly raise ignition-proof performance and change the structure of the oxide film on the surface of the molten metal as well as the surface tension values. Surface tension is an important physical parameter of the metal melts, and it plays an important role in the formation of surface oxide film. In this present work, the ignition temperature and the surface tension of Mg-9wt.%AI alloy with different Ce concentrations were studied. Surface tensions was measured using the maximum bubble pressure method （MBPM）. Ignition temperature was measured using NiCr-NiSi type thermocouples and was monitored and recorded via a WXT-604 desk recording device. The results show that the ignition point of Mg-9wt.%AI alloy can be effectively elevated by adding Ce. The ignition temperature reaches its highest point of 720 ℃ when the addition of Ce is lwt.%. The surface tension of the molten Mg-9wt.%AI alloy decreases exponentially with the increase of Ce addition at the same temperature. Similarly, the experiment also shows that the surface tension of Mg-9wt.%AI alloy decreases exponentially with the increase of temperature.

Safety distance for preventing hot particle ignition of building insulation materials

Trajectories of flying hot particles were predicted in this work, and the temperatures during the movement were also calculated. Once the particle tem- perature decreased to the critical temperature for a hot particle to ignite building insulation materials, which was predicted by hot-spot ignition theory, the distance particle traveled was determined as the minimum safety distance for preventing the ignition of building insulation materials by hot particles. The results showed that for sphere aluminum particles with the same initial velocities and diameters, the horizontal and vertical distances traveled by particles with higher initial tem- peratures were higher. Smaller particles traveled farther when other conditions were the same. The critical temperature for an aluminum particle to ignite rigid polyurethane foam increased rapidly with the decrease of particle diameter. The horizontal and vertical safety distances were closely related to the initial temper- ature, diameter and initial velocity of particles. These results could help update the safety provision of firework display.

Pyrolysis and combustion kinetics of lycopodium particles in thermogravimetric analysis

Biomass is a kind of renewable energy which is used increasingly in different types of combustion systems or in the production of fuels like bio-oil. Lycopodium is a cellulosic particle, with good combustion properties, of which microscopic images show that these particles have spherical shapes with identical diameters of 31 μm. The measured density of these particles is 1.0779 g/cm2. Lycopodium particles contain 64.06% carbon, 25.56% oxygen, 8.55% hydrogen and 1.83% nitrogen, and no sulfur. Thermogravimetric analysis in the nitrogen environment indicates that the maximum of particle mass reduction occurs in the temperature range of 250-550 ℃ where the maximum mass reduction in the DTG diagrams also occurs in. In the oxygen environment, an additional peak can also be observed in the temperature range of 500-600 ℃, which points to solid phase combustion and ignition temperature of lycopodium particles. The kinetics of reactions is determined by curve fitting and minimization of error.

Study on Ignition-Proof AZ91D Magnesium Alloy Added with Rare Earth

Magnesium alloy is prone to burning during its melting and casting processes in air, which is a major factor of obstructing its application. Fluxes and cover gases are currently used for the melting and production processes, and semi-solid casting is also used to shape composites made of magnesium alloy, but there still remain many problems. Alloying is a promising method of preventing magnesium from burning. The effect of RE additions on the ignition temperature of AZ91D magnesium alloy was investigated. The changes of the quality of oxidation film and the as-cast microstructure were analyzed, and the mechanical property was compared with that without rare earth. For AZ91D with RE in the range of 0.08% to 0.12%. It is shown that the ignition temperature point can be greatly heightened, the quality of oxidation film is obviously improved, the as-cast microstructure is refined greatly, and the mechanical property is bettered a little, therefore, such an alloy is promising.

Riemann problem of a Chapman-Jouguet combustion model for pressure-gradient system

In this paper,the Riemann problem of a Chapman-Jouguet combustion model for the pressure-gradient equations is considered.By analyzing in phase space,existence and uniqueness of the solution to the Riemann problem are obtained constructively under the global entropy conditions.

Thermal testing methods in determination ofcharacterization of charcoals

Thermal analysis testing methods were used in determination of the characterization of charcoals. Thermogravimetry (TG) method was adopted to determine the composition of charcoals, which include moisture, volatiles, fixed carbon and ash contents. The result showed that this method could detect the subtle change of charcoal composition, even the variation of different parts of material. Differential Thermal analysis (DTA) and related methods were also used to investigate reactivity of charcoals. The ignition temperature decrease with increasing carbon content was detected by these methods.

Ignition Conditions for Simulated Fuel Pellets in Degenerate Plasma

A high-density, low-temperature plasma can be obtained during the compression phase in inertial confinement fusion. When high density and low temperature are reached in the plasma in the fast ignition approach, the plasma electrons can be degenerate. The electronic stopping of a slow ion is smaller than that given by the classical formula, because some transitions between the electron states are forbidden. In this case, bremsstrahlung emission is strongly sup- pressed and the ignition temperature becomes lower than that in classical plasma. The equations that predict the behavior of these plasmas are different from the classical ones, and this is the main factor in the process of decreasing the ignition temperature of the plasma. In this work, physical conditions of ignition are studied by calculating the effect of radiation loss on the ignition temperature for a simulated fuel pellet, （D/Tx/3Hey）, in degenerate plasma. In fast ignition, the energy needed for obtaining high densities is minimized and the gain can be increased considerably.

Refining Soil Organic Matter Determination by Loss-on-Ignition

Wet oxidation procedure,i.e.,Walkley-Black (WB) method,is a routine,relatively accurate,and popular method for the determination of soil organic matter (SOM) but it is time-consuming,costly and also has a high potential to cause environmental pollution because of disposal of chromium and strong acids used in this analysis.Therefore,loss-on-ignition (LOI) procedure,a simple and cheap method for SOM estimation,which also avoids chromic acid wastes,deserves more attention.The aims of this research were to study the statistical relationships between SOM determined with the LOI (SOMLOI) and WB (SOMWB) methods to compare the spatial variability of SOM in two major plains,Shahrekord and Koohrang plains,of Chaharmahal-va-Bakhtiari Province,Iran.Fifty surface soil samples (0-25 cm) were randomly collected in each plain to determine SOM using the WB method and the LOI procedure at 300,360,400,500 and 550 ℃ for 2 h.The samples covered wide ranges of soil texture and calcium carbonate equivalent (CCE).The general linear form of the regression equation was calculated to estimate SOM LOI from SOM obtained by the WB method for both overall samples and individual plains.Forty soil samples were also randomly selected to compare the SOM and CCE before and after ignition at each temperature.Overall accuracy of the continuous maps generated for the LOI and WB methods was considered to determine the accordance of two procedures.Results showed a significant positive linear relationship between SOM LOI and SOM WB.Coefficients of determination (R2) of the equations for individual plains were higher than that of the overall equation.Coefficients of determination and line slopes decreased and root mean square error (RMSE) increased with increasing ignition temperature,which may be due to the mineral structural water loss and destruction of carbonates at higher temperatures.A temperature around 360 ℃ was identified as optimum as it burnt most organic carbon,destroyed less inorganic carbon,caused less clay structural water loss,and used less electrical energy.Although the trends of SOM in the kriged maps by the two procedures accorded well,low overall accuracy was observed for the maps obtained by the two methods.While not suitable for determination where high accuracy is required,determination of organic carbon through LOI is likely suitable for exploratory soil surveys where rough estimation of organic matter is required.

An experimental study on ignition of single coal particles at low oxygen concentrations

An experimental study on the ignition of single coal particles at low oxygen concentrations (XO_(2)<21%) was conducted using a tube furnace. The surface temperature (Ts) and the center temperature (Tc) of the coal particles were obtained from the images taken by an infrared camera and thermocouples respectively. The ignition processes were recorded by a high-speed camera at different XO_(2) values and furnace temperatures Tw. Compared with literature experimental data obtained at a high XO_(2) value, the ignition delay time τi decreases more rapidly as XO_(2) increases at the low XO_(2) region. The responses of Ts and Tc to the variation of XO_(2) are different: Ts decreases while Tc remains nearly constant with increasing XO_(2) at a low XO_(2) value. In addition, τi is less sensitive to Tw while the ignition temperature Ti is more sensitive to Tw at a low XO_(2) value than in air. Observations of the position of flame front evolution illustrate that the ignition of a coal particle may change from a homogeneous mode to a heterogeneous or combined ignition mode as XO_(2) decreases. At a low XO_(2) value, buoyancy plays a more significant role in sweeping away the released volatiles during the ignition process.

Ignition-Proof Properties of a High-Strength Mg-Gd-Ag-Zr Alloy

A high-strength Mg-15.3Gd-l.8Ag-0.3Zr （GQ152K, mass fraction） alloy was prepared by conventional ingot metallurgy process. The solution and aging （denoted as T6） treated alloy exhibits remarkable mechanical properties with ultimate tensile strength of 421 MPa and tensile yield strength of 309 MPa. It has higher igniting temperature of 1 208 K. Moreover, it can stand against flame at 1 203 K for over 6 min in vertical burning tests, and its flammability behavior is very similar to that of 6101A1 alloy. Vertical burning tests appear to be able to directly study the flammability behavior of Mg alloys and it appears to be a good approach to study the flammability behavior of Mg alloys in an aircraft fire accident.