Ignition Mass Research Articles

Effects of rock water with different acidity on microstructure and reburning ability of residual coal in goaf

To explore the influences of rock water acidity (PH = 4,5,7) over the microstructure and reburning behaviors of oxidized residual coal in the overlying goaf, the pore morphology, coal surface, functional group content and activity of pre-oxidized coal (O0) and water-immersed oxidized coal (OI) were analyzed by Low-temperature nitrogen adsorption and In-situ diffuse reflection experiments, combining with fractal dimension theory and functional group oxidation kinetics. The oxidation and reburning ability of coal samples has been analyzed by Thermogravimetric-Differential thermal analysis experiment. The results are as follows: Part of the type-III pores of pre-oxidized coal become type-II pores when immersed. The acidic solution has stronger corrosivity to O0 than distilled water, playing a role in smoothing coal and improving the uniformity of pore structure. The order of reburning ability of samples is OI7>OI4>O0>OI5 according to the ignition and stage average mass loss rate (RM). The reactivity of –OH may affect the reburning ability of coal more than its initial content. Soaking is beneficial to the decrease of activation energy of aliphatic groups, and the activity of –C=O- and -C-O- in acid-soaked coal molecules is stronger, so that they can take part in coal-oxygen composite reactions at low temperature.

Ignition probability and fuel consumption of boreal ground vegetation fuels – an experimental study in Finland

In boreal forests fires often ignite and spread within the dominant moss and lichen cover of the ground layer vegetation, which thus greatly influences fire hazard. We used an experimental set-up in greenhouse conditions to study the differences in how (1) fuel moisture and (2) wind velocity influence the ignition probability and fuel consumption among four common circumboreal ground vegetation fuels, Pleurozium schreberi (Willd. ex Brid.) Mitt., Hylocomium splendens Schimp., Dicranum spp. and Cladonia rangiferina (L.) F. H. Wigg. Our results show that the reindeer lichen C. rangiferina was clearly the most flammable species, with high ignition probability even at high moisture contents and low wind velocities. Of the mosses, Dicranum was the least flammable, with low ignition probability and mass loss at low wind velocities regardless of moisture content. P. schreberi and H. splendens behaved somewhat similarly with wind velocities quickly increasing the initially low ignition probability and mass loss observed in the absence of wind. However, especially for mass loss, among-species differences tended to disappear with stronger winds. The observed differences can be explained by the different structures and growth forms of the studied species and open a potential avenue for improving forest fire risk predictions.

Bridging the gap between intermediate and massive stars II: Mmas for the most metal-rich stars and implications for Fe CCSNe rates

ABSTRACT The minimum initial mass required for a star to explode as an Fe core collapse supernova, typically denoted Mmas, is an important quantity in stellar evolution because it defines the border between intermediate mass and massive stellar evolutionary paths. The precise value of Mmas carries implications for models of galactic chemical evolution and the calculation of star formation rates. Despite the fact that stars with super-solar metallicities are commonplace within spiral and some giant elliptical galaxies, there are currently no studies of this mass threshold in super metal-rich models with Z > 0.05. Here, we study the minimum mass necessary for a star to undergo an Fe core collapse supernova when its initial metal content falls in the range 2.5 × 10−3 ≤ Z ≤ 0.10. Although an increase in initial Z corresponds to an increase in the Fe ignition threshold for Z ≈ 1 × 10−3 to Z ≈ 0.04, we find that there is a steady reversal in trend that occurs for Z > 0.05. Our super metal-rich models thus undergo Fe core collapse at lower initial masses than those required at solar metallicity. Our results indicate that metallicity-dependent curves extending to Z = 0.10 for the minimum Fe ignition mass should be utilized in galactic chemical evolution simulations to accurately model supernovae rates as a function of metallicity, particularly for simulations of metal-rich spiral and elliptical galaxies.

Electrophoretic assembly of Al/CuBi2O4 based-energetic films and the effect of destructive behavior with fuel/oxidant ratio

Physical destruction of microchips for data security based on thermite cannot simultaneously fulfill the demands of energy release and pressure output. Here, we have successfully assembled microchips based on Al/bimetallic oxide (CuBi2O4) energetic films through electrophoretic deposition. Al/CuBi2O4exhibits excellent energy release and pressure output, the heat release of Al/CuBi2O4is more concentrated,as extensive heat released by Al/CuO triggered the reaction of Al and Bi2O3, which will be conducive to the destructive behavior. The effects of fuel and oxide with different ratios on exothermic performance were systematically investigated, including heat release, ignition threshold energy, ignition mass loss rate and pressure release. The best fuel/oxide ratio on Al/CuBi2O4 energetic films is found to be 5.06:1 through inductively coupled plasma atomic emission spectrometry. The distribution between Al fuel and CuBi2O4rods is the most uniform at this ratio, hence it possesses the maximum heat release (926.4 J/g), lower ignition threshold (0.25 mJ), and faster pressurization rate (179.80 MPa/s). Importantly, high-speed photography results show that the intense reaction destroyed the energetic microchip (the thickness is about 0.3 mm) in only 10 ms.

Experimental study on the fire behavior of the corrugated cartons under low-pressure environment with oxygen-enriched

Oxygen-enriched indoor in the high plateau can validly address the plateau reaction, but increases the probability of fire and the hazards after it occurs. The intention of this article was to estimate the influence of oxygen enrichment in low-pressure environment on the combustion behavior of characteristic combustibles based on indoor corrugated cartons, which is believed to be profitable for high plateau indoor fire safety. The ignition time, mass loss, flue gas properties, heat flux and axial temperature were investigated in comparative trials performed in a hypobaric chamber to emulation the particular environment. A new correlations to predict the burning rate of solid materials under varying pressures and oxygen concentrations was proposed and fitted by experimental data showing a good agreement. The results show that inhibition of solid combustion by low pressure can be significantly weaken by oxygen enrichment. As oxygen concentration increases, flame shape had a thin high type into a wide low type, the color had a blue-yellow gradually turned into a bright color. Moreover, at high oxygen concentration, pressure is weakly correlated with ignition time, mass loss and heat production. The fire performance index and thermal release index indicators show a significant raise in fire hazard of oxygen-enriched atmosphere.

A hybrid chemical source treatment for non-premixed combustion simulations

Different approximations based on the exact point implicit (EPI) chemical source treatment, including diagonal approximation (DA), multiscale diagonal approximation (MDA), and single-scale approximation (SA), are numerically assessed and theoretically analyzed with zero-dimensional and one-dimensional combustion simulations in detail. The results show that EPI performs the best in stability, accuracy, and mass conservation. For DA and MDA methods, the ignition delay time, equilibrium temperature, and mass conservation are predicted with a significant error when the time step is large due to the diagonally non-dominant coefficient matrix. However, the error is relatively small when the reactions are weak, thus rendering the accuracy acceptable. SA method performs best in the stability perspective, but the temporal evolution of ignition can not be predicted appropriately. Based on the above conclusions, a hybrid chemical source treatment(HCST) is proposed, where the EPI method is used in chemically active regions while the MDA method is adopted in chemically inactive regions. HCST is first examined with one-dimensional non-premixed flame of various fuels. Then, a Reynolds-averaged Navier–Stokes (RANS) simulation of a supersonic hydrogen/air combustion case is conducted. The same accuracy is achieved by HCST as that using the EPI method for the whole flowfield. In terms of efficiency promotion, for the hydrogen/air 9 species 19 reactions mechanism, an overall promotion of 17% is achieved, while for methane/air 53 species 325 reactions mechanism, a promotion of 75% is observed.

Flame behaviors and explosion characteristics of two‐phase propylene oxide/air mixture under different ambient pressures

AbstractPropylene oxide (PO) is widely used in fuel‐air explosives and pulse detonation engines. Based on computational fluid dynamics, the effects of ignition position, initial pressure, and mass concentration on the explosion characteristics of the PO/air mixture were studied by using a 20 L spherical container. The results showed that the ignition position had a significant effect on the flame structure. When the fuel cloud was ignited at the center, the flame structure experienced spherical, elliptical, and tulip shapes. The explosion time first decreased and then increased with the increase of ignition position, while the maximum explosion pressure decreased correspondingly. The maximum explosion pressure and the temperature had an inverted “U” correlation with concentration at normal pressure. However, the overpressure was insensitive to concentration in the negative pressure condition. The maximum flame temperature showed different flame behaviors under different initial negative pressures and cloud concentrations. This study provides a theoretical basis for understanding the explosion behaviors of PO/air mixture with different ignition positions and initial vacuum pressures, which is of great significance in preventing explosion accidents.

Controllable ignition, combustion and extinguishment characteristics of HAN-based solid propellant stimulated by electric energy

Hydroxyl ammonium nitrate (HAN)-based electrically controlled solid propellant (ECSP) is the advanced solid chemical propellant stimulated by electric energy, which has throttleable ability. This characteristic is impossible for traditional solid propellants, and greatly expands the potential applications for solid rocket motors that are fit with the ECSP. In this work, the ignition, combustion and extinguishment characteristics of propellant were studied at different voltages, initial temperatures and pressures. It is concluded that the incremental voltage, initial temperature and pressure enhance the burning rate, mass loss and extinguishment delay time, while reducing the ignition delay time, energy required for ignition and electrolysis mass ratio. Specially, as the initial temperature increases from -15 °C to 45 °C (at 200 V and 0.1 MPa), values of mean ignition delay time decrease from 247.4 ms to 116.2 ms, and values of mean burning rate and extinguishment delay time increase from 0.25 mm/s to 0.47 mm/s and 19.2 ms to 27.6 ms, respectively. Moreover, as the pressure increases from 0.1 MPa to 1.0 MPa (at 200 V and 25 °C), values of mean ignition delay time decrease from 151.6 ms to 74.2 ms, and values of mean burning rate and extinguishment delay time increase from 0.44 mm/s to 0.89 mm/s and 28.0 ms to 55.6 ms, respectively. Based on the experimental results, the processes of propellant from ignition to extinguishment were analyzed, and the ignition mechanism was proposed that the fracture of NOH in NH3OH+ in the electrochemical decomposition is a key step that affects the ignition of ECSP. Overall, those results reveal that the electrolysis reaction rather than the pyrolysis reaction exerts an important role for ECSP on achieving the controllable combustion.

Development of Ignition Time and Mass Loss Rate Prediction Models for Rigid Polyurethane Foam with Multi-Step Thermal Degradation Under Various External Heat Flux Conditions

Development of Ignition Time and Mass Loss Rate Prediction Models for Rigid Polyurethane Foam with Multi-Step Thermal Degradation Under Various External Heat Flux Conditions

A light curve model of V2491 Cyg: Classical nova outburst on a cool and massive white dwarf

Abstract The classical nova V2491 Cyg was once suggested to be a recurrent nova. We have broadly reproduced the light curve of V2491 Cyg by a nova outburst model on a cold 1.36 M⊙ white dwarf (WD), which strongly suggests that V2491 Cyg is a classical nova outbursting on a cold very massive WD rather than a recurrent nova outbursting on a warmer WD like the recurrent nova RS Oph. In the long-term evolution of a cataclysmic binary, an accreting WD has settled to a thermal equilibrium state with the balance of gravitational energy release and neutrino loss. The central temperature of the WD is uniquely determined by the energy balance. The WD is hot (cold) for a high (low) mass accretion rate. We present the central temperatures, ignition masses, ignition radii, and recurrence periods for various WD masses and mass accretion rates. In a classical nova, which corresponds to a low mass accretion rate, the WD is cool and strongly degenerated and the ignition mass is large, which result in a strong nova outburst. In a recurrent nova, the WD is relatively warmer because of a high mass accretion rate and the outburst is relatively weaker. The gravitational energy release substantially contributes to the luminosity during the recurrent nova outbursts. We compare physical properties between classical novae and recurrent novae and discuss the essential differences between them.

Effect of Natural Aging on Oak Wood Fire Resistance.

The paper deals with the assessment of the age of oak wood (0, 10, 40, 80 and 120 years) on its fire resistance. Chemical composition of wood (extractives, cellulose, holocellulose, lignin) was determined by wet chemistry methods and elementary analysis was performed according to ISO standards. From the fire-technical properties, the flame ignition and the spontaneous ignition temperature (including calculated activation energy) and mass burning rate were evaluated. The lignin content does not change, the content of extractives and cellulose is higher and the content of holocellulose decreases with the higher age of wood. The elementary analysis shows the lowest proportion content of nitrogen, sulfur, phosphor and the highest content of carbon in the oldest wood. Values of flame ignition and spontaneous ignition temperature for individual samples were very similar. The activation energy ranged from 42.4 kJ·mol−1 (120-year-old) to 50.7 kJ·mol−1 (40-year-old), and the burning rate varied from 0.2992%·s−1 (80-year-old) to 0.4965%·s−1 (10-year-old). The difference among the values of spontaneous ignition activation energy is clear evidence of higher resistance to initiation of older wood (40- and 80-year-old) in comparison with the younger oak wood (0- and 10-year-old). The oldest sample is the least thermally resistant due to the different chemical composition compared to the younger wood.

He-shell flashes on the surface of oxygen-neon white dwarfs

Accretion induced collapse (AIC) may be responsible for the formation of some interesting neutron star binaries (e.g., millisecond pulsars, intermediate-mass binary pulsars, etc). It has been suggested that oxygen-neon white dwarfs (ONe WDs) can increase their mass to the Chandrasekhar limit by multiple He-shell flashes, leading to AIC events. However, the properties of He-shell flashes on the surface of ONe WDs are still not well understood. In this article, we aim to study He-shell flashes on the surface of ONe WDs in a systematic approach. We investigated the long-term evolution of ONe WDs accreting He-rich materialwith various constantmass-accretion rates by time-dependent calculationswith the stellar evolution codeModules for Experiments in Stellar Astrophysics (MESA), in which the initial ONeWD masses range from 1.1 to 1.35 M ⊙. We found that the mass-retention efficiency increases with the ONe WD mass and the mass-accretion rate, whereas both the nova cycle duration and the ignition mass decrease with the ONe WD mass and the mass-accretion rate. We also present the nuclear products in different accretion scenarios. The results presented in this article can be used in the future binary population synthesis studies of AIC events.

Single particle combustion studies of coal/biomass fuel mixtures

Single particle combustion behaviours of coal-biomass fuel mixtures are studied. Different biomass i.e. sawdust, wood and rice husk is blended with locally available low grade coal to carry out the experimental investigation. The combustion of solid fuel consists of flaming combustion and char combustion. Rice husk showed higher flaming time and char glowing time because of higher ash and particle density. The burning time of coal-rice husk mixture fuel sample is higher compared to other samples due to the combine effect of particle density and ash content of the fuel samples. Ignition mass flux of saw dust is higher compared to rice husk and wood fuel particles because of the presence of higher volatiles in sawdust. The diameter index for flaming combustion, char combustion are 1.13 to 0.47 and 0.63 to 1.23 respectively for 0%–40% coal in coal/wood fuel mixtures. It is observed that with the increases in surface area/volume ratio, flaming and char combustion decreases due to reduction in effective surface area of the particle for combustion. This study concludes that particle size or surface area/volume together with particle density are the primary controlling parameter for better conversion of fuel mixtures in any co-combustion system.

A Theory for the Maximum Magnitude versus Rate of Decline Relation of Classical Novae

Abstract We propose a theory for the maximum magnitude versus rate of decline (MMRD) relation of novae using free–free emission model light curves built on the optically thick wind theory. We calculated for various sets of , where is the peak absolute V magnitude, t 3 is the 3 mag decay time from the peak, and is the mass accretion rate onto the white dwarf (WD) of mass M WD. The model light curves are uniquely characterized by , where M env is the hydrogen-rich envelope mass and M sc is the scaling mass at which the wind has a certain wind mass-loss rate. For a given ignition mass M ig, we can specify the first point on the model light curve and calculate the corresponding peak brightness and t 3 time from this first point. Our points cover well the distribution of existing novae. The lower the mass accretion rate, the brighter the peak. The maximum brightness is limited to by the lowest mass accretion rate of yr−1. A significant part of the observational MMRD trend corresponds to the yr−1 line with different WD masses. A scatter from the trend line indicates a variation in their mass accretion rates. Thus, the global trend of an MMRD relation does exist, but its scatter is too large for it to be a precision distance indicator of individual novae.

Comparative analysis of thermal oxidative decomposition and fire characteristics for different straw powders via thermogravimetry and cone calorimetry

Safety performance of straw powders, a primary component of biomass pellet fuel, remains challenging. In this work, three straw powders (soybean, peanut, and rape) were studied. Thermogravimetry and cone calorimetry were employed to investigate thermal oxidative decomposition characteristics and fire behaviors. Thermogravimetry (TG), micro-commercial thermogravimetry (DTG), and differential scanning calorimetry (DSC) curves showed that the thermal decomposition of the three samples proceeded in four stages. TG-DTG-DSC data also revealed that their ignition and burnout temperatures and mass loss rates were all distinct. Combustion indices of the three samples were ordered as RS>SS>PS. Based on the cone calorimetry results, critical heat fluxes for ignition were determined to be 25.31, 29.14, and 18.27kW/m2 for SS, PS, and RS, respectively. Critical fire properties such as ignition time, heat release rate intensity, and CO/CO2 ratio were influenced by biomass species and external heat fluxes. Compared with the other two samples, RS exhibited better burnout performance but was a greater fire hazard. Nevertheless, according to the hazard assessment, the three straw powder samples all had a high fire risk. Additional care must be taken in handling, storing, transporting, and utilizing straw powder in biomass pellet fuel processing.

Comprehensive models of novae at metallicity Z = 0.02 and Z = 10−4

ABSTRACT Novae are the observational manifestations of thermonuclear runaways on the surface of accreting white dwarfs (WDs). Although novae are an ubiquitous phenomenon, their properties at low metallicity are not well understood. Using the publicly-available stellar evolution code Modules for Experiments in Stellar Astrophysics (mesa), we model the evolution of accreting carbon–oxygen WDs and consider models that accrete matter with metallicity Z = 0.02 or 10−4. We consider both models without mixing and with matter enriched by CO-elements assuming that mixing occurs in the process of accretion (with mixing fraction 0.25). We present and contrast ignition mass, ejected mass, recurrence period, and maximum luminosity of novae for different WD masses and accretion rates for these metallicities and mixing cases. We find that models with Z = 0.02 have ignition masses and recurrence periods smaller than models with low Z, while the ejected mass and maximum luminosity are larger. Retention efficiency during novae outbursts decreases with increasing metallicity. In our implementation, inclusion of mixing at the H/He interface reduces accreted mass, ejected mass, and recurrence period as compared to the no-mixing case, while the maximum luminosity becomes larger. Retention efficiency is significantly reduced, becoming negative in most of our models. For ease of use, we provide a tabular summary of our results.

Evaluation of properties on performance and emission to turbocharged SI engine using fusel oil blend with gasoline

Biofuel has the potential to be used as an alternative fuel compared to petroleum gasoline for the purpose increase performance and reducing emissions. The objective of the study is to evaluate performance and emission on properties of 10–30% fusel oil blends with pure gasoline (Ron 95) at 3000 rpm. In this experiment, three fuels were designed from fusel oil to test engine performance and emission. The haltech ECU was an escalation to set ignition, injection timing and injection mass when using fusel oil blends to reach stoichiometric level. In this study, pure gasoline was set as a reference. The experiments were conducted on 1.8L turbocharged 4-cylinder, spark ignition engine, port injection and coupled with 100 kW eddy current dynamometer. During engine testing, the throttle position was applied to 10–40%. As a result, averaged BMEP increase at 11.9%, 17.8% and 21.3% for F10, F20 and F30 respectively compared to gasoline. The VE and BSFC averaged increased 8.3% and 6.17% compared to pure gasoline for 10–40% engine load. The emissions for CO and HC on these observations increased while the NOx decreased when fusel oil blends were utilized. The recommendation used in study is low proportion blends to assess different properties for engine test.

Experimental investigation of thermal properties and fire behavior of carbon/epoxy laminate and its foam core sandwich composite

According to structural characteristics, composites are classified as laminated structure and sandwich structure. Carbon/epoxy laminate and foam core sandwich composite are the most commonly used laminate and sandwich structure material in the aircraft industry. The flammability of epoxy resins and foam core material is an inherent hazard. Many previous studies focused primarily on their mechanical properties, while the studies on the thermal and fire properties of carbon/epoxy laminate and its foam core sandwich composite have rarely conducted. Therefore, to characterize their thermal and fire properties, a comprehensive experimental investigation and theoretical analysis were carried out in this work using thermogravimetric analysis, cone calorimeter, vertical/horizontal burning tests, limiting oxygen index and scanning electron microscope tests. Several typical characteristic parameters were obtained and analyzed, such as pyrolysis temperature, heat release rate, mass loss, flaming spread rate and limiting oxygen index. These experimental data coupled with theoretical analysis can provide support for fire risk assessment and fire protection design in aircrafts. The carbon/epoxy laminate and foam core sandwich composite are both characterized as the thermally thick materials. The ignition models and mass loss rate models were obtained. Foam core material negatively affects most of the thermal and fire properties of sandwich composite, but the foam core sandwich composite has self-extinguishing behavior during horizontal burning tests, whose LOI is higher than that of carbon/epoxy laminate. Thus, an important conclusion was reached that the ignition position and flame spread direction have critical effect on the fire behavior of foam core material.

Breaking the Habit: The Peculiar 2016 Eruption of the Unique Recurrent Nova M31N 2008-12a

Abstract Since its discovery in 2008, the Andromeda galaxy nova M31N 2008-12a has been observed in eruption every single year. This unprecedented frequency indicates an extreme object, with a massive white dwarf and a high accretion rate, which is the most promising candidate for the single-degenerate progenitor of a Type Ia supernova known to date. The previous three eruptions of M31N 2008-12a have displayed remarkably homogeneous multiwavelength properties: (i) from a faint peak, the optical light curve declined rapidly by two magnitudes in less than two days, (ii) early spectra showed initial high velocities that slowed down significantly within days and displayed clear He/N lines throughout, and (iii) the supersoft X-ray source (SSS) phase of the nova began extremely early, six days after eruption, and only lasted for about two weeks. In contrast, the peculiar 2016 eruption was clearly different. Here we report (i) the considerable delay in the 2016 eruption date, (ii) the significantly shorter SSS phase, and (iii) the brighter optical peak magnitude (with a hitherto unobserved cusp shape). Early theoretical models suggest that these three different effects can be consistently understood as caused by a lower quiescence mass accretion rate. The corresponding higher ignition mass caused a brighter peak in the free–free emission model. The less massive accretion disk experienced greater disruption, consequently delaying the re-establishment of effective accretion. Without the early refueling, the SSS phase was shortened. Observing the next few eruptions will determine whether the properties of the 2016 outburst make it a genuine outlier in the evolution of M31N 2008-12a.

Landscape variation in plant leaf flammability is driven by leaf traits responding to environmental gradients

AbstractLandscape differences in environmental conditions select for divergences among plant species in strategically important leaf traits such as leaf mass per area (LMA) and leaf area (LA). Interspecific variation in some of these same leaf traits has been associated to varying degrees with differences among species in leaf flammability, including the attributes ignitibility, sustainability, and combustibility. Yet, how environmentally selected variation in leaf traits drives variation in leaf flammability at landscape scales remains largely unknown. Here, we compared leaf traits and flammability attributes between species of sheltered forest vegetation (low light, moist habitat) and plant species of exposed woodland vegetation (high light, dry habitat) in a fire‐prone landscape of south‐eastern Australia. We found that leaves of sheltered forest species were significantly more flammable via both higher ignitibility and combustibility compared with exposed woodland species. These significant differences in leaf ignitibility and combustibility were underpinned by sheltered forest species having leaves with significantly larger LA and lower LMA compared with exposed woodland species. Further, multiple regression analyses revealed that both LA and LMA were significantly and uniquely related to faster time to ignition (TTI; ignitibility) and higher mean mass loss rate (combustibility). Most notably, although significantly higher fuel moisture content (FMC) of leaves of sheltered forest species significantly lengthened TTI, the lower LMA of these species played a more critical role in reducing TTI, with low LMA explaining more unique variation (partial r2 = 0.78) in high leaf ignitibility than low FMC (partial r2 = 0.49). Our findings provide the first evidence that landscape‐scale variation in leaf flammability is tightly coordinated with the primary strategic response of the leaf traits LMA and LA to an environmental gradient. Furthermore, projections for increasing wildfire frequency and intensity in the region will likely allow wildfires to overcome the once protective nature provided by topography to sheltered forest vegetation, which means that higher leaf flammability in sheltered forest species has the potential to exacerbate the effects of changing weather conditions to place sheltered forest habitat, their plants, and their animals, at even higher risk of catastrophic wildfire.