Amount Of Heat Release Research Articles

Optimizing the printability and dispersibility of functionalized zirconium oxide/acrylate composites with various nano-to micro-particle ratios

We develop highly concentrated vinyltriethoxysilane-coated zirconium oxide/acrylate composites with various nano-to micro-particle ratios as three-dimensional printing materials for use in a supportless stereolithography process. The incorporation of nano-particles with micro-particles at certain particle volume ratios resulted in densely packed network structures that generate good particle dispersion as well as a uniform particle distribution. Structural deformation and time-dependent structural recovery were analyzed by the three interval thixotropy test. We found sustained solid-like behaviors in the composites composed of 50:50 and 30:70 nano-particle to micro-particle ratios. Phase diagrams using structural deformation parameters confirm that the 50:50 and 30:70 composite's structure contributes to their good colloidal stability and printability. The addition of nano-particles also enhances the total heat release during the curing process due to improved light scattering, and the amount of heat release affects the degree of photo-polymerization in the printing material.

Badania hydratacji mieszanek na bazie cementu, hydratyzowanego wapna i pyłu z instalacji by-passu

The paper reports the results of the tests used to determine hydration kinetics, physical properties and microstructure of hydraulic road binders. Seven hydraulically bound mixes were produced by mixing Portland cement (CEM I 32.5R), hydrated lime, and cement by-pass dust (CBPD) in proportions established as per the experimental plan. Cement by-pass dust was found to have the greatest effect on the increased water demand, hydration heat and soundness of the binder paste. Minerals derived from the hydration of input components were identified in the composition of the binder phases. In CBPD rich binders sylvite and calcium chloro-aluminate hydrate were present. The test results show that when planning the use of normal setting hydraulic road binders containing CBPD in road construction, the water to binder ratio w/b must be taken into account to ensure proper consistency, soundness, and amount of hydration heat release.

Spatial structural characteristics of a combustion flow field in an ethylene-fueled supersonic combustor with a rear-wall-expansion cavity

A hybrid large eddy simulation (LES)/assumed subgrid probability density function (PDF) closure model was employed to investigate the structural characteristics of the combustion flow field in an ethylene-fueled supersonic combustor with a rear-wall-expansion cavity. The wall pressure distribution from numerical simulation was compared with experimental data, and the numerical results are in good agreement with the experimental data. The spatial distribution characteristics of combustion heat release in the flow field are obtained from the simulation results. The reaction heat release zone is mainly distributed in the cavity. The cavity shear layer forms a concentrated reaction zone that produces a large amount of chemical heat release, thus further maintaining local stable combustion and forming a flame base. The front part of the cavity shear layer has the highest temperature in the whole flow field. There is still excess fuel reaching the cavity rear wall and producing a certain intensity of reaction. In addition, a dispersed small flame intermittently forms in the downstream near-wall region. The premixed combustion mode dominates the cavity recirculation zone, while the combustion in the downstream region evidently shows a non-premixed mode.

Effect of heat flux on combustion of different wood species

The fire safety of wood is the most important concern in its structural and architectural applications. In this work, the combustion of three typical wood species, namely, oak, larch and red cedar exposed to various heat fluxes was studied using the cone calorimeter. The fire performance including heat release rate, charring rate, production of toxic carbon monoxide and release of carbon dioxide was quantified. It is found that the fire performance of the wood species exposed to a low heat flux of 20 kW/m2 differs completely from that exposed to a heat flux higher than 35 kW/m2. The effect of temperature on wood pyrolysis is attenuated with the increment of temperature. Compared with oak and larch, the fire performance of red cedar is more dependent on heat flux. Although red cedar requires less time to be ignited, it has the lowest heat release rate and the smallest amount of heat release, and exhibits a slower flame spread speed and the fastest charring rate with a high fire resistance rating. The satisfactory fire resistance of red cedar with a minimal heat flux effect on pyrolysis is correlated to the relatively high lignin content. Our findings provide guidance for woody structural design with a reduction in the emissions of harmful compounds.

Study on Intrinsic Relationship between Coal Mass Change and Heat Evolution during Different Stages of Coal Spontaneous Combustion

ABSTRACT A good understanding of the intrinsic relationship between heat evolution and mass change induced by coal–oxygen oxidation reaction is critical for accurately predicting the behaviour of spontaneous combustion. In this study, thermal subtraction method and six sets of characteristic temperatures were introduced to explore the intrinsic reaction between coal and oxygen which provides the main heat source responsible for coal self-heating. The heat evolution and mass change during coal spontaneous combustion were measured in real time using a sensitive differential scanning calorimeter (DSC) and a thermogravimetric analyzer (TG), respectively. The DSC and TG subtraction curves obtained from subtracting the results of nitrogen atmosphere from those of air atmosphere can reveal the heat change and mass change due only to the reaction between coal and oxygen. The term of q/m defined as the amount of heat release by the change of per unit of coal mass was introduced to study the intrinsic relationship between heat evolution and mass change during coal spontaneous combustion. The q/m values of the three coals show different evolution trends as coal temperature increases and are related to the mechanism of coal spontaneous combustion. The kinetics analysis of this intrinsic relationship was also carried out based on experimental data. Moreover, q/m can be used in the evaluation of spontaneous combustion propensity with respect to different coal types.

Ignition and Combustion Behavior of Sintered‐B/MgB2 Combined with KNO3

AbstractTo further enhance the performance of B/KNO3 (BPN) igniter, sintered B/MgB2 (s‐B/MgB2) powder was proposed to be used as a boron substitute. The amount of heat release was tested by oxygen bomb and thermogravimetry/differential scanning calorimetry (TG/DSC). s‐B/MgB2/KNO3 (sBPN) igniter could not release as much heat as BPN igniter in the oxygen bomb due to the reduced calorific value of the s‐B/MgB2. However, calculations show that s‐B/MgB2 reached an over 90 % heat release efficiency in oxygen bomb, compared to that of 53.34 % for boron. At heating rate of 10 K min−1 in TG/DSC experiment, 19.5 % sBPN (sBPN with 19.5 wt. % s‐B/MgB2 powder) has a heat release of 1815 J g−1 and experienced an exothermic span of 2.10 min, whereas it took 24.5 % BPN (BPN with 24.5 wt. % boron powder) 3.45 min to release 1465 J g−1. The pressure‐time curve (P‐t curve), burning rate and combustion temperature were determined. The P‐t curve indicates that the combustion pressure was more readily established with the sBPN than with the BPN. The maximum pressure rise of sBPN was 362.0 Pa ms−1, whereas the figure for BPN is 77.2 Pa ms−1. Coupled with infrared radiation (IR) temperature thermometer, the distribution of the flame temperature field during combustion was obtained. It is shown that the combustion temperature of 19.5 % sBPN igniter is approximately 800 K higher than that of 24.5 % BPN. IR images of the combustion process show that the temperature difference of the 19.5 % sBPN flame is smaller than that of the 24.5 % BPN. 19.5 % sBPN also produces more hot residue, which contains KMgF3, resulting in a longer high‐temperature duration. The higher combustion pressure and temperature and more residue may enable the sBPN to readily ignite the following charge.

Thermal hazard evaluation of AIBME by micro-calorimetric technique coupled with kinetic investigation

2,2′-Azobis (2-methylpropionate) (AIBME) is a new type of environmental-friendly oil-soluble azo initiator, extensively applied in the radical polymerization industry relying on its extraordinary thermal and physicochemical properties. Nevertheless, the special structure makes AIBME decompose easily under low ambient temperature with a tremendous amount of heat release. To qualify its thermal hazard and obtain the specific safety parameters such as time to maximum rate under adiabatic condition (TMRad) and self-accelerating decomposition temperature (SADT), differential scanning calorimeter (DSC), simultaneous thermogravimetric analyzer (STA), and accelerating rate calorimeter (ARC) were applied to analyze the thermal behaviors of AIBME while conducting the thermokinetic analysis and numerical curve fitting. The results indicate that AIBME decomposes at low temperature, and the SADT of AIBME in 25 kg UN package is 35.2 °C. Moreover, the temperature at TMRad = 8 h is determined at 51.6 °C using Townsend method. Compared with commercially used azo compounds, such as 2,2′-azobisisobutyronitrile (AIBN) and 2,2-azobis(2-methylbutyronitrile) (AMBN)), the predominant heat of decomposition, more gaseous degradation products, quicker heat release rate, and lower decomposition temperature make AIBME more hazardous during production, storage, and transportation. The results of this study can provide the references for the process safety assessment and the design of appropriate safety system in scale-up applications with the wish to avoid the occurrence of AIBME involved accidents.

Thermal-triggered insulating fireproof layers: A novel fire-extinguishing MXene composites coating

Abstract The use of intumescent flame-retardant (IFR) coatings is one of the most highly effective methods for polymeric materials to improve their fire safety. However, organic IFR coatings show “negative effect” in a large amount of heat and smoke release during the char-forming process. Developing nanocomposite coatings that can reduce their “negative effect” and simultaneously enhance the barrier effect of fireproof char layer is particularly desirable. Herein, a novel UV-curable IFR/MXene nanocomposite coating was developed by incorporation of surface-modified MXene nanosheets in the IFR coating system, and then constructed on the surface of rigid polyurethane (RPU) foam to fabricate coated RPU foams via spray-coating and UV-cured process. The IFR/MXene coated RPU foams show a fast self-extinguished behavior and a remarked decrease in heat and smoke production, indicating the great improvement of RPU fire safety in building. The fireproof layers combined with expanded char and MXene jammed networks generated rapidly during combustion can serve as physical shield to effectively delay the release of heat and volatile products, protecting the underlying substrate from further burning. Moreover, the mechanical properties and dispersion are enhanced due to the co-cross-linking networks between the IFR coating and MXene nanosheets. As a new member of the 2D nanomaterials, MXene nanosheets have potential to be a new choice for developing high-performance nanocomposite coating for polymers to reduce their risk of fire hazard.

Effect of octane number and thermodynamic conditions on combustion process of spark ignition to compression ignition through a rapid compression machine

Spark assistance in homogeneous charge compression ignition (HCCI) is a promising method to improve combustion stability. Fundamental experiments were carried out in a rapid compression machine along with chemical kinetics analysis to investigate the complete combustion process of spark ignition to compression ignition (SICI) using ethanol-blended fuels. Five fuels, consisting of n-heptane, iso-octane and ethanol with different fractions, are divided into two groups. The fuels with different research octane number (RON) and motor octane number (MON) but identical octane sensitivity (S) are in the same group. The equivalence ratio is fixed at 0.5, and the experimental pressure covers the engine-relevant conditions (10–35 bar) while the target temperature ranges from 735 K to 860 K, overlapping most regions with negative temperature coefficient (NTC) of n-heptane and iso-octane. Results show that octane sensitivity with low RON has poor ability to evaluate fuel reactivity especially in the vicinity of “beyond MON” area due to low-temperature oxidation acceleration of ethanol. The influence of fuel reactivity, auto-ignition heat release amount and flame compression effect on knock intensity enhancement decreases in turn. The lower transition temperature and pressure at the time of auto-ignition is observed in the fuel with lower RON regardless of S, resulted from stronger LTHR and greater temperature rise from cool flame. The fuel with medium RON and S based on ethanol blending is more suitable for SICI combustion since it can make a better balance among knock intensity, dilution tolerance and control authority from flame in the conditions studied, which gives an insight into the effect of ethanol blends on combustion process and provides a reference for fuel design aimed at lean SICI combustion.

Fast-cured UV-LED polymer materials filled with high mineral contents as wear-resistant, antibacterial coatings

Development of ultraviolet (UV) curing technique has greatly expanded the preparation and application of polymer composite coatings due to its unique characteristics of high efficiency curing and controllable operation. However, the inevitable hazards of high pressure mercury lamps, as well as difficulty resulting from large amount of heat release when coating products, greatly limit the practical application and development of such curing coatings. Herein, a series of novel controllable, fast-cured coatings filled with high mineral contents were successfully designed and synthesized based on progressive ultraviolet light emitting diode (UV-LED) technology with ultra-low energy consumption. Due to the addition of a large number of opaque mineral particles, a new polymerization mechanism for the system was proposed and verified. Inorganic particle fillers (μm-level) can produce various degrees of reflective or refractive points, thus effectively reducing the barrier effect of the filling particles and realizing a much deeper solidification. Silver nanoparticles (AgNPs) were then combined with this composite material to fabricate a long-term antibacterial interior wall base-coating without interference with the curing effects. More importantly, the various effects of reactants of polymeric composite coatings with high inorganic mineral content for such UV-LED curing systems (365 nm) were brought to as comprehensive a conclusion as possible. This coating remained stable over a 15-week period against bacteria with the bactericidal coefficient of approximately 99.5% for E. coli and about 97% for S. aureus. We believe that proposed applicable polymerization mechanism will greatly enrich the current UV polymerization system, especially for polymer composite material with high mineral contents, and our designed wear resistance, high-hardness, and long-term antibacterial coating will also have great application prospects in many practical fields.

Computer analysis of the thermal state of the object after cryotherapy

In this work, experimental data are presented that allows one to estimate the relative amount of heat release. It also provides the opportunity to state the general tendency of its change over time for patients with various individual characteristics of the organism. An important indicator of safety and effectiveness of cryotherapy is the temperature of the skin surface Tk, which should not fall below -2 °C during exposure. It is also planned to propose a method for studying the dynamics of Tk and heat flux from the human body using a thermoelectric module (TEM). The paper evaluates the experimental data on the TEM current changes during and after cryotherapy. Also, dynamics assessment of heat flow during cryotherapy is given and the possibility of evaluating Tk will be shown. It is planned to get an overall picture of the process of heat exchange of the measuring device with the skin of the test object. The results allow us to make recommendations regarding the duration and intensity of cryotherapy.

Development of Mg-Zn-Al-CO3 ternary LDH and its curability in epoxy/amine system

Labeling epoxy/layered double hydroxide (LDH) nanocomposites for properties requires a priori curability estimation. The co-precipitation method was applied in synthesis of Mg-Zn-Al ternary LDH and intercalation with carbonate anion led to development of Mg-Zn-Al-CO3-LDH. The structure of developed ternary LDH was studied by XRD, FTIR and TGA/DTG analyses. Nonisothermal differential scanning calorimetry (DSC) at heating rates of 2, 5, 7 and 10 °C/min was used to evaluate the curing potential of low-filled epoxy/LDH nanocomposite by labeling them for curability. It was unraveled by the use of Cure Index that even by using well-synthesized Mg-Zn-Al-CO3-LDH ternary structure the epoxy curing was hindered, underlining the importance of curability estimation before dealing with properties of epoxy/LDH systems. It can be concluded by accepting Poor label for the studied system that although carbonate ion deposition in between galleries enlarged interlayer space it inevitably confined collision between epoxy and amine curing precursor. This negative effect was signaled by a significant fall in heat release amount of nanocomposites sample compared to the neat epoxy irrespective of heating history.

A scaling law for the recirculation zone length behind a bluff body in reacting flows

The recirculation zone length behind a bluff body is influenced by the turbulence intensity at the base of the body in isothermal flows and also the heat release and its interaction with turbulence in reacting flows. This relationship is observed to be nonlinear and is controlled by the balance of forces acting on the recirculation zone, which arise from the pressure and turbulence fields. The pressure force is directly influenced by the volumetric expansion resulting from the heat release, whereas the change in the turbulent shear force depends on the nonlinear interaction between turbulence and combustion. This behaviour is elucidated through a control volume analysis. A scaling relation for the recirculation zone length is deduced to relate the turbulence intensity and the amount of heat release. This relation is verified using the large eddy simulation data from 20 computations of isothermal flows and premixed flames that are stabilised behind the bluff body. The application of this scaling to flames in an open environment and behind a backward facing step is also explored. The observations and results are explained on a physical basis.

Runaway reaction and thermal hazards simulation of 4-amino-1,2,4-triazole picrate by HP-DSC and ARC

4-Amino-1,2,4-triazole picrate (4-ATPA) is a type of ionic liquids, as well as an explosive with sound thermal stability and low mechanical sensitivity. However, under upset conditions such as high temperature and pressure, an unpredictable explosion would occur and result in huge casualties and property losses. The purpose of this research was to evaluate the thermal hazard and runaway reaction of 4-ATPA through high-pressure differential scanning calorimetry and accelerating rate calorimeter. The kinetic parameters of decomposition reaction under non-isothermal and different pressure conditions were calculated based on the experiment results. Experimental results showed that the β and test pressure had no effect on the amount of heat release. Adiabatic experiments indicated that 4-ATPA had a high onset temperature at 196.8 °C. The maximum self-heating rate (3567.9 °C min−1) and pressure rise rate (202.0 bar min−1) revealed the vulnerability of 4-ATPA to suffer a disastrous explosion. Moreover, the apparent activation energy and pre-exponential factor were evaluated as 110.2 kJ mol−1 and 1.8 × 10−15 s−1 by ASTM E698 method. The correctness of the thermodynamic calculation formula under adiabatic conditions is verified by ARC tests. Finally, the thermal hazard risk of 4-ATPA was classified as unacceptable based on the risk classification criteria.

Fire and explosion hazards of ionic liquid 1-methyl-1-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide

Low volatility materials that do not emit sufficient vapor to form a combustible mixture with air, under temperate conditions, are considered a lower fire hazard than materials with higher volatility. Because ionic liquids have very low volatility, they are widely considered to be green alternatives to organic solvents and have long been considered nonflammable. However, recent research has indicated some ionic liquids are flammable because of the auto-ignition of their thermal decomposition products rather than the combustion of the vapors itself. Ionic liquid 1-methyl-1-propylpyrrolidine bis(trifluoromethanesulfonyl)imide has been reported to be an electrolyte base candidate for lithium batteries, and many electrochemical characteristics of this ionic liquid have been extensively investigated. Characteristics about its fire and explosion hazards, however, are still not reported in the literature. It is obvious that such information is indispensable to safely use this ionic liquid.In this study, the fire and explosion hazards of ionic liquid 1-methyl-1-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide are investigated via auto-ignition tester, TGA/DSC and TGA-FTIR. It is found that the auto-ignition temperature of this ionic liquid is 441 °C with the ignition delay time of 38.2 s. The decomposition process of this ionic liquid is found to be endothermic in the nitrogen atmosphere, but it is exothermic in the air atmosphere. Further TGA/DSC experiments indicate that in the air atmosphere the amount of heat release will increase as the reaction gas purge rate increases, but in the nitrogen atmosphere the amount of heat absorbed is independent of the reaction gas purge rate. It is also found from TGA-FTIR experiments that in the air atmosphere the concentration of carbon dioxide in the evolved gas was much higher than that in the nitrogen atmosphere. Moreover, carbon monoxide is observed in the air atmosphere, but is not observed in the nitrogen atmosphere. If in the air atmosphere the spontaneous combustion of the gas-phase decomposition products occurs, aforementioned observations can be reasonably explained.

Synergistic effects of amine-modified ammonium polyphosphate on curing behaviors and flame retardation properties of epoxy composites

A flame retardation property of polymer composites is being considered important to minimize the amount of heat release and the smoke production during the combustion. Therefore, this work aims to improve the flame retardation property of epoxy composites using ammonium polyphosphate (APP), one of the intumescent flame retardants (IFRs). However, APP could be migrated to the surface of composite due to the weak compatibility with epoxy resin. To prevent the migration, the surface modification method has taken place using various amines, acting as charring agent. In this study, we select the 4,4′-diaminodiphenylmethane (DDM) as both curing agent and charring agent for the surface modification on the APP, and their epoxy composites were prepared. Interestingly, we observe both the fast curing effect by analyzing the curing behavior of epoxy composite by Friedman method, and significant improvements of the thermal degradation, and flame retardancy of epoxy with adding the amine-modified APP (mAPP). Moreover, the epoxy/mAPP composites showed higher flame retardation properties and formed the compact char structures due to the attached DDM, which acted as an efficient charring agent to promote to form the carbonaceous char structures. Finally, we also found the correlation between the improvements of flame retardation properties, and char structures of epoxy composites by calculating the crosslink density (Mc) using the theory of rubber elasticity.

Using Chemical Kinetics to Understand Effects of Fuel Type and Compression Ratio on Knock-Mitigation Effectiveness of Various EGR Constituents

<div class="section abstract"><div class="htmlview paragraph">Exhaust gas recirculation (EGR) can be used to mitigate knock in SI engines. However, experiments have shown that the effectiveness of various EGR constituents to suppress knock varies with fuel type and compression ratio (CR). To understand some of the underlying mechanisms by which fuel composition, octane sensitivity (S), and CR affect the knock-mitigation effectiveness of EGR constituents, the current paper presents results from a chemical-kinetics modeling study. The numerical study was conducted with CHEMKIN, imposing experimentally acquired pressure traces on a closed reactor model. Simulated conditions include combinations of three RON-98 (Research Octane Number) fuels with two octane sensitivities and distinctive compositions, three EGR diluents, and two CRs (12:1 and 10:1). The experimental results point to the important role of thermal stratification in the end-gas to smooth peak heat-release rate (HRR) and prevent acoustic noise. To model the effects of thermal stratification due to heat-transfer losses to the combustion-chamber walls, the initial temperature at the start of the CHEMKIN simulation was successively reduced below the adiabatic core temperature while observing changes in end-gas heat release and its effect on the reactant temperature.</div><div class="htmlview paragraph">The results reveal that knock-prone conditions generally exhibit an increased amount of heat release in the colder temperature zones, thus counteracting the HRR-smoothing effect of the naturally occurring thermal stratification. This detrimental effect becomes more pronounced for the low-S fuel due to its significant Negative Temperature Coefficient (NTC) autoignition characteristics. This explains the generally reduced effectiveness of dilution for the low-S fuel, and higher knock intensity for the cycles with autoignition.</div></div>

Economical and facile synthesis of a highly efficient flame retardant for simultaneous improvement of fire retardancy, smoke suppression and moisture resistance of epoxy resins

An economical flame retardant additive dimelamine pyrophosphate (DMPY) was synthesized from melamine and sodium pyrophosphate and its chemical structure was well characterized and confirmed. It was used to flame retardant epoxy resin (EP) thermosets and the fire retarded performance, mechanical properties, moisture resistance and flame retardant mechanism of EP thermosets were investigated in details. The samples achieved UL-94 V-0 grade during vertical burning tests and the limiting oxygen index value reached 28.7% when 9 wt% DMPY was incorporated. DMPY stimulated the degradation of EP matrix in advance and the formation of intumescent and compact char layer during combustion. Besides, the nonflammable gases generated from the decomposition of DMPY exerted flame retarded effect in gas phase. Thus, the rate and total amount of heat release and smoke production were significantly suppressed. The moisture resistance of EP/DMPY thermosets was improved comparing with that of pure EP. The samples remained superior flame retardant performance and mechanical properties after water resistance tests due to the excellent water resistance of DMPY. In summary, the EP/DMPY thermosets exhibited excellent flame retardancy, moisture resistance, mechanical properties and fire safety performance. The presented investigation provided a broad application prospect in the high-performance field of flame retardant EP thermosets because of the low cost and easy industrialization of DMPY.

Geometric Effects of Compartment Opening on Fuel-Air Mixing and Backdraft Behavior

메탄 연료성분이 가득 찬 축소 구획실을 대상으로 개구부에서 유입된 공기와 내부 연료의 혼합특성과 백드래프트발생특성을 규명하기 위해 대와동모사를 수행하였다. 통상의 문 형태(Door)와 가로 형태의 문이 벽면 상단(SlotU), 중단(SlotM) 및 하단(SlotL)에 있는 구획실의 4가지 개구부 조건들에 대해서 검토를 수행하였다. 점화원이 없을 경우 구획실 내부로 유입되는 산소의 양과 외부로 유출되는 연료의 양은 Door > SlotU ~ SlotM > SlotL의 순서로 크지만 SlotU의 경우가 구획실 내부에서 연료와 산소가 전체적으로 가장 잘 혼합되었고 SlotL의 경우에는 연료와 산소가 층을 이루어 혼합이 가장 잘 이루어지지 않는 것으로 나타났다. 구획실 내 산소량과 연료량으로 정의되는 총괄당량비는 구획실에서 발생하는 백드래프트의 강도와 잘 연관되지 않음을 확인하였다. 백드래프트 발생 시의 구획실 내부의 최고압력은 혼합이 가장 잘 이루어진 SlotU가 가장 높게 나타났으며 SlotL의 경우에는 압력상승이 낮아 백드래프트가 발생하지 않았다. 백드래프트 발생 시 Door와 SlotM 조건에서의 최고 압력값은 SlotU 다음 순서로 나타났으며, 각 조건들의 최고압력은 백드래프트 발생순간까지의 총 열발생량과 잘 연관되어 설명될 수 있었다.Mixing characteristics and backdraft dynamics were investigated using large eddy simulation for compartments initiallyfilled with methane fuel. Four different opening geometries, i.e. conventional door opening case (Door) and the cases wherehorizontal door was implemented on the upper (SlotU), middle (SlotM) and lower part (SlotL) of side wall, were consideredin the simulations. For cases without ignition, the amounts of inflow oxygen and outflow fuel from the compartmentopening were, from largest to smallest, Door > SlotU ~ SlotM > SlotL. However, the fuel and oxygen were the best mixedfor the SlotU case while the fuel and oxygen were not well mixed and in relatively separated two layers for the SlotL case. The global equivalence ratio defined by the amounts of fuel and oxygen in the compartment was not correlated reasonablywith the peak pressure of backdraft. The peak pressure during backdraft was the highest for the SlotU case, a well mixedcondition of fuel and air, and backdraft was not found for the SlotL where the pressure rise was not so high due to themixing status. The peak pressures for the Door and SlotM cases were in between Door and SlotL cases. The peak pressureduring backdraft was well correlated with the total amount of heat release until the instance of backdraft occurrence.

Flame suppression mechanism of aluminum dust cloud by melamine cyanurate and melamine polyphosphate.

The suppression effect of melamine cyanurate (MCA) and melamine polyphosphate (MPP) on the flame propagation of aluminum dust were studied experimentally. The results indicated that the concentration of MPP required to supress the aluminum dust explosion was lower than MCA. As the concentration of suppressant increased, the acceleration and the maximum flame speed extremely decreased, and the flame morphology became isolated spot flames. The MPP addition exerted a stronger suppression effect on the temperature of aluminum flame compared to MCA addition. Meanwhile, the mechanism of flame suppression was further investigated. Decomposition of MCA and MPP particles could absorb the heat released from the flame front. Scanning electron microscopy demonstrated that the gas phase reaction of aluminum particles was suppressed by MCA and MPP, resulting in a larger particle size of the explosion products. XRD results indicated that MCA and MPP did not react with aluminum. Gaseous products of suppressant decomposition altered flame chemistry by radically recombining O atom and reducing AlO, which resulted in less amount of heat release, lower flame speed and lower flame temperature.