Minimum Autoignition Temperature Research Articles

A study of unexpected autoignition temperature trends for pure n-alkanes

An experimental study of minimum autoignition temperatures (AIT) reveals unexpected behavior of pure, higher-carbon-number n-alkanes (C16 and larger) not predicted by current AIT prediction methods nor current phenomenological understanding of autoignition processes. The well-documented AIT trend for normal alkanes shows high AIT values for smaller members of the family with decreasing AIT, as carbon chain length increases, to a roughly constant value for C7 and larger. Measurements in this work show that values start to increase again at C16 and show a dramatic and previously unexplained step increase between C25 and C26.The impact of measurement methods on AIT values is discussed. Experimental modifications to compensate for AIT measurements at altitude are presented. Measured values for several n-alkanes using the ASTM E-659 method are reported and compared to data from other sources. Temperature-versus-time plots, external autoignition experiments, lag times, and decomposition measurements using differential scanning calorimetry are also reported and examined for several n-alkanes to illucidate the unexpected trends. A mechanistic explanation of these trends is proposed. Finally, the implications of this behavior for trends in other chemical families are discussed.

Effect of calcium chloride on the self-ignition behaviours of coal using hot-plate test

The effect of calcium chloride (CaCl2) on the self-ignition behaviours of coal was studied under air atmosphere in this paper. Aqueous CaCl2 solutions (50, 100, 200, and 300 g/L) was used to treat a non-caking coal sample with high self-ignition potential, and the minimum auto-ignition temperature (MAIT) of the coal dust layer was determined using hot plate test to affirm thermal runaway. Both thermogravimetric analyzer and differential scanning calorimetry (TGA-DSC) were applied to investigate the decomposition of the samples. Results showed that CaCl2 generated a coating film with dense slurry-like envelope on the particle surface, which took an inhibition effect at low thermal conditions (before crossing point) because of heat absorption of moisture evaporation and oxygen diffusion resistance of pore structure blockage. The MAIT of the CaCl2-treated coal sample was increased from 210 to 240 °C, with a max elevation of 30 °C in comparison to H2O-Coal sample. However, opposite effect was also found at higher temperatures (after the crossing point). For 50 g/L CaCl2-Coal sample on hot surface of 240 °C, the calculated inhibiting rate at 10 and 50 min was 54.8% and −115.6%, respectively, suggesting that the catalysis effect at the later stage after ignition was over two times than the inhibiting effect at the initial self-ignition process. The Ca2+ in the form of its oxides (CaO and CaO2) at higher thermal conditions promoted the diffusion of oxygen to the coal surface and expanded the main combustion zone, suggesting a catalytic role in the coal combustion.

Low temperature autoignition of Jet A and surrogate jet fuel

An experimental study of the low-temperature and low-pressure autoignition of Jet A and surrogate fuels was conducted using the ASTM-E659 standardized test method. Two surrogate fuels (Aachen and JI mixtures), their individual components and two batches (POSF-4658 and POSF-10325) of standardized Jet A were tested using the ASTM-E659 method for a range of fuel concentrations and temperatures. The ignition behaviors were categorized into four distinct ignition modes. The individual hydrocarbon components had a wide range of ignition behaviors and minimum autoignition temperatures (AIT) values depending on the molecular structure. The two Jet A batches showed similar ignition behavior with measured AITs of 229 ±3°C and 225 ±3°C respectively. Both surrogates exhibited similar ignition behavior to Jet A with comparable AITs of 219 ±3.1°C (Aachen) and 228 ±3°C (JI) with the JI mixture proving to be a more suitable surrogate to Jet A in the low-temperature thermal ignition regime.

Thermal Runaway Pressures of Iron Phosphate Lithium-Ion Cells as a Function of Free Space Within Sealed Enclosures

Mining vehicle manufacturers are developing lithium-ion (Li-ion) battery electric vehicles as an alternative to diesel-powered vehicles. In gassy underground mines, explosion-proof (XP) enclosures are commonly used to enclose electrical ignition sources to prevent propagation of an internal methane (CH4) air explosion to a surrounding explosive atmosphere. Li-ion batteries can create pressurized explosions within sealed enclosures due to thermal runaway (TR). Researchers at the National Institute for Occupational Safety and Health (NIOSH) measured TR pressures of lithium iron phosphate (LFP) cells as a function of free space within sealed enclosures and observed an inverse power relationship. A well-confined cell produced 294 bar (4260 psia) of pressure during a TR, far exceeding minimum pressure containment specifications for conventional XP enclosures. Results indicate that adding enough free space surrounding LFP cells can reduce TR pressures to levels below that expected for CH4-air ignitions. Measured TR temperatures were below the minimum autoignition temperature of CH4-air.

Self-ignition risk classification for coal dust layers of three coal types on a hot surface

Pulverised coal in industrial sites and their dust can experience spontaneous combustion and self-heating, increasing the risk of fire and dust explosion. The main objective of the present study was to resolve thermal combustibility (as reflected by comprehensive combustibility index [Sn] and kinetic properties) for three types of coal (S1-BN, S2-CY, and S3-JM) through thermal analysis. The Sn values of the samples indicated a degradation in the quality of comprehensive combustibility. Apparent activation energies (Ea) at the initial stage of spontaneous coal combustion (130–300 °C) were decided through Achar and Coats–Redfern methods. Moreover, thermal susceptibility (minimum auto-ignition temperature [MAIT] and thermodynamic parameters) was evaluated using the hot plate method. The MAIT values for the three coal dust layers were 210, 220, and 300 °C. The results exhibited that heat conduction was the dominant heat transfer mode that originated the temperature distribution within the coal dust layer under the subcritical conditions for ignition; while it converted chemical reaction controlled-mode after thermal runaway. Furthermore, the results based on an improved risk matrix approach showed the S1-BN and S2-CY samples had a high self-ignition risk, whereas the S3-JM sample had a moderate ignition risk.

Characterization of MILD Combustion of a Premixed CH4/Air Jet Flame versus Its Conventional Counterpart.

This study is performed to characterize moderate or intense low-oxygen dilution (MILD) combustion (MC) versus conventional combustion (CC) of a premixed CH4/air jet flame in a hot coflow under identical inlet and ambient conditions. The present CC and MC correspond to the cases using a bluff-body (BB) and a no bluff-body (NBB), respectively. It is demonstrated that the NBB combustion develops by entraining ambient hot low-oxygen gas so as to dilute the reactant mixture and simultaneously heat up beyond the minimum autoignition temperature (Tai), leading to the MC. By contrast, in the BB case, the conventional flame is established and stabilized by a steady heat source of the recirculation zone (RZ) behind the BB with highly intense mixing and rapid ignition. A large reaction zone with uniform temperature distribution (i.e., low temperature rise) is found in the MC mode, while the CC has a much smaller size of the intense reaction zone with the concentrated high temperature and species distributions. Significantly, it has been first revealed that, in the BB case, there is a secondary combustion in the MC mode formed far downstream from the BB flame under the environmental condition of a high-temperature hot coflow.

페놀의 연소특성치의 측정 및 예측

The fire and explosion properties necessary for waste, safe storage, transport, process design and operation of handling flammable substances are lower explosion limits(LEL), upper explosion limits(UEL), flash point, AIT( minimum autoignition temperature or spontaneous ignition temperature), fire point etc., An accurate knowledge of the combustion properties is important in developing appropriate prevention and control measures fire and explosion protection in chemical plants. In order to know the accuracy of data in MSDSs(material safety data sheets), the flash point of phenol was measured by Setaflash, Pensky-Martens, Tag, and Cleveland testers. And the AIT of phenol was measured by ASTM 659E apparatus. The explosion limits of phenol was investigated in the reference data. The flash point of phenol by using Setaflash and Pensky-Martens closed-cup testers were experimented at 75℃ and 81℃, respectively. The flash points of phenol by Tag and Cleveland open cup testers were experimented at 82℃ and 89℃, respectively. The AIT of phenol was experimented at 589℃. The LEL and UEL calculated by using Setaflash lower and upper flash point value were calculated as 1.36vol% and 8.67vol%, respectively. By using the relationship between the spontaneous ignition temperature and the ignition delay time proposed, it is possible to predict the ignition delay time at different temperatures in the handling process of phenol.

Experimental and Kinetic Modeling Study of Autoignition Characteristics of n-Heptane/Ethanol by Constant Volume Bomb and Detail Reaction Mechanism

The purpose of this work is to investigate the autoignition characteristics of n-heptane/ethanol including the autoignition temperature (AIT), ignition delay time (τig) and the low/intermediate/high-temperature ignition. The AIT is measured by the combustion bomb under wide range conditions (φ = 0.2–2.0, Pinit = 0.772–3.861 MPa) while the influencing factors of τig and the dominant reactions of the high/intermediate/low-temperature ignition are investigated by detail chemical kinetic model. The results indicate that first, the maximum AITs difference is 46, 56, 62, 84, and 124 °C when the ethanol blending ratio is 0%, 25%, 50%, 75%, and 100% while the minimum AITs usually locate at the region of φ = 1.0–2.0, Pinit = 3.282–3.861 MPa. Second, the AITs become more vulnerable to the pressure and equivalence ratio at 3.809–3.861 MPa and the maximum AIT difference increases from 6 to 44 °C as the ethanol blending ratio increasing from 0% to 100%. Third, the sensitive factors for τig rank as initial mixture temp...

The effects of coal dust concentrations and particle sizes on the minimum auto‐ignition temperature of a coal dust cloud

SummaryFlash fires and explosions in areas containing an enriched combustible dust atmosphere are a major safety concern in industrial processing. An experimental study was conducted to analyse the effects of atmospheric coal dust particle sizes and concentrations on the minimum auto‐ignition temperature (MAIT) of a dust cloud. Two different coal samples from Australian coal mines were used. The coal dust particles were prepared and sized in 3 ranges, of below 74 μm, 74 to 125 μm and 125 to 212 μm, by using a series of sieves and a sieve shaker. A humidifier was used to increase the moisture content of the particles to the required level. All the experiments were conducted in accordance with the ASTM E1491‐06 method in a calibrated Goldbert‐Greenwald furnace.The results from this study indicate that coal dust properties, such as the chemical nature (H/C), concentration, particle size (D50), and moisture content, impact on the MAIT. For coal dust concentrations less than 1000 g.m−3, the MAIT decreases with increasing coal dust concentrations. On the other hand, for low concentrations of 100 to 15 g.m−3, the MAIT becomes more reliable for particle size D50 rather than for volatile matters.

Experimental investigation of the minimum auto-ignition temperature (MAIT) of the coal dust layer in a hot and humid environment

Ventilation Air Methane (VAM) abatement technology is recognized as a promising and value adding technique for reducing fugitive methane emissions, however, it also increases the potential fire and explosion risks of overheated coal dust. To eliminate these risks from the abatement systems it is necessary to determine the critical combustion characteristics of the minimum auto ignition temperature (MAIT) for a coal dust layer.This study investigates the auto-ignition behavior of coal dust layers in a humid environment with Relative Humidity (RH) >80%. The MAIT of four different coal dust samples (Australian coal) with particle sizes below 212μm and dust layer thicknesses of 5, 12 and 15mm were measured using a dust layer auto ignition temperature apparatus in accordance with the ASTM E2021 standard.It was concluded that the MAIT of the coal dust layer significantly decreases with decreasing particle size. The MAIT for the coal samples with a smaller D50 size were observed to be lower in comparison with samples with a larger D50 size. The dust layer thickness was shown to significantly impact on the MAIT. The MAIT increased proportionally with the increasing thickness of the coal dust layer. The effect of the coal dust moisture content and humidity on the MAIT for compacted dust layers was noticeable, whereas, this effect was less important with loose dust layers. In addition, this work investigated and compared the MAIT for a typical coal dust sample based on the existing ASTM and International Electrotechnical Commission (IEC) standard procedures for ignition of coal dust layers.

Propionic acid와 3-Hexanone 계의 최소자연발화온도의 측정

The autoignition temperaturs (AIT) of solvent mixture is important index for the safe handling of flammable liquids which constitute the solvent mixtures. This study measured the AIT and ignition delay time for Propionic acid and 3-Hexanone system by using ASTM E659 apparatus. The AITs of Propionic acid and 3-Hexanone which constituted binary system were 511 C and 425 C, respectively. The experimental AIT of Propionic acid and 3-Hexanone system were a good agreement with the calculated AIT by the proposed equations with a few average absolute deviation (A.A.D.). And Propionic acid and 3-Hexanone system was shown the minimum autoignition temperature behavior (MAITB).

N-Propanol과 Formic acid계의 최소자연발화온도의 측정

The autoignition temperatures (AITs) of solvent mixture was important index for the safe handling of flammable liquids which constitute the solvent mixtures. This study measured the AITs and ignition delay time for n-propanol and formic acid system by using ASTM E659 apparatus. The AITs of n-Propanol and Formic acid which constituted binary system were 435 o C and 498 o C, respectively. The experimental AITs of n-propanol and formic acid system were a good agreement with the calculated AITs by the proposed equations with a few A.A.D. (average absolute deviation). And nPropanol and formic acid system was shown the minimum autoignition temperature behavior (MAITB).

Measurement of Minimum Autoignition Temperature(MAIT) for binary Mixtures

본 연구에서는 ASTM E659 장치를 이용하여 가연성 혼합물인 ethylbenzene + n-pentanol계의 발화지연시간과 AIT관계를 측정하였다. 2성분계를 이루는 순수물질인 ethylbenzene과 n-pentanol의 측정된 최소 발화온도는 각각 285℃, 473℃ 였으며, 측정된 발화시간은 제시된 식에 예측된 발화시간과 적은 평균절대오차에서 일치하였다. 그리고 ethylbenzene + n-pentanol계에서 측정된 자연발화온도는 몰분율에 따라 분석하였다.

N-Decane과 Acetic acid 혼합물의 최소자연발화온도 거동

The autoignition temperature(AIT) is important index for the safe handling of flammable liquids which constitute the solvent mixtures. This study measured the AITs and ignition delay time for n-Decane and Acetic acid system by using ASTM E659 apparatus. The AITs of n-Decane and Acetic acid which constituted binary system were <TEX>$212^{\circ}C$</TEX> and <TEX>$512^{\circ}C$</TEX>, respectively. The experimental AITs of n-Decane and Acetic acid system were a good agreement with the calculated AITs by the proposed equations with a few A.A.D.(average absolute deviation). And n-Decane and Acetic acid system was shown the minimum autoignition temperature behavior(MAITB).

Overall characterization of cork dust explosion

Explosibility and ignitability studies of air/cork dust mixtures were conducted in a near-spherical 22.7 L explosibility test chamber using pyrotechnic ignitors and in a furnace of 1.23 L. The suspension dust burned as air-dispersed dust clouds and the uniformity of the dispersion inside the chamber was evaluated through optical dust probes. The range of tested particle sizes went from a mass median diameter of 47.4 to 438.3 μm and the covered dust cloud concentration was up to 700–800 g/m 3. Measured explosion parameters included minimum explosible concentration, maximum explosion pressure, maximum rate of pressure rise and minimum autoignition temperature. The effect of dust particle size on flammability was evaluated and it was found that the minimum explosible concentration is around 40 g/m 3 and it is relatively independent of particle size below 180 μm. Maximum explosion pressure of 7.2 bar and maximum rate of pressure rise of 179 bar/s were detected for the smallest tested sizes. The limitations on the rates of devolatilization of the solid particles became rate controlling at high burning velocities, at high dust loadings and for large particle sizes. The effect of initial pressure on the characteristic parameters of the explosion was studied by varying the initial absolute pressure from 0.9 bar to 2.2 bar, and it was found that as initial pressure increases, there is a proportional increase of minimum explosion limit, maximum explosion pressure, and maximum rate of pressure rise. The influence of the intensity of the ignition energy on the development of the explosion was evaluated using ignition energies of 1000 J, 2500 J and 5000 J, and the experimental data showed that the value of 2500 J is the most convenient to use in the determination of minimum explosion concentration. The behavior of the cork dust explosion in hybrid methane air mixtures was studied for atmospheres with 2% and 3.5% (v/v) of methane. The effect of methane content on the characteristic parameters of the explosions was evaluated. The conclusion is that, the hazard and explosion danger rise with the increase of methane concentration, characterized by the reduction of the minimum dust explosion concentration. The minimum autoignition temperature obtained with the thermal ignition tests was 540 °C and the results have shown that this value is independent of particle size, for particles with mass median diameters below 80 μm.

Safety strategy against potential hazards due to the handling of powders in a blending unit

Abstract To ensure and maintain process safety in the chemical industry a systematic hazard search and evaluation, i.e. “Risk Analysis” is indispensable. The knowledge of the ignition behavior of dust-air is important for such a risk assessment in a chemical production plant. This paper describes, based on a practical example, the strategy of performing a Risk Analysis and the use of the minimum ignition energy and minimum auto ignition temperature as very important safety indexes in practice.

Fire and explosion hazards induced by repressurization of air driers

AbstractAdsorbers used to dry or purify air typically contain 4A or 13X molecular sieves which are intermittently reactivated by thermal regeneration. This article shows that nitrogen adsorbs preferentially relative to oxygen in freshly reactivated 4A, 5A and 13X molecular sieves during the repressurization step. This produces an oxygen‐enriched, high‐pressure gas within the adsorber vessel which emerges immediately after the air‐drier is brought on‐line. The enriched oxygen concentration widens the flammability range of hydrocarbons, markedly diminishes the minimum autoignition temperature of hydrocarbons, and produces both a higher explosion pressure and a higher rate of explosion pressure rise relative to air at standard temperature and pressure. Thus, the oxygen‐enriched, high‐pressure gas can lead to fires, explosions, and other deleterious effects in and downstream of thermally regenerated air driers which contain large pore molecular sieves. Substituting 3A molecular sieve provides a simple, safe and inexpensive way to prevent transient oxygen enrichment and the problems associated with it. Because activated aluminas and silica gels can also enhance fire and explosion hazards, type 3A molecular sieve becomes the adsorbent of choice for air drying applications.

Autoignition temperatures for coal particles dispersed in air

The apparent discrepancies in the data for the ignition temperature of coal particles measured within extended isothermal sources can be resolved, in part, by considering the marked difference in the mixture test volumes used by the various investigators. Data obtained with systems whose mixture test volumes are too small compared to their isothermal source volumes are not considered here because they are too strongly ‘overdriven’ to be of practical use. The consequences of ignition events in such overdriven systems are of trivial significance for the system as a whole. Data are presented and analysed for the autoignition temperatures of dispersed carbonaceous dusts in a 1.21 furnace whose test volume and source volume are comparable, and in which an ignition event leads to a dust explosion involving drastic changes in the composition, temperature and pressure of both the test volume and the source volume. In the limit of fine particle sizes, the minimum autoignition temperatures for carbonaceous dust clouds in air vary from as low as 400 °C for the totally volatilizable polyethylene to as high as 925 °C for a non-volatile graphite, with coal values at intermediate temperatures depending on the coal's rank or yield of combustible volatiles. On the basis of the available data presented for the coals, for the oil shale dusts and for artificial mixtures of polyethylene and graphite, it is concluded that the pyrolysis and devolatilization process is generally rate controlling.

Flammability Characteristics of HCFC 141b and HCFC 142b

HCFC 141b and HCFC 142b are potential alternative foam blow ing agents for the fully halogenated CFCs 11 and 12. A lack of available infor mation has prompted a study of the flammable characteristics of these alter natives. This paper presents the results of flammability limit testing according to ASTM E-681-85. The effects of temperature, humidity, ignition source, and volume of apparatus are discussed. Other flammability properties, such as heat of combustion, minimum ignition energy, autoignition temperature, and maxi mum rate of pressure rise, are compared to more common flammable materials.

Thermal Autoignition Temperatures for Hydrogen-Air and Methane-Air Mixtures

The autoignition temperature and ignition delay times for hydrogen-air mix tures and methane-air mixtures as a function of concentration were measured in the Bureau of Mines 1.2-L ignitability furnace. The data shows that the minimum autoignition temperature (MAIT) values obtained for hydrogen-air and methane-air mixtures are in excellent agreement with previously reported AIT values of other researchers. There is also good agreement in the gas con centrations at which the minimum AITs occurred.