汽车“自燃”的起因与预防措施

近来,私家车、出租车和公交车等一些车辆发生自燃的情况已屡屡见诸新闻媒体。为什么有的汽车容易发生自燃?又该如何防止这个现象?

“缓慢氧化”是“自燃”吗

现实生活中，如果“缓慢氧化”产生的热量达到可燃物的着火点就能引起可燃物的“自燃”。“自燃”由于是一种自发性的、不需要人为去点燃或加热的氧化反应，于是在初中化学学习中，许多同学经常把“缓慢氧化”等同于“自燃”，把它们当成是一回事，其实它们之间既有联系，也有区别，是两种不同的化学现象。

谈汽车“自燃”

汽车“自燃”事故。近年来有频繁发生的趋势。因而引起了消防、环保、保险及车主等各方的关注。

“自燃”与“外燃”是赔付的分水岭

投保人梁某的车辆在运行过程中发生火灾造成车辆全部烧毁。经当地公安消防勘查结果是由于该车行李架上货物起火导致燃烧。围绕“自燃”还是“外燃”这一焦点 ,保险公司与法院的认识和理解产生分歧。一、二审法院均认为是“外燃” ,属保险责任 ,保险公司应当赔付 ,而事实火灾属“自燃” ,但由于保险公司解释工作不到位 ,法院又倾向于被保险人 ,再加上现时社会环境 ,保险公司只好委曲求全 ,同意有限赔偿。这一案件警示我们保险事业任重道远 ,要想真正按《保险法》办案 。

古山煤矿易自燃倾斜煤层综放面防灭火措施数值模拟

文中针对古山煤矿煤层自然发火隐患大、开采条件复杂、防灭火形势十分严峻的问题,通过现场测试、实验分析、数值模拟进行研究,确定了最佳防灭火方案。由于工作面采煤方式为综采放顶煤工艺,采空区遗煤多并且工作面上部有小煤窑火区和上分层火区造成采煤条件复杂,一般的防灭火措施很难保证工作面安全回采。通过对几种防灭火措施进行数值模拟,得出:在风量为642m^3/min且注氮量为320 m^3/h时,工作面采空区"自燃带"宽度为42 m;上下隅角挡风墙对于工作面的防火工作只在初期有效果,随着挡风墙进入采空区对自燃带的影响在急速下降,当挡风墙进入采空区4 m时就已经失去了作用,所以挡风墙必须要连续构筑;所筑挡风墙规格相同的情况下,在下隅角筑挡风墙的效果要比在上隅角的效果好;不放顶煤采空区"自燃带"宽度的影响成阶段性变化,当煤柱被埋进到30 m时,采空区的"自燃带"宽度达到最小值;当煤柱被埋进采空区70 m以后对采空区"自燃带"长度的作用减小为零。研究结果对防治煤矿采空区自然发火有重要指导意义。

Apparent activation energy for spontaneous combustion of sulfide concentrates in storage yard

In order to evaluate the spontaneous combustion hazard of sulfide concentrates in storage, three different kinds of sulfide concentrates （sulfur-rich sulfide concentrate, iron sulfide concentrate and copper sulfide concentrate） were obtained from a storage yard in Dongguashan Copper Mine, China. The reaction processes at different heating rates of 5, 10, 15, 20, and 25 ℃/min in air flow from ambient temperature to 1 000 ℃ were studied by TG-DTG-DSC analysis. By the peak temperatures of DTG curves, the whole reaction process for each sample was divided into different stages, and the corresponding apparent activation energies were calculated by the Ozawa-Flynn-Wall method. It is found that the reaction process of each sample is considerably complex; the apparent activation energy values change from 36 to 160 kJ/mol in different temperature ranges; sulfur-rich sulfide and iron sulfide concentrates have lower apparent activation energy than copper sulfide concentrate below 150 ℃; so they are more inclined to cause spontaneous combustion at ambient temperature.

Infrared thermography for prediction of spontaneous combustion of sulfide ores

The method of infrared thermography to predict the temperature of the sulfide ores has a large error. To solve this problem, the temperature of the sulfide ores is measured by thermal infrared imager and recording thermometric instrument contrastively. The main factors, including emissivity, distance, angle and dust concentration that affect the temperature measurement precision, are analyzed. The regression equations about the individual factors and comprehensive factors are obtained by analyzing test data. The application of the regression equations improves the precision of the thermal infrared imager. The geometric information lost in traditional infrared thermometry is determined by visualization grid method and interpolation method, the relationship between the infrared imager and geometry information is established. The geometry location can be measured exactly.

Mechanism of mechanical activation for spontaneous combustion of sulfide minerals

In order to uncover the intrinsic reasons for spontaneous combustion of sulfide minerals,representative samples were collected from typical metal mines to carry out the mechanical activation experiment.The structures and heat behaviors of activated samples were characterized by scanning electron microscopy（SEM）,X-ray diffraction（XRD） analysis,and simultaneous thermal analysis（STA）.It is found that the sulfide minerals after mechanical activation show many changes with increased specific surface areas,aggregation phenomenon,decreased diffraction peak intensity,broadened diffraction peak,declined initial temperatures of heat release and self-ignition points.A new theory for explaining the spontaneous combustion of sulfide minerals is put forward：the chemical reaction activity of sulfide minerals is heightened by all kinds of mechanical forces during the mining,and the spontaneous combustion takes place finally under proper environment.

An Air-Breathing Micro Direct Methanol Fuel Cell with 3D KOH-Etched Cathode Structure

A micro direct methanol fuel cell （μDMFC） using MEMS technology is reported. The prototype features a unique 3D air-breathing cathode structure fabricated using KOH etching and double-side lithography. The optimization of the MEMS fabrication process is analyzed. The experimental results show the prototype generates a maximum power density of 2.52mW/cm^2 at room temperature. This performance is better than the published resuits of other silicon-based passive μDMFCs. Moreover,it is comparable with that of our previous active μDMFCs which require an external pump, certificating the feasibility of this new configuration.

Effects of pyrite on the spontaneous combustion of coal

Abstract Pyrite has a significant effect on the spontaneous combustion of coal. The presence of pyrite can change the propensity of coal towards spontaneous combustion. The influences of various pyrite contents on the parameters of spontaneous combustion, such as index gases, temperature and released heat etc., were investigated in this study, Coal samples with different pyrite contents （0 %, 3 %, 5 %, 7 % and 9 %） were made by mixing coal and pyrite. The oxidation experiments under temperature-programmed condition were carried out to test the release rate of gaseous oxidation products at different temperatures. Differential scanning calorimeter （DSC） was employed to measure the intensity of heat release during coal oxidation for various pyrite contents. The results indicate that pyrite can nonlinearly accelerate the process of spontaneous combustion. The coal sample with a pyrite content of 5 % has the largest CO release rate and oxygen adsorption as well. However, the coal sample with a pyrite content of ？ % has the largest rate of heat flow according to the results from the DSC tests. Pyrite contents of 5 %-7 % in coal has the most significant effects on spontaneous combustion within the range of this study. The conclusions are conducive to the evaluation and control for the spontaneous combustion of coal.

Application of a novel detection approach based on non-dispersive infrared theory to the in-situ analysis on indicator gases from underground coal fire

Coal mine fires,which can cause heavy casualties,environmental damages and a waste of coal resources,have become a worldwide problem.Aiming at overcoming the drawbacks,such as a low analysis efficiency,poor stability and large monitoring error,of the existing underground coal fire monitoring technology,a novel monitoring system based on non-dispersive infrared(NDIR)spectroscopy is developed.In this study,first,the measurement principle of NDIR sensor,the gas concentration calculation and its temperature compensation algorithms were expounded.Next,taking CO and CH_(4) as examples,the liner correlation coefficients of absorbance and the temperature correction factors of the two indicator gases were calculated,and then the errors of concentration measurement for CO,CO_(2),CH_(4) and C_(2)H_(4) were further analyzed.The results disclose that the designed NDIR sensors can satisfy the requirements of industrial standards for monitoring the indicator gases for coal fire hazards.For the established NDIR-based monitoring system,the NDIRbased spectrum analyzer and its auxiliary equipment boast intrinsically safe and explosion-proof performances and can achieve real-time and in-situ detection of indicator gases when installed close to the coal fire risk area underground.Furthermore,a field application of the NDIR-based monitoring system in a coal mine shows that the NDIR-based spectrum analyzer has a permissible difference from the chromatography in measuring the concentrations of various indicator gases.Besides,the advantages of high accuracy,quick analysis and excellent security of the NDIR-based monitoring system have promoted its application in many coal mines.

Development of a spontaneous combustion TARPs system based on BP neural network

Spontaneous combustion of coal is a major cause of coal mine fires.It not only poses a severe hazard to the safe extraction of coal resources,but also jeopardizes the safety of mine workers.The development of a scientific management system of coal spontaneous combustion is of vital importance to the safe production of coal mine.This paper provides a comparative analysis of a range of worldwide prediction techniques and methods for coal spontaneous combustion,and systematically introduces the trigger action response plans(TARPs)system used in Australian coal mines for managing the spontaneous heating of coal.An artificial neural network model has been established on the basis of real coal mine operational conditions.Through studying and training the neural network model,prediction errors can be controlled within the allowable range.The trained model is then applied to the conditions of Nos.1 and 3 coal seams located in Weijiadi Coal Mine to demonstrate its feasibility for spontaneous combustion assessment.Based upon the TARPs system which is commonly used in Australian longwall mines,a TARPs system has been developed for Weijiadi Coal Mine to assist the management of spontaneous combustion hazard and ensure the safe operation of its mining activities.

Comparative analysis of coal and coal-shale intrinsic factors affecting spontaneous combustion

Coal and coal-shales tend to undergo spontaneous combustion under favourable atmospheric conditions. Spontaneous combustion liability index and intrinsic properties of coals and coal-shales varies between （above and below） coal seams. The spontaneous combustion liability index （obtained from the Wits-Ehac Index） and intrinsic properties （obtained from proximate, ultimate, and petrographic analysis） of fourteen samples representative of in situ coal （bituminous） and fourteen coal-shales obtained in Witbank coalfield, South Africa were experimentally studied. Comparative analysis of the relationships between the spontaneous combustion liability index and intrinsic properties of coals and coalshales were established to evaluate their effects on self-heating potential. The intrinsic properties show linear relationship with spontaneous combustion liability and therefore, identifies the factors affecting spontaneous combustion of these materials. The influence of coal-shales intrinsic properties towards spontaneous combustion liability shows higher correlation coefficients than the coals. Both coals and coal-shales show inertinite maceral as major constituents than the vitrinite and liptinite macerals, hence the reactivity of inertinite macerals may show greater influence on spontaneous combustion liability. A definite positive or negative trends exists between the intrinsic properties and spontaneous combustion liability index. This research is part of a larger project which is considering the influence of intrinsic properties of coals and coal-shales on spontaneous combustion liability.

Experiment study of optimization on prediction index gases of coal spontaneous combustion

The coal of Anyuan Mine has the characteristic of easy spontaneous combustion. Conventional method is difficult to predict it. Coal samples from this mine were tested in laboratory. The data obtained from laboratory determination were initialized for the value which was defined as "K". The ratio of each index gas and value of "K", and the ratio of combination index gases and value of "K", were analyzed simultaneously. The research results show that for this coal mine, if there is carbon monoxide in the gas sample, the phenomenon of oxidation and temperature rising for coal exists in this mine; if there is C_2H_4 in the gas sample, the temperature of coal perhaps exceeds 130 °C. If the coal temperature is between 35 °C and 130 °C, prediction and forecast for coal spontaneous combustion depend on the value of Φ(CO)/K mainly; if the temperature of coal is between 130 °C and 300 °C, prediction and forecast for coal spontaneous combustion depend on the value of Φ(C_2H_6)/Φ(C_2H_2) and Φ(C_2H_6)/K. The research results provide experimental basis for the prediction of coal spontaneous combustion in Anyuan coal mine, and have better guidance on safe production of this coal mine.

Study on partition of spontaneous combustion danger zone and prediction of self-ignition in coalmine based on numeric simulation

By solving steady model of air flow diffusion and chemical reaction in loose coal, distribution of oxygen concentration and flow velocity magnitude were obtained. Compared the simulating results with critic value as well as duration of spontaneous combustion from large-scale spontaneous combustion experiment, 'three zones' of spontaneous combustion were partitioned and mining conditions to avoid spontaneous combustion were obtained. The above method was employed to partition 'three zones' in gob of fully mechanized top-coal caving long wall face and got fairly good result. Calculation of the above method is much smaller than simulating the whole process of coal spontaneous combustion, but the prediction precision can satisfy the demand of predicting and extinguishing spontaneous combustion in mining.

Numerical Simulation Study of Goaf Methane Drainage and Spontaneous Combustion Coupling

In order to study the coupling problem between methane drainage and spontaneous combustion of residual coal in the collapsed zone after mining ignitable coal seams with high methane,we have analyzed the effects of differ-ent methane drainage modes on spontaneous combustion of residual coal through numerical simulation. The results show that deep and large flux methane drainage modes increases the air leakage from work faces to the goaf and formed new spontaneous combustion zones induced by drainage near vents,which increases the risk of self-ignition of coal—reducing the self-ignition period and enlarging the scale of self-ignition. The spontaneous upstream combustion oxidation of the main fire zone can be suppressed when both drainage and nitrogen injection were adopted. Our research results provide an effective technical measure and theoretical basis to determine the best methane drainage scheme and drainage parameters.

Numerical simulation for determining three zones in the goaf at a fully-mechanized coal face

According to the theory of ventilation network, a model for a filtration flow field in goaf was built and simulation soft- ware for determining the three zones in goaf has been developed. This software uses no-gap-connection between Visual Basic (VB) and Excel to exchange data, uses Component Object Model (COM) component of MATLAB to plot charts of the three zones and to export the corresponding coordinates of the isolines. An example shows that this software is convenient and simple. By using it, the three zones can be easily determined. The software is convenient in studies and analyses of the three zones in goaf.

A new apparatus to establish the spontaneous combustion propensity of coals and coal-shales

Coal and coal-shale both tend to undergo spontaneous combustion under favourable atmospheric conditions. The Wits-Ehac index has been developed in South Africa since the late 1980's to test the spontaneous combustion liability of coal. However, in some cases, the Wits-Ehac index fails to produce tangible results when testing coal-shales. To overcome this problem, a new apparatus has been developed to test carbonaceous materials such as coal and coal-shale under chemical reactions with oxygen and an index has been obtained. This index is called the Wits-CT index. The equipment emulates the influence of oxygen adsorption on carbonaceous material for a period of 24 h without a heating system.The Wits-CT index uses the total carbon content of the sample and the temperature variations obtained from the samples during reaction with oxygen to predict the spontaneous combustion liability. Eighteen samples have been analyzed using both indices and the results are in-line. It was found that coals and coal-shales with higher values of the Wits-CT index are more liable to spontaneous combustion.Further research on different coal-shales is underway in order to establish an extensive database for coal and coal-shales, together with known incidences of self-heating.

Oxidation kinetics regularity in spontaneous combustion of gas coal

In order to investigate the oxidation kinetics of gas coal at low temperatures, we derived a rate equation of oxygen consumption during low-temperature oxidation of gas coal and deduced an E-c equation, expressing the relation between active energy E and oxygen concentration c. The reaction order n and active energy E were calculated with this equation based on experiments of static oxygen consumption tests. In addition, we proved the rationality of the E-c equation using a kinetic compensation effect and obtained the isokinetic temperature Tc. The results show that： 1） the gas coal oxidizes easily with increasing temperature and the oxidation tends to be spontaneous at higher temperatures; 2） the oxygen concentration c affects oxygen consumption very much at lower temperatures but has only a small effect at higher temperatures; 3） the isokinetic temperature Tc was 127 ℃ which has been experimentally validated as the key turning point during low-temperature spontaneous combustion of gas coal.

Recognition of Spontaneous Combustion in Coal Mines Based on Genetic Clustering

Spontaneous combustion is one of the greatest disasters in coal mines. Early recognition is important because it may be a potential inducement for other coalmine accidents. However, early recognition is difficult because of the complexity of different coal mines. Fuzzy clustering has been proposed to incorporate the uncertainty of spontaneous combustion in coal mines and it can give a clear degree of classification of combustion. Because FCM clustering tends to become trapped in local minima, a new approach of fuzzy c-means clustering based on a genetic algorithm is there- fore proposed. Genetic algorithm is capable of locating optimal or near optimal solutions to difficult problems. It can be applied in many fields without first obtaining detailed knowledge about correlation. It is helpful in improving the effec- tiveness of fuzzy clustering in detecting spontaneous combustion. The effectiveness of the method is demonstrated by means of an experiment.