Showing papers on "Spontaneous combustion published in 1997"
TL;DR: In this article, the spontaneous ignition of a range of alkanes (C4-C8) and of mixtures of the primary reference fuels (PRF), n-heptane + i-octane (2.4 trimethylpentane), have been investigated.
100 citations
TL;DR: In this paper, the ignition and combustion of a solid cylinder of Al was studied experimentally by using the stagnation region of impinging O 2 N 2 (20 80 ) mixture streams over a wide range of pressure and velocity of the streams.
73 citations
TL;DR: In this paper, the role of oxygen diffusion as the cause of self-heating of coal is re-examined and a model for the spontaneous combustibility and ignition behavior of coal stored in confined spaces is presented.
20 citations
TL;DR: The spontaneous ignition of hydrogen at pressures between 3.5 and 7 MPa has been investigated in this article, where a free piston compressor was used to rapidly increase the temperature and pressure of a mixture of hydrogen, oxygen, and helium.
17 citations
TL;DR: In this article, the experimental observations and measurements to show the mechanistic structures for hydrocarbon oxidation that lead to the observed combustion characteristic and provide more recent chemical evidence from combustion studies in support of those interpretations.
Abstract: Publisher Summary Numerical analyses can be used with some success to simulate the chemical features of low-temperature hydrocarbon oxidation. This chapter describes the experimental observations and measurements to show the mechanistic structures for hydrocarbon oxidation that lead to the observed combustion characteristic and provides more recent chemical evidence from combustion studies in support of those interpretations. The kinetics and mechanism of certain classes of compounds, such as the alkenes and aromatics, have not been investigated fully in the low-temperature region, therefore, information on aromatic compounds being, particularly sparse. Apart from the studies of neo-pentane and i-butane, experimental evidence in support of these mechanisms and the determination of appropriate rate constants has yet to be forthcoming. The ability to predict, by numerical methods, the spontaneous ignition of single-component fuels or mixtures of hydrocarbons and the dependences on experimental conditions is extremely important with regard to ignition hazards or the performance of fuels in spark-ignition and diesel engines. However, improved numerical simulations of the variation in the low-temperature reactivity among alkanes and their isomers are likely to emerge, and there is progress yet to be made on a number of fronts by both experimentalists and numerical modelers.
15 citations
01 Jan 1997
TL;DR: In this paper, an experimental and modelling study of the promoting effect of CF3 H. C2 F6 and CF3 Br on the ignition delay of methane- oxygen-argon mixtures behind shock waves is presented.
Abstract: This paper describes an experimental and modelling study of the promoting effect of the addition of CF3 H. C2 F6 and CF3 Br on the ignition delay of methane- oxygen-argon mixtures behind shock waves. Reflected shock waves permitted to obtain temperatures from 1500 to 1950 K and pressures from 9.5 to 10.5 atm. Under these conditions, a promoting effect has been observed for each of the three compounds studied for 10% of additive with respect to the amount of methane. A mechanism including 79 reactions has been used to compute the ignition delays and has permitted to obtain a good agreement between the simulated values and the experimental data. A sensitivity analysis has shown that the additional initiation steps induced by the halogenated compounds studied are particularly influential.
14 citations
01 Jan 1997
TL;DR: In this paper, Grewern et al. developed a practical test for spontaneous combustion, an autoignition test and spontaneous combustion oven tests, which were carried out using standard apparatus available in the laboratory.
Abstract: The phenomenon of spontaneous combustion can be problem where coal is found,nstored or transported. Most studies regarding the spontaneous combustion of coal havenbeen undertaken specifically through study of the situation at the minesite, at points ofnstockpile or utilisation facilities. It is not clear, however, whether there is a relationshipnbetween the propensity of coal to spontaneous combustion as it is moved within anmaterials handling system from the mine through washing and transportation to thenutilisation facilities.nnnnnnnnnnnnn n The main aim of this thesis is to investigate the trend in the liability of a unit coalnto spontaneous combustion within the coal stream from the mine to the utilisation plant.nSeveral tests and experiments have been undertaken to determine the liability of coal tonspontaneous combustion at various points within the coal stream. The major tests were annewly developed qpractical testq for spontaneous combustion, an autoignition test andnspontaneous combustion oven tests. In addition, coal analyses, including petrographic,nproximate and elemental analyses were undertaken to examine the relationship betweennspontaneous combustion and these parameters.nnnnnnnnnnn n The qpractical test apparatusq was developed as a modification of a devicendeveloped by a previous researcher. This apparatus was designed to model the behaviournof a stockpile of large mass and differs from the original apparatus in that the testednsample is in an qas receivedq condition to simulate field conditions closely and to avoidnchanging some parameters, including moisture content, due to sample preparation. This isnone major factor that makes the present study different from previous studies whichnnormally use crushed samples.nnnnnnnnnnnn n The new design for the practical test apparatus is one of the contributions of the lpresent study to spontaneous combustion research. The principle of this test is to measuren1mnthe temperature rise of coal under adiabatic conditions. This is achieved mby passingnregulated rates of airflow through an insulated, vertically mounted, cylindrical tube of 2 mnlength and 200 mm diameter. A comparison of recorded temperature rise of each samplenwas made to determine different liability of tested coals to spontaneous combustion. Details of the apparatus design are provided m the thesis and the results of testsnundertaken are discussed.nnnnnnnnnnn n The autoignition tests and spontaneous combustion oven tests were carried outnusing standard apparatus available in the laboratory. An apparatus developed by Grewernwas used in the autoignition tests. Tested coals and a reference substance were heated innreaction tubes in a furnace at a constant rate of temperature rise with air moving until thencoal temperature reached the reference temperature, established as the autoignitionntemperature. Different autoignition temperatures of the tested coals indicate differentnpropensities to spontaneous combustion. A spontaneous combustion index can bendeveloped using the results of this test.nnnnnnnnnnnnnnnnnnn n In the spontaneous combustion oven tests, the assessment was based on thenanalyses of combustion gases produced from the coal samples when heated gradually in annoven from room temperature up to certain preset temperatures. The relative tendency ofncoal to spontaneous combustion was assessed by comparing the composition of the outletngas stream of each coal sample.nnnnnnnnnnnnnnnnnnnn n The results obtained from the various tests were discussed to determine the trendnin the propensity of coal to spontaneous combustion within the coal flow from the mine tonthe utilisation plant. They were also correlated with the results of the coal analyses to drawnthe relationship between spontaneous combustion of coal and parameters including ashncontent, maceral composition and particle size. The future application of the apparatusndeveloped in this study and the implications of the present study for the coal industry arendiscussed.nnnnnnnnnnnnnnnnnnnnnn n The practical test for spontaneous combustion indicated that coal taken at thenpower station was the most liable to spontaneous combustion, while no substantialndifference was recorded between coal sampled at the washing plant and run of mine. Thenauto ignition test, on the other hand, showed a clear difference in the propensity of testedncoal to spontaneous combustion. Liability of coal to spontaneous combustion from high tonlow is coal taken at the power station followed by that taken at the washing plant and thennrun of mine. In general, the results of the spontaneous combustion oven tests showed thatncoal taken at the power station and run of mine was the most and the least liable tonspontaneous combustion respectively. nnnnnnnnnnnnnnnnnnn n The relationship between spontaneous combustion and maceral analysis showednthat coal with a high vitrinite composition correlates with a high susceptibility tonspontaneous combustion. In contrast, the higher the ash content of coal, the less liable isnspontaneous combustion. The results of the gas analyses to determine the relationshipnbetween spontaneous combustion and coal particle size showed that no consistentnconclusions could be made. However, from sieve analysis it was shown that coal whichnhas the smallest average size was the most susceptible to spontaneous combustion.nSamples of coal were from the Ebenezer and Jeebropilly mines and the Swanbank powernstation, Queensland, Australia.nn
12 citations
06 Jul 1997
TL;DR: Theoretical and experimental studies dealing with the spray ignition phenomenon are reviewed in this paper, where an attempt is made to provide a common link between spray ignition, individual droplet ignition, and droplet cluster ignition.
Abstract: Theoretical and experimental studies dealing with the spray ignition phenomenon are reviewed. Topics related to external-source ignition and spontaneous ignition in liquid fuel sprays are covered. An attempt is made to provide a common link between the spray ignition, individual droplet ignition, and droplet cluster ignition. In a similar way, common features of external-source ignition and spontaneous ignition in sprays are identified. Available experimental data for the model validation is also presented. Potential topics for further research are suggested.
10 citations
TL;DR: A review of the brief history of catalytic combustion in internal combustion (IC) engines suggests that catalytic combustions may aid in fuel ignition, but can also cause increased flame-quenching because of surface catalytic oxidation of unburned fuel in the gas boundary layer.
Abstract: A review of the brief history of catalytic combustion in internal combustion (IC) engines suggests that catalytic combustion may aid in fuel ignition, but can also cause increased flame-quenching because of surface catalytic oxidation of unburned fuel in the gas boundary layer. The effect of catalytic combustion on heat transfer measurements in engines is also discussed, with the controversial Woschni effect, wherein thermal insulation appears to increase heat rejection from the combustion chamber, being shown to be probably only a manifestation of catalytic combustion.
9 citations
TL;DR: In this article, the authors investigated the dependence of the ignition distance on the values of the velocity and temperature gradients that exist at the trailing edge of a thin splitter plate separating two parallel streams of fuel and oxidizer.
Abstract: Ignition in the laminar wake that forms at the trailing edge of a thin splitter plate separating two parallel streams of fuel and oxidizer is studied in the limit of large activation energy. The analysis presented covers ignition events ocurring in the Rott–Hakkinen and Goldstein regions, where self-similar solutions for the different frozen flow variables are available. Because of the strong exponential sensitivity of the reaction rate on the temperature, ignition becomes a self-accelerating phenomenon on the temperature increment that leads to a thermal runaway a finite distance downstream from the splitter plate. The dependence of the ignition distance on the values of the velocity and temperature gradients that exist at the trailing edge of the splitter plate is investigated. In particular, it is seen that, for sufficiently large values of the activation energy, the small temperature variations that exist across the wake must be taken into account in calculating the ignition distance. As the transverse gradient of temperature at the trailing edge increases, the reaction zone becomes thinner and migrates towards the hotter side of the mixing layer, where convection becomes the dominant transport mechanism, causing the thermal runaway distance to be determined in the first approximation by a convective-reactive balance across the thin reaction layer. Ignition in the wake when one of the streams is initially stagnant is also addressed. The character of the resulting solution is seen to depend strongly on the Lewis number of the reactant supplied by the colder stream, yielding three distinct ignition regimes that are analyzed separately.
8 citations
Patent•
31 Mar 1997
TL;DR: An autoignition system for use in an inflator or method of inflating includes a separator which divides a composition capable of spontaneous combustion or auto-ignition so that it cannot combust until the separator is removed or altered in form as mentioned in this paper.
Abstract: An autoignition system for use in an inflator or method of inflating includes a separator which divides a composition capable of spontaneous combustion or autoignition so that it cannot combust until the separator is removed or altered in form. The separator is made of a material which melts at a select temperature so that autoignition will occur upon melting of the separator. The system can also use the separator or a burst disc to sensitize a desensitized spontaneous combustion mixture to achieve autoignition at a desired temperature.
TL;DR: In this article, the effect of several retardants on bituminous coal has been investigated experimentally in a temperature-controlled oven and the activation energy of coal treated with retardants has been evaluated over the temperature range from 60 "C to 220 O C using the FrankKamenetskii model.
Abstract: To identlfy an effective inhibitor to retard the self-heating and spontaneous ignition of coal, the effect of several retardants on bituminous coal has been investigated experimentally in a temperature-controlled oven. The activation energy of coal treated with retardants has been evaluated over the temperature range from 60 "C to 220 O C using the FrankKamenetskii model and the rate of temperature rise. One retardants was found to increase the activation energy by up to 20 57 kJ/mol for different particle sizes of the coal. Various factors influencing the inhibition effect are considered. On the basis of experimental results, a kinetic interpretation of the retardation mechanism is put forward involving both radical reaction and active centre theories. It has been observed that there are possibly two regimes for the oxidation of a bituminous coal in the temperature range studied, viz., a chemically controlled regime and a combination of pore-diffusionally and chemically controlled regime. Finally, the possibility of using DDS-series inhibitors in practical situations is discussed.
01 Jan 1997
17 May 1997
TL;DR: The main technique used for mining at Houilleres du Bassin de Lorraine (HBL) consists in retreat faces, mainly as a consequence of strata pressure at a current depth of 1000-1200 m.
Abstract: French coal mines are deep, gassy and prone to spontaneous combustion. The main technique used for mining at Houilleres du Bassin de Lorraine (HBL) consists in retreat faces, mainly as a consequence of strata pressure at a current depth of 1000-1200 m.
TL;DR: In this article, the authors investigated the influence of ATAC operation with weakening premixed gas and raising temperature of the combustion chamber wall on cyclic variation of ignition and combustion, from which they clarified the correlation between autoignition timing and combustion duration.
Abstract: ATAC (Active Thermo-Atmosphere Combustion) is stable in the lean limit, because it is "bulk-like" and/or "nonpropagating" combustion caused by self-ignition. In a low-heat-rejection methanol-fueled engine, we investigated the influence of ATAC operation with weakening premixed gas and raising temperature of the combustion chamber wall on cyclic variation of ignition and combustion. We analyzed the cyclic variation of autoignition timing, combustion duration, combustion quantity and instantaneous heat flux on the wall of the combustion chamber, from which we clarified the correlation between autoignition timing and combustion duration, autoignition timing and combustion quantity, and combustion duration and combustion quantity.
01 Jan 1997
Patent•
09 Dec 1997
TL;DR: In this paper, low-grade coal is ground into =270 deg.C and the slurry is subjected to hot water treatment at the same temperature for >=5min to convert the ground coat into modified coal.
Abstract: PROBLEM TO BE SOLVED: To provide a method for producing coal fuel molding capable of lowering characteristic water content and suppressing collapse of shape and spontaneous ignition. SOLUTION: Low-grade coal is ground into =270 deg.C and the slurry is subjected to hot water treatment at the same temperature for >=5min to convert the ground coat into modified coal. Then, the modified coal is separated by a dehydrator 31 and dried by a drier 32 and compressed under 2 ton/cm pressure by a molding machine 42 to afford a coal fuel molding. Since pores of raw coal are made to collapse and characteristic water content as well as hygroscopic property are lowered by modification, a molding obtained from the modified coal has characteristic low water content and hardly causes collapse of shape and since the specific surface area of the molding is small, the molding hardly causes spontaneous ignition.
TL;DR: In this article, the possibility of improving air-fuel mixture ignition by optimal contouring of the wall on which the jet is incident is confirmed, and a decrease in the limiting temperature and in the ignition delay leads, in turn, to an increase in fuel-combustion efficiency, which ensures faster stabilization of engine operation after starting.
Abstract: The possibility of improving air-fuel mixture ignition by optimal contouring of the wall on which the jet is incident is confirmed. It is also shown that a decrease in the limiting temperature and in the ignition delay leads, in turn, to an increase in fuel-combustion efficiency, which ensures faster stabilization of engine operation after starting. Under diesel-engine nominal rating conditions, secondary mixing no longer has a profound effect on ignition and combustion processes.
01 Jun 1997
TL;DR: In this article, the combustion characteristics of laser-induced spark ignition were investigated for quiescent methane-air mixtures in an optically-accessible, constant volume combustion chamber.
Abstract: The combustion characteristics of laser-induced spark ignition were investigated for quiescent methane-air mixtures in an optically-accessible, constant volume combustion chamber. Initial pressure and the equivalence ratio as well as spark energy were varied in order to explore the combustion behavior with laser-induced spark ignition. A shadowgraphs for early stages of combustion process showed that the ignition kernel exhibit nearly separated two kernels, one of which grows back towards the original ignition laser. Eventually after a short time the two flame kernels separate into two flame fronts propagates individually which is unique to laser-induced ignition. For a given mixture, lower initial mixture pressure and higher spark energy resulted in shorter flame initiation period and faster flame propagation.
01 Oct 1997
TL;DR: In this paper, boron filaments were electrically heated in air and argon/oxygen mixtures while their resistance, temperature, and radiation at the wavelengths of BO and BO2 bands were monitored.
Abstract: Boron filaments were electrically heated in air and argon/oxygen mixtures while their resistance, temperature, and radiation at the wavelengths of BO and BO2 bands were monitored. The filaments 'burned' in two distinct stages. Samples of the filaments were quenched at different times before and during the burning and analyzed using electron microscopy. The beginning of the first stage combustion characterized by a local resistance minimum, a sharp spike in boron oxide radiation emission, and a rapid rise in temperature, occurred at 1500 +/- 70 deg. C, independent of pre-heating history and oxygen content (540%) in the gas environment. The data suggest that a phase transition occurs in the filaments at this temperature that triggers stage one combustion. Significant amounts of oxygen were found inside quenched filaments. Large spherical voids formed in the boron filaments during their second stage combustion which is interpreted to indicate a crucial role for the gas dissolution processes in the combustion scenario.
19 Dec 1997
TL;DR: In this paper, the authors measured the total ignition time delay for Hypergolic bipropellants in missile systems where the oxidizer and fuel are gelled using a droplet contact technique.
Abstract: : The combustion of Hypergolic bipropellants in missile systems where the oxidizer and fuel are gelled involve important areas of research: ignition time delay, chemical kinetics, atomization, and liquid phase mixing Measurements of the total ignition time delay for Hydrazine and Red Fuming Nitric Acid (RFNA) and UDMH/RFNA have been accurately measured using a droplet contact technique The results show the effect of fuel/oxidizer ratio an the total ignition time delay involves initial contact, quiescent mixing in the liquid phase, gas evolution and combustion in the vapor phase The liquid phase mixing and the gas evolution comprise the most significant fraction of the total ignition time delay in comparison to the chemical ignition time delay
Patent•
29 Apr 1997
TL;DR: In this article, the sinterability of a copper/tungsten green compact is improved by using copper oxide, tungsten oxide or both as the copper and/or Tungsten source.
Abstract: The sinterability of a copper/tungsten green compact is improved by using copper oxide, tungsten oxide or both as the copper and/or tungsten source. Sinterability is further enhanced by including steam in the sintering atmosphere. Spontaneous combustion of the source powders used to form the sintering compacts can be reduced or eliminated by including corrosion inhibitor in the powders.