Showing papers on "Spontaneous combustion published in 2004"

Experimental research on index gas of the coal spontaneous at low-temperature stage

Abstract: Compositions and quantities of gases produced by different coal samples at different temperature ranges were analyzed by simulating experiments in the laboratory. It is found that they are related to three major factors, temperature, external water content and retardant ratio. The quantitative relations between gas makers and temperature are established. CO and C 2 H 4 could be used as index gases for the prediction of coal spontaneous combustion in the low-temperature range for the experimental mine coal. The MEA-1A retardant had good performance in fixing the external water content of coal and inhibiting coal oxidation; it could be used in preventing the spontaneous combustion of coal prevention and its appropriate ratio was determined.

Three-dimensional modeling of self-ignition in hcci and conventional diesel engines

Abstract: This paper addresses the problem of self-ignition modeling of diesel-related fuels in the framework of engine combustion three-dimensional computational fluid dynamics simulations. A model based on the evolution of a self-ignition progress variable is proposed and implemented in the KMB code. The evolution of the progress variable is determined cell by cell and is a function of a local self-ignition delay that depends on the cell fresh mixture thermodynamic conditions. These are temperature, pressure, equivalence ratio, and residual gas percentage. The local delays are calculated via interpolation inside an extensive ignition delay database created a priori. Each delay in the database is determined through complex chemistry calculations using SENKIN along with a kinetic mechanism from the literature developed for self-ignition modeling of n-heptane. The mechanism has been validated over a broad range of thermodynamic conditions. The ignition database covers the cold flame regime allowing application of th...

Optically accessible high-pressure combustion apparatus

Abstract: The design and operation of a novel optically accessible high-pressure combustion apparatus is presented. The apparatus provides optical access for the direct observation of the morphology and development of premixed reaction fronts at elevated pressures. A chamber-in-chamber design with an innovative connecting system allows for safe, constant-pressure measurements, alleviating the extreme overpressures encountered in high-pressure combustion processes within closed bombs. Auxiliary design features include gap-adjustable electrodes for spark ignition and ports for jet stirring. As a result, the apparatus is well suited for the study of laminar premixed flames, flame instabilities, turbulent flames, and detonations. Results from the study of centrally ignited hydrogen and methane fuels in oxygen-inert mixtures up to 60 atm initial pressure demonstrate the suitability of the apparatus for high-pressure combustion experiments.

Ignition threshold for impact-generated fires

Abstract: [1] Widespread fires can be generated after large impact events by atmospheric heating caused by the reaccretion of high-energy, vapor-rich plume material. We examine the threshold irradiance levels necessary for spontaneous and pilot ignition of various types of vegetation and define three specific cases for investigation: (1) 51 kW/m2 for a period of at least 2 min to spontaneously ignite wood; (2) 20 kW/m2 for a period of at least 20 min to ignite wood in the presence of an ignition source; and (3) 28 kW/m2 for a period of at least 1 min to ignite foliage, rotten wood, and forest litter. The threshold ejected plume mass for continent-wide spontaneous ignition of wood is ∼2 to 6 × 1015 kg, independent of impact location but dependent on the details of the ejecta speed distribution. The threshold ejected plume mass for global spontaneous ignition of wood is in the range ∼1 to 2 × 1016 kg. The threshold plume masses for continent-wide and global fires are very nearly the same for piloted ignition of wood, while the threshold plume masses for continent-wide and global ignition of leaves and forest litter are significantly lower, by a factor of ∼2 to 3. Impact craters of at least 85 km diameter are needed to produce continental-scale fires, and craters of ∼135 km diameter are needed for global-scale fires.

Control device for compression self-ignition type internal combustion engine

Abstract: PROBLEM TO BE SOLVED: To enable stabilization of self-ignition combustion by suppressing dispersion of a firing delay period, in a system to effect self-ignition combustion of air-fuel mixture. SOLUTION: In a self-ignition combustion mode, air-fuel mixture in a cylinder is self-fired and burnt by bringing it into a high temperature high pressure state at a compression stroke. Multiplex ignition that an ignition plug is ignited a plurality of times is executed, when air-fuel mixture is self-fired in a self-ignition combustion mode. Dispersion of endothermic reaction B is suppressed through promotion of the endothermic reaction B by effecting ignition again and giving auxiliary energy at a timing corresponding to the endothermic reaction B during an ignition lag period γ or just before that after auxiliary energy is given during first ignition and a self-ignition condition is established. This process suppresses dispersion of the ignition lag period γ and stabilizes self-ignition combustion. Further, it is good to cause the number of firing times and the ignition timing of multiplex ignition to change in correspondence to a change of a firing lag period according to an engine operation state and a fuel feed amount (an air-fuel ratio) and the like. COPYRIGHT: (C)2006,JPO&NCIPI

An Experimental Investigation of Hypergolic Ignition Delay of Hydrogen Peroxide with Fuel Mixtures

Abstract: An experimental investigation of hypergolicity and ignition delay of fuel mixtures with hydrogen peroxide is presented. Example results of high speed photography and schleiren from drop tests are shown. Also, a discussion of the sensitivity to experimental parameters such as drop size and subsequent uncertainty considerations of ignition delay results is presented. It is shown that using the described setup on the mixtures presented, the precision uncertainty is on the order of 6% of average ignition delay and 5% of average decomposition delay. This represents sufficient repeatability for first order discrimination of ignition delay for propellant development and screening. Two mixtures, each using commonly available amines and transition metal compounds, are presented as examples that result in ignition delays on the order of 10 milliseconds.

Spontaneous ignition of n-alkane droplets with various volatility

Abstract: Ignition delays of a cool flame (τ1) and a hot flame (τt) were measured experimentally for single n-decane, n-dodecane, n-tetradecane and n-hexadecane droplets, which have similar volatilities to common commercial hydrocarbon fuels, in hot air. Droplet diameter was 0.7 mm. Ambient pressure was 0.3 and 1.0 MPa. Ambient temperature was 550 K to 1000 K. Results show the similarity of the examined fuels in terms of reactivity of the low- and high-temperature reactions. Values of τ1 and τt were longer for fuels with lower volatility. Values of τ2 (=τt−τ1) were similar for examined fuels. Both the ignition limits of cool and hot flames were similar between fuels, but were slightly lower for less-volatile fuels.

Control system for compression ignition internal combustion engine

Abstract: A control system for a compression ignition internal combustion engine, which is capable of properly estimating the temperature of combustion gases, and thereby accurately controlling the temperature of working medium according to the estimated temperature of the combustion gases, to thereby prevent knocking and misfire from occurring. A compression ignition internal combustion engine causes combustion of an air-fuel mixture by self-ignition in a combustion chamber, and includes an EGR device that causes part of combustion gases generated by the combustion to exist as EGR gases in the combustion chamber. The control system estimates the amount of EGR gases existing in the combustion chamber, estimates the temperature of combustion gases generated by combustion of working medium including the air-fuel mixture and the EGR gases, according to the estimated amount of the EGR gases, and determines the amount of the EGR gases which should be caused to exist in the combustion chamber, according to the estimated temperature of the combustion gases.

Internal combustion engine and operation control device and operation control method for internal combustion engine

Abstract: PROBLEM TO BE SOLVED: To suppress preignition. SOLUTION: This internal combustion engine 1 detects a combustion ion current inside a combustion chamber 1b by an ignition plug 10 igniting air fuel mixture inside the combustion chamber 1b. Based on the detected combustion ion current, the internal combustion engine 1 determines whether or not postignition that is a precursory phenomenon of the preignition is generated in the combustion chamber 1b. When the postignition is generated, the internal combustion engine 1 suppresses preignition through increase in fuel amount, delay of ignition timing or the like. COPYRIGHT: (C)2006,JPO&NCIPI

Research advances on microgravity combustion

Abstract: Understanding the combustion process is essential for the energy utilization in a safe, efficient and clean way However, in normal gravity, the buoyant convection and gravitational sedimentation make the process complicated Such effects nearly disappear in microgravity, which will simplify the research on combustion In view of the combustion process occured on ground and the fire safety problem for manned spacecraft, the research on microgravity combustion involves various fields of combustion science, including premixed gas combustion, gaseous diffusion combustion, droplet combustion, particle combustion, dust combustion and flame spread over fuel surface, during the development of about a half century, especially the last decade Through the research, the droplet combustion with spherical symmetry, dust combustion without sedimentation effect and combustion in quiescent or low speed convection environment have been realized, the flame ball, self-extinguishing flame and other phenomena were observed, and the thermophoresis effect during soot formation, flammability limit and flame instability and other mechanism were clarified The research has deepened the knowledge of combustion phenomenon and especially deepened the understanding on radiation effect It is shown that, for premixed gas combustion, gaseous diffusion combustion and droplet combustion, there is also the quenching extinction limit caused by large radiative heat loss, besides the blowoff extinction limit caused by short residence time The former can be found only under microgravity condition Some of these results have already been absorbed into the textbook The fact that the combustion under microgravity shows different characteristics from that under normal gravity is important for fire safety for manned spacecraft Acounting for the condition of our country and present research advances, the coal particle combustion, the dust combustion, the mechanism related to soot, radiation effect and chemical dynamics would serve as the promising future directions

Shock Tube Study of Ignition of Methanol-Oxygen-Argon Mixtures

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Study on predication model of coal spontaneous combustion stage

Abstract: In light of the theoretical analysis of coal self-ignition and entire parameter, the spontaneous combustion stage is related with the parameters B{sub I} (which presents outer heating condition), {alpha} (which presents the coal transmit ratio of temperature during the course of coal self-heating) and A{asterisk} which presented the nature of coal self-heating. Based on the experimental results of coal spontaneous combustion in the self-ignition test-bad of coal, the coal equivalent self-heating intensity in the time of ignition stage was calculated and the relation between the equivalent self-heating intensity and characteristic self-heating intensity was obtained. The mathematic model for the predication of the experimental spontaneous combustion stage was proposed. It needs only the experimental data form the small scale self-heating test. The unknown parameters of the model are few and easy to obtain. The predication error of the model is less than 15%. 9 refs., 3 figs., 1 tab.

Mechanised Spraying Device: A Novel Technology for Spraying Fire Protective Coating Material in the Benches of Opencast Coal Mines for Preventing Spontaneous Combustion

Abstract: Spontaneous combustion in coal mines play a vital role in occurrences of fire. Fire in coal, particularly in opencast mines not only causes irreparable loss of national wealth but damages the surface structure and pollutes the environment. The problem of spontaneous combustion/fire in opencast coal benches is acute. Presently over 75% of the total production of coal in Indian mines is being carried out by opencast mining. Accordingly a mechanised spraying device has been developed for spraying the fire protective coating material for preventing spontaneous combustion in coal benches of opencast mines jointly by Central Mining Research Institute, Dhanbad and M/s Signum Fire Protection (India) Pvt. Ltd., Nagpur under Science & Technology (S&T) project funded by Ministry of Coal, Govt. of India. The objective of this paper is to describe in detail about the mechanised spraying device and its application for spraying fire protective coating material in the benches of opencast coal mines for preventing spontaneous combustion/fire.

Possibility Of Refuse Derived Fuel Fire Inception By Spontaneous Ignition

Abstract: The possibility of fire inception caused by spontaneous ignition of piled RDF was elucidated. Various properties of RDF were measured. Pyrolysis behavior of RDF was examined by TG-DTA and apparent activation energy of RDF was calculated. In addition, the critical ignition temperature (Tc) of RDF was predicted by the theory of thermal explosion by Frank-Kamenetskii, and the relation between the Tc and the height of RDF pile was calculated. The results show that the relation between the Tc and the height of RDF pile is almost identical for RDFs of different states, although the thermal conductivity and bulk density of RDF sample depend on its state. This implies that the powdering of RDF does not lower the Tc largely.

Simulation of complex multiphase, multi-component, reacting flows in porous media

Abstract: In this study we are concerned with the modelling of multi-component, multiphase chemically reacting flows in porous media, with particular application to the spontaneous combustion of coal and the extraction of coalbed methane. These two related problems involve complex multiphase, multi-component flow in a porous medium. Chemical reactions, adsorption, gaseous diffusion and changes in porosity and permeability are important in one or both of these problems. These matters are discussed in general in the first few chapters of the thesis. Several models for the spontaneous combustion of coal that include the effect of a diminishing reaction rate are investigated and a new formulation in the form of a generic power law model is introduced. A numerical module for modelling the spontaneous combustion of coal is described, based on the TOUGH2 code. A new equation of state (EOS) module is developed including realistic physical properties for all gases involved. The modified version of TOUGH2 is used for modelling the adiabatic method for testing the reactivity of coal samples. The results agree very well with experimental measurements for coal samples from different mines in New Zealand and Australia. Moisture effect on the reaction rate was then introduced to TOUGH2 using a new twophase EOS module with water and air broken into its main components (Nitrogen, Oxygen, Carbon dioxide and Argon). Finally the production of methane from low rank coalbeds is investigated. A new EOS for mixture of water and methane is developed and incorporated into the TOUGH2 code to produce a new and versatile coalbed methane simulator. It is validated by running some simple test problems and comparing results with those obtained with the commercial COMET simulator.

Physical, biological and chemical processes during storage and spontaneous combustion of waste fuel

Abstract: Physical, biological and chemical processes during storage and spontaneous combustion of waste fuel

Innovative techniques for detection and control of underground spontaneous combustion of coal

Abstract: In recent years, the frequency and intensity of spontaneous combustion of coal in Australian underground coal mines has shown worrying signs of increasing. To enhance spontaneous combustion management capabilities in the Australian coal industry, a study was undertaken to investigate three innovative techniques that have been successfully used in China. These three are the radon detection technique, the infrared technique and the colloid injection technique. The radon detection technique is for remotely locating the areas of underground spontaneous combustion from a surface location. The infrared detectio n technique is for locating the spontaneous combustion within a short distance. The colloids injection technique is for controlling spontaneous combustion after it is located. This paper describes these techniques including their principles, operations, applications in China, and applicability in Australia.

Infrared thermography applied to spontaneous combustion monitoring of coal tips

Abstract: Spontaneous combustion of coal tips can generate dangerous slips and it is necessary to monitor this phenomena. Aerial IR thermography is one of methods widely used but, in the case of coal tips, it appears costly and not adapted to survey the evolution of reaction. It is for these reasons that the LAMTI in liaison with Charbonnages de France Group develops a method using topographic, thermographic and atmospheric survey that is intended to be more reliable and less expensive. 1. Introduction Coal tips are conical or truncated-cone hills formed by piling up the waste from mining operations. Some of them still possess 5-15% of residual coal, the percentage varying according to the sorting techniques used. The oldest tips thus often contain more residual coal. The porous nature of the tip enables air and water to circulate, causing the coal to oxidise. Any iron sulphides such as marcassite and pyrites present in the tip will tend to catalyse the exothermal oxidation reaction, causing spontaneous combustion of the residual coal [1]. 10% of coal tips are undergoing a process of spontaneous combustion, the effects of which are as follows [2], slipping of the tip, accompanied by clouds of inflammable dust, formation of cavities, emission of noxious gases, creation of water-gas, a compound that explodes in air. Most failures occur during heavy rains, with penetrating water having the following additional direct effects (increase in the density of the materials, drop in shear strength, increase in pore pressures, downward movements, creating destabilising forces). The effects can be particularly catastrophic. Slips are not classic rotational ones but, on account of the high water content in the schists, are more similar to mud slides; these can be deadly, as experienced in Virginia in the 1940s. There is also the added problem of major atmospheric pollution due to the release of sulphurous fumes [3]. As it is very expensive to fight coal tip fires, attempts have been made since the second half of the 20th century to prevent such fires during the formation of coal tips by taking precautions, such as for example not creating them above carbonate materials or spreading them out in order to reduce internal pressures. In the case of tips formed before this period, spreading them can be dangerous and costly if high-risk areas are not known, and monitoring then appears to be a necessary step.

The application of numerical modelling to the assessment of the potential for, and the detection of, spontaneous combustion in underground coal mines

Abstract: Numerical modelling has been used to examine the relationship between the results of two commonly used methods of assessing the propensity of coal to spontaneous combustion, the R70 and Relative Ignition Temperature tests, and the likely behaviour in situ. The criticality of various parameters has been examined and a method of utilising critical self-heating parameters has been developed. This study shows that on their own, the laboratory test results do not provide a reliable guide to in situ behaviour but can be used in combination to considerably increase the ability to predict spontaneous combustion behaviour.

Gray prediction model of spontaneous combustion stage of coal

Abstract: Based on the experimental results of spontaneous combustion stages of nine kinds of coal samples and indexes denoting the oxidation of coal which can be macro-determined, the G(0,5) gray prediction model is built by the gray system theory. The average relative error is about 1.45% and the most relative error is -21.27% in the prediction model. It can show the relation of the spontaneous combustion stage and the indexes such as ash, volatilization, sulphur and oxygen in coal. And the spontaneous combustion stage can be predicted with the gray model.

Ignition and transition to flame spread over a thin solid fuel on the floor

Abstract: A numerical study was made on the time-dependent ignition and subsequent transition to steady flame spread of a thin solid fuel on the floor, which is heated by an external radiation in a quiescent normal-gravity environment. The computational results indicate that little solid fuel is consumed before ignition occurs and the solid fuel surface reaches pyrolysis temperature when ignition occurs. Ignition is initiated at the middle of the sample to give a disk-shaped point flame at the instant of ignition. The point flame grows and immediately becomes an arch-shaped flame with two flame fronts at its bases. Then the arch-shaped flame breaks into two individual flames at the top, spreading in opposite directions. The flames spread rates in both directions were found to be faster than that of the vertical downward flame. The two spreading flames are in opposed mode because the directions between entrainment flow and flame spread are opposite. The entrainment velocity at the flame fronts, which are set up by t...

Development of Multi Cluster Burner for Fuel Grade DME

Abstract: Recently, DME (dimethyl ether: CH3 OCH3 ) has attracted attention as a clean next-generation fuel, but it has the possibility of spontaneous ignition in gas turbine use. To avoid spontaneous ignition or flash-back, a coaxial jet cluster nozzle burner configuration was proposed previously, which can mix air and fuel effectively within a short distance. In this research, the full size multi cluster burner composed of coaxial jet cluster nozzle burners was designed, and combustion tests for gaseous fuel grade DME were carried out. (Fuel grade DME includes minor amounts of methanol and water as impurities.) In making the configuration tests of the multi cluster burner, the robust design method was applied. Characteristics of NOx emission, combustion efficiency, combustion stability, etc. were evaluated, and the optimal configuration of the combustor was determined. Also, the influences of impurities of fuel grade DME on the combustion performance were evaluated. With the optimal combustor, the prospects were good for achieving the targets, NOx 99.9%, and pressure oscillation < 3.5 kPa. Regarding the influences of impurities of fuel grade DME, there was no great difference in combustion efficiency and pressure oscillation with addition of impurities in this test range.Copyright © 2004 by ASME

Energy-Efficient Transient Plasma Ignition and Combustion

Abstract: : Transient plasma discharges utilizing short (30 to 100 nsec), spatially distributed streamers energized by pulsed power were investigated as a potential new method for flame ignition. Experimental results showed shorter ignition delay and pressure rise time (typically by a factor of 3 for methane-air mixtures), as well as higher maximum pressure compared to conventional spark ignition. In all cases significant modification of initial combustion chemistry appeared to be occurring, leading to more effective combustion over a wider range of pressures and fuel composition rates.