An experimental evaluation of critical surface temperature as a criterion for piloted ignition of solid fuels

With a view to developing a simple engineering method for the prediction of piloted ignition, the validity of the critical surface temperature criterion for piloted ignition is examined experimentally for seven thermoplastic materials. The results indicate that the surface temperature at piloted ignition for each material studied varies by ±15 K or less. As such, the surface temperature criterion appears to be suitable for engineering calculations.

Analysis of time-surface temperature histories shows that the radiant heat source temperature has a significant effect on the material heating over the range of source temperatures utilized (700–1050 K). The variations in material heating are of sufficient magnitude to cause changes in ignition times by a factor of two or more for different heat sources present in typical fire scenarios.

Our current level of understanding of piloted ignition is shown to be insufficient to support extrapolation procedures to determine the minimum incident radiant flux required for piloted ignition. An experimental approach to determination of the minimum radiant flux required for piloted ignition is demonstrated to be feasible.     

Measurement of instantaneous flame spread rate over solid fuels using image analysis

Spread rate is an overall property of flame propagation that characterizes the condition of a flame better than any other property. As a result, prediction and measurement of spread rate is central to flame spread studies over solid fuels. Significant amount of data have been collected over last four decades of research on flame spread over various fuels under different conditions. In most of these studies, however, only average spread rate is reported which is adequate for steady phenomena. Given that a flame may not face the same conditions during the spread, it is possible for the spread rate to change during the duration of the spread continually. In this work a methodology for image analysis is presented with the goal of evaluating instantaneous spread rate to study time-dependent phenomena. The parameters that control the error and time resolution of the flame spread history are identified, and a sensitivity study is carried out to validate the results of a scale analysis. A MATLAB-based Flame Image Analyzer (FIA) package is developed and applied to flame spread videos recorded in several experiments in different regimes of opposed-flow flame spread. An expression for the error in spread rate for a given time resolution is expressed in terms of the imaging parameters. The two parameters that are found most important are the pixel resolution and the frame rate. A non-dimensional imaging parameter is identified that is shown to govern the quality of imaging for spread rate measurement. Theoretical prediction from the error analysis is confirmed by doing various case studies using the Analyzer.     

Experimental study of the channel effect on the flame spread over thin solid fuels

We experimentally burn thin solid fuels and obtain the speed of the flame front when it propagates (1) within a narrow channel (closed cross section), (2) within a channel with lateral walls only and (3) through a free cross section (plain case). The latter configuration is the classical one and it has been extensively studied with analytical, numerical and experimental methods by other authors. Our experiments have been carried out at different geometrical configurations and angles of inclination of the sample and also at several values of oxygen molar fraction. All experiments are restricted to purely buoyant flow. Our main results are as follows: (1) sidewalls reduce the flame spread rate in a non-monotonous trend when varying its height; (2) in horizontal flame spread, two simultaneous flame fronts that propagate at different velocities may arise in the channel case at high oxygen levels. The fastest flame front speed may be higher than that obtained in the plain case; (3) in upward flame spread, the channel effect configuration produces the highest flame front speed. We finally analyze the correlation of the downward flame front speed data in terms of the Damkohler number.     

Experimental investigations of direct injection compression ignition engine by using Coconut,and Karanja biodiesel fuels with emulsions of microalgae based antioxidant

The Compression Ignition (CI) engines are playing vital role in the transportation sector; because of their lower maintenance cost even. The practice of Diesel or biodiesel is increasing Green House Gases (GHG) such as NO_x, particulate matter in the environment. Among all GHG emissions, NO_x is most harmful to human, environment. The use of additives in Diesel, biodiesel their blends in CI engine is very well practicing fuel modification technique to reduce GHG emissions. The higher cost of phenol, amine-based antioxidants are causing to increase CI engine operating cost. In this work, to investigate unmodified Direct Injection Compression Ignition engine characteristics. The Mixed culture Microalgae (MCM) biomass particles used as an antioxidant additive in pure Coconut, Karanja biodiesel. The brake thermal efficiency improved because of the explosion of MCM particles. The NO_x emissions reduced due to the absorption of heat from the combustion chamber by microalgae particle.     

Environmental monitoring of benzene and toluene produced in indoor air due to combustion of solid biomass fuels

Exposure to benzene and toluene from the combustion of solid biomass fuels is one of the important causes of morbidity and mortality in developing countries. In this study, we assessed the exposure of cooks to benzene and toluene from biomass fuel combustion in 55 rural homes. The GC-MS was used for quantification while a personnel sampler was used for environmental monitoring. The benzene exposure differed significantly (p < 0.0001) across different types of indoor kitchen fuel combinations. The geometrical mean (GM) of benzene exposure for cooks during cooking hours in an indoor kitchen using mixed fuel was 75.3 microg/m3 (with partition) and 63.206 microg/m3 (without partition), while the exposure was 11.7 microg/m3 for open type. The benzene exposure was significantly higher (p < 0.05) in an indoor kitchen with respect to open type using mixed fuels. Concentration of benzene (114.1 microg/m3) for cooks in an indoor kitchen with partition using dung fuel was significantly higher in comparison to non-cooks (5.1 microg/m3) for open type. Benzene exposure was not significantly different for kitchen with ventilation (31.2 microg/m3) and without ventilation (45.0 microg/m3) using wood fuel. However, this value was significantly (p < 0.05) lower than in indoor kitchens with or without partition. An almost similar trend was observed for toluene but the difference was statistically non-significant. This study may be helpful in developing a regional exposure database and in the facilitation of health risk assessment due to volatile organic pollutants in our day-to-day environment.     

Minimum ignition energies

In this, the final part of a two-part report, the authors take a look at the electrical energy required to ignite certain solids in air and in oxygen both at 1 atmosphere and at hyperbaric pressures. Increased use of oxygen-enriched atmospheres in medicine, undersea exploration, and the space program (twice with tragic results) has caused attention to be focused on the effects of oxygen enrichment on the flammability of materials. Note: This paper is based on research sponsored by the U.S. Public Health Service, Department of Health, Education and Welfare under Appropriation 7560370. Reference to trade names is made for identification only and does not imply endorsement by the Bureau of Mines.     

Flammability of aircraft fuels

How does the Navy cope with the hazard presented by the vast quantities of flammable liquids used aboard aircraft carriers? The authors examine the hazards and discuss the Navy's approach to hazard reduction.     

Radiant smoldering ignition of plywood

This paper investigates the role of self-heating in the smoldering ignition of 18 mm (three-quarter inch) thick maple plywood exposed to radiant heat fluxes between 6 and 15 kW/m² in the cone calorimeter for up to 8 h. The minimum heat flux for smoldering ignition was experimentally determined to be 7.5 kW/m². This compares favorably to predictions made using classical self-heating theory. The role of self-heating was explored via temperature measurements distributed within the specimens. Elevated subsurface temperature profiles indicated self-heating was an important ignition factor resulting in ignition at depth with smolder propagation to the surface and into the material. The ignition depth was shown to be a function of the heat flux with the depth moving towards the surface as the heat flux increased.     

Extinction of surface stabilized gaseous diffusion flames: Part I Simplified numerical model and implications for solid fuels in fires

In this work a previously proposed empirical and analytical criterion for extinction is numerically extended and validated for varying fuel dilution, oxidant dilution, strain rate, and surface temperature. The output of this work is presented in two parts: the current Part I uses simple kinetics and constant thermal transfer properties and Part II uses detailed kinetics, varying thermal transfer properties, flame radiation feedback and flame suppression agents in order to demonstrate that conclusions from the simplified model are still valid. In addition this work goes beyond the concept of critical flame temperature or mass flux for extinction by including the influence of slow chemical kinetics through the Damkohler number which becomes even more important for commonly used fire retarded materials.Extinction of flames on solid fuels is modeled by decoupling the pyrolysis chemistry from the gas-phase combustion chemistry using the flame energy feedback versus pyrolysis rate curves and an energy balance at the surface. This approach has the advantage of identifying and deducing key materials properties for solid and gaseous phase from experiments. Simulations are performed in a planar stagnation-point flow diffusion flame configuration using one-step Arrhenius chemical kinetics and a simplified transport model with Lewis number equal to unity. Only quasi-steady conditions are considered for the gaseous phase even if the pyrolysis rate of the solid is transient because the response time for the solid phenomena is, in general, much larger than the response (diffusion) time for the gaseous phenomena.It is found that at high pyrolysis rates and low straining rates (infinitely fast kinetics regime) there is no leakage of oxygen to the surface of solid fuel. However, as the solid fuel extinction is approached, oxygen leakage occurs because the effective air to fuel mass stoichiometric ratio becomes less than one owing to fuel dilution near the surface. At high straining rates, solid combustion cannot be sustained at any pyrolysis rate. In the infinitely fast kinetics regime, an appropriate scaling has been developed which collapses the convective heat flux curves onto a single one. In general, the critical pyrolysis fuel mass flux exhibits a universal behavior for variation of various model parameters when plotted versus a modified Damköhler number, and becomes constant when the latter is sufficiently high. Comparison with experiments is discussed, and the implications of the criterion for characterizing ignition flammability properties of solid fuels are also discussed.     

Automatic determination of ignition temperature

An electronic circuit has been designed and tested which can automatically determine ignition temperatures of shredded combustible materials. Note: The authors hold the positions of Assistant Professor, Electronics Technician, Graduate Research Assistant, and Engineering Technician, respectively. This paper is Scientific Article No. A2618, Contribution No. 5655 of the Maryland Agricultural Experiment Station, Department of Agricultural Engineering.     

城镇燃料气化方案选择论述

城镇燃料气化问题,是当今城镇现代化建设发展、提高人们生活质量、减少大气污染、改善环境卫生等至关重要的大问题。倘若一个城镇未能实现燃料气化,即如照明没有电灯一般,是十分落后的,决不可能进入文明先进城镇的行列。但由于各城镇地理资源和环境条件之不同,城镇燃料气化有多种不同的途径和方案。如何选择经济、科学、先进、合适的城镇燃料气化方案,乃是一个需要很好决策的问题。文章介绍并加以比较了几种燃料气化的方案     

Flame spreading across liquid fuels

The various mechanisms postulated to control the rate of flame propagation across a liquid fuel surface are discussed in detail. Major consideration is given to the surface tension induced flows which control the propagation at liquid temperatures well below the closed cup flash point and the cause of the flame pulsation noted at liquid temperatures just below the flash point. Some new considerations are given to the concepts and methods of experimentally evaluating flash and fire point phenomena. Analytical developments which correctly predict the very high propagation rates across liquids at temperatures well above their flash points are discussed.     

Wetting-induced ignition in cellulosic materials

A mathematical model of the ignition of cellulose is described which includes both the dry oxidation reaction and also the water-mediated exothermic reaction which is probably hydrolysis. It also takes account of endothermic evaporation of water inside the porous material, exothermic condensation of water vapour and transport of water vapour by diffusion. Appropriate boundary conditions are chosen and the results reported here are restricted to one spatial dimension, but are time dependent. Experimental data obtained recently for bagasse (ground extracted sugar cane) are used as input for the model. However, it is quite likely that the results are of general interest for other cellulose-based materials, many of which are of considerable commercial importance and many of which are believed to undergo spontaneous ignition induced by the presence of water or water vapour.A significant number of experimental observations and conjectures made over a long period are shown to be predictable and interpretable by use of the model, and good agreement with experiment occurs where results are available.     

佛甲草辐射特性的研究

在对植被屋顶进行热工性能研究时,绿化植物的发射率、长波辐射吸收率和太阳辐射吸收率是3个基本参数,对分析和计算植被屋顶的能量平衡有着重要意义。然而,目前学术界缺少常用绿化植物辐射特性的基本数据。本文研究了国内最常见的绿化物种——佛甲草的辐射特性,测得佛甲草叶片对太阳辐射的吸收率为0.67～0.69,发射率为0.81～0.84;同时利用太阳辐射传感器现场测得单位土地面积上密植的佛甲草草坪对太阳辐射的吸收率为0.83,估算得到其长波辐射吸收率约为1,在无进一步实验结果之前,可暂时认为单位土地面积上密植的佛甲草草坪发射率等同于叶片的发射率(0.83)。     

Pilot ignition of building materials by radiation

The ignition characteristics of building materials influence the spread of fire from one building to another. With some materials tested, there are significant differences in radiation levels to which materials can be safely exposed.     

香烟引燃特性的实验研究

通过香烟火源引燃几种家庭常见物品的实验,研究香烟火的引燃特性。实验结果显示:香烟火温度虽高,但不一定引起有焰燃烧,可能只有炭化痕迹或持续阴燃;判断材料有无蓄热能力,不能只考虑材料自身组分的燃烧特性,而是要具体问题具体分析;蓄热材料也不一定能被香烟火点燃;阴燃反应相对缓慢,产生较多有毒气体,没有火焰,潜伏期长,不易察觉。     

如何实现隧道窑顺利点火

隧道窑以其窑内断面温差小 ,全线可以实现机械化和自动化 ,可以减轻工人劳动强度 ,提高产品质量和产量等优点 ,越来越受到砖瓦厂的青睐。近几年来 ,新建生产规模较大的砖瓦企业几乎清一色地选择了隧道窑 ,隧道窑无疑将会成为我国今后焙烧多孔砖和空心砖的主要焙烧设备。在新世纪来临之际 ,我们邀请窑炉专家就隧道窑点火前的准备工作、点火位置及点火设施的设置、点火程序等有关问题进行了详细的描述。我们希望随着 2 1世纪的到来 ,我国砖瓦焙烧设备也能有一个跨世纪的发展。