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.     

Self induced buoyant blow off in upward flame spread on thin solid fuels

Upward flame spread experiments were conducted on long thin composite fabric fuels made of 75% cotton and 25% fiberglass of various widths between 2 and 8.8 cm and lengths greater than 1.5 m. Symmetric ignition at the bottom edge of the fuel resulted in two sided upward flame growth initially. As flame grew to a critical length (15–30 cm depending on sample width) fluctuation or instability of the flame base was observed. For samples 5 cm or less in width, this instability lead to flame blow off on one side of the sample (can be either side in repeated tests). The remaining flame on the other side would quickly shrink in length and spread all the way to the end of the sample with a constant limiting length and steady spread rate. Flame blow off from the increased buoyancy induced air velocity (at the flame base) with increasing flame length is proposed as the mechanism for this interesting phenomenon. Experimental details and the proposed explanation, including sample width effect, are offered in the paper.     

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.     

Outdoor,indoor, and personal black carbon exposure from cookstoves burning solid fuels

Black carbon (BC) emissions from solid fuel combustion are associated with increased morbidity and mortality and are important drivers of climate change. We studied BC measurements, approximated by particulate matter (PM_2.5) absorbance, in rural Yunnan province, China, whose residents use a variety of solid fuels for cooking and heating including bituminous and anthracite coal, and wood. Measurements were taken over two consecutive 24‐h periods from 163 households in 30 villages. PM_2.5 absorbance (PM_abs) was measured using an EEL 043 Smoke Stain Reflectometer. PM_abs measurements were higher in wood burning households (16.3 × 10^?5/m) than bituminous and anthracite coal households (12 and 5.1 × 10^?5/m, respectively). Among bituminous coal users, measurements varied by a factor of two depending on the coal source. Portable stoves (which are lit outdoors and brought indoors for use) were associated with reduced PM_abs levels, but no other impact of stove design was observed. Outdoor measurements were positively correlated with and approximately half the level of indoor measurements (r = 0.49, P < 0.01). Measurements of BC (as approximated by PM_abs) in this population are modulated by fuel type and source. This provides valuable insight into potential morbidity, mortality, and climate change contributions of domestic usage of solid fuels.     

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.     

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.     

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.     

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.     

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.     

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.     

Snapshot review of refuse-derived fuels

Refuse-derived fuel (RDF) is generated by selected Municipal Solid Waste (MSW) fractions. Due to MSW composition changes by location, it is challenging to sell RDF as a product in the market. This article compiles the significant standards and rules governing RDF manufacture and usage. Additionally, it emphasizes the key actors that have already made a business of its commercialization and energy production through thermochemical processes. Combustion is the most often utilized thermochemical process, and this paper gathers information from several works on the combustion of RDF and RDF blends. Pyrolysis and gasification are also discussed, along with the primary benefits and drawbacks of RDF usage. Finally, the market's potential and significant constraints are examined. The primary constraint is the RDF price due to commercialization fees. However, RDF is aligned with the circular economy, sustainable development goals, and CO₂ reductions by avoiding the extraction of new fossil fuels.     

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     

典型点火源引燃特性表征指标体系研究

为了预防和消除火灾和爆炸性环境潜在点火源,开展了点火源识别和引燃特性研究。通过国内外相关标准和文献调研分析,从点火源防控和火灾爆炸事故调查角度,划分为热点火源、电点火源、机械点火源、化学点火源、波点火源、烟火材料和杂项7大项26类。研究提出了包含温度、能量、火焰形貌、时频特性和引燃能力等点火源引燃特性的表征指标体系,给出点火源属性定量表征参数,分析点火源能量分布、温度范围和引燃概率影响因素。研究结果表明：该点火源引燃特性表征指标体系可反映点火源与可燃物之间的关联性,有助于确定火灾和爆炸性环境有效点火源,降低事故的发生概率。开发PC端软件及移动端APP,附有安全专家知识库,便于在线咨询和数据共享。     

Indoor concentrations of nitrogen dioxide and sulfur dioxide from burning solid fuels for cooking and heating in Yunnan Province,China

The Chinese national pollution census has indicated that the domestic burning of solid fuels is an important contributor to nitrogen dioxide (NO₂) and sulfur dioxide (SO₂) emissions in China. To characterize indoor NO₂ and SO₂ air concentrations in relation to solid fuel use and stove ventilation in the rural counties of Xuanwei and Fuyuan, in Yunnan Province, China, which have among the highest lung cancer rates in the nation, a total of 163 participants in 30 selected villages were enrolled. Indoor 24‐h NO₂ and SO₂ samples were collected in each household over two consecutive days. Compared to smoky coal, smokeless coal use was associated with higher NO₂ concentrations [geometric mean (GM) = 132 μg/m³ for smokeless coal and 111 μg/m³ for smoky coal, P = 0.065] and SO₂ [limit of detection = 24 μg/m³; percentage detected (%Detect) = 86% for smokeless coal and 40% for smoky coal, P < 0.001]. Among smoky coal users, significant variation of NO₂ and SO₂ air concentrations was observed across different stove designs and smoky coal sources in both counties. Model construction indicated that the measurements of both pollutants were influenced by stove design. This exposure assessment study has identified high levels of NO₂ and SO₂ as a result of burning solid fuels for cooking and heating.     

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.