Ignition of Combustible Fuel Beds by Hot Particles: An Experimental and Theoretical Study

The process of spotting occurs in wildland fires when fire-lofted embers or hot particles land downwind, leading to ignition of new, discrete fires. This common mechanism of wildland fire propagation can result in rapid spread of the fire, potentially causing property damage and increased risk to life safety of both fire fighters and civilians. Despite the increasing frequency and losses in wildland fires, there has been relatively little research on ignition of fuel beds by embers and hot particles. In this work, an experimental and theoretical study of ignition of homogeneous cellulose fuel beds by hot metal particles is undertaken. This type of well-characterized laboratory fuel provides a more controllable fuel bed than natural fuels, and the use of hot metal particles simplifies interpretation of the experiments by reducing uncertainty due to unknown effects of the ember combustion reaction. Spherical steel particles with diameters in the range from 0.8 mm to 19.1 mm heated to temperatures between 500°C and 1300°C are used in the experiments. A relationship between the size of the particle and temperature required for flaming or smoldering ignition is found. These results are used to assess a simplified analysis based on hot-spot ignition theory to determine the particle size-temperature relationship required for ignition of a cellulose fuel bed.     

Spread and burning behavior of continuous spill fires

Spill fire experiments with continuous discharge on a fireproof glass sheet were conducted to improve the understanding of spill fire spread and burning. Ethanol was used as the fuel and the discharge rate was varied from 2.8 mL/s to 7.6 mL/s. Three ignition conditions were used in the experiments; no ignition, instantaneous ignition and delayed ignition. The spread rate, regression rate, penetrated thermal radiation and the temperature of the bottom glass were analyzed. The experiments clearly show the entire spread process for spill fires. Further, the regression rate of spill fires at the quasi-steady burning was lower than that of pool fires and the ratio of the spill fires’ regression rate to the pool fires’ regression rate was found to be approximately 0.89. With respect to the radiative penetration and the heat conduction between the fuel layer and the glass, a regression rate expression for spill fires was developed based on some modifications on existing expressions for pool fires. In addition, a complete phenomenological model for spill fires was developed by combining the characteristics of spread and burning. The model was verified by the experimental data and found to predict the spread process for spill fires with reasonable accuracy.     

Liquid Fuel Spill Fire Dynamics

Despite the fact that liquid fuel spills present a potential fire hazard in numerous industrial and residential settings there has been minimal research conducted to understand the spill and burning dynamics of these types of scenarios (Gottuk et al., NRL/MR/6180-00-8457, 2001; Putorti, NIJ-604-00, 2001; Mealy et al., NIJ-2008-DN-BX-K168, 2010; Ma et al., Fire Technol 40:227–246, 2004). While the findings of these studies were significant in that they demonstrated a substantial decrease in the peak fire size achieved in spill fire scenarios compared to pool fires, the empirical data sets collected were not sufficient to fully understand the phenomena causing this reduction. In general, both studies attributed the decrease to thermal losses to the substrate but indicated that further investigation was required. In order to address this general lack of empirical data, a research program was conducted to characterize fuel spill fire dynamics with respect to the key variables that potentially impact these types of fires. A discussion of the test results is presented in two parts: the first being the development of a liquid spill, specifically spill depths and spill progression, and the second being fuel burning dynamics, specifically the impacts of substrate, ignition delay, and substrate temperature. The development of a spill and the associated liquid depths are described for various fuels and fuel simulants, whose properties provide bounding spill scenarios for most fuels of interest. The burning dynamics of various fuel spill scenarios are evaluated relative to numerous substrates, ignition delay times ranging from 30 s to 300 s, and substrate temperatures ranging from 12°C to 38°C (54°F to 100°F). The impact of these variables was evaluated relative to the heat release and mass burning rates measured during these tests.     

Performance characteristics of CI engine using blends of waste cooking oil methyl ester,ethanol and diesel

ABSTRACT

The main emphasis of this work is to explore the biodiesel obtained from waste cooking oil and its utilisation in CI engine blended with ethanol and conventional diesel. Waste cooking oil methyl esters (WCOME) was prepared by transesterification with a heterogeneous catalyst such as CaO. Diesel and WCOME blends of five different proportions with 5% of ethanol uniformly added to them were used as a fuel in a variable compression ratio, constant speed, compression ignition engine. The performance, emission and combustion characteristics of the engine at part and full load conditions were compared with that of neat diesel, varying the compression ratio from 18 to 22. From the experimental results, the blend comprising 20% waste cooking oil, 5% ethanol and 75% mineral diesel showed ameliorated performance and emission characteristics, compared with all the other fuel blends at an optimum compression ratio of 21.     

Burning Rate of Liquid Fuel on Carpet (Porous Media)

The occurrence of a liquid fuel burning on carpet has been involved in many incendiary and accidental fires. While the research on a liquid fuel fire on carpet is still limited, much work on porous media has been performed using sand or glass beads soaked with liquid fuel. In this study, a heat and mass transfer theory was first developed to analyze the burning process of liquid on carpet, and then several small-scale tests were performed to validate the theory. This analysis is valid for pool fires intermediate in size (5–20 cm. in diameter). The experimental apparatus consisted of a circular pan (105 mm) and a load cell. Varying amounts of fuels (heptane, kerosene and methanol) were spilled onto the carpet, which was allowed to burn in a quiescent environment. It was found that due to the different controlling mechanisms, the liquid burning rate could be less or more than that of a similarly spilled free-burning pool fire. For the worst-case scenario in fires, the maximum enhancement of the burning rate due to the porous media is predictable through the physical properties of the fuel. This analysis is valid for both combustion and evaporation. Several similar results in the scientific literature are analyzed to further describe the trend. This work explains the role of carpet in liquid pool fires and also helps to explain special risks related to the presence of carpet involved in arsons and will be useful in reconstruction of the early development of an incendiary or accidental fire.     

电缆燃烧典型火源模拟方法综述

针对电缆火灾问题,综述了国内外电缆火灾模拟试验及电缆燃烧测试中使用的火源模拟方法,并对比探讨了多种火源模拟方法的点火时间、火源温度、火源面积、火源功率、可扩展性、可移动性以及可持续使用性等方面的差异:燃气喷灯法和辐射加热法(锥形量热计)所需点火时间短;电加热法火源温度高,操作简便易移动;燃油点火法的点火面积大,可扩展性...     

Performance,emission and combustion characteristics of a single cylinder spark ignition engine using ethanol–petrol-blended fuels

The performance, exhaust emission and combustion analyses of a single cylinder spark ignition engine fuelled with extended range of ethanol–petrol blends were carried out successfully at full load conditions. Ethanol produced from raffia trunks was blended with petrol at different proportions by volume. In order to establish a baseline for comparison, the engine was first run on neat petrol. The engine performance parameters (engine torque, brake power, brake specific fuel consumption, brake mean effective pressure and brake thermal efficiency), exhaust emission parameters (CO, HC, CO₂ and O₂ emissions) and combustion parameters were determined for each blend of fuel at different engine speeds. The test results interestingly revealed that the addition of ethanol to petrol causes an improvement in combustion characteristics and significant reduction in exhaust emissions which in turn improved engine performance. In all, ethanol and its blends with petrol exhibited performance characteristics trends similar to that of petrol thus confirming them as suitable alternative fuels for spark ignition engines.     

Wildland fire spot ignition by sparks and firebrands

Wildland and Wildland Urban Interface (WUI) fires are an important problem in many areas of the world and may have major consequences in terms of safety, air quality, and damage to buildings, infrastructure, and the ecosystem. It is expected that with climate changes the wildland fire and WUI fire problem will only intensify. The spot fire ignition of a wildland fire by hot (solid, molten or burning) metal fragments/sparks and firebrands (flaming or glowing embers) is an important fire ignition pathway by which wildfires, WUI fires, and fires in industrial settings are started and may propagate. There are numerous cases reported of wildfires started by hot metal particles from clashing power-lines, or generated by machines, grinding and welding. Once the wildfire or structural fire has been ignited and grows, it can spread rapidly through ember spotting, where pieces of burning material (e.g. branches, bark, building materials, etc.) are lofted by the plume of the fire and then transported forward by the wind landing where they can start spot fires downwind. The spot fire problem can be separated in several individual processes: the generation of the particles (metal or firebrand) and their thermochemical state; their flight by plume lofting and wind drag and the particle thermo-chemical change during the flight; the onset of ignition (smoldering or flaming) of the fuel after the particle lands on the fuel; and finally, the sustained ignition and burning of the combustible material. Here an attempt has been made to summarize the state of the art of the wildfire spotting problem by describing the distinct individual processes involved in the problem and by discussing their know-how status. Emphasis is given to those areas that the author is more familiar with, due to his work on the subject. By characterizing these distinct individual processes, it is possible to attain the required information to develop predictive, physics-base wildfire spotting models. Such spotting models, together with topographical maps and wind models, could be added to existing flame spread models to improve the predictive capabilities of landscape-scale wildland fire spread models. These enhanced wildland fire spread models would provide land managers and government agencies with better tools to prescribe preventive measures and fuels treatments before a fire, and allocate suppression resources and issue evacuation orders during a fire.     

Influence of dimethoxymethane addition on performance,emission and combustion characteristics of the diesel engine

This paper assesses the effects of dimethoxymethane (DMM) blends on combustion characteristics, fuel economy, emissions and engine’s power. Experiments were carried out on a single-cylinder, four-stroke compression ignition engine of direct injection with volume fractions of DMM blends of 5%, 10%, 15% and 20% v/v starting from base diesel. Experimental results suggest that 20% DMM blended with diesel achieved better performance in terms of efficiency as well as in exhaust emissions. Carbon monoxide emission levels, hydrocarbon and smoke are reduced considerably with DMM additions, while the oxides of nitrogen emission in exhaust increase due to higher in-cylinder temperature. The oxygen content in the DMM blends plays a greater role in the combustion process compared to neat diesel fuel. The combustion profile was smoother, and no knocking was experienced while operating with DMM blends. Also, it is observed that addition of DMM in diesel shortens the ignition delay and total combustion duration.     

The effect of diameter on the burning of crude oil pool fires

In order to understand the combustion characteristics of crude oil pool fires, an experimental study was carried out at the Fire Research Institute (FRI) large scale test facility. The radiative output, burning rate, and the concentrations of CO, CO₂, and smoke (above the flame tip) were measured during the burning of Arabian light crude oil, heptane, toluene, and kerosene floating on water. The effect of scale was studied by using steel pans ranging from 0.6 to 3 meters in diameter.Crude oil burned less rapidly and gave off less thermal radiation compared with heptane, but when water boiling, i.e., boilover, occurred, the burning rate increased by a factor of two or more. The intensity of boilover is related to pan diameter and initial fuel layer thickness.     

Thermal exposure from large scale ethanol fuel pool fires

The growing use of ethanol as fuel for combustion engines has dramatically increased the need for large scale storage of ethanol in tanks. There are new risks related to fires in storage tanks having larger volumes. Very little experimental data exist to support risk assessments regarding emitted radiation and burning rate for large pool fires. Experience from small scale tests show that the exposure to nearby surroundings is less for alcohols than for hydrocarbon fuels like gasoline and these results are often extrapolated to fires of large sizes. This paper describes the results of two pool fires conducted within the frame of the ETANKFIRE project, one with 97% ethanol and 3% gasoline and the other with 85% ethanol and 15% gasoline, both with a surface area of 254 m². The results show, contrary to experience from small scale pool fires, that the exposure to nearby surroundings is much larger for ethanol-rich fuels compared to the calculated radiative heat flux from a pure gasoline fire of same fuel area.     

Combustion characteristics of the direct injection diesel engine fuelled with corn oil methyl ester

Petroleum-based fuels is a finite resource that is rapidly depleting. Consequently, petroleum reserves are not sufficient enough to last many years. In this research, an experimental investigation has been performed to give insight into the potential of biodiesel as an alternative fuel for direct injection (DI) diesel engines. The experimental work has been carried out to estimate the combustion characteristics of a single-cylinder, four-stroke, DI diesel engine fuelled with corn oil methyl ester (COME) and diesel blends. The COME was preheated to temperatures namely 50°C, 70°C and 90°C before it was supplied to the engine. The optimised preheated temperature of 70°C was chosen based on the higher brake thermal efficiency and lower specific fuel consumption. The performance, emission and combustion characteristics are evaluated by running the engine with COME and diesel blends at this preheated temperature. In this paper, the combustion characteristics are only discussed. The combustion characteristics such as ignition delay, maximum rate of pressure, heat release rate, cumulative heat release rate, mass fraction burned and combustion duration of COME methyl ester and diesel were evaluated and compared with neat diesel. The rate of pressure rise and maximum combustion pressure inside the cylinder were high for COME blends compared with neat diesel. The heat release rate of diesel is higher compared with COME blends. The ignition delay and combustion duration are decreased for COME blends compared with neat diesel. The cumulative heat release rate and mass fraction burnt of COME blends are higher than neat diesel.     

The timing of vegetation fire occurrence in a human landscape

Vegetation fires in urban and peri-urban (human) landscapes damage property and infrastructure, threaten lives and incur considerable suppression costs. This study investigated the timing of fires burning in vegetation within and around the city of Perth, Western Australia. The timing of fires from 16 different cause types were investigated at hourly, daily, monthly and annual scales, and using fire danger indices and fuel moisture. Ignitions from most causes were shown to have hourly and monthly profiles that reflect fire danger and fuel availability. Some causes with low heat outputs, such as cigarettes and sparks from cutting and welding, were more sensitive to fire danger and fuel availability than others. Causes related to arson and recreational activities, such as camp fires, were more likely to occur on weekends and public holidays. Arson prevention measures appear to have reduced the incidence of deliberately lit fires, and may have reduced the number of fires occurring on days of total fire ban, although these days have much higher rates of ignition than other days. High profile fire events also increase public awareness and reduce ignition rates. Lessons learned from analyses of fire occurrence can help fire agencies more effectively apply prevention and mitigation programs.     

Combustion analysis of Jatropha methyl esters and Pongamia methyl esters with the addition of ethanol as fuel in a diesel engine

The aim of our project is to experimentally access the practical applications of ethanol and blending it with some lubricating oils in a direct injection compression ignition engine. This replacement of conventional diesel with ethanol requires some of the properties of ethanol to be altered. In order to increase the lubricating property of ethanol, it is blended with some lubricating oils. Some of the preferred lubricating oils are methyl esters of Jatropha oil, Pongamia oil, etc. Ethanol is blended with these lubricating oils to reduce the corrosive property of ethanol. The different fuel blends [Pongamia–ethanol (50–50) and Jatropha–ethanol (50–50)] are used in the direct injection CI engine, the combustion characteristics are calculated and they are compared with diesel and a perfect blend is analysed. The engine combustion parameters such as peak pressure, heat release rate (HRR) and cumulative heat release rate were computed. The combustion analysis revealed that the early rate of pressure rise causes the cylinder pressure to rise early in the case of alternate fuels with a resulting lower rate of pressure rise and peak pressure. However, HRR and cumulative HRR show a maximum for Pongamia–ethanol (50–50) when compared with the neat diesel fuel.     

Effects of ethanol-blended gasoline on air pollutant emissions from motorcycle

The effect of ethanol-gasoline blends on criteria air pollutant emissions was investigated in a four-stroke motorcycle. The ethanol was blended with unleaded gasoline in four percentages (3, 10, 15, and 20% v/v) and controlled at a constant research octane number, RON (95), to accurately represent commercial gasoline. CO, THC, and NOx emissions were evaluated using the Economic Commission for Europe cycle on the chassis dynamometers. The results of the ethanol-gasoline blends were compared to those of commercial unleaded gasoline with methyl tert-butyl ether as the oxygenated additive. In general, the exhaust CO and NOx emissions decreased with increasing oxygen content in fuels. In contrast, ethanol added in the gasoline did not reduce the THC emissions for a constant RON gasoline. The 15% ethanol blend had the highest emission reductions relative to the reference fuel. The high ethanol-gasoline blend ratio (20%) resulted in a less emission reduction than those of low ratio blends (< 15%). This may be attributed to the changes in the combustion conditions in the carburetor engine with 20% ethanol addition. Furthermore, the influence of ethanol-gasoline blends on the reduction of exhaust emissions was observed at different driving modes, especially at 15 km/h cruising speed for CO and THC and acceleration stages for NOx.     

Ignition of Mediterranean Fuel Beds by Several Types of Firebrands

An experimental laboratory study on the probability of ignition and ignition time delay of new fires for 11 pairs of burning embers and fuel beds of species common in Mediterranean forests is presented. For the no wind conditions of the present tests it was found that positive ignition was achieved only for embers with flaming combustion. Fuel bed moisture content was identified as a very important parameter to assess probability of ignition and ignition time delay. In the range of the present tests it was found that ignition depended more on fuel bed properties than on ember characteristics.     

基于CFD的开放空间油池火燃烧速率和热辐射研究

采用混合组分燃烧模型和有限体积辐射模型,通过液体表面蒸发模型对液态燃料和火羽流进行耦合,建立开放空间油池火模型.利用CFD方法分别对不同直径的庚烷油池火进行模拟,研究其燃烧速率、热释放速率随直径的变化以及火焰中轴上的温度和单位体积热释放速率(HRRPUV)分布,并得出油池表面的热辐射反馈以及油池外部水平和垂直方向的热辐射强度分布规律.部分模拟结果与实验进行对比,验证该模型的适用性和有效性.     

Burning behavior of sedan passenger cars

Four full-scale fire experiments using 4-door sedan passenger cars were carried out. The cars were ignited either at the splashguard of the right rear wheel or at the left front seat in the passenger compartment with a gasoline spill. The temperature inside the burning car and the mass loss rate were measured. The burning of the 4-door sedan was composed of three compartmental fires: the engine compartment, the passenger compartment, and the rear part inclusive of the fuel. In the experiments where ignition was initiated at the splashguard, the flame spread in the following order: to the rear part of the car, to the passenger compartment, and to the engine compartment. Breakage of the window glass markedly affected the spread of fire into the passenger compartment. The quantity of gasoline in the fuel tank also affected the speed of spread of the fire, because the gasoline ignited at an early stage of the fire. In the experiment where ignition was initiated in the passenger compartment, the fire gained force after the windshield was broken entirely. The flame spread in the following order: to the passenger compartment, to the engine compartment, and to the rear part of the car. The temperature within the passenger compartment peaked at 1000 °C. The heat release rate (HRR) curves showed several peaks depending on the burning of the three compartments. The HRR increased markedly when the fire spread to several different parts of the car at the same time. The HHR peaked at 3 MW when the passenger compartment and fuel (gasoline) burned simultaneously. The measured HRR curves were characterized by superposition of a Boltzmann curve and a Gaussian curve in order to obtain a model, which allowed us to make a more precise prediction of the fire spread probability from a burning car to nearby structures. The HRRs of burning cars were described by the sum of HRR from each compartment.     

Investigation on the gaseous and particulate emissions of a compression ignition engine fueled with diesel-dimethyl carbonate blends

The effect of dimethyl carbonate (DMC) on the gaseous and particulate emissions of a diesel engine was investigated using Euro V diesel fuel blended with different proportions of DMC. Combustion analysis shows that, with the blended fuel, the ignition delay and the heat release rate in the premixed combustion phase increase, while the total combustion duration and the fuel consumed in the diffusion combustion phase decrease. Compared with diesel fuel, with an increase of DMC in the blended fuel, the brake thermal efficiency is slightly improved but the brake specific fuel consumption increases. On the emission side, CO increases significantly at low engine load but decreases at high engine load while HC decreases slightly. NO_x reduces slightly but the reduction is not statistically significant, while NO₂ increases slightly. Particulate mass and number concentrations decrease upon using the blended fuel while the geometric mean diameter of the particles shifts towards smaller size. Overall speaking, diesel-DMC blends lead to significant improvement in particulate emissions while the impact on CO, HC and NO_x emissions is small.     

掺混比对混煤燃烧特性的影响实验研究

采用热重分析仪,对3种单煤以及不同掺混比(质量比)下两两掺混的混煤进行了热重分析实验。根据实验结果,对不同掺混比混煤的着火温度、可燃特性、稳燃特性、燃尽特性及综合燃烧特性等进行了探讨。按一定比例掺混,可有效改善燃煤的燃烧特性。