Characterization of ignition and combustion characteristics of phenolic fiber-reinforced plastic with different thicknesses

The present study focuses on ignition and combustion characteristics of phenolic fiber-reinforced plastic (FRP) with different thicknesses under different external heat fluxes using cone calorimeter, which receives little attention to date. A series of parameters including ignition time, thermal thickness, mass loss factor, mass loss rate (MLR), heat release rate (HRR), total heat release (THR), fire performance index (FPI) and fire growth index (FGI) are measured or calculated. Results indicate that the ignition time increases with the thickness, but decreases with the external heat flux. Phenolic FRP with thickness of 3 mm may be considered as thermally thin material. However, phenolic FRP with thickness of 5 and 8 mm is prone to be thermally thick material. The critical heat flux, minimum heat flux and ignition temperature are deduced and validated. The thermal thickness increases with the external heat flux. Linear correlations of the thermal thickness with the ratio of specimen density and external heat flux are demonstrated and presented. The mass loss factor decreases with the thickness. Three and two peak MLRs occur in the cases of low and high external heat fluxes, respectively. The average MLR increases with the external heat flux and thickness. The average and maximum HRR increases with the external heat flux. The FGI for the maximum HRR increases with the external heat flux. Linear correlations of the average MLR, the average and maximum HRR and the FGI for the maximum HRR with the external heat flux are demonstrated and presented.

     

Experimental study on combustion characteristics of diesel–hydrogen dual-fuel engine

As a clean and sustainable energy source, hydrogen is widely considered as an engine fuel by top researchers. In view of the fact that the uneven fuel mixture of diesel fuel deteriorated the combustion and emissions process, it is expected to adopt diesel and hydrogen dual-fuel combustion technology to optimize combustion and heat release of diesel engine. In this study, experiments are carried out on a diesel engine and the combustion characteristics of the engine with different hydrogen ratios (RH) are compared. It has been found that hydrogen addition is conducive to accelerate the heat release rate and improve the thermal efficiency. Specifically, compared with pure diesel conditions, the peak pressure increased by 7.7% and the cumulative heat release rate increased by 3.7% under the condition of RH of 20%. Moreover, although the effect on the ignition delay period is not clear, the higher RH brings about earlier heat release center and more cumulative heat release while enhancing the heat release of premixed combustion reducing the diffusion combustion and post-combustion.

     

Evaluate the flammability of a PU foam with double-scale analysis

Two-scale tests, microscale and bench scale, are conducted to analyze the flammability of a flexible polyurethane foam. Microscale tests include simultaneous thermal analysis coupled to Fourier transform infrared spectroscopy, and microscale combustion calorimeter (MCC). Evolved gas components, heat release rate per unit mass, total heat release, derived heat release capacity, and minimum ignition temperature are obtained. Bench scale tests are performed on cone calorimeter. Peak heat release rate per unit area, effective heat of combustion, minimum incident heat flux for ignition, and total heat release per unit area of different incident heat fluxes are obtained. FO-category of the PU foam is estimated by multiple discriminant function analysis based on the results of cone calorimeter test. The relationship between the two-scale tests is analyzed. The minimum ignition temperatures derived from multi heating rate MCC tests are used to predict the time to ignition and compared with the results from cone calorimeter tests. This PU foam is evaluated as a high fire hazard polymer having low heat release capacity, low ignition temperature, and short ignition time.

     

Treated and untreated foam core particleboards with intumescent veneer

The effectiveness of treatments for the surface layer of novel foam core particleboards was evaluated by means of Cone calorimeter tests. Foam core particleboards with variations of surface layer treatment, adhesives, and surface layer thicknesses under similar processing conditions were used to produce the test specimen for the Cone calorimeter tests. Ignitability, heat release rate profile, peak of heat release rate, total heat released, effective heat of combustion, mass loss rate, gaseous emissions, and specific extinction area were measured using the cone irradiance of 50 kW m^?2. Additional analysis of this data provided fuel composition information that could reveal the pyrolysis events of the composite boards. Thermocouples at various depths were used to provide further verification of pyrolysis events. The unprotected foam core panels generally had much higher heat release rates, somewhat higher heat of combustion and much higher smoke production due to the polymeric foam component of tested panels, whereas time to ignition and total heat release were not pronounced from the veneer treated boards. Adding the commercial fire retardant veneer to the face particleboard provided a dramatic improvement to the measured flammability properties. It worked sufficiently well with a 3 mm thick surface layer to improve the predicted flame spread rating of the foam core particleboards.     

热辐射通量对沥青改性PMMA燃烧特性的影响

采用本体聚合法制备沥青改性聚甲基丙烯酸甲酯(PMMA)块体,研究了热辐射通量对其热释放速率平均值、质量损失速率平均值、点燃时间、CO及CO_2产率的影响。结果表明,添加沥青的PMMA点燃后300 s内平均热释放速率由569 kW/m~2降低到了525 kW/m~2,沥青使其燃烧更加平稳;沥青改性PMMA的平均热释放速率、质量损失速率和CO产率与热辐射通量成线性递增关系;点燃时间随着辐射通量的增加而呈指数衰减趋势;CO_2产率在热辐射通量低于40 kW/m~2时基本不变,高于40 kW/m~2时呈线性递增。添加沥青之后PMMA能够平稳燃烧使其可以作为锥形量热仪标准物质候选物,得到的燃烧特性与热辐射通量的函数关系式为其不确定度评估提供了依据。     

Heat release and structural collapse of flexible polyurethane foam

Flexible polyurethane foam used in upholstered furniture remains one of the major fire hazards to date. The heat release rate of burning items made of foam depends strongly on the foam's physical behavior, notably its collapse to a burning liquid that can result in a pool fire. In this contribution, the cone calorimeter was used to study the physical processes and to determine their influence on foam combustion over a range of external heat fluxes. The initial stage of foam collapse can be described as the propagation of a liquid pyrolysis layer through the foam sample. The rate of propagation of the liquid layer was found to depend strongly on the convective heat transfer from the flame, which simultaneously defined and depended on the sample shape. The effective heat of combustion during foam collapse and pool fire was matched to the heat release potential of the components of the foam formulation to deduce which are consumed. The proposed analysis can serve to clarify the mechanism of flame retardant action, as demonstrated for a commercial brominated-phosphorous compound.     

Large‐scale Experimental Study on the Effects of Flooring Materials on Combustion Behavior of Thermoplastics

The effects of flooring materials on the combustion behavior of thermoplastics is investigated. Based on the ISO 9705 fire test setup, an experimental rig was designed. Full‐scale experiments of PP combustion were carried out using five flooring boards, namely gypsum, steel, wood, ceramic tile and PVC. The experimental results indicate that the flooring boards play an important role in the heat release rates of typical thermoplastics combustion. Specifically, the time for the sharp increase of heat release rate is generally later for the flooring boards with larger thermal conductivity, except for the case of PVC. Preliminary analyses suggest that the reason for the exception of PVC is the expansion and carbonization of PVC at high temperature. In addition, experimental results also show that the corresponding peak heat release rate of thermoplastics combustion would be generally smaller for the flooring board with a larger thermal mass, except for the case of gypsum. The primary cause for the exception of gypsum may be the heat absorption by the crystal water released from the gypsum during the burning of hot pool oil.     

Fire hazard assessment on polyurethane sandwich panels for temporary accommodation units

Fire hazard assessment on sandwich panels used for constructing temporary accommodation units (TAUs) is discussed. The requirements imposed by the three responsible local government departments, i.e. Buildings Department, Fire Services Department and Labour Department, are outlined. A typical sandwich panel used for constructing TAUs was assessed by a cone calorimeter. Four radiative heat fluxes of 20, 25, 50 and 65 kW m⁻² were applied to study the sustained ignition time, peak heat release rate, average heat release rates in 60 and 180 s after ignition, total heat release rate, mass loss percentage, total smoke release, carbon monoxide and carbon dioxide yields. From these data, the possibilities of flashover and smoke aspects were studied. Preliminary recommendations on what should be considered in specifying fire tests for new regulations on the use of these sandwich panels are made.     

Fire reaction properties of polystyrene-based nanocomposites using nanosilica and nanoclay as additives in cone calorimeter test

Using nanofiller additives in the polymer matrix to form nanocomposites is a potential way of reducing the flame spread and enhancing flame retardancy of polymeric materials during fire. To understand the fire reaction properties and the relative performance of flame-retardant additives in polymer during well-developed fire, neat polystyrene, polystyrene–silica and polystyrene–nanoclay (MMT) have been tested in a cone calorimeter. The neat polystyrene and the polystyrene nanocomposites have been prepared via an in situ polymerization method. An external heat flux of 50 kW m^?2 was applied in the test, and parameters such as heat release rate, peak heat release rate, time to ignition, smoke toxicity, CO and CO₂ yield have been investigated. Both neat polystyrene and polystyrene nanocomposites have shown the trend of a thermally thick charring polymer in the heat release rate over time data. The nanocomposites had an overall better flame retardancy than the neat polystyrene in terms of lower peak heat release rate, lower average mass loss rate and enhanced char formation. The nanocomposites had also reduced smoke emission with lower CO and CO₂ yield compared to the neat polystyrene. The overall flame retardancy was enhanced as the nanofiller loading was increased for both the nanosilica and MMT nanocomposites.

     

汽油多组分表征燃料简化动力学模型的系统化构建及验证

提出了一套系统化多级机理简化策略,包含基于误差传播的直接关系图法、峰值浓度分析法、线性同分异构体集总法、主组分分析法、温度敏感性分析和产率分析法,并将其应用于汽油四组分表征燃料详细反应机理的简化,构建了适用于HCCI发动机燃烧边界下的简化机理模型,包含149个物种、414个反应。通过与激波管、快速压缩机、增压HCCI发动机实验数据的对比验证表明,新机理可以准确地预测较宽范围条件下的着火滞燃期,在HCCI发动机的单区模型计算中,该机理对缸内燃烧和排放的预测结果是令人满意的。放热率分析表明, R + O₂反应是控制中间温度区放热的关键基元反应,在高压低温下,异辛烷的放热起到决定性作用。添加2-戊烯之后,使得四组分模型相较于三组分模型更为准确,尤其是对于第一阶段着火滞燃期有显著影响,为进一步探索调和燃料组分比例控制HCCI燃烧提供了一条新思路。     

Correlation analysis of cone calorimetry and microscale combustion calorimetry experiments

Flammability studies are conducted to evaluate the behavior of materials exposed to fire. In this study, microscale combustion calorimetry (MCC) and cone calorimetry methods were applied to acquire the flammability characteristics of red and grey extruded polystyrene (XPS) samples. To understand the effect of changes between parameters, Pearson’s correlation coefficient was used to examine their linear relationships. From the research, moderate and weak correlations were recorded between the total heat release rates from both methods for red and grey XPS, respectively. Plotting peak heat release rate against heat release temperature for MCC and ignition temperature for cone test showed that 25, 35 and 50 kW m^?2 incident heat fluxes of the cone test fall within 0.2 K s^?1 and 0.5 K s^?1 heating rates of MCC. Also, all the MCC parameters except char yield and total heat release presented good correlations with the cone calorimetry flammability characteristics. Hence, MCC could be used in conjunction with cone calorimetry to accurately and reliably assess the flammability of materials.

     

Experimental investigation of thermal properties and fire behavior of carbon/epoxy laminate and its foam core sandwich composite

According to structural characteristics, composites are classified as laminated structure and sandwich structure. Carbon/epoxy laminate and foam core sandwich composite are the most commonly used laminate and sandwich structure material in the aircraft industry. The flammability of epoxy resins and foam core material is an inherent hazard. Many previous studies focused primarily on their mechanical properties, while the studies on the thermal and fire properties of carbon/epoxy laminate and its foam core sandwich composite have rarely conducted. Therefore, to characterize their thermal and fire properties, a comprehensive experimental investigation and theoretical analysis were carried out in this work using thermogravimetric analysis, cone calorimeter, vertical/horizontal burning tests, limiting oxygen index and scanning electron microscope tests. Several typical characteristic parameters were obtained and analyzed, such as pyrolysis temperature, heat release rate, mass loss, flaming spread rate and limiting oxygen index. These experimental data coupled with theoretical analysis can provide support for fire risk assessment and fire protection design in aircrafts. The carbon/epoxy laminate and foam core sandwich composite are both characterized as the thermally thick materials. The ignition models and mass loss rate models were obtained. Foam core material negatively affects most of the thermal and fire properties of sandwich composite, but the foam core sandwich composite has self-extinguishing behavior during horizontal burning tests, whose LOI is higher than that of carbon/epoxy laminate. Thus, an important conclusion was reached that the ignition position and flame spread direction have critical effect on the fire behavior of foam core material.

     

Mechanical, thermal, and fire properties of polylactide/starch blend/clay composites

Polylactide (PLA)/starch blend/clay and PLA/clay composites are prepared by melt blending. Structural and thermal characterizations are performed by differential scanning calorimetry, X-ray diffraction analysis, and thermogravimetric analysis. The fire properties are assessed on a dual cone calorimeter. Combustion residue and char formation is characterized by optical microscopy and attenuated total reflection infrared spectroscopy. Although the clay is not fully intercalated/exfoliated, the composites exhibit a higher thermal stability and much reduced peak heat release rate, and the PLA/starch blend composite retains its mechanical properties. For the PLA/starch blend composite, smoke release is also considerably reduced. Catalyzed, oxidative decomposition is shown to occur early in the thermal decomposition of the composites, prior to increased thermal stability. The inclusion of clay promotes char formation and increases the quantity of carbonaceous char in the combustion residue. There is minimal migration of the clay to the surface prior to ignition and char is formed mainly after ignition and during burning. During the later stages of burning some of the char formed is converted to CO₂.     

Experimental study on suppressing PVC fire with water mist in a confined space

In this paper, the effect of water mist on PVC fires in a confined space under different external radiant heat fluxes has been studied and the re-ignition of the PVC fires was analyzed. Water mist was generated by a single pressure nozzle. Spatially resolved information on droplet size and velocity distributions of the fine water mist was measured by LDV/APV system. The heat release rate, oxygen, carbon monoxide concentrations and other important parameters of the interaction under various conditions were measured by cone calorimeter. The experimental study illustrated that water mist would suppress the PVC fire mainly by flame cooling and fuel surface cooling. When the fire was extinguished, water mist was shut off and fire would re-ignite after a period of time. The re-ignition time depends on the total quantity of water mist.     

F-T柴油在直喷式柴油机中燃烧与排放特性的研究

煤通过Fischer-Tropsch (F-T)合成可得到十六烷值高、硫和芳香烃质量分数极低的F-T柴油。研究分析了未作改动的单缸直喷式柴油机燃用F-T柴油时的燃烧和排放特性。结果表明,与燃用0号柴油相比,燃用F-T柴油时的滞燃期平均缩短18.7%,预混燃烧放热峰值降低26.8%,扩散燃烧放热峰值较高,燃烧持续期相当。燃用F-T柴油时的最高燃烧压力略低,最大压力升高率显著下降,机械损失和燃烧噪音较小,燃油消耗率和热效率都得到显著改善。燃用F-T柴油可同时降低CO、HC、NOx和炭烟排放,其中NOx和炭烟分别平均降低16.7%和40.3%。研究表明,F-T柴油是柴油机良好的清洁代用燃料。     

Investigation on effects of thickness on ignition characteristics and combustion process of the oil-impregnated transformer insulating paperboard

Effects of thickness on ignition characteristics and combustion process of the oil-impregnated transformer insulating paperboard were investigated experimentally by cone calorimeter. Five thicknesses of transformer insulating paperboard, including 0.5, 1.0, 1.5, 2.0 and 3.0 mm were taken into account together with five radiation intensities between 25 and 80 kW m^?2. According to the experimental results on ignition characteristics, the 0.5-mm paperboard for all radiation intensities and the 1.0-mm paperboard with the radiation heat flux less than 35 kW m^?2 were thermal thin material. The 1.0-mm paperboard under higher radiation intensities and the paperboard with the thicknesses of 1.5, 2.0 and 3.0 mm were thermal thick material. The heat release rate (HRR) of oil-impregnated transformer insulating paperboard decreased with its thickness. Due to the different pyrolysis processes, the number of HRR peaks increased with the thickness of paperboard. The CO and CO₂ production rate and the O₂ consumption rate were all decreased with the paperboard thickness basically. There was an increase in the CO production rate at the end of fire duration, since the incomplete combustion process occurred at this stage. The increase in the CO production rate was more obvious in the experiments under lower external radiation heat fluxes.     

Burning of thermally thin polyethylene mixtures

The burning of polyethylene in the mixture with aluminium hydroxide, aluminium oxide, cellulose and Irganox 1010 has been examined by cone calorimeter under non-standard sizes of the sample. The time to ignition of pure polyethylene decreases with decreasing initial amount of polyethylene powder. The subtraction of the mass of water released from the total mass lost for polyethylene with aluminium hydroxide give the same values of effective heats of combustion as for pure polyethylene up to the load about 50 mass% of aluminium hydroxide. The mean heats of combustion determined from the cone calorimeter software are higher than those determined from the total oxygen consumed and mass lost multiplied by the factor 13.1. The additivity rule was found for effective heat of combustion and total smoke released for polyethylene with cellulose. The free radical scavenger Irganox 1010 does not show a significant effect on the flammability of polyethylene except for the increase of the total smoke released. The equation describing the heat release rate evolution in time has been proposed showing a good fit to the experimental runs.     

Cetane number and thermal properties of vegetable oil,biodiesel, 1-butanol and diesel blends

Vegetable oil derived fuels for diesel engines are becoming important as alternative to petroleum diesel fuels due to their environmental friendliness and availability. Ignition quality in compression ignition (CI) engines is influenced by thermal characteristics and fuel properties. In this study, the effects of vegetable oil transesterification and vegetable oil–1-butanol-diesel blends on fuel properties, cetane number (CN) and thermal characteristics were experimentally investigated. Methyl esters (biodiesel) and 10% vegetable oil–10% 1-butanol–80% diesel blends were prepared from croton oil (CRO), coconut oil (COO) and jatropha oil (JAO). CN was measured in a CFR F-5 engine, and a thermogravimetric analysis (TG), as well as the determination of fuel properties of vegetable oils, biodiesels and blends was carried out. It can be observed for vegetable oils that they possess low volatility characteristics, low CN and high viscosity different from those of biodiesels, blends and diesel fuel. It was observed that biodiesels and blends exhibit similarities with diesel in the fuel characteristics, CN and TG curves.     

Fire behaviors study on 18650 batteries pack using a cone-calorimeter

To investigate the effects of different state of charges (SOCs), external heating powers and charging/discharging treatment on the fire behaviors of 18650 batteries pack, three groups of abuse experiments were conducted with the help of a cone-calorimeter. The fire hazards of batteries pack were characterized by measuring the flame photographs, battery surface temperature, ignition time, thermal runaway time, heat release rate and radiative heat flux. According to the results, it is found that the fire behaviors of batteries pack will appear in advance and behave more violent with the increase in SOC. Additionally, the higher heating power will exacerbate the fire hazards of batteries pack by increasing the surface temperature rise rate, the total heat released and the total heat flux of pack leading to an earlier thermal runaway and more rigorous consequence. Finally, the pack with discharging/charging treatment has a much lower heat released compared to the pack without any treatment due to the incomplete burning and incomplete release of energy. Besides, their fire behaviors also exhibit earlier and severer.

     

Numerical study of the laminar flame propagation in ethane-air mixtures

The structure of premixed free one-dimensional laminar ethane-air flames was investigated by means of numerical simulations performed with a detailed mechanism (GRI-Mech version 3.0) by means of COSILAB package. The work provides data on ethane-air mixtures with a wide range of concentrations ([C₂H₆] = 3.0–9.5 vol.%) at initial temperatures between 300 and 550 K and initial pressures between 1 and 10 bar. The simulations deliver the laminar burning velocities and the profiles of temperature, chemical species concentrations and heat release rate across the flame front. The predicted burning velocities match well the burning velocities measured in various conditions, reported in literature. The influence of initial concentration, pressure and temperature of ethane-air mixtures on maximum flame temperature, heat release rate, flame thickness and peak concentrations of main reaction intermediates is examined and discussed.