Heat Release Rate Data Research Articles

Comparison of results from large-scale and small-scale tunnel experiments

A series of 1:20 small-scale tunnel experiments have been carried out as a scaled down representation of a previously undertaken large-scale heavy goods vehicle (HGV) cargo load tunnel fire experiment. The small-scale tunnel has dimensions of 0.365 m (W) × 0.260 m (H) × 11.9 m (L) and a maximum forced ventilation velocity of 0.68 m/s is adopted corresponding to the velocity of 3 m/s used at large-scale. A gas burner and cribs constructed of medium density fireboard (MDF) have been used as the fuel sources with temperatures, heat release rate (HRR) and velocity data recorded in the small-scale tunnel experiments. A scaled down HRR curve derived from the large-scale experiment was reproduced by the gas burner. Temperatures in the small-scale gas burner experiment can effectively represent those at large-scale during the fire growth and decay stages although measurements at the fully developed stage are lower than the results from the large-scale tunnel experiment. In the small-scale tunnel experiments using the cribs time delays are applied to correct the recorded data in order to obtain the instantaneous HRR. Temperature profile comparisons between the small-scale crib and large-scale HGV cargo load experiments are not applicable since the HRR curves from the crib experiments only approximately reproduce the large-scale HRR profile.

Numerical and optical analysis of heterogeneous gas combustion with diesel pilot ignition in a commercial vehicle engine

A new optical measurement technology and a simulation methodology for supporting the combustion system development of a high-pressure gas-diesel combustion system are presented for the first time. With this combustion system, natural gas is directly injected with high pressure into the combustion chamber near top dead center. The simulation methodology is being validated by comparison with a commercial vehicle single-cylinder metal engine and combustion imaging on a commercial vehicle optical engine with full optical access to the combustion chamber through a contoured piston window. For the optical analysis of the gas-diesel combustion system, a measurement setup for the combined two-dimensional imaging of the OH* chemiluminescence and the soot luminescence is being developed. These images allow the ignition characterization and the cyclic stability of combustion to be analyzed. With the support of the simulation methodology, the nozzle-bowl configuration can be designed with regard to optimum mixture formation and low emissions. A thermodynamic validation of the simulation results shows good agreement of the ignition timing and the following combustion phases with heat release rate data obtained from measurements. Furthermore, the end of engine soot concentrations are captured quantitatively well. A local comparison of optical images and simulation data demonstrates that the simulation is able to capture the gas ignition zones well. The combustion intensity and thus the local soot formation are slightly underpredicted in the center of the gas jets. However, the mixture formation and the overall regions of soot formation are in good agreement with the optical images.

Investigation of the effect of tunnel ventilation on crib fires through small-scale experiments

This paper adopts a series of 1:20 scale tunnel experiments based on a series of large-scale tunnel experiments to study the influence of forced ventilation on fires. The small-scale tunnel has dimensions of 0.365m (W)×0.26m (H)×11.9m (L). Cribs using a wood-based material provide the fuel source and forced ventilation velocities from 0.23 to 1.90m/s are used. From the study of the measured heat release rate (HRR) and mass loss rate data it is found that the forced air velocity affects the fire spread rate and burning efficiency and further affects peak HRR values at different air velocities. A simple model to describe these influences is proposed. This model is used to reproduce the enhancement of peak HRR for cribs with different porosity factors noted by Ingason [1] and to assess the effects of using different length of cribs on peak HRR. The results from these analyses suggest that different porosity fuels result different involvement of burning surface area and result different changes in peak HRR. However, no significant difference to the enhancement on fire size is found when the burning surface area is similar. It is also found that the trend in the enhancement on fire size by using sufficiently long crib and available ventilation conditions matches the predictions of Carvel and Beard [2] for two-lane tunnel heavy goods vehicle fires.

New Development in Flame Retardant Finishing of Cotton Blend Fabrics

Blending cotton with synthetic fibers drastically improved durability for use in protective clothing. Developing new flame retardant finishing technology for cotton blends was critical for producing low cost, durable and high performance fire resistance military protective clothing. In this paper, we discussed the flame retardant finishing of the Nomex/cotton (65/35) blend fabric using a hydroxy-functional organophosphorus oligomer (HFPO) in combination with 1,2,3,4-butane-tetracarboxylic acid (BTCA) as a bonding agent and triethanolamine (TEA) as a reactive co-additive. Because cotton was a highly flammable fiber, the Nomex/cotton blend fabric containing more than 20% cotton required flame-retardant finishing treatment. BTCA reacted with HFPO, cotton and TEA to form BTCA/HFPO/TEA/cotton crosslinked polymeric network, which improved the hydrolysis resistance of HFPO, whereas TEA provided synergistic nitrogen to enhance the performance of HFPO. The Nomex/cotton blend treated with the HFPO/BTCA/TEA system shows high flame retardant performance and excellent laundering durability at relatively low add-on levels. We also discussed the flame retardant finishing of the 50/50 nylon/cotton blend military fabrics using the combination of HFPO and dimethyloldihydroxyethyleneurea (DMDHEU), which formed HFPO/DMDHEU crosslinked networks on both cotton and nylon in the blends. The treated blend fabric passed the vertical burning test after 40-50 launderings cycles with negligible fabric strength loss. The heat release rate data indicated that the nylon and cotton fibers interacted with each other during their thermal decomposition on the blend fabric treated with the HFPO/DMDHEU system.

Effects of stratification on locally lean, near-stoichiometric, and rich iso-octane/air turbulent V-flames

The effects of partial premixing on locally rich, near-stoichiometric, and lean flame regions were investigated in stratified, iso-octane/air turbulent V-flames by varying the mean equivalence ratio gradient along the exit plane of a rectangular slot burner. Instantaneous heat release rate (HRR) images were obtained from the product of spatially registered, near-simultaneously acquired OH and CH2O planar laser induced fluorescence (PLIF) images. HRR data were analyzed within a region of interest (ROI) that was determined from separate 3-pentanone tracer PLIF measurements. The ROI was unique to each gradient flame setting, and was configured to ensure the mean range of equivalence ratios being analyzed was constant among gradient conditions. This allowed distinction of the effects of mean equivalence ratio gradient at the flame front from effects associated with having different ranges of equivalence ratios within the flame zone.Individual flame realizations were studied for differences in the local peak HRR and instantaneous flame thickness δt as they varied with curvature among gradient conditions. While general trends for the fully-premixed cases were consistent with Lewis number theory, subtle changes in the normalized distribution of local peak HRR vs. curvature were observed for locally rich and locally lean flames propagating in different mean ϕ gradients. Negligible changes were observed for near-stoichiometric flames, suggesting that gradient effects may influence the local thermodiffusive stability of off-stoichiometric mixtures more significantly.Ensemble averages of individual peak HRR and δt values within each ROI were separately evaluated, and differences among gradient conditions were greater than those observed for the normalized distributions with curvature. For all flame settings considered, an increase in either of the peak HRR or δt led to a decrease in the other. Gradient effects were observed when comparing back- and front-supported locally rich flames, which experienced opposite changes in peak HRR of +10.1% and −5.2% for gradient settings ∂ϕ/∂y = −0.014 mm−1 and ∂ϕ/∂y = 0.012 mm−1 respectively, coupled with a thinning and thickening of δt of −7.2% and +2.4%. Similar but weaker trends were observed for near-stoichiometric flame regions, with a decrease in peak HRR of up to −3.5% and a thickening up to +2.8% for the steepest gradient ∂ϕ/∂y = 0.029 mm−1. Locally lean flames showed small increases in peak HRR of up to +3.8%, and decreases in δt of up to −2.1% for back-supported gradient case ∂ϕ/∂y = 0.024 mm−1, however, variations were not as significant as those observed for back-supported rich flame regions of equivalent gradients. The presented results show that mean gradients of equivalence ratio can alter the local characteristics of partially premixed flames. Through subtle differences in the local distribution of peak HRR with curvature, more pronounced variations in the magnitude of the mean local peak HRR and δt, and opposing effects in both peak HRR and δt for back- and front-supported rich flames, the data reveal the specific influence of equivalence ratio gradients in experiments where the mean range of equivalence ratios in the analysis region is fixed.

Correlation analysis of heat flux and cone calorimeter test data of commercial flame-retardant ethylene-propylene-diene monomer (EPDM) rubber

The effects of the heat flux on the thermal decomposition of the commercial flame-retardant ethylene-propylene-diene monomer rubber in a cone calorimeter with a piloted ignition were quantitatively investigated. Correlation analysis of the heat flux and various characteristic parameters, including the ignition time, the thermal thickness, the mass loss rate (MLR), the heat release rate (HRR) and the effective heat of combustion, was conducted. It was found that the transformed ignition time (1/t ig)0.55 and 1/t ig, the peak and average MLR, the first and second peak HRR, the HRR in the quasi-steady stage and the average HRR all increased linearly with the heat flux. The thermal thickness (δ P) decreased with the heat flux and was proportional to $$ \rho/\dot{q}^{\prime\prime} $$ . The specimens under the heat fluxes ≤35 kW m−2 behaved as thermally thin solids, while the thermal decomposition behavior of the specimens under the heat fluxes >35 kW m−2 may be characterized employing the thermally thick heating model. The flammability properties including the critical heat flux, the minimum heat flux, the ignition temperature, the heat of gasification and the heat of combustion, which were calculated theoretically based upon the correlations of the ignition time data, the MLR data and the HRR data with the heat flux, were in accordance with the experimental measured values.

Full-Scale Fire Test of an Intercity Train Car

Fire development inside a train car is a topic that has not been studied extensively due to the complexity of the problem and the need for a real train car and the appropriate facilities to conduct these tests in a controlled environment. This paper presents detailed experimental data on fire development inside a real intercity train car. The facility used for the tests is capable of conducting such large-scale fires and measuring the heat release rate using oxygen consumption calorimetry. Thermocouples and plate thermometers were installed inside the train car to provide an insight of the fire development. A number of cameras were also placed inside the car and in the tunnel providing live videos during the test. The peak heat release rate was 32 MW at 1081 s after ignition, and the fire burned 83% of the initial fire load. Flame spread data and recordings of window breaking events are discussed and compared to the heat release rate data. A local flashover-type phenomenon where the fire involved all combustibles at the rear of the car was found to occur.

Numerical simulation of wood crib fire behavior in a confined space using cone calorimeter data

The simulation of wood crib fire behavior in a confined space with fire dynamics simulator (FDS) was presented in this paper, including the heat release rate, flame temperature, central temperature of crib, and oxygen concentration. In the simulation, the cone calorimeter data, such as ignition temperature and heat release rate of wood material measured from cone calorimeter test, were inputted into FDS. Simulations were compared with the results of practical wood crib burning experiments. The simulation results shown that the inputted heat release rate data from cone calorimeter tests obtained with different external heat flux (35–50 kW m−2) had little influence on the simulation results. The heat release rates were in good agreement with the experimental measurement with the biggest difference of 13.9 % in peak value. FDS underestimated the flame temperatures at lower positions about 10 % during the steady state, and the difference between simulation and experiment in flame temperature decreased as the height of measurement position increased. Although there was a big difference in decay phrase, the temperatures in the middle of wood crib were successfully simulated for the overlapped curves during (I) Fast growth stage and (II) Moderate growth stage of burning. The oxygen concentrations were overestimated because the oxygen concentrations measured at the height of 1.8 m in the space were higher than the experimental data with an average difference of 15.5 %. On the whole, an effective way was provided with reasonable results to study the burning characteristics of wood crib fire with numerical simulation.

Effects of Thickness and Ignition Location on Flame Spread Rates in Furniture Calorimeter Tests of Polyurethane Foam

Furniture calorimeter tests of polyurethane foam specimens were conducted to determine the effects of ignition location and specimen thickness on measured flame spread rates. These measurements were made using a new procedure that measured flame areas using infrared video records. Furniture calorimeter tests were conducted using specimens with thicknesses ranging between 2.5 cm and 10 cm, which were ignited in either the centre or on one edge. Flame spread rates increased with foam thickness, and flame spread rates in centre ignition tests were quicker than in edge ignition tests. These flame spread measurements will be used in a model, along with heat release rate data from cone calorimeter tests of the same foam, in order to predict heat release rates in furniture calorimeter tests of polyurethane foam slabs.

An Application Method of Free Burn HRR Data to Room Fire Scenarios

An application method of free burn heat release rate (HRR) data for a single seater sofa to predict the burning behavior in a compartment is proposed. A single seater sofa was burnt in an open environment to measure the HRR using a furniture calorimeter. The time-HRR curve was fitted with a model of burning of a cubic polyurethane block developed earlier. The model included the flame spread over horizontal, downward and lateral directions. The flame spread rates were increased if the block received radiative heat from external heat sources other than from the flame. The thermal radiation feedback from the flame, smoke layer, and heated wall surfaces was coupled with the burning model. Using the coupled model, the burning and spread rate of several sofas and a table in a small compartment was calculated and compared with experimental results. The model could reproduce the trend for the increase in HRR qualitatively. However, the time to spread to an adjacent object was not in good agreement. If the time to spread was given input to the model, other parameters such as compartment temperature and so on could be calculated with reasonable agreement.

Distribution analysis of the fire severity characteristics of single passenger road vehicles using heat release rate data

Fires associated with vehicles have the potential to impact on life safety and property protection. The fire severity characteristics of single passenger vehicle fires are presented in this paper by the total energy released, peak rate of heat release and the time to peak rate of heat release using experimental data collated from the literature. Risk-based fire design can be supported by data presented in a statistical form such that passenger vehicles are categorized by their curb weight and probability distribution curves are obtained for each fire severity characteristic. Analysis of the data shows that the total energy released and the time to peak rate of heat release are generally shown to exhibit an increasing trend with curb weight.

Determination of Heat Release Rate Disturbances in Unconfined Flames Based on Fluctuations in the Travel Time of Ultrasonic Waves

The article presents a new method to measure heat release rate disturbances from flames when optical access is limited. The technique is based on the determination of the travel time of ultrasonic waves propagating through the flow. The link between heat release rate and sound travel time disturbances depends on the configuration considered. An expression is established here for the case of unconfined premixed flames driven by buoyancy forces associated with the Kelvin–Helmholtz instability formed by the interaction between accelerating hot burned gases and cold ambient air at rest. The system and the principle used for the determination of the sound travel time are then presented and validated under nonreacting conditions. Effects of the main parameters on the precision of this detection technique are examined experimentally. Measurements in reacting conditions are compared to heat release rate data obtained with another technique based on the chemiluminescence emission. A good agreement is obtained between both signals for the different cases explored demonstrating the sensitivity of the proposed technique.

Evaluating Models for Predicting Full-Scale Fire Behaviour of Polyurethane Foam Using Cone Calorimeter Data

Two models that can be used to predict full-scale heat release rates of polyurethane foam slabs were evaluated in this study. Predictions were compared with results of furniture calorimeter tests of 10 cm thick polyurethane foam specimens which were ignited in the centre or on the edge. Furniture calorimeter results indicated that peak heat release rates and fire growth rates were higher during centre ignition tests than edge ignition tests. For both situations, the growth phase of the heat release rate curves measured in the full-scale tests was successfully predicted using t2 design fires; the choice of a specific t2 fire depended on the surface area of the specimen and ignition location. A model originally developed during the European Combustion Behaviour of Upholstered Furniture (CBUF) project was also evaluated using heat release rate data from cone calorimeter tests and flame area burning rates measured using infrared video records of the furniture calorimeter tests. This model was able to successfully predict the initial growth phase of the fires and predictions of peak heat release rates were within 17% of measured values. The model had less success in predicting heat release rates later in the growth phase and during the decay phase of the fires, and did not appear to capture all of the physics of the full-scale tests, in particular foam melting and subsequent liquid pool burning. As the model did show promise, future work is planned to address these shortcomings and to develop improved flame spread models for polyurethane foam.

直接噴射PCCI燃焼における混合の進展とNO_x生成量ならびに最大熱発生率との関係に関する基礎研究(熱工学,内燃機関,動力など)

To obtain the strategy for reducing NO_x emissions and pressure rise rate in PCCI-based diesel combustios, a fundamental study was performed on spray combustion with long ignition delays using a constant volume vessel. NO mass in the combustion chamber was measured with a total gas sampling method and heat release rate data were analyzed varing injection pressure, nozzle orifice size, ambient oxygen mole fraction and fuel ignitability. To cralify the fuel-air mixing conditions which provide reduced NO formation and maximum heat release rate, the data are plotted against the fuel mass fraction in a spray at ignition, which is proposed as an index of mixing progress. Based on the results, explanations are given for the difference of the trend between NO mass and maximum heat release rate.

Diesel combustion modelling using LES turbulence model with detailed chemistry

Diesel spray combustion and emissions are modelled in this study using large eddy simulation (LES) turbulence models coupled with spray breakup and detailed chemistry models. The objective of this study is to develop numerical models that can be used to predict the diesel spray combustion process. The LES filtering procedure yields unknown subgrid scale terms that need to be modelled. A one-equation, non-viscosity dynamic structure model is used to model the subgrid stress tensor and the gradient method is used to model the subgrid scalar flux. The model uses a tensor coefficient determined by a dynamic procedure and the sub-grid kinetic energy that is to enforce a budget on the energy flow between the resolved and unresolved scales. A skeletal n-heptane reaction mechanism is used to simulate the diesel fuel chemistry. A reduced NO x mechanism is incorporated into the n-heptane mechanism to simulate NO x formation, and the soot emission process is simulated by a phenomenological model that uses a competing formation and oxidation rate formulation. The present models were validated by comparing predicted results against experimental data of a diesel engine. The predicted and measured cylinder pressure history and heat release rate data are in good agreement. Trends of NO x and soot emissions are also captured with respect to different injection timings and exhaust gas recirculation (EGR) levels. Results indicated that the present models can capture the overall combustion process and can be further developed into a useful tool for engine combustion simulations.

Steady heat release rate by the moment–area method

AbstractA simple mathematical procedure is described for computing temporal averages of heat release rate (HRR) data from the moments and area of the history. The moment–area method was used to calculate average HRRs for over 200 specimens having a wide range of chemical composition and sample thickness tested on a bench‐scale fire calorimeter at various external heat fluxes. The average values of HRR obtained by the moment–area method are essentially independent of sample thickness and are potentially useful for ranking material flammability and determining material combustion properties. Published in 2007 by John Wiley & Sons, Ltd.

An experimental study of the dual-fuel performance of a small compression ignition diesel engine operating with three gaseous fuels

A dual-fuel engine is a compression ignition (CI) engine where the primary gaseous fuel source is premixed with air as it enters the combustion chamber. This homogenous mixture is ignited by a small quantity of diesel, the ‘pilot’, that is injected towards the end of the compression stroke. In the present study, a direct-injection CI engine, was fuelled with three different gaseous fuels: methane, propane, and butane. The engine performance at various gaseous concentrations was recorded at 1500 r/min and quarter, half, and three-quarters relative to full a load of 18.7 kW. In order to investigate the combustion performance, a novel three-zone heat release rate analysis was applied to the data. The resulting heat release rate data are used to aid understanding of the performance characteristics of the engine in dual-fuel mode. Data are presented for the heat release rates, effects of engine load and speed, brake specific energy consumption of the engine, and combustion phasing of the three different primary gaseous fuels. Methane permitted the maximum energy substitution, relative to diesel, and yielded the most significant reductions in CO2. However, propane also had significant reductions in CO2 but had an increased diffusional combustion stage which may lend itself to the modern high-speed direct-injection engine.

Flame Retardation of Ethylene-Vinyl Acetate Copolymer Using Nano Magnesium Hydroxide and Nano Hydrotalcite

The flame-retardant effects of nano magnesium hydroxide (NMH) and nano hydrotalcite (NLDH) in ethylene-vinyl acetate copolymer (EVA) are studied by using the limited oxygen index (LOI), UL-94 test, cone calorimeter test (CCT), thermogravimetric analysis (TGA), laser Raman spectroscopy (LRS), and scanning electron microscopy (SEM). The LOI values of both EVA-NMH and EVA-NLDH blends increase gradually on increasing the NMH and NLDH content, respectively. The LOI value of EVA-NLDH is higher than that of EVA-NMH at the same additive level. In the UL-94 test, for EVA-NMH blend, there are no ratings at all even if the loading of NMH is up to 150 phr (60%). However, the EVA-NLDH blend at the additive level of 120 phr reaches the V-1 rating, and the blend with 150 phr NLDH reaches the V-0 rating. The heat release rate (HRR) data of EVA-NLDH blends are much lower than that of the EVA-NMH blends. From the LOI, UL-94, and HRR data, it can be seen that the flame-retardant effect of NLDH is better than that of NMH. The TG and differential TG (DTG) data show that additives NMH and NLDH increase the thermal stability of the EVA copolymer. The LRS results confirm that the charred layers formed during the burning of the nano EVA blends have a graphite-like structure. The mechanical properties of EVA-NMH blends are better than those of EVA-NLDH blends.

High Throughput Flammability Characterization Using Gradient Heat Flux Fields

Abstract The quest for small-scale flammability tests useful for predicting large-scale fire test performance is an enduring undertaking. Often, this work is motivated by limited access to larger quantities of samples, in the case of materials development efforts, and by the slow turn-around and high cost of large scale flammability testing. Use of Cone calorimeter data such as heat release rate (HRR) and ignition data has been coupled with various models to attempt to predict the performance of materials in medium and large scale fire tests. In some instances this has been successful; however, the extensive amount of data that needs to be acquired has motivated the High Throughput (HT) Flammability program at the National Institute of Standards and Technology (NIST) to develop flammability characterization methods which significantly increase the rate of data generation. The goal is to keep pace with our sample preparation rate, which is a significant challenge since our capability to produce samples, either extruded rod, or gradient coatings, has developed to a rate of one sample per minute! The efforts described here are those specifically focused at developing HT flammability analysis methods. The method of evaluating the flammability of a sample at a variety of fluxes simultaneously involves use of a radiant panel to create a gradient heat flux field. Samples are ignited in the high flux region and burned until they self-extinguish. The local flux at this position is termed the minimum flux for flame spread (MFFS). The same general technique has also been accomplished on a smaller scale using the Cone calorimeter. Here MFFS and HRR can be measured concurrently.

Numerical model of upward flame spread on practical wall materials

The focus of this paper is the development of a thermal, finite difference numerical model to describe one-dimensional upward flame spread on practical wall materials. Practical materials include composite materials and those that char, in addition to clean burning, homogeneous materials. A set of equations used in the model is developed and the methods for obtaining necessary “fire properties” are discussed. Some of the particular features of the model include the use of a correlation for flame heat feedback and the use of an experimentally measured mass loss rate to incorporate the burning characteristics of practical materials. A comparison of the numerical predictions with the experimental results for flame heights and temperatures are shown for Douglas fir particle board. The model correctly predicts trends but underpredicts the flame heights and pyrolysis height in the cases tested. Two additional cases are shown for materials for which experimentally measured heat release rate data are used in place of the mass loss rate data. The flame and pyrolysis height predictions are in much better agreement for these cases. Further efforts to obtain material property data that is appropriate for flame spread modeling is indicated by this work.