Heat Release Rate Measurements Research Articles

CFD Investigation of Large Scale Pallet Stack Fires in Tunnels Protected by Water Mist Systems

A series of full-scale fire suppression tests was conducted at the San Pedro de Anes test tunnel facility near Gijon, Asturias, Spain in February 2006. The fuel was wooden pallets or a mixed load of wood and high density polyethylene pallets. Fire protection was provided by water mist systems in different configurations. Because of facility restrictions, some scenarios of great interest, such as a free burn fire, could not be investigated. However, in order to complement the experimental results, a number of computational fluid dynamics simulations were conducted on a 140 m section of the tunnel facility. The Fire Dynamics Simulator, version 4, was used for the numerical investigation. An algorithm was developed to allow the fire to spread along the top of a series of pallet loads in such a way that the measured heat release rate was reproduced. Verification and validation studies confirmed that the model predicted the measured ventilation speeds and peak temperatures. The agreement between the simulations and the field measurements was very good prior to activation of the water mist. Back-layering was modeled well. After activation of the mist, the simulations predicted a large drop in gas temperatures, and retreat of the back-layer, but under-predicted the thermal cooling by the water mist downstream of the fire. With the suppression system, high temperatures and heat fluxes were limited to the immediate vicinity of the burning pallets. The model was then used to simulate a free burn fire in the tunnel. The simulation demonstrated the catastrophic conditions created by an unsuppressed fire in a tunnel when compared against the thermally managed conditions under suppressed conditions.

Development of a Standard Flammability Test for Water-Based Hydraulic Fluids

Abstract This paper is a review of the development of a standard flammability test method for hydraulic fluids since the 1970s. Over the past years, the test methodology for qualifying hydraulic fluids has been transformed from a qualitative assessment to a quantitative and model based assessment. The present standard test method deals with the calorimetric measurement of heat release rate of a highly atomized spray fire, fire point temperature measurement, and the determination of adiabatic flame temperature utilizing an existing NASA Combustion Equilibrium and Application Code. In this paper, we have emphasized on the detailed development of evaluating water-based hydraulic fluids.

Mitigation of thermoacoustic instability utilizing steady air injection near the flame anchoring zone

The objective of this work is to investigate the effectiveness of steady air injection near the flame anchoring zone in suppressing thermoacoustic instabilities driven by flame–vortex interaction mechanism. We perform a systematic experimental study which involves using two different configurations of air injection in an atmospheric pressure backward-facing step combustor. The first configuration utilizes a row of micro-diameter holes allowing for air injection in the cross-stream direction just upstream of the step. The second configuration utilizes an array of micro-diameter holes located on the face of the step, allowing for air injection in the streamwise direction. The effects of each of these configurations are analyzed to determine which one is more effective in suppressing thermoacoustic instabilities at different operating conditions. The tests are conducted while varying the equivalence ratio and the inlet temperature. The secondary air temperature is always the same as the inlet temperature. We used pure propane or propane/hydrogen mixtures as fuels. Combustion dynamics are explored through simultaneous pressure and heat release-rate measurements, and high-speed video images. When the equivalence ratio of the reactant mixture is high, it causes the flame to flashback towards the inlet channel. When air is injected in the cross-stream direction, the flame anchors slightly upstream of the step, which suppresses the instability. When air is injected in the streamwise direction near the edge of step, thermoacoustic instability could be eliminated at an optimum secondary air flow rate, which depends on the operating conditions. When effective, the streamwise air injection prevents the shedding of an unsteady vortex, thus eliminating the flame–vortex interaction mechanism and resulting in a compact, stable flame to form near the step.

Investigation of the flammability of different textile fabrics using micro-scale combustion calorimetry

Evaluating and analyzing the performance of flame retardant (FR) textiles are a critical part of research and development of new FR textiles products by the industry. The testing methods currently used in the industry have significant limitations. Most analytical and testing techniques are not able to measure heat release rate (HRR), the single most important parameter in evaluating the fire hazard of materials. It is difficult to measure HRR of textile fabrics using cone calorimetry because textile fabrics are dimensionally thin samples. The recently developed micro-scale combustion calorimetry (MCC) is able to measure the following flammability parameters for textile using milligram sample sizes: heat release capacity, HRR, temperature at peak heat release rate (PHRR), total heat release and char yield. In this research, we applied MCC to evaluate the flammability of different textile fabrics including cotton, rayon, cellulose acetate, silk, nylon, polyester, polypropylene, acrylic fibers, Nomex and Kevlar. We also studied the cotton fabrics treated with different flame retardants. We found that MCC is able to differentiate small differences in flammability of textile materials treated with flame retardants. We were also be able to calculate the limiting oxygen index (LOI) using the thermal combustion properties of various textile samples measured by the MCC. The calculated LOI data have yielded good agreement with experimental LOI results. Thus, we conclude that MCC is an effective new analytical technique for measuring textile flammability and has great potentials in the research and development of new flame retardants for textiles.

The impact of equivalence ratio oscillations on combustion dynamics in a backward-facing step combustor

The combustion dynamics of propane–air flames are investigated in an atmospheric pressure, atmospheric inlet temperature, lean, premixed backward-facing step combustor. We modify the location of the fuel injector to examine the impact of equivalence ratio oscillations arriving at the flame on the combustion dynamics. Simultaneous pressure, velocity, heat-release rate and equivalence ratio measurements and high-speed video from the experiments are used to identify and characterize several distinct operating modes. When the fuel is injected far upstream from the step, the equivalence ratio arriving at the flame is steady and the combustion dynamics are controlled only by flame–vortex interactions. In this case, different dynamic regimes are observed depending on the operating parameters. When the fuel is injected close to the step, the equivalence ratio arriving at the flame exhibits oscillations. In the presence of equivalence ratio oscillations, the measured sound pressure level is significant across the entire range of lean mean equivalence ratios even if the equivalence ratio oscillations arriving at the flame are out-of-phase with the pressure oscillations. The combustion dynamics are governed primarily by the flame–vortex interactions, while the equivalence ratio oscillations have secondary effects. The equivalence ratio oscillations could generate variations in the combustion dynamics in each cycle under some operating conditions, destabilize the flame at the entire range of the lean equivalence ratios, and increase the value of the mean equivalence ratio at the lean blowout limit.

Flame–vortex interaction driven combustion dynamics in a backward-facing step combustor

The combustion dynamics of propane–hydrogen mixtures are investigated in an atmospheric pressure, lean, premixed backward-facing step combustor. We systematically vary the equivalence ratio, inlet temperature and fuel composition to determine the stability map of the combustor. Simultaneous pressure, velocity, heat release rate and equivalence ratio measurements and high-speed video from the experiments are used to identify and characterize several distinct operating modes. When fuel is injected far upstream from the step, the equivalence ratio entering the flame is temporally and spatially uniform, and the combustion dynamics are governed only by flame–vortex interactions. Four distinct dynamic regimes are observed depending on the operating parameters. At high but lean equivalence ratios, the flame is unstable and oscillates strongly as it is wrapped around the large unsteady wake vortex. At intermediate equivalence ratios, weakly oscillating quasi-stable flames are observed. Near the lean blowout limit, long stable flames extending from the corner of the step are formed. At atmospheric inlet temperature, the unstable mode resonates at the 1/4 wavemode of the combustor. As the inlet temperature is increased, the 5/4 wavemode of the combustor is excited at high but lean equivalence ratios, forming the high-frequency unstable flames. Higher hydrogen concentration in the fuel and higher inlet temperatures reduce the equivalence ratios at which the transitions between regimes are observed. We plot combustion dynamics maps or the response curves, that is the overall sound pressure level as a function of the equivalence ratio, for different operating conditions. We demonstrate that numerical results of strained premixed flames can be used to collapse the response curves describing the transitions among the dynamic modes onto a function of the heat release rate parameter alone, rather than a function dependent on the equivalence ratio, inlet temperature and fuel composition separately. We formulate a theory for predicting the critical values of the heat release parameter at which quasi-stable to unstable and unstable to high-frequency unstable modes take place.

CH∗ chemiluminescence modeling for combustion diagnostics

CH∗ chemiluminescence is often employed in combustion diagnostics, for example as a measure of heat release rate and for equivalence ratio sensing. However, most interpretations of CH∗ chemiluminescence rely either on heuristic arguments or empirical data gathered under limited conditions. More rigorous analysis is required to understand the effects of combustion conditions, e.g., pressure, reactant composition and preheat, strain and exhaust gas recirculation, on CH∗ chemiluminescence. Chemiluminescence modeling holds promise in this regard. The predictive accuracy of four proposed CH∗ chemiluminescence formation models were experimentally tested in premixed, methane–air and prevaporized Jet-A–air flames. Two of the models, based on CH∗ formation via reactions between C2H and O or O2, are able to predict the experimental data within the experimental uncertainty, in both room temperature methane and preheated Jet-A flames. The utility of CH∗ chemiluminescence for sensing heat release rate and equivalence ratio (ϕ), when combined with OH∗ chemiluminescence, is then analyzed in methane flames for varying pressure, preheat temperature and strain. The CH∗/OH∗ chemiluminescence ratio is found to be useful for sensing equivalence ratio in lean methane systems, but only at certain pressure and reactant temperature conditions. The relationship between CH∗ chemiluminescence and heat release varies with ϕ, pressure, temperature and strain. At high pressures, however, the dependence on ϕ and strain are small, making CH∗ attractive for heat release sensing applications in gas turbine combustors.

Comments to the Paper Uncertainty of Heat Release Rate Calculation of the ISO5660-1 Cone Calorimeter Standard Test Method

In a paper in this Journal by Enright and Fleischmann [1] some years ago, the authors gave an interesting presentation of the uncertainty associated with the measurement of heat release rate (HRR) for the Cone Calorimeter. This paper which is a major contribution on the subject was a first attempt at analytical quantification of uncertainty due to instrument and calculation assumptions. In order to illustrate the uncertainty calculation, data from the cone calorimeter were used. The sample tested was an upholstered furniture composite. It has been shown that the greatest component uncertainties can be attributed to the assumed effective heat of combustion E, the assumed stoichiometric expansion factor b and the measured oxygen concentration. They concluded among others that the heat release rate uncertainty is very strongly coupled with any assumed stoichiometric expansion factor b at lower heat release rate values. They showed that b contributes significantly to the relative uncertainty of the HRR calculation at low HRR levels; see Fig. 3 of the paper [1], p. 165: component uncertainty history for the stoichiometric expansion factor. However, a mistake seems to have been made in the calculation of this component uncertainty. At low HRR levels, the contribution of the stoichiometric expansion factor b on the HRR uncertainty should be negligible and not ‘‘significant’’. In order to illustrate this statement let us recall that the HRR is proportional to the mass flow rate of the incoming air which can be related to the mass flow rate of the exhaust gases according to the following equation: _ me Me ¼ð 1 � /Þ _ ma Ma þ a/

A guide to characterizing heat release rate measurement uncertainty for full‐scale fire tests

AbstractAccurate heat release rate measurements provide essential information to defining the fire safety characteristics of products. The size, complexity, and cost of full‐scale fire tests make achieving accurate and quantitative results a serious challenge. A detailed uncertainty analysis of a large‐scale heat release rate measurement facility is presented as a guide to the process of estimating the uncertainty of similar facilities. Quantitative heat release rate measurements of full‐scale fires up to 2.7 MW were conducted using the principle of oxygen consumption calorimetry. Uncertainty estimates were also computed for the heat input measurements from a well‐controlled natural gas burner. The measurements of heat input and heat release rate were performed independently, and the discrepancy between the two was well within the uncertainty limits. The propagation of uncertainty was performed at the level of voltage and temperature measurements, which avoided using mutually dependent measurement parameters. Reasons for the significant contribution to the combined uncertainty from the oxygen concentration and exhaust flow measurements are demonstrated. Also presented is a first‐order effort to account for the uncertainty due to factors in full‐scale fire tests such as operator error and environmental influences that are not modeled by the heat release rate equation. Published in 2008 by John Wiley & Sons, Ltd.

The analysis of research results concerning heat release rates of ship materials with regard to dynamic parameters of the research station

The analysis of research results concerning heat release rates of ship materials with regard to dynamic parameters of the research stationBased on the results of author's research it was stated that significant differences between heat release rates measured according to ISO 5660-1 and FTP Code Part 5 (Res. A. 653 (16)) are not caused by measurement uncertainties. A basic factor determining the lack of correlation is treating the heat release rate in the category of static measurements in the normalized measurement methods. Taking into account dynamic parameters of the test station allowed the coincidence rate (reproducibility and correlation) of the results of heat release rates measured using different methods to be improved, without changing test stations and procedures. Author's research performed on 42 materials has revealed that the relative dynamic errors of the heat release rate measurements are significant (2%÷120%). The average value of these changes for the tested group of materials was equal to 39%.

Assessment of Commodity Classification for Sprinkler Protection Using Representative Fuels

In order to assess the classification of commodities for sprinkler protection, fire suppression tests were conducted using representative fuels. The measured heat release rates and applied water fluxes are used to calculate the critical delivered flux (CDF) and develop a suppression correlation for each tested commodity. The heat release rate (HRR) measurements together with the CDF calculations show that the CDF can be obtained within an uncertainty of ±3 mm/min. The CDF values are then combined with the measured convective HRR to project the critical sprinkler discharge flux (SDF) – the minimum water flux above which the fire will be controlled. Comparison of SDF values and full-scale sprinkler test results shows that the SDF is a reasonable choice for ranking commodities. Examination of the calculated CDF values using the suppression correlations suggests that the ranking remains the same for various fuel array heights. Furthermore, the responses to suppression by the exposed plastics are very different from those of the cartoned fuels, indicating that these two types of commodities require different treatment.

The Effect of Fuel Quantity and Location on Small Enclosure Fires

Results from an experimental program undertaken to study the effect of fuel quantity and location on ethanol pool fires in the open and in a small enclosure (an ISO 9705 room) are compared with simulations using the Fire Dynamics Simulator version 4.03 (FDS4). The fuel in trays is placed at three locations (front, back, and center) within the room enclosure as well as directly under the calorimeter hood. The measured heat release rate (HRR) is found to vary substantially when a fuel package consisting of different quantities of ethanol is placed at different locations within the room. Instead of prescribing this HRR into the FDS simulation, these experimental results are compared with HRR predictions obtained using the FDS4 combustion model. The comparison reveals that there are significant and variable differences between the experimental results and the FDS4 predictions in contrast to simulations where the HRR is prescribed.

Test of total heat flux from wood crib fire in and outside compartment

Woo d crib fires were studied by using of ISO 9705 Room. These free burning tests with different heat release rate were conducted inside room and outside room (under the hood). Thermal condition around crib fire was measured by using of thermocouples, total heat flux gauge, gas concentration analyzer, and standard instrumentations for heat release rate measurement in ISO 9705 Room. This paper focuses on the total heat flux to the surrounding area from wood crib fire. The correlation between heat release rate and total heat flux is presented. Wall and space effect is also analyzed.

Heat release rate measurements of thin samples in the OSU apparatus and the cone calorimeter

The Ohio State University (OSU) apparatus and the cone calorimeter are two devices commonly used to measure the heat release rate (HRR) of materials and products in forced flaming combustion. Each operates on a different principle but is calibrated in the same way. However, HRR results from these two test methods do not agree in most cases. For the present study, the OSU was modified to measure oxygen consumption and sensible enthalpy (temperature rise) of the apparatus in addition to the usual sensible enthalpy of the exhaust gases during the test. After calibration, total sensible heat (exhaust gases+apparatus) and oxygen consumption methods gave similar results for thin samples in the OSU. However, OSU results for thin samples did not agree with results from the cone calorimeter (ASTM 1354/ISO 1556) unless the HRR history in the cone calorimeter was corrected for smearing that results from dilution of the combustion gases with air in the sample chamber, exhaust duct, and scrubbers and the response time of the oxygen analyzer.

Spatially resolved heat release rate measurements in turbulent premixed flames

Heat release rate is a fundamental property of great importance for the theoretical and experimental elucidation of unsteady flame behaviors such as combustion noise, combustion instabilities, and pulsed combustion. Investigations of such thermoacoustic interactions require a reliable indicator of heat release rate capable of resolving spatial structures in turbulent flames. Traditionally, heat release rate has been estimated via OH or CH radical chemiluminescence; however, chemiluminescence suffers from being a line-of-sight technique with limited capability for resolving small-scale structures. In this paper, we report spatially resolved two-dimensional measurements of a quantity closely related to heat release rate. The diagnostic technique uses simultaneous OH and CH 2O planar laser-induced fluorescence (PLIF), and the pixel-by-pixel product of the OH and CH 2O PLIF signals has previously been shown to correlate well with local heat release rates. Results from this diagnostic technique, which we refer to as heat release rate imaging (HR imaging), are compared with traditional OH chemiluminescence measurements in several flames. Studies were performed in lean premixed ethylene flames stabilized between opposed jets and with a bluff body. Correlations between bulk strain rates and local heat release rates were obtained and the effects of curvature on heat release rate were investigated. The results show that the heat release rate tends to increase with increasing negative curvature for the flames investigated for which Lewis numbers are greater than unity. This correlation becomes more pronounced as the flame gets closer to global extinction.

Uncertainty analysis of heat release rate measurement from oxygen consumption calorimetry

AbstractOxygen consumption calorimetry remains the most widespread method for the measurement of the heat release rate from experimental fire tests. In a first step, this paper examines by theoretical analysis the uncertainty associated with this measurement, especially when CO and soot corrections are applied. Application of theoretical equations is presented for chlorobenzene which leads to high values of CO and soot yields. It appears that the uncertainty of CO and soot corrections are high when the fuel composition is unknown. In a second step, a theoretical analysis is provided when the simplest measurement procedure is used for oxygen consumption calorimetry. The overall uncertainty can be dominated either by the uncertainty associated with the oxygen concentration, the assumed heat of combustion, the fumes mass flow rate or the assumed combustion expansion factor depending on the oxygen depletion. Copyright © 2005 John Wiley & Sons, Ltd.

Acoustic Considerations Regarding Pulsations During Large-scale Fire Tests In A Tunnel

Large-scale fire tests have been carried out with Heavy Goods Vehicle (HGV) cargos in the Runehamar tunnel in Norway. During two of the fire tests, large pulsations of the gas flow inside the tunnel occurred. These pulsations were registered only when the measured heat release rates (HRR) were higher than 125 MW - 135 MW. Two different periods of the pulsations were registered, short periods of about 4 s and longer periods of approximately 18 s. In the article, the pulsations are presented and some plausible explanations are given, using an acoustic approach. There are several factors that can affect the pulsations, e.g., the size of the experimental set-up, the size of the fire, the thermal expansion at the site of the fire, the slope of the tunnel, the wind outside the tunnel, etc., but the calculations show that the oscillation periods are properties of the system, and can be what is referred to as thermoacoustic instabilities.

Local measurements of the time-dependent heat release rate and equivalence ratio using chemiluminescent emission from a flame

Chemiluminescent emissions from OH ⋅ , CH ⋅ , and C ⋅ 2 and continuous emissions from CO ⋅ 2 have been measured in natural-gas-fuelled, premixed, counterflow flames operating with an equivalence ratio between 0.7 and 1.3 and strain rates between 80 and 400 s −1, achieved by varying the exit velocity of the jet between 1 and 5 m s −1. Cassegrain receiving optics coupled to a high-performance spectroscopic unit allowed local, temporally resolved measurements of intensity of chemiluminescence in flat flames, which were compared with measurements along a line of sight obtained from flame spectra. This study allowed independent evaluation of the effects of strain rate and equivalence ratio on intensity of chemiluminescence and the ability of intensity of chemiluminescence to indicate heat release rate. Results suggest that intensities of chemiluminescence from OH ⋅ and CH ⋅ and background intensity from CO ⋅ 2 are good indicators of heat release rate, whereas that from C ⋅ 2 is not. The study also evaluated the ability to measure equivalence ratio of the reacting mixture using intensity of chemiluminescence and found that the intensity ratio OH ⋅ /CH ⋅ has a monotonic decrease with equivalence ratio for lean and stoichiometric mixtures, while remaining independent of flame strain rate. The results indicate that the intensity ratio OH ⋅ /CH ⋅ can measure with uncertainties of 5% the equivalence ratio up to values of 1.1 and with uncertainties of 20% for richer mixtures due to the low sensitivity of the intensity ratio OH ⋅ /CH ⋅ for rich mixtures. The intensity ratios of C ⋅ 2/OH ⋅ and C ⋅ 2/CH ⋅ have a non-monotonic dependence on equivalence ratio and a dependence on strain rate and are thus not suitable for measurements of equivalence ratio. An approach to measuring the time-dependent equivalence ratio of the reacting mixture is suggested and data processing methods and associated uncertainties are presented. The potential of the technique for local measurements in practical burners is discussed and further evaluation of the spatial resolution is required in such flames. However, suggestions have been provided on how the spatial resolution can be improved in practical flames.

Estimation of heat release rate for polymer–filler composites by cone calorimetry

Effects of endothermic behaviour of typical flame retardant fillers on the heat release rate measurement using the cone calorimeter have been studied. It was found that without appropriate corrections, the heat release rate measured by the cone calorimeter for the polymer composites containing large quantities of endothermic fillers would be overestimated. Some typical materials have been studied quantitatively, including alumina trihydrate and magnesium hydroxide added in three different polymers. The theoretical calculations show that for alumina trihydrate at 70 wt% loading level, the total heat released from the polypropylene based composite would be 6.5% less than that for the composite without the corrections, 11.2% less for the PMMA based composite and 17.0% less for the plasticised polyvinyl chloride (PVC) based composite. For magnesium hydroxide at the filler loading level of 70 wt%, the total heat released for the polypropylene based composite would be 7.7% less, for the PMMA based composite 13.4% less and for the plasticised PVC based composite 20.3% less. A procedure for correcting the heat release rate measured by the cone calorimeter is put forward in the paper, which uses the decomposition heat of the fillers to modify the effective heat of combustion measured for the composites and then multiply the modified effective heat of combustion by the mass loss rates measured for the composites to re-calculate the heat release rates, giving a more accurate measurement. Also, the heat release rates corrected by the proposed method and the heat release rates initially measured by the cone calorimeter for the polypropylene–alumina trihydrate composite were compared, demonstrating the necessity and significance of the corrections.

A New Test Method For Rating Materials As Noncombustible

Several test methods commonly employed to rate the combustibility of materials are evaluated and compared to criteria for the stability of flaming combustion in the fire science literature. These science-based criteria are then used to analyze measurements and visual observations obtained when four prototype “noncombustible” materials are tested in the Fire Propagation Apparatus (ASTM E 2058). Based on this analysis, it is proposed that observation of the presence of flame and measurement of heat release rate at an applied heat flux of 50 kW/m2 and an inflow oxygen concentration of 40% can be used to determine whether a material should be rated as “noncombustible.