Heat Release Curves Research Articles

Kinetic Analysis via Microwave Dielectric Measurements

In the chemical industry, a key step for the assessment of thermal risk and runaway is the identification of autocatalytic reactions. In this field, many estimation methods based on dynamic differential scanning calorimetry (DSC) measurements have been developed. As a rule, a screening of the most hazardous chemicals is conducted. In the first step, the measured heat release curve from dynamic DSC gives the apparent activation energy level. In the second step, the characteristic behaviour of a possible autocatalytic decomposition is pointed out with an isothermal DSC measurement. Unfortunately, when an endothermic process precedes the exothermic decomposition, identification is rather difficult or even impossible. A new method based on microwave dielectric measurements of chemicals has been developed. This method consists of a preliminary recording of the initial reactants and final product dielectric properties. Then the normalized extent of a chemical process is determined from the behaviour of its complex permittivity. As an illustration, the thermal decomposition of a well known curing agent, 2,2’-azobis-isobutyronitrile is studied.

２ストローク低速ディーゼル機関の熱発生率波形の解析（第２報 燃焼経過の推定）

The purpose of this paper is to estimate the combustion process in two-stroke slow-speed diesel engines with side fuel injection type for marine use. The rate of heat release data is generally utilized as an indication of diesel combustion process. In the first report, the characteristics of the rate of heat release obtained from the cylinder pressure data in the test engine were discussed. In this paper, the combustion process which can be induced directly from the analyzed data of the rate of heat release curve, were estimated. As a result, it is found that the combustion rate decreases when the fuel spray arrives at a certain circumferential angle, which almost corresponds to the position of the next nozzle. Also, the rate of heat release curve shows double peaks in such case that combustion suspended period due to interference of the combustion gas from the nozzle at upstream side is short and the fuel that should be injected still remains a lot.

Self-heating and drying in two-dimensional bagasse piles

This paper describes a two-dimensional model for self-heating and changes in water levels in bagasse piles of constant rectangular or triangular cross section. (Bagasse is the residue, mainly cellulose, that remains after sugar has been extracted from sugar-cane.) After milling, the bagasse has almost 50% water by weight, as hot water is used to remove the last of the sugar. The bagasse can be used as fuel in electrical power stations, but needs to be dried out before use. This paper discusses the way in which the drying out of a pile depends on the ambient conditions, and the shape and size of the pile. Accordingly, the energy equation, and equations for liquid water, water vapour and oxygen are solved numerically using the method of lines. The equations include terms describing heat conduction, diffusion of water vapour and oxygen, condensation and evaporation and an Arrhenius self-heating term. In addition, recent measurements show that there is also self-heating due to the presence of water in the bagasse, with a maximum effect near 60 °C, which is modelled by a modified Arrhenius expression. The local maximum in the heat release curve for the problem leads to approximate steady-state behaviour on short time scales that eventually is lost as the pile dries out. This interesting physical behaviour motivates an approximate analytical model for the rate at which liquid water is reduced in the pile. Analytical and numerical results are presented for a variety of pile configurations and some fairly general conclusions are drawn.

A reaction-diffusion model of stored bagasse

AbstractThe storage of bagasse, which is principally cellulose, presents many problems for the sugar industry, one of which is bagasse loss due to spontaneous combustion. This is an expensive problem for the industry as bagasse is used as a fuel by sugar mills, and for cogeneration of electricity. Self-heating occurs in the pile through an oxidation mechanism as well as a moisture dependent reaction. The latter reaction is now known to exhibit a local maximum, similar to the heat release curves found in cool-flame problems. Bagasse typically contains 45–55% by weight of water when milling is completed and the question of how to reduce the moisture content is important for two reasons. Firstly, wet bagasse does not burn nearly as efficiently as dry bagasse, and secondly, self-heating is greatly enhanced in the presence of water, for temperatures less than 60–70°C.An existing mathematical model is used, but modified to take into account the newly observed peak in the moisture dependent reaction. Most of the previously reported complex bifurcation behaviour possible in this model is not realized when physically realistic parameter values are used. The bifurcation diagram describing the long-time steady-state solution is the familiar S-shaped hysteresis curve. In the presence of the new form of the moisture dependent reaction, an intermediate state can be found which is not a true steady-state of the system as, in reality, the characteristics of the pile slowly change as water is lost. This state corresponds to observations of an elevated temperature (around 60–70°C) which persists for long periods of time. Approximate equations can then be defined which predict this intermediate state, and hence a different hysteresis curve is found. A simple explanation for the process by which water is lost from the pile is obtained from these equations and an analytical expression is given for the exponential decay of water levels in the pile.

Effect of curprous oxide in combination with molybdenum trioxide on smoke suppression in rigid poly(vinyl chloride)

AbstractFurther investigation of the synergistic effect of smoke suppression between cuprous oxide and molybdenum trioxide in rigid poly(vinyl chloride) (PVC) was carried out by using a cone calorimeter (cone) at a high incident heat flux of 50 kW m−2. Experimental data derived from the cone calorimeter indicated that binary mixtures of Cu2O and MoO3 clearly showed the synergistic effect in reducing smoke by decreasing total smoke production (TSP), average specific extinction area (av‐SEA), and smoke production rate (SPR). This result is in good agreement with that obtained from the NBS smoke chamber. However, the combustion process of rigid PVC could clearly be seen from the heat release rate (HRR), curve, SPR, and fire degradation obtained from the cone test, which could not be determined from the NBS smoke chamber. It was also found that the binary mixture showed the synergistic effect by increasing was also found that the binary mixture showed the synergistic effect by increasing char residue and reducing the fire degradation of the PVC backbone at a high incident heat flux of 50 kW.m−2. All experimental data well supported the early cross‐linking mechanism of the PVC backbone mentioned in the literature and were consistent with the fire degradation behavior obtained from the cone calorimeter.

Application of a one‐dimensional thermal flame spread model on predicting the rate of heat release in the SBI test

AbstractA one‐dimensional thermal flame spread model was applied to predict the rate of heat release in the single burning item (SBI) test on the basis of the cone calorimeter data. The input parameters were selected according to the features of the SBI test and using particle board as a model tuning material. The features of the measured and calculated rate of heat release curves were compared for a series of 33 building products. The fire growth rate (FIGRA) indices were calculated to predict the classification in the forthcoming Euroclass system. The model gave correct classification for 90% of the products studied. An essential feature of the model is that only one cone calorimeter test at the exposure level of 50 kW m−2 is needed. The model, therefore, provides a practical tool for product development and quality control. Copyright © 2001 John Wiley & Sons, Ltd.

Comprehensive study of the degradation of an intumescent EVA-based material during combustion

In this work, we have studied the evolution of an flame retardant intumescent EVA-based material during combustion. The formulation uses an original concept of the laboratory, i.e., use of char forming polymer (here the polyamide-6) as carbonisation agent associated to a carbonisation catalyst in an intumescent formulation. The fire behavior was modelled using the cone calorimeter and we have explained the evolution of the rate of heat release curve in terms of chemistry of the system using FTIR and solid state NMR.

Precipitation kinetics in an air-cooled aluminum alloy: A comparison of scanning and isothermal calorimetry measurement methods

The purpose of this work is to establish for the first time the equivalence of determinations of both precipitation time constants, τ, and activation energies, E act, by two calorimetric techniques: differential scanning calorimetry (DSC) and differential isothermal calorimetry (DIC). To accomplish this, kinetics and energetics of precipitation in air-cooled (ACO) aluminum alloy 339 were determined by both methods, using Perkin–Elmer instruments. The ACO alloy was chosen as the subject of the study because of its calorimetric simplicity: a single precipitation exotherm dominates each DSC scan. The DSC data were analyzed using a modified Kissinger equation, from which both time constants and activation energies were derived. From differential isothermal calorimetry experiments, we determined precipitation time constants by fitting the almost exponential decay of DIC heat release curves, using analyses developed in our laboratory. Arrhenius plots of the time constants then yielded values of E act. Both activation energies and time constants from the DSC/Kissinger analysis agreed rather well with those from DIC provided DSC temperature scan rates were slow compared to the calorimeter's instrumental equilibration time (lag time). Thus, the equivalence of the DSC and DIC techniques has been established, at least for this test case.

Effect of Alternative Diesel Fuels on Heat Release Curves for Cummins N14-410 Diesel Engine

A Cummins N14-410 engine was operated on 12 fuels produced by blending methyl tallowate, methyl soyate, and fuel ethanol with no. 2 diesel fuel. Engine in-cylinder pressure data were collected and used to evaluate the rate of heat release, mass fraction of fuel burned, and charge temperature with respect to crank angle. It was observed that the rate of heat release decreased with increasing engine speed. Peak rates of heat release for all fuel blends were less than for no. 2 diesel fuel. When methyl tallowate was blended with no. 2 diesel fuel, the shift in the location of peak heat release was away from top dead center (TDC) whereas the addition of ethanol to the blend shifted the location towards TDC. Ignition delay slightly decreased when methyl tallowate was blended with diesel fuel. However, ignition delays were not affected by the methyl tallowate content of the blend. The addition of ethanol to the fuel blends did not affect ignition delay. The charge temperature decreased with decrease in diesel content of the fuel blends. A reduction in charge temperature can reduce NOX emissions.

Comprehensive Thermodynamic Approach to Modeling Refrigerant-Lubricating Oil Mixtures

A comprehensive thermodynamic approach for modeling mixtures of refrigerants and lubricating oils is presented. The new approach includes generalized methods for predicting the following thermodynamic properties of refrigerant-oil mixtures: bubble point temperatures, local oil concentrations, liquid specific heats and enthalpy changes during evaporation. Using this comprehensive method, heat release (enthalpy) curves are easily generated and also the effect of oil on the LMTD (log mean temperature difference) of evaporators can be modeled. Importantly, the definition of the boiling heat-transfer coefficient based on the bubble point temperature is included in the method. This new approach provides the basis for advances to be made in two-phase refrigeration heat-transfer research and design.

Investigation of coal-water slurry fuel combustion in reciprocating, internal combustion engine

Coal-water slurry(CWS) engine tests designed to investigate the ignition and combustion processes of the fuel are described in this paper. The effects of three different parameters, namely, (a) needle lift pressure, (b) fuel injection timing, and (c) percent coal loading in the slurry fuel are studied in detail. Successful operation of the engine using the coal water slurry required modifications to the engine and support systems. The physical trends of combustion under single parametric variations are presented in terms of the cylinder pressure, heat release rates, and cumulative heat release curves. The major conclusions of the work include: (a) higher needle lift pressures led to shorter ignition delay times for the CWS fuel: (b) the ignition delay time of the advanced injection start was little different from that of retarded fuel injection timing due to poor atomization: and (c) dilution of the slurry with water can significantly affect the combustion processes and ease of fuel handling.

Characterization of the fire behaviour of a burning passenger car. Part II: Parametrization of measured rate of heat release curves

A simple model which describes the fire behaviour of a burning passenger car is presented. Rate of heat release (RHR) curves obtained from car fire experiments are characterized by superposition of one Boltzmann curve and three symmetrical Gaussian curves. The car fire is described by two fire plumes, one emerging from the car at the centre of the windscreen, the other at the centre of the rear window. Gas temperatures are calculated using Alpert's equations for maximum ceiling jet temperature and compared to temperatures measured in car fire experiments. Good accordance between the calculated and measured temperatures is obtained.

An In-Situ Combustion Reservoir Simulator With a New Representation of Chemical Reactions

Summary Numerical simulation of in-situ combustion processes poses numerical problems related to the representation of chemical reactions in the burning zone. This paper presents a new approach to the description of the combustion front. The fully implicit thermal compositional model developed to simulate oil recovery by wet or dry forward combustion is formulated to handle three dimensions, three phases, gravity and capillary forces, heat transfer by convection and conduction within the reservoir, and conductive heat loss to adjacent strata. Two options are available. The first includes four components and one fuel combustion reaction. The second allows any number of components and several reactions. The first option emphasizes description of the combustion front with a new formulation that uses a heat-release curve to improve numerical stability and to give accurate temperature distribution with large gridblocks. The paper compares different representations of chemical reactions and includes results of a sensitivity study on the mesh size. Thermal-balance considerations are given for wet or dry combustion to provide calculated values of the peak temperature and steam-plateau characteristics. The thermal-balance results agree well with those predicted by the numerical model.

Combustion of Coal-Water Slurry in a Two-Cycle Diesel Engine: Effects of Fuel Amount and Timing

Coal-water slurry having micronized coal particles with approximately 50 percent coal loading is successfully ignited and combusted in one cylinder of a two-cylinder 645 EMD engine by using diesel fuel pilot ignition aid. The effects of three different parameters, namely, (a) pilot timing, (b) pilot amount, and (c) CWS fuel amount, are investigated in detail. The physical trends of combustion under single parametric variations are presented in terms of the cylinder pressure, temperature, heat release rates, and cumulative heat release curves. CWS combustion with less than 5 percent of the energy of combustion coming from pilot fuel is achieved.

The heat release rates and cool flames of acetaldehyde oxidation in a continuously stirred tank reactor

The continuously stirred tank reactor (CSTR) technique is applied toequimolr acetaldehyde oxygen mixtures across a wide range of vessel residence times. Heat release curves are obtained in each case in the regions where stable steady state exists. In the regions of oscillatory cool flames the steady state is unstable and cannot be obtained experimentally. The oscillatory region always contains part of the region of negative temperature coefficient, as expected on theoretical grounds. At very short residence times a new effect is shown in this system, i.e., a discontinuous transition from the familiar type of cool flames to flames with quite different amplitude, frequency, and shape. In the immediate region of this bifurcation the system shows “indecision” or interspersed flames of each type for a short period. The reverse transition occurs at quite a different ambient temperature, showing hysteresis of as much as 25K. A tentative qualitative description of the nature of this bifurcation is given.

Mean Temperature Difference for Shell-and Tube Heat Exchangers with Condensing on the Shell Side

Shetl-and-tube heat exchangers with condensing on the shell side usually have a nonlinear heat release curve and a variable shell-side heat transfer coefficient. Using an effective average coolant temperature, it is possible to separate the calculation of the mean temperature difference from the heat transfer coefficient. Thus, it is possible to calculate the weighted mean temperature difference before the heat transfer coefficients are calculated. As a result, the complexity of the calculations is greatly reduced from present incremental procedures. When compared to a detailed incremental calculation of the mean temperature difference, tht maximum error is about 2%. A manual incremental method is also presented, which requires only moderately more work than industrial methods that use average heat transfer coefficients.