Calculated Heat Release Research Articles

Flame evolution and pressure dynamics of premixed stoichiometric ammonia/hydrogen/air in a closed duct

Ammonia is regarded as a promising energy carrier due to its zero-carbon emissions and its suitability for long-distance, large-scale storage, and transportation. Ammonia/hydrogen mixed combustion is an important way to solve the problem of high ignition temperature and low flame speed in the process of ammonia combustion. This study systematically investigates the evolution of flames and pressure dynamics in a closed duct for ammonia/hydrogen/air mixtures with varying hydrogen blending ratio (0–100 %). Simultaneously, the study assesses the impact of flame instability and heat release on the evolution of ammonia/hydrogen/air flames and pressure dynamics. The results show that the flame tip speed and overpressure increase with the increase of hydrogen blending ratio and initial pressure, and when the hydrogen blending ratio is more than 25 %, the growth range of flame tip speed peak and overpressure peak value increases significantly. At the same time, the flame thickness decreases after hydrogen blending, the hydrodynamic instability increases, and the degree of wrinkles on the flame surface increases, which promotes flame acceleration. The Froude number increases significantly, the influence of buoyancy instability gradually weakens, and the flame core does not undergo significant displacement. In the later stage of flame propagation, both the flame front propagation velocity and pressure show significant pulsation phenomena. The heat release calculation results show that hydrogen blending significantly increases the adiabatic flame temperature. Consistent with the evolution law of overpressure, when the hydrogen blending ratio is greater than 25 %, the net heat release increases significantly. The elementary reaction with the highest heat release rate changes from the chain termination reaction R41 to the chain termination reaction R3. The research results can provide theoretical basis and experimental data support for the formulation of safety standards during the regulation and utilization of the combustion structure of ammonia/hydrogen/air mixtures.

Uncertainties in the use of oxygen consumption calorimetry for heat release measurements in lithium-ion battery fires

Accurate measurement of the heat release from a battery fire is vital for risk management, product development and construction of accurate models. Oxygen consumption calorimetry is the most common method for heat release measurements in experimental fire tests. The strength of the method is that it can be applied to unknown compositions of fuel with sufficient accuracy. Despite that this method is used to estimate heat release from battery fires, the method is subject to discussion. In this work, the method is studied in-depth, and potential errors are structured and quantified. Uncertainties associated with self-generated oxygen and internal heat generation, total gas release from the battery and impact on the heat release calculations, as well as the assumed E-factor (i.e., heat release per unit mass of oxygen consumed), are thoroughly discussed. For a Li-ion battery fire, it is concluded that oxygen consumption calorimetry will exclude internal heat generation and underestimate the total heat released from the external flaming fire by up to 10 %. In addition, high rate of combustion reactions can result in that the measured peak heat release rate is underestimated much more, up to 100 %.

A new approach in calculation of heat release during high geothermal tunnels construction considering ventilation time effect

A new approach in calculation of heat release during high geothermal tunnels construction considering ventilation time effect

Portable automatic detection system with infrared imaging for measuring steel wires corrosion damage

Accurate, cost-efficient and lightweight quantitative detection of steel wire corrosion in cable is an unsolvable issue that puzzles researchers and bridge owners. This paper proposed a portable automatic detection system for quantitative corrosion detection of replaced steel wires. The developed system consists of three parts (an automatic detection device, high-precision infrared imager, and corrosion evaluation algorithm). The proposed method is derived on the basis of Joule's law and the formula for calculating heat release. Then, the corroded specimens with different corrosion degrees and corresponding mass loss ratio were obtained by pre-corroded test to simulate industrial air corrosion and pickling test. The prior knowledge acquisition test utilizing presented automatic detection equipment was conducted to acquire the surface temperature of steel wires with various corrosion ratios by infrared camera after electric heating. Subsequently, the optimal quantitative corrosion prediction model after electric excitation is selected after infrared image processing, outlier filtering, theoretical method comparison, and model modification. Finally, the damaged steel wires from an in-service cable-stayed bridge are chosen to validate the proposed model's generalization ability and predictive accuracy. Furthermore, based on the discovery of characteristics on surface temperature of corroded steel wires after heating, the automatic detection device can be upgraded to realize the quantitative detection of in-situ corrosion of bridge cable.

Experimental and numerical investigations of forced response of multi-element lean-premixed hydrogen flames

Understanding the distinctive thermoacoustic properties of multi-element lean-premixed hydrogen flames is crucial for the development of hydrogen-capable gas turbines. Extending our earlier investigations of the self-excited dynamics of a cluster of lean-premixed pure hydrogen-air flames, here we explore the dynamic response to harmonic velocity perturbations, using an integrative approach combining loudspeaker-forced direct measurements and LES-based numerical simulations. Electronically-excited OH intensity distribution, generally assumed to be equivalent to the flame's heat release rate, shows an anchored conical reaction zone. Numerical simulations of heat release rate contours, however, reveal the formation of a more concentrated thin annulus region resembling an inverted V shaped layer, created by preferential diffusion of hydrogen molecules. This difference between OH-intensity distribution and heat release rate contours suggests consequential uncertainties in surrogate-dependent flame transfer function evaluations; the transfer function gains from measured data are well defined by a fast-decaying low-pass filter behavior, but the simulation result exhibits slowly-decaying large gain with slight overshoot over the entire range of frequency. Because the systematic uncertainties associated with the estimation of the flame's heat release rate cannot be accurately quantified, we rely on a reduced-order network modeling framework combined with direct measurement to test the accuracy of the prediction of the growth of self-sustained pressure fluctuations. We demonstrate that LES-based transfer functions predict the system's stability more accurately, and this suggests that the calculated heat release rate data are closer to the hydrogen flame's true heat release response than the wavelength-specific light intensity measurement. This assessment enables us to identify structurally simple moderate transverse oscillations of local regions containing atypically concentrated energy as pivotal processes controlling high-frequency hydrogen combustion dynamics.

Calculating Heat Release Rates from Lithium-Ion Battery Fires: A Methodology Using Digital Imaging

Measuring flame lengths and areas from turbulent flame flares developing from lithium-ion battery failures is complex due to the varying directions of the flares, the thin flame zone, the spatially and temporally rapid changes of the thermal runaway event, as well as the hazardous nature of the event. This paper reports a novel methodology for measuring heat release rate from flame flares resulting from thermal runaway of electric vehicle lithium-ion modules comprising eight 56.3Ah lithium nickel manganese cobalt (NMC) pouch cells using digital cameras and a newly developed numerical code to process the distortion of the flame size based on distance, direction, and shape. The model is tested with a set of experiments using lithium-ion battery packs and validated with a reference set of measurements using calibration boxes, a method commonly used in the reconstruction of flame areas. The experiments showed that the effect of calibration is large, and thus digital imaging without the appropriate calibration can give very large errors in measurement of flames. The combined imaging and processing method proposed in this work allows the determination of heat release rates from lithium-ion battery packs, one of the most challenging variables to quantify during the failure of a battery pack outside the laboratory. In the example experiment that this method was applied to, almost double the heat released was accounted for, meaning 50% of the total heat released would not have been accounted for without this image processing method.

Non-Intrusive Accelerometer-Based Sensing of Start-Of-Combustion in Compression-Ignition Engines

<div class="section abstract"><div class="htmlview paragraph">A non-intrusive sensing technique to determine start of combustion for mixing-controlled compression-ignition engines was developed based on an accelerometer mounted to the engine block of a 4-cylinder automotive turbo-diesel engine. The sensing approach is based on a physics-based conceptual model for the signal generation process that relates engine block acceleration to the time derivative of heat release rate. The frequency content of the acceleration and pressure signals was analyzed using the magnitude-squared coherence, and a suitable filtering technique for the acceleration signal was selected based on the result. A method to determine start of combustion (SOC) from the acceleration measurements is presented and validated. In-cylinder pressure (used to calculate heat release rate) and accelerometer data were collected on a 1.9-L compression-ignition direct-injection engine (Z19DTH) over a wide range of speeds (1000-3250 RPM) and loads (2-8 bar IMEP<sub>g</sub>), for single- and double-injection strategies, and for fuels of several different cetane numbers (35.5 and 48.5). The relationship between engine block acceleration and the time derivative of heat release rate was verified using the experimental results and indicates that unsteadiness in the rate of heat release is the driving factor for the engine block acceleration signal. The accelerometer-based method developed allows detection of SOC for the main injection with a root mean square error less than 0.75 CAD for the range of conditions tested in this work.</div></div>

Dynamics of Thermoacoustic Oscillations in Swirl Stabilized Combustor without and with Porous Inert Media

Lean premixed (LPM) combustion processes are of increased interest to the gas turbine industry due to their reduction in harmful emissions. These processes are susceptible to thermoacoustic instabilities, which are produced when energy added by an in-phase relationship between unsteady heat release and acoustic pressure is greater than energy dissipated by loss mechanisms. To better study these instabilities, quantitative experimental resolution of heat release is necessary, but it presents a significant challenge. Most combustion systems are partially premixed and therefore will have spatially varying equivalence ratios, resulting in spatially variant heat release rates. For laminar premixed flames, optical diagnostics, such as OH chemiluminescence, are proportionally related to heat release. This is not true for turbulent and partially premixed flames, which are common in commercial combustors. Turbulent eddies effect the strain on flame sheets which alter light emission, such that there is no longer a proportional relationship. In this study, phased, averaged, and spatially varying heat release measurements are performed during a self-excited thermoacoustic instability without and with porous inert media (PIM). Previous studies have shown that PIM can passively mitigate thermoacoustic instabilities, and to the best of the authors’ knowledge, this is the first-time that heat release rates have been quantified for investigating the mechanisms responsible for mitigating instabilities using PIM. Heat release is determined from high-speed PIV and Abel inverted chemiluminescence emission. OH ∗ chemiluminescence is used with a correction factor, computed from a chemical kinetics solver, to calculate heat release. The results and discussion show that along with significant acoustic damping, PIM eliminates the direct path in which heat release regions can be influenced by incoming perturbations, through disruption of the higher energy containing flow structures and improved mixing.

Determination and Calculation of Sodium Phenol Carboxylation Heat Release

Determination and Calculation of Sodium Phenol Carboxylation Heat Release

Математическое моделирование тепловых процессов в системе «Бетон-грунт»

The calculation of concrete curing modes and the development of mathematical models are greatly influenced by the temperature field in the concrete of channel linings. The problem is reduced to solving a nonlinear heat equation that takes into account the exothermic heat release of concrete and the phase transformation of moisture, and time-varying boundary conditions that allow taking into account the impact on concrete of the external environment during laying and maintenance. Variable thermophysical coefficients make it possible to take into account the inhomogeneity of the medium (in the case of laying concrete on the ground) and the change in the aggregate state of the substance when the phase transformation temperature is reached. Since it is impossible to obtain an analytical solution in a general form, a numerical solution method is used, based on a combination of a finite-difference solution with a method for calculating heat release and concrete strength from the corresponding fields of isothermal curves obtained experimentally. When constructing a difference scheme, an integro-interpolation method (balance method) is used, based on the law of conservation of heat. For an extended body of sufficiently large dimensions, the process of heat transfer in it is assumed to be linear, and the coordinate system with the center is taken to be on the axis of the body. The presented mathematical model of thermal processes in the “concrete-soil” system makes it possible to predict the modes of holding monolithic concrete to achieve the necessary technological requirements, as well as to apply the most economical modes.

Thermodynamic characteristics of deep space: hot hazard control case study in 1010-m-deep mine

Control of heat hazards in deep tunnels is vital to underground safety production. Taking a 1010-m-deep coal mine as an example, this paper revealed the variation characteristics of geo-temperature along the depth direction in plain area and the variation characteristics of country rock temperature along the horizontal direction in deep tunnels and the thermodynamic characteristics of the deep space. Using theoretical analysis, numerical simulations, field tests, etc., a new method for calculating cooling loads of deep tunnels and working faces was studied, and heat release law and calculation method of hot water flowing in open canal were discussed. Based on local resource and meteorological conditions and the condition of limited water inflow, the authors designed and implemented the phase-Ⅰ project and phase-Ⅱ project of hazard control system in the 1010-m-deep tunnels. The results showed that the environmental control temperature dropped to 26 ∼ 29 °C, and the average relative humidity was reduced by 5%–15%, which met the comfort standards of underground workers. The failure rate of underground equipment was reduced by half, the investment and operation cost of the heat hazard control system were small, and good environmental and economic and social benefits were achieved.

Numerical Simulation of Converter Station Fire: A Study focus on the Fire Hazard of Valve Tower

The fire hazard of a valve tower in converter station fires were investigated by using the Fire Dynamics Simulator (FDS). The 2 m2, 5 m2 and 10 m2 transformer oil pool fires with the calculated heat release rate (HRR) of 2.02, 6.23 and 13.78 MW were considered in the simulations, and the smoke propagation process, smoke temperature and visibility were mainly concerned. The results showed that the whole valve tower was immersed in the fire smoke at about 600 s in 2 m2 fire condition, and the maximum temperature rise inside the valve hall was about 20ºC. In the 5 m2 fire condition, the smoke layer height descended to the bottom of the valve tower at about 300 s, and the visibility around the valve modules was lower than 5 m at about 450 s. The maximum smoke temperature inside the valve hall was over 60ºC, and the temperature of smoke around the valve modules ranged from 43 to 52ºC. In the 10 m2 fire condition, the valve tower was immersed in the fire smoke at about 210 s, and the visibility around the valve modules was lower than 5 m at about 300 s. The smoke temperature beneath the ceiling of the valve hall was over 100ºC, and the temperature at the height of valve towers ranged from 65 to 80ºC. It was observed that the larger the fire size was, the higher the fire hazard of the valve tower would be found. In the 5 m2 and 10 m2 pool fire conditions, the thermal damage to the valve tower was non-negligible. The normal operation of the electrical components in the valve tower might be affected, and the failure of electrical components might be occurred.

ТЕРМОДИНАМИЧЕСКИЙ АНАЛИЗ ГИДРАТАЦИИ ТРЕХКАЛЬЦИЕВОГО СИЛИКАТА

Thermodynamic analysis of the hydration processes of tricalcium silicate 3CaO•SiO2 is difficult due to the unreliability of the initial data for hydration products. In addition, there are disagreements about the basicity of the hydration phases (3CaO•SiO2•3H2O or 2CaO•SiO2•2H2O). For the latter, there is no free energy of formation in the reference literature. There are also no data on the water solubility of these calcium hydrosilicates. The proposed values of ∆G0298 for these hydrosilicates, equal to 1064,3 and 639,7, as well as the enthalpies of formation (∆Н0298), equal to 1157,2 and 696,9 kcal/mol, re-spectively. Further thermodynamic calculations were performed using these values. To calculate the composition of the liquid phase, a simplified Born-Haber cycle is used. The values of the calculated heat release of tricalcium silicate with the formation of C3S2H3 and C2SH2, obtained using the pro-posed values of enthalpies, differ little from each other and are close to the experimental data. The calculated solubility of C3S2H3 is 0,7 g/l CaO, and C2SH2 is 0,92 g/l CaO. Since the solubility of C3S2H3 is much lower than of Ca(OH)2 (portlandite), which is formed during hydration of tricalcium silicate in large quantities, C3S2H3 is unstable under these conditions and its basicity increases. It is suggested that C3S2H3 is the main hydration product of CEM III and other cements with a high content of active mineral additives, and C2SH2 is CEM I and CEM II.

Measurement of heat release during hydration and carbonation of ash disposed in landfills using an isothermal calorimeter

Temperatures as high as 100 °C have been reported at a few municipal solid waste (MSW) landfills in the U.S. A recently published model describing landfill heat accumulation identified reactions that contribute significant heat to landfills including the hydration and carbonation of Ca-containing wastes such as ash from MSW and coal combustion. The objective of this study was to develop a method to measure heat release from Ca-containing ash by isothermal calorimetry. The method was confirmed by comparing measured heat release from hydration and carbonation of pure CaO and Ca(OH)2 to the theoretical heat. Theoretical heat release was determined by characterizing test materials before and after experiments using thermogravimetric analysis (TGA) and X-ray diffraction (XRD). Heat recovery efficiencies with both water and synthetic leachate ranged from 79 to 90% for CaO hydration and between 65 and 74% for Ca(OH)2 carbonation, with no effect attributable to leachate. Additionally, simultaneous hydration and carbonation of CaO/Ca(OH)2 mixtures resulted in efficiencies of 65 to 74%. The developed method was applied to eight samples that were excavated from a landfill and known to contain coal ash, and the ratio of measured to theoretical heat was 0.5 to 4. Thus, calculation of theoretical heat release from XRD data was not a good predictor of the experimentally measured heat release. The developed method can be used by landfill operators to evaluate the heat potential of a waste, thereby facilitating decisions on the quantity of a waste that can be buried in consideration of landfill temperatures.

The performance of laminated glass subjected to constant heat fluxes related to building fires

SummaryA series of six exploratory experiments are presented investigating the behaviour of laminated glass when exposed to radiative heating of 25, 50 and 75 kW/m2. The laminated glass type used is typical of that which might be used in balustrades. Three experiments examined the potential for achieving flaming ignition of the inter‐layer should the glass break. At a radiant heat flux of 25 kW/m2, although the glass did not shatter, piloted ignition of the volatile gases released from the specimen edge was possible. At radiant heat fluxes of 50 and 75 kW/m2, the exposed glass layer shattered after 5 minutes 7 seconds and 2 minutes 24 seconds, respectively, and subsequently there was auto‐ignition of the volatile gases from the inter‐layer. Eventually flames were observed over the whole face of the specimen. Using an average measured mass loss and representative heat of combustion for the inter‐layer result in calculated heat release rates per unit area of 65 to 69 kW/m2. A further three experiments were carried out to examine the potential for the glass layers to separate when heated. Only one layer of glass was supported, and unsupported layer nearest the radiant heat source was observed to slip away from the other layer, exposing the inter‐layer, resulting in ignition and flaming.

Analysis on the determination of specific heat of air at constant pressure

Heat calculation is often encountered in industrial production and life. For example, the calculation of flue gas heat release or the heat absorption of working medium in thermal equipment in thermal power plant boiler is a common heat calculation. This paper mainly introduces the experimental principle and method of specific heat of gas, and measures the average specific heat of air at constant pressure. Through this experiment, we can be familiar with the basic measurement methods of temperature, pressure, heat and flow in the experiment. In this paper, we compare the experimental data with the actual data, and analyze the cause of the error.

Combustion and emissions of isomeric butanol/gasoline surrogates blends on an optical GDI engine

The combination of distinctive physicochemical properties of biofuels and recent engine technologies offer benefits in terms of efficiency improvement and emissions reduction. The recent development in butanol bio-based production pathways encourage researchers to study their combustion characteristics. This paper experimentally evaluates the combustion and emissions of a gasoline direct injection (GDI) engine fueled with the butanol isomer/gasoline surrogate blends, in which primary reference fuel (PRF) and toluene primary reference fuel (TPRF) are selected as the gasoline surrogates, respectively. The flame propagation behaviors, in-cylinder pressure, apparent heat release rate, along with PN emissions from this optical GDI engine are discussed. First, butanol addition to the gasoline surrogates is found to slow down flame propagation, reduce peak cylinder pressure and heat release rate, and extend ignition delay and combustion duration. Further, among the four butanol isomers, n-butanol and tert-butanol are the most and least reactive fuels, respectively, whereas iso-butanol and sec-butanol show reactivities in between, as supported by the measured flame propagation and pressure traces, calculated heat release rates, as well as time scales describing the combustion progress, e.g. ignition delay and combustion duration. Finally, butanol addition reduces the PN emissions from the GDI engine, and the PN emissions reduction capacity of the four butanol isomers ranks as sec-butanol > iso-butanol > n-butanol > tert-butanol. Also, compared to the PRF/butanol blends, the PN emissions are reduced to a less extent when butanol is blended with TPRF.

Criteria Justification for Assessing the Technical Condition of Gearboxes of Mining Machines Based on Infrared Thermography

The paper presents the relevance of advanced assessment of the technical condition of complex technical systems. One of which is the gearbox of a mining machine. The main reasons for early failures of bearings are shown. The main share is occupied by problems of lubrication, incorrect installation and maintenance. The analysis of types of destruction of gears of mining machines is presented. The main share is occupied by the surface coloring of the teeth and sudden fracture of the tooth as a result of dynamic load. The theoretical basis for determining the heat release of bearings is given. The calculation of heat release is given of a shaft belt conveyor gearbox as an example, which is confirmed by thermographic studies under operating conditions. Justification of criteria for evaluating the technical condition of gearboxes of mining machines in the form of temperature anomalies recorded on the surface of the body, The actual load on the output shaft is taken into account.

Quantitative measurement of density fluctuations with a full-field laser interferometric vibrometer

Modern, lean and premixed gas turbine combustion concepts for low NOx emissions are prone to combustion instabilities. In a previous work it was shown that laser interferometric vibrometry (LIV) can be used to record global as well as local heat release fluctuations in swirl-stabilized premixed methane flames quantitatively, if other effects influencing density are small. In this work a newly developed camera-based full-field LIV system (CLIV) was applied to a lean, confined, premixed and swirl-stabilized methane flame under atmospheric conditions. Instead of time-consuming pointwise scanning of the flame, CLIV records full-field line-of-sight density fluctuations with high spatio-temporal resolution. With a recording rate of 200 kHz, CLIV enables the visualization of highly unsteady processes in fluid dynamics and combustion research. As an example for an unsteady process, the propagation of the flame front through a lean, premixed gas volume is visualized during an ignition process. A discussion of algorithms and assumptions necessary to calculate heat release oscillations from density oscillations is presented and applied to phase-averaged data recorded with CLIV for this type of flame. As reference, OH* chemiluminescence data were recorded simultaneously. While density gradients travelling with the flow are recorded by LIV and CLIV, chemiluminescence imaging will show nothing in the absence of chemical reaction.Graphic abstracta Time-averaged density gradient within the combustor in lateral direction. b Density fluctuations along line-of-sight 7 ms after ignition. c Phase-averaged and local heat release fluctuations at 225 Hz perturbation frequency

Nonlinear Estimation of Variables for Heat Release Calculation Using a Gradient Method

Advanced combustion such as the partially premixed combustion (PPC) is characterized by high energy efficiency. However, they are sensitive to the inlet condition and injection of a combustion engine. Therefore, it is essential to use combustion feedback. The accuracy of the feedback variables, derived from the cylinder pressure signal, is crucial for effective combustion feedback control. This paper proposes a nonlinear least-squares regression method to estimate the pressure offsets and variable polytropic exponent in heat release calculation automatically. The combustion feedback variables derived from the auto-tuned heat-release rate were applied to a heavy-duty compression ignition (CI) engine burning with gasoline fuel.