Reaction Heat Release Research Articles

Effect of pressure on the interaction of saturates, aromatics, and resins (S-Ar-R) during the oxidation of heavy crude oil

The oxidation characteristics of crude oil are fundamental to studying in-situ combustion and establishing the chemical reaction models. To clarify the effect of pressure on the mutual interactions among the saturate, aromatic, and resin (SAR) fractions of heavy oil, crude oil, single fractions, and binary mixtures (S/A, S/R, A/R) were investigated by using a high-pressure thermogravimetry and differential scanning calorimetry. The results indicate that the increase of pressure does not necessarily promote the heat release of saturates and aromatics during the low-temperature oxidation stage, and it does not significantly alter the reaction initial temperature and heat release of resins during the high-temperature stage. The increase in pressure accelerates the consumption of oxidants within saturates, thereby weakening their influence on other fractions. At the same time, the change in pressure can also interfere with the oxidation reactions between aromatics and resins. Overall, the increase in pressure significantly weakens the interactions among different components during co-oxidation. This conclusion is significant for simplifying the reaction model of crude oil under high pressure.

The oxygen vacancy defect induced by Ar plasma significantly reduces the initial reaction energy barrier of micron thermite and improves its combustion reaction efficiency

In order to reduce the initial reaction energy barrier and combustion reaction efficiency of micron thermite, this work firstly combined Ar plasma surface treatment technology and defect engineering strategy, and applied MoO3, Co3O4 and CuO containing oxygen vacancy to micron thermites to explore the effect of oxygen vacancy defect on the combustion reaction performance of thermites system. Taking the Al/MoO3 thermite system as an example, the results of thermal analysis and molecular dynamics simulation show that the presence of oxygen vacancy promotes the atomic migration of the thermite component atoms at the contact interface, thus reducing the initial reaction activation energy of Al/MoO3 by 29.8 % and increasing the reaction heat release by 56.7 %. This work expands the application of plasma in the field of energetic materials and provides a more efficient and safer method for their modification.

Computational investigation on the formation of liquid-fueled oblique detonation waves

Utilizing a two-phase supersonic chemically reacting flow solver with the Eulerian-Lagrangian method implemented in OpenFOAM, this study computationally investigates the formation of liquid-fueled oblique detonation waves (ODWs) within a pre-injection oblique detonation wave engine operating at an altitude of 30 km and a velocity of Mach 9. The inflow undergoes two-stage 12.5° compression, followed by uniform mixing with randomly distributed n-heptane droplets before entering the combustor. The study examines the effects of droplet breakup models, gas-liquid ratios, and on-wedge strips on the ODW formation. Results indicate that under the pure-droplet condition, the ODW fails to form within the combustor, irrespective of the breakup models used. However, increasing the proportion of n-heptane vapor in the fuel/air mixture facilitates the ODW formation, because the n-heptane vapor rapidly participates in the gaseous reactions, producing heat and accelerating the transition from low- to intermediate-temperature chemistry. Additionally, the presence of on-wedge strips enhances ODW formation by inducing a bow shock wave within the combustor, which significantly increases the temperature, directly triggering intermediate-temperature chemistry and subsequent heat-release reactions, thereby facilitating the formation of ODW.

Simulation study on combustion reaction mechanism and heat release rate of ammonia/methane fuels

ABSTRACT Ammonia/methane combustion has the potential to be a viable method for achieving low-carbon combustion. However, further research is required to enhance the combustion mechanism and to gain a deeper understanding of the heat release rate associated with ammonia/methane combustion. A one-dimensional simulation of premixed laminar ammonia/methane flame simulation was carried out based on Okafor ammonia/methane reaction mechanism. The mole fraction of radicals and heat release rate in the ammonia/methane combustion process under different conditions were calculated using CHEMKIN-PRO. The results show that the optimized reaction mechanism was in line with the experimental results in predicting the laminar flame velocity in the fuel-lean zone. The distances between the peak values of NH and heat release rates were small at XNH3 = 0.1 ~ 0.6 and fuel-rich condition. The correlation between NH and the heat release rate was significant, indicating that NH radicals are suitable as markers of the heat release rate in the ammonia/methane flames. The abilities for characterizing heat release rate of [CH][OH], [CH][NO], [NH][OH], [NH][NO], [NH2][OH], and [NH2][NO] were further evaluated. The exponent was added to the radical combination to improve the correlation with heat release rate. [NH]0.88[OH]0.01, [NH]0.92[NO]0.25, [NH2]0.92[OH]0.42, and [NH2]0.97[NO]1.27 correlate well with heat release rates from ammonia/methane flames and they can be used as good markers of heat release rates.

Numerical and experimental investigation of the correlation between inlet flow rates, temperature, and [formula omitted] emissions in pure hydrogen combustion

Many industrial burners currently in use have been designed for fossil fuels and have not been tested with hydrogen. The successful utilization of hydrogen fuel in industrial applications demands the optimization of operating conditions. Optimizing the inlet flow rate is important particularly for industrial burners to ensure safe and efficient operation over a long period. This study investigates the effects of inlet flow rate on temperature distribution and NOx emissions in a multi-purpose pure hydrogen-fueled industrial burner through numerical simulations and experiments. The numerical simulations, employing the realizable k-ε turbulence model and the eddy dissipation concept for turbulence and combustion modeling, are validated against experimental data, achieving a mean absolute percentage error of approximately 5 % for temperature and less than 2 % for NOx emissions at 4 % O2. The results demonstrated that increasing the inlet flow rate enhances reaction intensity and heat release, subsequently increasing combustion temperatures and promoting NOx formation. However, with a substantial increase in the inlet flow rate, the rate of temperature growth diminishes, and NOx emissions reach a plateau. This suggests that the burner is approaching maximum capacity, with the combustion process becoming limited by the burner’s ability to efficiently mix and react the fuel and oxidizer. Finally, an optimal inlet flow rate of 50.4 LPM for hydrogen in the fuel inlet and 200 LPM for air in the oxidizer inlet, balancing temperature and NOx emissions, was identified through the weighted sum performance indicator proposed in this work. This study provides critical insights into pure hydrogen burner performance, advancing previous efforts by offering quantitative data essential for improving burner efficiency and reducing harmful emissions in carbon-free combustion.

The Discussion of Ignition Criterion About the Mechanical Spark Ignition of Near-Limit Methane-Air Mixtures.

An optimal ignition criterion must be selected for the numerical prediction of the ignition parameters for mechanical spark ignition of near-limit methane-air fuel mixtures based on fuel mixture equivalency ratio; wherein, the vast majority of ignition criteria can be used for stoichiometric fuel mixtures. However, the viability of each criterion must be individually determined for near-limit fuel mixtures. This study developed a high-resolution algorithm that can be used to model the mechanical spark ignition and combustion of methane-air fuel mixtures of varying equivalence ratios. Three ignition criteria, Van't Hoff, reaction heat release rate, and -OH concentration, were evaluated at varying equivalence ratios based on their respective distributions at varying times. The widely used Van't Hoff criterion cannot be used to predict near-limit fuel mixtures due to a high required ignition temperature and low rates of combustion. -OH concentration criterion is significantly affected by the rate of combustion and reaction temperature; therefore, it tends to erroneously overestimate ignition parameters for near-limit fuel mixtures. This study has found that reaction heat release rate criterion can be used at all equivalence ratios and faithfully produces ignition parameter trends for fuel mixture reaction schemes of varying simplifications. Reaction heat release rate is a valid ignition criterion because the location of peaks in reaction released heat at varying times corresponds to flame front location, which is its physical counterpart.

Effects of Dolomitic Limestone on the Properties of Magnesium Oxysulfate Cement.

This study investigated the effects of substituting magnesium oxide (MgO) with dolomitic limestone (DL) on the mechanical and physical properties of magnesium oxysulfate (MOS) cement. Additionally, the hydration formation phases and the influence of the molar ratio on the MOS cement's performance were examined. The corresponding action mechanisms were identified and explored by compressive strength tests, scanning electron microscopy (SEM), X-ray diffraction (XRD), isothermal calorimetry, and a thermogravimetric analysis (TGA). The results showed that replacing MgO with DL decreased the reaction speed and heat release rate generated in the hydration process of the MOS cement. This substitution also reduced the quantity of non-hydrated MgO particles and delayed the formation of Mg(OH)2. The diminished formation of Mg(OH)2 contributed to an increase in the apparent porosity of pastes containing DL, thus alleviating internal stresses induced by Mg(OH)2 formation and enhancing their mechanical strength after 28 days of curing. Conversely, the increased porosity improved the CO2 diffusion within the structure, promoting the formation of magnesium carbonates (MgCO3). Through the characterization of the cement matrix (XRD and TGA), it was possible to identify phases, such as the brucite, periclase, and 318 phases. The obtained results revealed the potential of incorporating mineral fillers like limestone as a promising approach to producing MOS cement with a reduced environmental impact and better properties at higher curing ages.

Experimental studies on mechanism whereby premixed chamber length and equivalence ratio collaboratively influence self‐excited thermoacoustic instability

AbstractSelf‐excited thermoacoustic instability (SETAI) is a dangerous phenomenon in combustion equipment. While it is widely acknowledged that SETAI behavior is determined by the couple between pressure and heat release oscillation, their phase difference is difficult to predict, which impedes the development of SETAI control technology. With the aim of passive control technology development, this paper conducted experiment on a premixed hedge combustor to explore the mechanism whereby premixed chamber length (LP) and equivalence ratio (φ) collaboratively influence SETAI behavior. Results showed LP mainly affects the pressure mode shape within premixed chamber and consequently alters the phase difference between pressure and flowrate oscillation at combustion chamber inlet. Changing φ gives rise to different reaction time‐lag (τ), thus altering the phase difference between flowrate and reaction heat release oscillation. By introducing this flowrate oscillation, how LP and φ collaboratively determine phase difference between pressure oscillation and heat release oscillation was clarified. The mechanisms identified in this study are consistent with the emerging rationalization of the factors contributing to SETAI, and also provides better understanding on Rayleigh criterion and guidance for SETAI control. With further work on heat release and flow rate measurement, as well as the development on τ description, SETAI can be better predicted and controlled.

Characterization of oxygen initiation process in the autothermic pyrolysis in-situ conversion of Huadian oil shale

The oxygen initiation process, one of the key processes in the early stage of the autothermic pyrolysis in-situ conversion technology, has not been deeply investigated, which seriously limits its development. In this study, the reaction behaviors, kinetic parameters, heat and product release characteristics during the isothermal oxygen initiation process of Huadian oil shale in O2/N2 mixtures with different oxygen concentrations and initiation temperatures were investigated via TG/DSC-FTIR. The results show that the samples exhibit three different reaction behaviors during the initiation stage, consisting of two main parts, i.e., the oxidative weight-gain and the oxidative reaction phases. The former phase is mainly characterized by the oxygen addition reaction that produces oxidizing groups which increase the sample mass. And the latter stage consists of two main subreactions. The first subreaction involves the oxidative cracking and pyrolysis of oxidizing groups and kerogen to produce fuel deposits such as residual carbon, while the second subreaction focuses on the oxidation of the resulting fuels. Furthermore, increasing the oxygen concentration significantly promotes the above reactions, leading to an increase in the reaction intensity and reaction rate. Owing to the combined effect of oxygen concentration and residual organic matter content, the total heat release increases with the increasing initiation temperature and reaches its maximum at 330–370 °C. In addition, the preheating stage primarily produces hydrocarbon gases, while the initiation stage predominantly generates CO2. As the preheating temperature increases, the CO2 output intensifies, the required reaction time shortens, and the release becomes more concentrated. Based on these findings, a reaction mechanism for the oxygen initiation process of Huadian oil shale was proposed, and recommendations were provided for optimizing the construction process.

Thermal safety effect of three alkaline impurities on 1, 2, 4-triazole

1,2,4-Triazole is a common intermediate used in the synthesis of pesticides and medicine, and has a very wide range of applications. As a kind of polynitrogen heterocycles, 1,2,4-triazole will release a lot of heat during thermal decomposition. If there is no comprehensive understanding of its pyrolysis behavior, there will be a very large thermal safety risk in the process involving 1,2,4-triazole in industrial production. At the same time, the instability of the substance may be affected by the presence of impurities, and the existing research on this aspect is quite scarce. Therefore, it is very necessary to study the effect of adding other substances on the thermal decomposition of 1,2, 4-triazole. The thermal decomposition characteristics and thermal runaway behavior of 1,2, 4-triazoles were revealed by thermodynamic experiments and various kinetic theoretical methods. According to the risk matrix, the thermal runaway danger level of 1,2, 4-triazole was determined to be level Ⅲ, which was an unacceptable risk. The results show that 1,2, 4-triazole has a huge heat release and the effect of thermal runaway is serious. In this study, three substances involved in the industrial production of fluconazole and flutriafol mixed with 1,2, 4-triazole were selected to explore their influence on the thermal decomposition of 1,2, 4-triazole under non-working conditions. DSC and ARC experiments consistently showed that these three impurities could reduce the reaction heat release of 1,2, 4-triazole to varying degrees, and confirmed that these three impurities could reduce the risk of thermal runaway of 1,2, 4-triazole to varying degrees. Among them, sodium hydride has the most outstanding performance, both in terms of reducing reaction heat release and reducing adiabatic temperature rise. The results can provide reference for loss control of 1,2,4-triazole in industrial applications.

Three-Dimensional Thermo-Chemo-Mechanical Coupled Curing Analysis for the Filament Wound Composite Shell.

Carbon fiber resin-based composite materials are widely employed in the manufacturing of composite shells. During the curing process, the temperature gradients and cure degree gradients make it easy to generate thermal strains in both carbon fibers and resin, with the resin experiencing cure shrinkage strain due to the curing reaction, ultimately leading to residual stresses and strains. In this paper, a three-dimensional thermo-chemo-mechanical coupled curing model of the composite shell was established based on a resin test, and the changes of temperature, curing degree, residual stress, and strain during the solidification of the composite shell were investigated. First, the curing property parameters and elastic modulus of HCM-2184 resin were obtained through a curing dynamic test and a tensile test. Then, considering the heat release and shrinkage reaction of solidification, a coupled thermo-chemo-mechanical curing model was developed with the CHILE (α) elastic model, and the curing process of the composite shell was simulated numerically. The results show that the resin used in the test belongs to the autocatalytic reaction. For thin composite shells, the heat accumulation inside the shell during curing is not obvious. During the curing process, the curing shrinkage behavior of the resin is an important factor for the generation of residual stress and residual strain.

Narrow polydispersity P(AN-MA) copolymers synthesized in continuous flow as potential carbon fiber precursors

In this work, poly (acrylonitrile-methyl acrylate) [P(AN-MA)] copolymers with controllable molecular weights and narrow polydispersity were successfully synthesized in continuous flow without pre-deoxygenation. A dual-reactor method was designed to prepared P(AN-MA) with higher molecular weight and achieve a high yield from 62.57 % to 70.16 %. To facilitate industrial production of P(AN-MA), pre-mixing stage was added in continuous flow for replacing the ultrasonic mixing process. The characteristic mixing time is 27.80 min and the length of Polyfluoroalkoxy (PFA) tube exceeds 74.625 m for thoroughly mixing. Higher molecular weight P(AN-MA) copolymers possess poorer preoxidation properties such as higher initiation temperature, more concentrated heat release and larger activation energy of cyclization reaction as well as lower extent of stabilization and poorer thermal stability against high-temperature treatment. Moreover, 192 g P(AN-MA) was continuously prepared by the dual-reactor method for 105 min without suffering from notable pressure increase.

Experimental investigation on the combustion characteristics of electrolyte jets containing flame retardant tris (2-chloroethyl) phosphate

Abstract It is critical to well understand the combustion characteristics of the electrolytes inside lithium-ion batteries for safety concerns, particularly the electrolyte jet flames after thermal runaway. An electrolyte jet fire setup is developed in this study to investigate the combustion characteristics of electrolyte jets with the flame-retardant additive tris (2-chloroethyl) phosphate (TCEP) under high-temperature circumstances. Jet and ignition delay times and flammability are defined to characterize the flame-retardant effects. The fundamental parameters of self-extinguishing time and propagation rate are also measured for a comprehensive comparison. The experimental results show that the propagation of electrolyte flame at ambient temperature can be entirely stopped with 40 wt % of TCEP additives and 50 wt % can make the electrolyte nonflammable. Owing to the high boiling temperature and vaporization enthalpy of TCEP, more heat is required for the decomposition of electrolytes and TCEP mixtures, resulting in lower decomposition reaction rates and heat release rates. Thus, both the jet delay times and the ignition delay times significantly increase with the TCEP additives. Moreover, analyses on the spectrum of electrolyte jet flame reveal that the suppressing effects of TCEP on the combustion of electrolyte jets are operated by scavenging the OH radical and heat release.

Core–Shell Catalyst Pellets for Reaction Heat Release Control in Fixed-Bed Reactors

Core–Shell Catalyst Pellets for Reaction Heat Release Control in Fixed-Bed Reactors

Structural characterisation and reactivity measurement of chemically activated kaolinite

This study examines the structural evaluation of differently activated kaolins for potential use as supplementary cementitious materials (SCM) or as precursor for alternative cementitious materials (ACM). Chemical activation involved amorphizing the kaolinite structure using varying phosphoric acid concentrations, reaction times, and temperatures. Metakaolin obtained via thermal activation served as a comparison. Inductively Coupled Plasma – Optical Emission Spectroscopy (ICP-OES) characterization of the activating solutions revealed phosphoric acid activation leading to dealumination in kaolinite structures, with temperature emerging as the most significant parameter. X-ray diffraction (XRD) confirmed amorphization, attributed to the dealumination process causing Al loss and creating new Si–O–Si interlayered bonds, as monitored by 29Si magic-angle spinning nuclear magnetic resonance (MAS NMR) tracking the change from Q3 to Q4 environments. Furthermore, pozzolanic activity was assessed through Ca(OH)2 consumption and reaction heat release via modified Chapelle and R3 tests, respectively. Kaolinite subjected to intensive chemical activation exhibited high reactivity and increased specific surface area, indicating its potential as a pozzolanic material. Keywords: Kaolin; Chemical activation; Supplementary cementitious materials; Alternative cementitious materials; Dealumination; Pozzolanic reactivity.

Experimental investigation of CaCO3/CaO reaction pair in a fixed bed reactor for CSP application

CaCO3/CaO thermochemical energy storage (TCES) system has been widely studied on laboratory scale for its potential in concentrated solar power (CSP) plants. However, there is still need for the large-scale experiments based on which a detailed analysis can be obtained to improve this system for real-time applications. In this study, we developed a packed bed reactor capable of operating at high temperature and pressure providing the carbonation and decarbonation reactions of CaCO3/CaO reaction pair. The heat storage process is studied with the aspect of different decarbonation temperatures and different sample sizes (amount of sample in grams) placed in the reactor. Furthermore, we compared the heat storage performance of pure and composite samples. The heat release process is performed by varying the concentration of CO2 and the sample size of the loaded material. The results showed that the heat storage rate and efficiency improve by increasing the temperature of the decarbonation, implying that this reaction must be carried out above 925 °C for better performance. The heat is released smoothly and at a good rate when the concentration of CO2 is high in the reactor. Also, carbonation reaction (heat release process) depicts that CaCO3/CaO TCES system has a great potential to be used as a heat pump and is capable of upgrading the temperature of the released heat from lower to higher value.

Poly(vinyl alcohol)-based polyester nanofiltration membranes for fractionation of dye/salt mixtures: Alcoholysis degree matters

Poly(vinyl alcohol) (PVA)-based polyester loose nanofiltration (LNF) membranes present an ideal material for achieving dye/salt separation from dye/salt mixtures. Owing to the intrinsic features of the material, PVA with varying degrees of alcoholysis may exhibit different roles and functions, allowing for performance tailoring in PVA-based LNF membranes. In this work, we have demonstrated a facile approach for regulating the performance of polyester (PE) LNF membranes by tailoring the degree of alcoholysis. Stopped-flow mass spectrometry and various characterization techniques showed that an increase in the degree of alcoholysis accelerates reaction rates, increases reaction heat release, and boosts nanobubble formation during interfacial polymerization. The resulting LNF membrane featuring folds and a dense PE film demonstrated a permeance of 44.9 L m-2h−1 bar−1 and a CR/Na2SO4 selectivity of 240, as well as satisfactory stability, showing dye/salt separation performance superior to that of other LNF membranes. This work provides novel insights into tailoring high-performance LNF membranes for selective salt/dye separation.

Visualization of supersonic combustion using high-speed camera/dual-component planar laser-induced fluorescence simultaneous diagnostic technique

High-spatiotemporal-resolution diagnostics are important for capturing fine physicochemical structures in supersonic combustion. In this study, a high-speed camera (HSC)/dual-component planar laser-induced fluorescence (PLIF) simultaneous diagnostic technique is developed and applied to an ethylene-fueled scramjet to determine the flame structures and heat release characteristics of cavity shear-layer stabilized combustion. CH2O-PLIF and OH-PLIF simultaneous imaging techniques are used to capture the transient structures in the preheat and product zones of the flame, while the heat release zone (HRZ) is identified by the product of these two signals. Synchronized HSC techniques are used to capture the full-band flame fluorescence. The flame base was found to stabilize in the cavity shear layer at a certain distance downstream of the leading edge. The HRZ was initiated near the flame base and gradually spread into the mainstream. Upstream of the HRZ, the partially premixed fuel jet undergoes preheating oxidation reactions, forming the preheat zone adjacent to the HRZ. Downstream of the HRZ, hot products were produced, forming the product zone distributed in both the cavity and mainstream. The central role of the cavity is to provide a favorable environment for stabilizing the flame base rather than participating in heat release reactions. Schlieren images and wall pressure distributions are also documented, constituting a dataset that could be used to validate computational models.

Effect of thermal boundary condition and turbulent models on the combustion simulation of ethylene-fueled scramjet combustor

Wall thermal boundary conditions and turbulent models can affect flow and combustion simulations but are seldom considered in the turbulent modeling of supersonic combustors. This work investigated the effect of thermal boundary conditions and four turbulent models on turbulent combustion in a cavity-stabilized scramjet combustor. Results showed that the thermal boundary condition had a noticeable influence on the temperature fields. Changing the thermal boundary condition from zero gradient to a fixed lower temperature considerably reduced the maximum temperature but did not affect the temperature distribution. The fixed temperature boundary condition generated a slightly larger reaction heat release near the upper region of the cavity. However, the mass fraction of carbon dioxide was low for a fixed low temperature. The pressure increased near the rear of the cavity but decreased elsewhere at a fixed temperature. Reynolds-averaged models (k-epsilon, k-omega, and realizable k-epsilon) tend to over-predict the temperature and turbulent kinetic energy but under-predict the mass fraction of carbon dioxide. The detached Eddy simulation also under-predicts carbon dioxide but predicts a more accurate temperature.

Identifying the enhancement mechanism of Al/MoO3 reactive multilayered films on the ignition ability of semiconductor bridge using a one-dimensional gas-solid two-phase flow model

Energetic Semiconductor bridge (ESCB) based on reactive multilayered films (RMFs) has a promising application in the miniature and intelligence of initiator and pyrotechnics device. Understanding the ignition enhancement mechanism of RMFs on semiconductor bridge (SCB) during the ignition process is crucial for the engineering and practical application of advanced initiator and pyrotechnics devices. In this study, a one-dimensional (1D) gas-solid two-phase flow ignition model was established to study the ignition process of ESCB to charge particles based on the reactivity of Al/MoO3 RMFs. In order to fully consider the coupled exothermic between the RMFs and the SCB plasma during the ignition process, the heat release of chemical reaction in RMFs was used as an internal heat source in this model. It is found that the exothermal reaction in RMFs improved the ignition performance of SCB. In the process of plasma rapid condensation with heat release, the product of RMFs enhanced the heat transfer process between the gas phase and the solid charge particle, which accelerated the expansion of hot plasma, and heated the solid charge particle as well as gas phase region with low temperature. In addition, it made up for pressure loss in the gas phase. During the plasma dissipation process, the exothermal chemical reaction in RMFs acted as the main heating source to heat the charge particle, making the surface temperature of the charge particle, gas pressure, and gas temperature rise continuously. This result may yield significant advantages in providing a universal ignition model for miniaturized ignition devices.