Combustion Reaction Research Articles

Design of Litchi-Like Al/PTFE with Superior Reactivity and Application in Solid Propellants.

The combustion efficiency and reactivity of aluminum (Al) particles, as a crucial component in solid propellants, are constrained by the inert oxide layer aluminum oxide (Al2O3). Polytetrafluoroethylene (PTFE) can remove the oxide layer, however, carbon deposition generated during the reaction process still limits the reaction efficiency of Al/PTFE fuel. Here, a litchi-like Al/PTFE fuel with the nano-PTFE islands distributed on the Al particles surface is successfully designed, based on localized activation and synergistic reaction strategies, to solve the Al2O3 layer and carbon deposition. This unique PTFE-coated structure can achieve localized activation of Al by surface etching, creating reaction channels, and exposing the active Al. Such a channel network promotes the circulation of fluorine and oxygen, stimulating the synergistic reactions of Al-F and Al-O and energy output. Regulating the PTFE content can maximize the elimination of carbon deposition and achieve the full combustion reaction of Al/PTFE. The maximum flame area and pressure output of the litchi-like Al/PTFE fuel increased by 241.9%, 734.7%, 118.4%, and 265.2%, respectively, compared with traditional physical mixture and core-shell structure Al/PTFE fuels. The localized activation and synergistic effects of litchi-like structure effectively transform carbon waste into a valuable resource, introducing a novel approach for the propellants.

Optimization of coal spontaneous combustion characteristics and reaction kinetic model under lean-oxygen conditions

Optimization of coal spontaneous combustion characteristics and reaction kinetic model under lean-oxygen conditions

Theoretical Study on the Kinetics of Secondary Oxygen Addition Reactions for N-Butyl Radicals.

Chemical kinetics for second oxygen addition reactions (·QOOH + O2) of long-chain alkanes are of great importance in low-temperature combustion technologies. However, kinetic data for key reactions of ·QOOH + O2 systems are often difficult to obtain experimentally and are primarily estimated or calculated by using theoretical methods. In this work, barrier heights (BHs), reaction energies (ΔEs), and relative energies (REs) of stationary points for key reactions of two representative ·QOOH + O2 systems in the low-temperature oxidation of n-butyl as well as pressure-dependent rate constants for the involved reactions are calculated with the high-level quantum chemical method CCSD(T)-F12b/CBS. These results can be employed in the development of low-temperature combustion mechanisms for n-butane and longer straight-chain alkanes. In addition, the performance of some quantum chemistry methods with a lower computational cost on BHs, ΔEs, and REs as well as rate constants is also investigated. Our results indicate that the maximum error on these energies with PNO-LCCSD(T)-F12a is within 1 kcal/mol, and rate constants with this method are in the best agreement with reference values, with a maximum relative error of about half the reference values. Due to its low computational cost and memory requirements, this method is strongly recommended for studying low-temperature combustion reactions involving larger hydrocarbon fuels.

Evaluating sulfur-impurity removal and modern carbon contamination in different preparation methods for radiocarbon dating of soil samples by accelerator mass spectrometry

Abstract Radiocarbon (14C) dating of soil samples by accelerator mass spectrometry (AMS) has been proven useful for studying carbon (C) cycling in terrestrial ecosystems. However, this application has two primary difficulties in sample preparation: inhibition of graphite formation due to sulfur (S)-containing impurities and contamination of samples with modern C (MC). Herein, we evaluated these effects using three sample preparation methods (silver foil, silver wire, and Sulfix) by conducting AMS-14C measurements of a 14C-dead charred wood and S-rich soil samples. The preparation methods were all successful in graphite formation and AMS-14C measurement for soil samples with an organic S content <6.9 wt%. The methods showed different percent modern carbon (pMC) values from 0.16% to 0.64% for the 14C-dead sample. The results also revealed that across different methods, MC contamination can be significantly reduced by applying two-step procedure (combustion and subsequent reaction to remove S-containing impurities) during sample preparation. The three methods had a negligible influence on determining the 14C age for samples that were at least younger than 12,000 yr BP. As the 14C ages of the soil samples are typically younger than 12,000 yr BP, any method explored in this study can be employed for 14C dating with sufficient accuracy for application to C cycle studies.

Preparation, Thermal Properties and Decomposition Course of Highly Resistant Potato Starch Graft Poly(Cinnamyl Methacrylate) Materials.

The properties of starch graft poly(cinnamyl methacrylate) copolymers were presented. The "grafting from" method and different ratios of starch to methacrylic monomer were used. The copolymers with the maximum grafting percent (G: 55.3% ± 0.4) using a ratio of starch to methacrylic monomer of 1:3 were obtained. The heterogeneous, non-porous structure materials were prepared. They were characterized by significant lower swelling in polar solvents and moisture absorption but higher swelling in non-polar solvents compared to unmodified potato starch. The chemical resistance in acidic, alkaline and neutral environments for all the tested copolymers was significantly higher compared to the chemical resistance of potato starch. The tested copolymers decomposed in at least three main stages in inert conditions and in at least four main stages in oxidative conditions. Their pyrolysis with the emission of the mixture of volatiles such as aldehyde, acid, ester, alcohol, aromatic, alkene, alkane, H2O, CO2 and CO based on the TG/FTIR studies was proved. The oxidative decomposition included pyrolysis processes combined with oxidation and combustion reactions of volatiles and the formed residues. As a result, the emission of the unsaturated and saturated compounds with carbonyl, hydroxyl, carboxyl and/or ester groups, alkane, alkene, aromatics and its oxidized forms, H2O, CO2 and CO, was observed.

A review of chemical kinetic mechanisms and after-treatment of amino fuel combustion.

Ammonia is a highly promising carbon-neutral fuel. The use of ammonia as a fuel for internal combustion engines can reduce fossil energy consumption and greenhouse gas emissions. However, the high ignition energy required for ammonia and the slow flame propagation rate result in low combustion efficiency when ammonia is used directly in internal combustion engines. The combination of ammonia with highly reactive fuels improves combustion quality and increases efficiency. However, the combustion of these combined fuels generates particulate matter, CO, hydrocarbon, and significant amounts of NOx. Therefore, pollutant emissions must be reduced through after-treatment technologies. In this paper, a series of combustion and post-treatment challenges faced by amino fuel combustion in internal combustion engines are extensively discussed and the combustion reaction mechanisms of different amino fuels are also analyzed. The paper then reviews five key technologies applicable to the reprocessing of amino fuels, including selective catalytic reduction, selective catalytic reduction filter technology, electrochemical methods for NOx removal, direct catalytic decomposition of N2O, and ammonia sliding catalysts. An in-depth discussion of the catalytic materials and reaction mechanisms involved in these technologies is also provided in this paper. Finally, the paper summarizes the main technical challenges that must be addressed for the future application of amino fuels in internal combustion engines. These discussions can serve as an essential reference for developing and applying critical technologies for combustion control and pollutant treatment of amino fuels.

Insight into the flammability limit and combustion reactions behaviors of R1233zd(E)/R1270 mixtures refrigerants

Insight into the flammability limit and combustion reactions behaviors of R1233zd(E)/R1270 mixtures refrigerants

Don't forget the trans: double bond isomerism radical-acetylene growth reactions affect the primary stages of PAH and soot formation.

In combustion, acetylene is a key species in molecular-weight growth reactions that form polycyclic aromatic hydrocarbons (PAHs) and ultimately soot particles. Radical addition to acetylene generates a vinyl radical intermediate, which has both trans and cis isomers. This isomerism can lead to profound changes in product distributions that are as yet insufficiently investigated. Herein, we explore acetylene addition to substituted trans-vinyl radicals, including potential rearrangement to cis structures, for eight combustion-related hydrocarbon radicals calculated using a composite method (G3X-K). Of these eight systems, the phenyl trans- and cis-Bittner-Howard HACA (hydrogen abstraction, C2H2 Addition) process, where acetylene successively adds to a phenyl radical via a β-styryl intermediate, is simulated using a unified Master Equation model. Including the trans-Bittner-Howard pathway changes the products significantly at all simulated temperatures (550-1800 K) and pressures (5.33 × 102-107 Pa), relative to a cis-only model. Typically, naphthalene remains the dominant product, but its abundance decreases at higher temperatures and pressures. For example, at 1200 K and 105 Pa, its branching ratio decreases from 78.5% to 62.9% when the trans pathway is included. At higher temperatures this decrease corresponds to the formation of alternative C10H8 isomers, including the cis product benzofulvene with 8% maximum abundance at 1200 K and 5.33 × 102 Pa, and E-2-ethynyl-1-phenylethylene, a trans product with 26% maximum abundance at 1800 K, with little pressure dependence. At higher pressures, our model predicts a range of C10H9 radicals, including resonance-stabilised radicals (RSRs). The impact of trans-vinyl radical chemistry in reactive environments means that they are essential to accurately describe combustion reactions and inhibit soot formation.

Laminar burning velocity and cellular instability of spherical propagation NH3/H2/air premixed flames under elevated temperature and pressure

ABSTRACT Due to their carbon-free emission characteristics, ammonia and hydrogen are increasingly valued as clean energy sources. Laminar burning velocity and flame stability are two key indicators for assessing the combustion characteristics of fuels. Nonetheless, research on ammonia/hydrogen/air mixture flames under high-temperature and high-pressure conditions still requires further exploration. Consequently, this study measured the specific impact of hydrogen concentration on laminar burning velocity and flame instability under high-temperature and high-pressure conditions. Experiments were conducted under a range of conditions, including a temperature of 423 K, pressures from 1 to 3 atm, and hydrogen concentrations ranging from 0.1 to 0.5. To gain a comprehensive understanding of the combustion characteristics of ammonia/hydrogen/air mixture flames, the experiments also examined different equivalence ratios, varying from 0.8 to 1.4. The results showed that as the hydrogen concentration in the mixture increases, the laminar burning velocity (LBV) of the NH3/H2/air mixture increases exponentially. The pressure dependence of laminar burning velocity showed a negative correlation across different equivalence ratios, suggesting that pressure inhibits the laminar burning velocity of ammonia/hydrogen/air mixtures. A fictitious gas approach distinguished between thermal and chemical effects on the laminar burning velocity of premixed flames, indicating that the chemical effect outweighs the thermal effect. Schlieren images of ammonia/hydrogen/air flames under varying hydrogen concentrations revealed an increase in flame surface wrinkles as hydrogen concentrations increased. The stability of the ammonia/hydrogen/air flame was further investigated using linear stability theory. The dimensionless growth rate transitioned from negative to positive with increasing hydrogen concentration, indicating enhanced flame instability. Sensitivity analysis highlighted that the promoting effect of reaction R1 is particularly significant at high hydrogen concentrations, resulting in increased production of O and OH radicals, which facilitates the combustion reaction.

Experimental and numerical investigation of abnormal combustion phenomena in high-performance hydrogen direct-injection engine operated in stochiometric conditions

Nowadays the use of Hydrogen (H2) within Internal Combustion Engine (ICE) represents a valuable solution also for high-performance applications since it allows carbon free combustion process preserving, at the same time, the driving experience of the engines fuelled with conventional fuels. On the other side, the low ignition energy and the high flammability range may lead to a high probability of abnormal combustion events especially at high engine loads. Therefore, this work aims at investigating the occurrence of knock and pre-ignition phenomena in a high-performance Direct Injection (DI) single cylinder Spark Ignition (SI) engine through the synergistic use of numerical simulations and experimental activities. A 3D-CFD model was calibrated against a set of experimental measurements. The engine model showed satisfactory predictive capabilities with a good matching with the experimental in-cylinder pressure traces. This virtual test rig was then used to investigate the impact of a different coolant temperature and different injector recess in terms of knock and pre-ignition tendency, and most of all, to define a robust simulation methodology to estimate the risk of hydrogen abnormal combustion events.

"Орловский" кенішінің мысалында өзін-өзі қыздыру себебін және эндогендік өрттердің ықтимал пайда болуын талдау

Almost all mining companies developing deposits of polymetallic ores are faced with the phenomenon of self-heating and spontaneous combustion of ore as a result of oxidation. Sometimes, when it is impossible to conduct mining operations, such exceptional measures are taken as the liquidation of the mine by flooding. The current state of knowledge of the causes of the occurrence of underground endogenous fires in the development of copper-sulfide deposits suggests that the presence of wood in the worked-out area contributes to the faster occurrence and more intense flow of endogenous fires, since spontaneous combustion of sulfide ore is possible at a temperature of 350-500°C, and the temperature ignition of hydrolyzed wood – 180-200°С. The purpose of the article was to establish the causes of self-heating of the ore body and contacts of host rocks based on studies of the thermodynamic consequences of the oxidation of sulfide ores. The evaluation of the results on the analysis of the problem of endogenous fire hazard in the underground development of sulfide ores at the stage of exploration of the Orlovsky deposit of copper-and-titanium ores was carried out. The research methods are thermographic studies of ores and host rocks that were carried out in the laboratory conditions of the UNIIPROmed and consisted in determining the ignition temperature and the conditional oxidation rate with a continuous uniform temperature increase.

Fire Inside the Cavity of a Non-flammable Facade: Step-by-Step Development of Multiphysics Computer Simulations

AbstractThe cavities in a building facade can significantly increase the fire hazard, acting as pathways and accelerators for the vertical spread of flames and smoke, even in non-combustible facades. Ensuring fire safety during facade design requires a thorough understanding of how cavity geometry influences fire dynamics. However, established theories for this phenomenon are lacking. Therefore, in this study, we use the computational fluid dynamics code FireFOAM to develop step-by-step multiphysics simulations incorporating fluid mechanics, heat transfer, buoyancy, and combustion phenomena to investigate the non-linear behaviour in narrow vertical cavities. Four scenarios of increasing complexity are modelled and validated against experimental data from the literature. The simulations predict flow velocities and convective heat fluxes within 20% error and buoyancy-driven flow, radiative heat flux, and flame height predictions within 30% error across a range of cavity widths. The study also highlights the limitations of the models, offering insights for future refinement. The results demonstrate that computer simulations can reliably be used to study critical phenomena of cavity fires and, with future improvements, predict fire behaviour across various facade designs and conditions.

How did investigations into spontaneous human combustion influence alcohol medicine? An examination of the medical and literary discussions that brought the two together.

The presence of sections or chapters on spontaneous human combustion in more than half of the key texts in English on the action of alcohol on the body and mind in the first half of the nineteenth century demonstrates the seriousness with which it was considered. We aimed to chart discussions about the links between spontaneous human combustion and spirit drinking in medical texts and representations in fiction through three key chronological periods from 1804 to 1900. A contextual analysis using eighteenth- and nineteenth-century historical, literary and medical sources to chart and reflect on public and medical discourses. The development of new theories about the action of alcohol on the body and mind appears to have been influenced by the now-discredited eighteenth- and nineteenth-century idea that the phenomenon of human combustion, spontaneous or not, was linked to spirit drinking. As an extreme example of the consequences of heavy drinking, spontaneous human combustion was used to underpin early theories on the clinical chemistry of alcohol.

Thermodynamic model of coal direct chemical looping combustion

ABSTRACT Chemical looping combustion (CLC) technology offers cost-effective CO2 emission reduction. Coal direct chemical looping (CDCL) emerges as a promising solid fuel CLC technology owing to its ability to directly utilize coal without prior gasification, enhancing system integration and efficiency. Despite significant progress in CDCL, challenges persist, including carbon deposition and insufficient oxidation and reduction of oxygen carriers (OCs). This study conducted a thermodynamic equilibrium analysis of a CDCL combustion reactor using Cantera 3.0, a chemical calculation module developed at the California Institute of Technology. The analysis explored the impact of different temperatures, OC-to-coal molar ratios (θ), and OCs types on combustion products. By employing the minimum Gibbs function method and analyzing intrinsic reaction mechanisms, the study provides insights for predicting and optimizing system performance. Thermodynamic equilibrium analysis revealed that with CuO as the OC, insufficient OC (θ < 0.6) led to Cu as the reduction product, while sufficient OC (0.6 < θ < 1.3) yielded Cu and CuO, and excess OC (θ > 1.3) resulted in Cu2O. To optimize CO2 capture, a molar ratio of θ of at least 1.4 and a temperature of at least 800°C are recommended. When Fe2O3 served as the OC, insufficient OC (θ < 0.45) produced Fe and FeO, while excess OC generated FeO and Fe3O4. Optimal operational performance and CO2 capture efficiency required an OC-to-coal molar ratio exceeding 1.4 and a temperature higher than 700°C. This study demonstrates that in CDCL combustion systems, selecting appropriate OCs, temperatures, and OC-to-coal molar ratios ensures stable and efficient combustion and CO2 capture. These findings offer crucial guidance for optimizing system operation.

Oxygenated VOC Detection Using SnO2 Nanoparticles with Uniformly Dispersed Bi2O3.

Bi2O3 particles are introduced as foreign additives onto SnO2 nanoparticles (NPs) surfaces for the efficient detection of oxygenated volatile organic compounds (VOCs). Bi2O3-loaded SnO2 materials are prepared via the impregnation method followed by calcination treatment. The abundant Bi2O3/SnO2 interfaces are constructed by the uniform dispersion of Bi2O3 particles on the SnO2 surface. The results of oxygen temperature-programmed desorption suggest that Bi2O3-loaded SnO2 samples display improved surface oxygen ions than neat-SnO2 NPs. As a result, the gas sensor based on 1 mol% Bi2O3-loaded SnO2 (1Bi-L-SnO2) composites shows significantly higher sensitivity and a faster response speed toward various oxygenated VOCs compared with SnO2, especially at 200 °C and 250 °C. The results of catalytic combustion and temperature-programmed reaction measurements reveal the dominant role of adsorption and partial oxidation during ethanol combustion on SnO2 and 1Bi-L-SnO2 surfaces. In this case, the improvement in the sensing performance of the 1Bi-L-SnO2 sensor can be associated with the increase in surface oxygen ions at Bi2O3/SnO2 interfaces. The results confirm the significant role of surface functionalization for sensing materials. The obtained outstanding sensing performance provides the potential application for the simultaneous detection of total oxygenated VOCs in practice.

Generation of Charges During the Synthesis of Nanopowders of Doped Cerium Dioxide in Combustion Reactions.

The development and characterization of synthesis techniques for oxide materials based on ceria is a subject of extensive study with the objective of their wide-ranging applications in pursuit of sustainable development. The present study demonstrates the feasibility of controlled synthesis of Ce1-xMxO2-δ (M = Fe, Ni, Co, Mn, Cu, Ag, Sm, Cs, x = 0.0-0.3) in combustion reactions from precursors comprising glycine, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, and cellulose as organic components. Controlled synthesis is achieved by varying the composition of the precursor, the type of organic component, and the amount of organic component, which allows for the influence of the generation of high-density electrical charges and outgassing during synthesis. The intensity of charge generation is quantified by measuring the value of the precursor-ground potential difference. It has been demonstrated that an increase in the intensity of charge generation results in a more developed morphology, which is essential for the practical implementation of ceria as a catalyst to enhance contact with gases and solid particles. The maximum value of the potential difference, equal to 68 V, is obtained during the synthesis of Ce0.7Ni0.3O2-δ with polyvinyl alcohol in stoichiometric relations, which corresponds to a specific surface area of 21.7 m2 g-1. A correlation is established between the intensity of gas release for systems with different organic components, the intensity of charge generation, morphology, and the value of the specific surface area of the samples.

Effect of deep eutectic solvent on combustion characteristics of lignite under thermal treatment conditions

AbstractThe substantial moisture content of lignite imposes considerable constraints on its deep processing and subsequent utilization. A deep eutectic solvent (DES), synthesized from choline chloride (ChCl) and zinc chloride (ZnCl₂), was used to upgrade lignite under thermal treatment conditions. The effects of the DES molar ratio and its addition on the physicochemical and combustion characteristics of lignite were systematically analyzed at 280°C. The results demonstrated that the moisture content of lignite decreased from 22.63% to 5.18%, and then to 6.05%, as the molar ratio of DES was adjusted from 1:1 to 1:3, with the addition of 3 g of DES. This suggests that a DES molar ratio of 1:1 is more effective for lignite upgrading. As the DES addition increased from 1 g to 3 g, the moisture content of lignite decreased from 9.19% to 5.18%. As the molar ratio of ZnCl₂ in DES increased, the maximum combustion rate (Vmax) and ignition index (C) of the upgraded coal sample gradually decreased, indicating that lignite upgraded with DES at a 1:1 molar ratio exhibited good combustion performance. The sample treated with 3 g of DES demonstrated the best overall combustion characteristic index (S = 1.8), optimal ignition index (C), and combustion index (Rj), when the DES addition increased from 1 g to 3 g. Compared to raw coal, the activation energy of the upgraded lignite was lower (Eₐ = 63.99 kJ/mol), indicating enhanced combustion reactivity.

Combustion Characterization and Kinetic Analysis of Coupled Combustion of Bio-Syngas and Bituminous Coal

The coupled combustion of bio-syngas and bituminous coal is an effective technology to reduce pollutant emissions from coal-fired power plants and improve the utilization rate of biomass energy. However, the effects of bio-syngas blending on bituminous coal combustion characteristics and reaction kinetics remain unclear, restricting the development of bio-syngas and bituminous coal combustion technology. In this study, the experimental studies on the coupled combustion of bio-syngas and bituminous coal under different bio-syngas lower-heating-value-based blending ratio (BLBR) were carried out by Micro-Fluidized Bed Reaction Analyzer (MFBRA), the coupled combustion characteristics and kinetic reaction mechanism of coupled combustion of bio-syngas and bituminous coal were analyzed. The results indicated that the nucleation and growth model (F1 Model) provided a reasonable description of the bituminous coal combustion process on the coupled combustion of bio-syngas and bituminous coal in MFBRA. The blending of bio-syngas significantly reduces the apparent activation energy and pre-exponential factor of bituminous coal combustion reaction. In particular, when the BLBR is 5, 10, 20, and 30%, the apparent activation energy is 48.70, 45.45, 46.75, and 42.35 kJ·mol−1, and the pre-exponential factor is 9.26, 7.10, 8.95, and 6.70 s−1, respectively. This research is helpful for improving the coupled combustion efficiency and ensuring the efficient operation of the coupled combustion system.

The Conversion of Ethanol to Syngas by Partial Oxidation in a Non-Premixed Moving Bed Reactor

An experimental investigation into the conversion of ethanol to syngas by partial oxidation in a non-premixed counterflow moving bed filtration combustion reactor was carried out. Regimes of conversion depending on the mass flow rates of fuel and air (separate feeding), as well as a granular solid heat carrier, were studied. Depending on the mass flow rate of the heat carrier, two combustion modes were realized—reaction trailing and intermediate—with different temperature patterns in the gas preheating, combustion, and cooling zones along the reactor. The product gas composition is far from the predictions of the equilibrium model; it contains substation fractions of methane and ethylene. Combustion temperature and conversion are limited by the relatively high level of heat loss from the laboratory-scale reactor. The effect of the heat loss can be reduced by enhancing the absolute flow rate of the reactants.

Temperature-sensitive intelligent gel to prevent coal spontaneous combustion: Large-scale simulation fire extinguishing experimental study

Coal spontaneous combustion seriously endangers mine safety production. In this study, a temperature-sensitive intelligent gel was synthesised from methylcellulose (MC), polyethene glycol (PEG) and sodium chloride (NaCl). The flow characteristics of temperature-sensitive intelligent gel (abbreviated as TSIG) under different conditions were analyzed by viscosity test. An infrared spectrometer also analyzed the microscopic flame retardant mechanism of temperature-sensitive intelligent gel. A large-scale simulation fire extinguishing test bench was designed at the coal mine site to analyze the flame retardant effect of the temperature-sensitive intelligent gel on coal oxidation reaction at different injection temperatures. The results show that the temperature-sensitive intelligent gel undergoes a liquid–solid phase transition at a temperature higher than 60 °C. When MC: PEG: NaCl = 1: 6: 5, the temperature-sensitive intelligent gel showed the best flow characteristics. The large-scale simulation fire extinguishing experiments show that the CO concentration is significantly reduced after the temperature-sensitive intelligent gel is injected at the coal temperature of 300–900 ℃, and both show excellent fire extinguishing effects. The addition of temperature-sensitive intelligent gel can inhibit the number of free radicals in the process of coal oxidation, block the chain reaction of coal spontaneous combustion, and comprehensively inhibit the process of coal spontaneous combustion. The research results provided theoretical support for the application of temperature-sensitive intelligent gel in coal spontaneous combustion areas. Additionally, they guided the design of temperature-sensitive intelligent gel to prevent coal spontaneous combustion technology.