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In this paper, ammonium perchlorate (AP) as a strong oxidant has been added into Al/polyvinylidene difluoride (PVDF) nanothermites. Based on homogeneous structure of PVDF, shorter reaction contact between components can be obtained for more outstanding ignition and combustion performance. Water contact angle experiments were conducted to evaluate the hydrophobicity of the composite films, indicating that the suitability of composite material has enhanced under wet environment. According to TG-DSC results, the thermal decomposition of AP can improve the whole heat release process, which theoretically has excellent combustion performance advantages. Constant volume pressure tests were conducted to assess the energy release properties of the films compared with Al@PVDF films. Combustion performance in air was evaluated by employing optical sensors and a high-speed camera to measure factors such as the ignition delay time, light intensity and combustion flame propagation. After adding 15 % AP, the maximum pressure of Al/AP@PVDF film is 0.0960 Mpa, and that of Al@PVDF film is 0.0805 Mpa. The maximum pressure of the film is increased by nearly 19.25 %. Compared with Al@PVDF film, the ignition delay time of Al/AP@PVDF film is shortened by 45 ms, and the light intensity is increased by nearly 93.39 %. However, excessive AP content adversely impacted film formation efficiency, leading to the deterioration of various properties. Therefore, an optimal AP content of approximately 15 % in Al/AP@PVDF system was finally identified. [ABSTRACT FROM AUTHOR]

• The flame propagation process of R152a under different RH conditions was recorded • The R152a reaction activation energy is reduced in O 2 and O 2 /H 2 O environments. • OH is the crucial active fragment that promotes the oxidation of R152a. • The combustion mechanism of R152a in humid air was revealed. 1,1-difluoroethane (R152a) is one of the most prospective low GWP refrigerants but may trigger fires and explosions once it leaks. Understanding the flame propagation process and combustion mechanisms at different relative humidity conditions is essential to use flammable refrigerants safely. In this study, a high-speed camera has recorded the flame propagation of R152a combustion near the flammability limit. Combining with macroscopic experimental phenomena, we revealed the effect of H 2 O on the microscopic mechanism of R152a combustion by using reactive force field molecular dynamics simulations with a reliable force field. The promotion effects of H 2 O on the oxidation of R152a were revealed from an atomistic perspective. The differences of oxidation intermediates and products in different environments were analyzed for the first time. The H 2 O/O 2 environment was the most potent promoter of R152a decomposition, followed by the O 2 and the pyrolysis environment. The O 2 /H 2 O environment reduced the apparent activation energy of R152a, significantly enhanced the consumption rate of R152a, and enriched the number of species. O 2 reacts with H 2 O or H to form OH to accelerate the reaction process. The H 2 O could provide more OH active fragments for the reaction. Moreover, it promotes the formation of HF and H 2, H 2 O + F→HF + OH, H 2 O + H→H 2 + HO. This study aims to provide a guiding theory for the safe application and disaster prevention of flammable refrigerants. [ABSTRACT FROM AUTHOR]

The investigation of syngas flame propagation has great benefits for the effective use of gas turbines. This essay sets out to study the flame propagation of premixed oxygen-rich combustion (oxygen enrichment coefficient in volume Ω: 0.21, 0.27, 0.32, 0.37) of syngas (H2:CO=2:8) in half-closed rectangular ducts at elevated temperatures (T: 300 K, 400 K, 500 K) and evaluate the effects of initial temperature and oxygen enrichment coefficient on the LBV from sensitivity analysis and kinetic analysis. This paper presents the effect of the expansion effect on laminar burning velocity for the first time, and separates the effect of the expansion effect on laminar burning velocity by a new method. Research shows that as the initial temperature goes up, the faster the exponential growth phase of the flame front velocity, the slower the slow growth phase. The smaller and earlier the maximum flame front velocity arrives, the slower the average flame speed is. As the oxygen enrichment coefficient goes up, the peak value of the flame front velocity gradually decreases. Oxygen-rich combustion and increasing initial temperature inhibit flame propagation in a half-open tube, but promote laminar burning velocity, which increases the key chemical bond and adiabatic flame temperature. The net reaction rate shows that oxygen-rich combustion mainly promotes the combustion reaction of H2(R2). However, increasing the initial temperature mainly promoted the oxidation of CO(R29). Analysis of the reaction path showed that oxygen-rich combustion and increased initial temperature promoted the reaction of H2 and CO with key chemical bonds, increased OH concentration, and inhibited OH cracking reaction. [ABSTRACT FROM AUTHOR]

As a kind of substitute fuel of hydrocarbon fuel, ammonia has gained increasing attention for its potential to reduce carbon emissions. Blending with carbon-neutral methanol is expected to deal with the slow flame speed of ammonia. Nevertheless, the emission of N 2 O, a byproduct of ammonia combustion, would undermine the carbon reduction benefits due to its high global warming potential. This study employed Chemkin to construct a Chemical Reaction Network (CRN) model to analyze the reaction kinetics of ammonia combustion when blended with a small amount of methanol. It finds that the increases in the methanol blending ratio, pressure, and temperature can reduce greenhouse gas emissions effectively. Further analysis indicates that pressure and temperature have distinct effects on the emission mechanisms of N 2 O and NO. Increasing the combustion pressure weakens the chain reactions, thereby reducing the formation of both NO and N 2 O; the increase in initial temperature raises NO emissions, but also promotes the decomposition of N 2 O due to the abundance of H in the post-combustion phase. Optimizing post-combustion efficiency and controlling the formation of NO are crucial for N 2 O emission control. Thus, a staged methanol injection strategy is proposed, where early injection reduces NO emissions and late injection facilitates the decomposition of N 2 O. • Utilize CRN model to analyze the ammonia-methanol combustion kinetics and identify significant N 2 O emission mechanisms. • Different effects of pressure and temperature on N 2 O and NO emissions have been revealed synthetically. • Methanol injection strategies are proposed to efficiently control NO and subsequently decrease N 2 O emissions. • Identify key factors influencing N 2 O emissions, for which, a predictive formula is developed. [ABSTRACT FROM AUTHOR]

In this study, the combustion and emission characteristics of natural gas/diesel dual-fuel engines under low load in diesel pilot ignition (DPI) and reactivity controlled compression ignition (RCCI) combustion modes were compared and analyzed by parametric study. The results show that compared with DPI mode, RCCI mode has lower NOx, CO and HC emissions and relatively higher thermal efficiency. However, under low load conditions, the in-cylinder mean temperature and combustion efficiency were reduced, and HC and CO emissions were still high in the RCCI combustion mode. The combustion characteristics of the fuel in the cylinder are changed by adding argon, hydrogen and syngas into the cylinder. The ability of additives to expand the low load operation range of natural gas/diesel RCCI engine was discussed and compared from the aspects of macroscopic combustion process and microscopic chemical reaction kinetics. The results show that argon, hydrogen and syngas can change the combustion characteristics of fuel. When argon, hydrogen and syngas are added, the gross indicated efficiency (GIE) can be increased from 38.1% to more than 50% compared to the basic condition. Maximum GIE and low HC emissions can be achieved with the introduction of 10% argon mass fraction, while a 20% hydrogen or syngas mass fraction is required to maintain low HC emissions. Therefore, argon has the greatest potential to improve the performance of natural gas/diesel RCCI engines under low load conditions. [Display omitted] • The effect of using Ar, H 2 and syngas on natural gas/diesel RCCI engine at low load. • The RCCI mode has lower NOx, HC, and CO emissions than the DPI mode. • The use of Ar, H 2 and syngas can improve the combustion of RCCI engine at low load. • Ar has the greatest potential to improve the performance of RCCI engines at low load. [ABSTRACT FROM AUTHOR]

Catalyzed diesel particulate filter (CDPF) is the most effective device to control the pollution of particle matter. The regeneration of CDPF is the most important step to maintain efficient work. The combustion kinetics of soot with lubricant-derived ash are investigated over powder and waffle catalysts. The kinetic tests of powder and monolithic mixtures from the engine bench show that the combustion rate constant under 0.25% NO2 is much higher than that under 10% O2. The high combustion rate constants are associated with a low apparent activation energy. Due to the inhibition of the soot–catalyst and soot–NO2 contact, the ash accumulation increases the combustion temperature and decreases the rate constant. Moreover, as the soot particles pack tightly together, the combustion on monolithic CDPF is more difficult than that in the powder mixture. Our study implies that the ash on the CDPF decreases the combustion activity of catalysts in the passive regeneration and affects the triggering of active regeneration controlled by pressure drops. Future development of catalysts needs to focus on uniform porous but stable catalyst layers on CDPF. A practical indicator of effectiveness of such catalysts is the combustion temperature from an engine bench. [ABSTRACT FROM AUTHOR]

Reduction of large combustion mechanisms is usually conducted based on the detection and elimination of redundant species and reactions. Reaction elimination methods are mostly based on sensitivity analysis, which can provide insight into the kinetic system, while species elimination methods are more efficient. In this work, the species‐targeted local sensitivity analysis (STLSA) method is proposed to evaluate the importance of species and eliminate non‐crucial species and their related reactions to simplify kinetic models. This paper comprehensively evaluates the effectiveness of STLSA across various combustion scenarios, including high and low‐temperature ignition and laminar flame speed, using diverse mechanisms like USC Mech II, JetSurf 1.0, POLIMI_TOT_1412, NUIGMech1.1 and so on. Comparisons with graph‐based methods, such as DRG and DRGEP, highlight STLSA's superior efficiency and accuracy. Moreover, STLSA is compared to species‐targeted global sensitivity analysis (STGSA), demonstrating significant computation cost savings and comparable model reduction capabilities. The study concludes that STLSA is a robust and versatile tool for mechanism reduction, offering substantial improvements in computational efficiency while maintaining high accuracy in predicting key combustion properties. [ABSTRACT FROM AUTHOR]

The co-combustion characteristics and synergy of distillery effluent sludge (DES) and sugar mill waste (SMW) were studied by thermogravimetric (TG) analysis. TG data were used to evaluate the combustion indices, synergy, kinetic parameters, and heterogeneous reaction mechanisms. The blend D1S3 (25% DES and 75% SMW) exhibited optimal combustion parameters (Ci = 2.69 × 10−4% min−3, Cb = 1.34 × 10−6% min−4, and CCI = 13.02 × 10−7%2 °C−3 min−2). Mixing DES with SMW resulted in a positive synergy that facilitated effective combustion owing to the presence of Fe, Ca, and Mg in DES, which served as catalysts during combustion. For D1S3, the apparent activation energy (*Ea) calculated using FWO, KAS, and ST iso-conversional methods were 173.3, 172.4, and 172.7 kJ mol−1, respectively. The master plots revealed that the combustion process was governed by the D1, D3, F2, and F3 solid-state kinetic models in different conversion (α) ranges for the wastes and their blends. Finally, the presence of alkaline and alkaline-earth elements (Na, K, Mg, and Ca) was confirmed through ash characterization. Thus, the ash can be considered a possible supplementary cementing material for end-use applications. [ABSTRACT FROM AUTHOR]

Flue gas recirculation has emerged as a promising low-NOx emission technology in advanced gas turbines, while the slower oxidation rate induced by the low oxygen content could potentially cause combustion instability. We conducted an experimental investigation in a single-nozzle swirl combustor to examine the impact of oxygen content, inlet flow rate as well as temperature on combustion instability under oxygen-lean conditions. The results show that reducing oxygen content from 23.3% to 21% leads to reduced amplitudes of pressure pulsation and exothermic pulsation, indicating improved combustion stability. However, further reduction in oxygen content to 18.6% causes a decrease in the combustion reaction rate, resulting in an increase in the amplitude of pressure pulsation. As the oxygen content drops to below 18.6%, the exothermic intensity decreases, which results in a decrease in the amplitude of pressure pulsation. Besides, under oxygen-lean conditions, increasing the inlet temperature is conducive to reducing the amplitude of pressure pulsation and enhancing combustion stability. Additionally, as the incoming flow rate increases from 7.4 to 9.9 m/s, the refined fuel atomization and improved uniformity of oil-gas mixing contributed to decreased pressure pulsation amplitude. Nonetheless, when the incoming flow rate further increases to 12 m/s, the amplitude of exothermic and pressure pulsation increases. [ABSTRACT FROM AUTHOR]

This paper examines a new Conditional Source-term Estimation (CSE) implementation in which an integral inversion is performed for species mass fractions without any chemistry tabulation. To tackle the numerical stiffness due to chemistry, a constant-pressure chemical reactor is considered in conditional space. The objective of this work is to investigate this new method in CSE by comparing its numerical performance (accuracy of predictions and computational efficiency) with previous CSE implementations using tabulated chemistry. For the first time, the constraints for mass and mixture fraction conservation in conditional space are included in the inversion process. The investigation is performed in a Reynolds Averaged Navier-Stokes (RANS) framework using a well-documented turbulent flame with detailed measurements in conditional and physical spaces for many reacting scalars. A chemical mechanism including 16 species and 35 reactions is incorporated. CSE predictions of conditional and Favre averaged temperature and different species mass fractions are analysed. CSE with full chemistry performs as well as CSE with tabulated chemistry, if not slightly better. Numerical errors are discussed. The new CSE implementation is made possible by the proposed numerical treatment of stiffness due to chemistry and first-order Tikhonov regularisation technique with additional physical constraints. The new approach is found to be more CPU intensive than CSE with a pre-tabulation technique, but as a preliminary analysis, the computational cost of CSE with direct integration of a chemical mechanism appears to be much smaller than the run time associated with CMC for a similar set-up. Further investigation is required to refine this initial conclusion. These results open new opportunities towards CSE simulations that involve fuel blends and more complex operating conditions for example with spray and multi-stream inlets with non-uniform compositions for which accurate chemistry tabulations are difficult to generate. [ABSTRACT FROM AUTHOR]

In order to solve the problems of conventional water injection development difficulties and low recovery factor in low-permeability reservoirs, the method of high-pressure air drive is adopted to achieve the purpose of reservoir energy enhancement and efficiency improvement. This paper conducted an experimental study on the mechanism of low-temperature oxidation (LTO) for crude oil in the process of high-pressure air flooding, elaborated the relationship between the LTO properties of crude oil and the temperature, pressure, and water saturation of the reservoir, and analyzed the differences in LTO oxygen consumption and oil components under different reaction conditions. In addition, combined with the air flooding physical simulation experiment, the dynamic evolution law of recovery rate in the air flooding process was revealed. Findings from this inquiry indicate that an escalation in the oxidation temperature significantly amplifies the oxygen incorporation reaction within the crude oil matrix. This augmentation in oxidative conditions leads to an uptick in oxygen consumption, which subsequently precipitates a reduction in the lighter fractions of the oxidized oil while enriching its heavier components. Elevated pressures were found to enhance the propensity for the amalgamation of unstable hydrocarbons with oxygen, fostering comprehensive and heterogeneous oxidation reactions. Notably, an excessive presence of water was observed to detrimentally affect the thermal efficacy of crude oil oxidation processes. In the context of low-permeability reservoirs, air injection techniques have emerged as superior in effectuating oil displacement, although an increase in injection pressures has been associated with the phenomenon of gas channeling. Interestingly, adopting a sequential strategy of initiating water flooding before air flooding facilitated the conveyance of high-pressure air via established flushing channels, although it appeared to attenuate the intensity of crude oil oxidation, culminating in an oil recovery efficiency peaking at 51%. [ABSTRACT FROM AUTHOR]

As an emerging environmentally friendly fuel, biodiesel has excellent fuel properties comparable to those of petrochemical diesel. Oleic acid methyl ester, as the main component of biodiesel, has the characteristics of high cetane number and low emission rate of harmful gases. However, the comprehensive chemical conversion pathway of oleic acid methyl ester is not clear. In this paper, the reactive force field molecular dynamics simulation (ReaxFF-MD) method is used to construct a model of oleic acid methyl ester pyrolysis and combustion system. Further, the chemical conversion kinetics process at high temperatures (2500 K–3500 K) was studied, and a chemical reaction network was drawn. The research results show that the density of the system has almost no effect on the decomposition activation energy of oleic acid methyl ester, and the activation energies of its pyrolysis and combustion processes are 190.02 kJ/mol and 144.89 kJ/mol, respectively. Ethylene, water and carbon dioxide are the dominant and most accumulated products. From the specific reaction mechanism, the main pyrolysis path of oleic acid methyl ester is the breakage of the C-C bond to produce small molecule intermediates, and subsequent transformation of the ester group radical into carbon oxides. The combustion path is the evolution of long-chain alkanes into short-carbon-chain gaseous products, and these species are further burned to form stable CO2 and H2O. This study further discusses the microscopic combustion kinetics of biodiesel, providing a reference for the construction of biodiesel combustion models. Based on this theoretical study, the understanding of free radicals, intermediates, and products in the pyrolysis and combustion of biomass can be deepened. [ABSTRACT FROM AUTHOR]

Co-combustion is a technology that enables the simultaneous and efficient utilization of biomass and coal gangue (CG). Nevertheless, the factors that affect the combustibility of co-pyrolytic char, which represents the rate-determining step of the entire co-combustion process, remain unclear. This study investigates the impact of the physicochemical properties of co-pyrolytic char, including pore structure, carbon structure, and alkali metals, on the combustion characteristics. The TGA analysis indicates that the ignition and burnout temperatures of the co-pyrolytic char increase as the CG mixing ratio increases, resulting in a prolonged combustion. This is due to the fact that the carbon structure of the co-pyrolytic char becomes increasingly aromatic, accompanied by a reduction in aliphatic hydrocarbons and oxygen-containing groups as the CG mixing ratio increases. Furthermore, the high ash content of the CG is another significant factor contributing to the observed reduction in combustibility. The reaction between mullite, quartz in CG, and alkali metals in biomass results in the formation of aluminosilicate, which reduces the catalytic ability of alkali metals. Furthermore, the char combustion kinetics are analyzed by the KAS method, and the results indicate that the introduction of CG increases the activation energy of the entire char combustion process. The activation energy of the 80RS20CG is within the range of 102.22–164.99 kJ/mol, while the RS char is within the range of 89.87–144.67 kJ/mol. [ABSTRACT FROM AUTHOR]

The oxidative combustion and pyrolysis characteristics of gas coal with different water content (2.86%, 9.06%, 15.81%, 22.83%, and 30.12%) were systemically investigated by thermogravimetric – differential scanning calorimetry and low-temperature oxidation experiments. Results show that the mass loss and heat absorption-exothermic pattern are inconsistent in oxidative combustion and pyrolysis processes of gas coal containing water. The behavior of internal water dissipation in gas coal is consistent in oxidative combustion and pyrolysis processes, but the influence on them is significantly different in high-temperature stage (450–600 ℃), the internal water dissipation behavior makes the coal pyrolysis reaction faster and makes the coal oxygen reaction slower. [ABSTRACT FROM AUTHOR]

The goal of the present study is to build a computational combustion model and numerically investigate the stoichiometric mixture fraction generated from blending liquid n-pentane fuel with liquid hydrogen applied in the form of combustible spray droplets. The mixture fraction-probability density function is used to construct the combustion model. The role of the mixture fraction that is generated from blending n-pentane and hydrogen at different mass fraction ratios. From the numerical results, the increase in H 2 blending in the C 5 H 12 /H 2 mixture increases the temperature and velocity of the flame. Furthermore, the addition of hydrogen expands the reaction zone to locations downstream of the flame. The enrichment of the reactive mixture with H 2 reduces the emission of CO. Only in the reaction zone does hydrogen fuel enrichment decrease the mass fractions of CO and OH. The results confirm that the PDF-RANS model gives satisfactory agreement with the experimental data. [Display omitted] • The addition of liquid hydrogen to the n-pentane liquid fuel. • New implementation for the PDF combustion model. • The spray combustion model is being examined in relation to the addition of liquid hydrogen. • Simulation for the spray combustion cases in different blending ratios. • The analyses of the spray combustion zones are made. [ABSTRACT FROM AUTHOR]

The feasibility of the autothermic pyrolysis in situ conversion (ATS) process for low-grade oil shale (OS) has not been determined. In this research, the pyrolysis and combustion properties of Tongchuan OS, with a 4.04% oil yield, were systematically analyzed. The findings revealed that temperatures between 350 and 425 °C favored oil production, while temperatures from 450 to 520 °C resulted in a higher rate of gaseous generation. At 300 °C, the volume expansion and ignition coking caused by the large amount of bitumen generated resulted in severe pore plugging, which significantly increased the combustion activation energy of the residue, while the presence of substantial flammable bitumen also significantly decreased the ignition and combustion temperatures. From 300 to 520 °C, the combustion performance of residue decreases continuously. In addition, pyrolysis residues of Tongchuan exhibited a slightly higher calorific value, between 425 and 520 °C, owing to its higher fixed carbon content (10.79%). Based on the ideal temperature screening method outlined for Tongchuan OS, the recommended preheating temperature for Tongchuan OS was 425 °C, while the optimum temperature for the retorting zone should be 510 °C, considering a heat utilization rate of 40%. These findings contribute valuable insights for the application of the ATS process to low-grade OS. [ABSTRACT FROM AUTHOR]

The contents of alkali and alkaline earth metals are higher in Zhundong coal, and there are serious problems of slagging and fouling during the combustion process. Therefore, it is of great significance to reveal the mechanism of slagging and fouling in the boiler of Zhundong coal. In this paper, first-principle calculations based on density functional theory are used to study the competition mechanism of alkaline metal oxides during the combustion process in Zhundong coal by establishing the Na2O(110)/CaO(100)-SiO2(100) double-layer interface model. The results show that the bond lengths of the surface of Na2O(110) and CaO(100) with SiO2(100) after adsorption were generally lengthened and the value of bond population became smaller, which formed a stable binding energy during the reaction. The electron loss of Na is 0.05 e, the electron loss of Ca is 0.03 e, and the electron loss of Na2O is greater than that of CaO. The charge transfer on the surface of Na2O with SiO2 is obviously higher than that of CaO and the orbital hybridization on the surface of CaO with SiO2 is weaker than that on the surfaces of Na2O with SiO2. Na2O is easier to react with SiO2 than CaO. The adsorption energies on the surface of Na2O and CaO with SiO2 are −5.56 eV and −0.72 eV, respectively. The adsorption energy of Na2O is higher than that of CaO, indicating that Na2O is more prone to adsorption reactions and formation of Na-containing minerals and other minerals, resulting in more serious slagging. In addition, the XRD analyses at different temperatures showed that Na-containing compounds appeared before Ca-containing ones, and the reaction activity of Na2O is stronger than that of CaO in the reaction process. The experimental results have good agreement with the calculation results. This provides strong evidence to reveal the slagging and fouling of Zhundong coal. [ABSTRACT FROM AUTHOR]

The energy release process of the Mg-based hydroreactive fuels directly affects the performance of water ramjet engines, and the burning rate is one of the key parameters of the Mg-based hydroreactive fuels. However, there is not enough in-depth understanding of the combustion process of Mg-based hydroreactive fuels within the chamber of water ramjet engines, and there is a lack of effective means of prediction of the burning rate. Therefore, this paper aims to examine the flame structure of Mg-based hydroreactive fuels with a high metal content and analyze the impact of the water injection velocity and droplet diameter on the combustion property. A combustion experiment system was designed to replicate the combustion of Mg-based hydroreactive fuels within water ramjet engines, and the average linear burning rate was calculated through the target line method. On the basis of the experiment, a combustion–flow coupling solution model of Mg-based hydroreactive fuels was formulated, including the reaction mechanism between Mg/H2O and the decomposition products from an oxidizer and binder. The model was validated through experimental results with Mg-based hydroreactive fuels at various pressures and water injection velocities. The mean absolute percentage error (MAPE) in the experimental results was less than 5%, proving the accuracy and validity of the model. The resulting model was employed for simulating the combustion of Mg-based hydroreactive fuels under different water injection parameters. The addition of water injection resulted in the creation of a new high-temperature region, namely the Mg/H2O non-premixed combustion region in addition to improving the radial diffusion of the flame. With the increasing water injection velocity, the characteristic distance of Mg/H2O non-premixed combustion region is decreased, which enhances the heat transfer to burning surface and accelerates the fuel combustion. The impact of droplet parameters was investigated, revealing that larger droplets enhance the penetration of the fuel-rich gas, which is similar to the effect of injection velocity. However, when the droplet size becomes too large, the aqueous droplets do not fully evaporate, resulting in a slight decrease in the burning rate. These findings enhance the understanding of the mechanisms behind the burning rate variation in Mg-based hydroreactive fuels and offer theoretical guidance for the optimal selection of the engine operating parameters. [ABSTRACT FROM AUTHOR]

To overcome the major challenge of reactive flow simulation for chemical kinetics dominated flame dynamics in supersonic combustion, on-the-fly mechanism reduction for high fidelity simulation of scramjet becomes mandatory. For dynamic adaptive chemistry (DAC) methodology, there are three major factors controlling the accuracy and efficiency of the overall simulation, namely, the mechanism reduction method, error threshold value $${\varepsilon _{DAC}}$$ ε DAC , and search initiating species (SIS). In the present work, systematic investigations of the three influential factors were conducted for large eddy simulation of ethylene-fueled supersonic combustion within a unified DAC framework. The results show that all the four mechanism reduction methods, i.e., DRG, DRGEP, PFA, and DAC-L, are adequate for the combustor's global performance prediction regarding the wall pressure, stable combustion productions, and temperature. However, for intricate flame stabilization characteristics, the DRG, DRGEP, and DAC-L methods yield comparable prediction accuracy in radical distributions, whereas the PFA method leads to relatively large discrepancies compared to direct integration with the detailed mechanism. The DRGEP method obtains the best balance between numerical accuracy and computational efficiency among the four methods, while the PFA method is the most computationally demanding one. Regarding the mechanism reduction error threshold value, the relative errors in physical property predictions increase as the relaxation of the error threshold value. And the comparative study suggests that the $${\varepsilon _{DAC}}$$ ε DAC should not exceed $${10^{- 4}}$$ 10 − 4 for high fidelity simulations of supersonic combustion. Furthermore, the stable species combination, namely, fuel, O2, and N2 incurs larger relative errors in radical mass fraction prediction than the combination including fuel and intermediate species HO2 and CO. Nevertheless, the latter is less computationally efficient than the former as it requires 15% more CPU time to solve the stiff ODE system of the resultant skeletal mechanism. It should be noted that the computational overheads for mechanism reduction under various $${\varepsilon _{DAC}}$$ ε DAC values and SIS combinations are almost the same, and the overall computational efficiency is mainly determined by the CPU time for solving the stiff ODE system of the size-reduced skeletal mechanisms. [ABSTRACT FROM AUTHOR]

A new carrier explosive TNBA was batch synthesized by a chemical method. The prepared samples were characterized using SEM, EDS, XRD, IR, XPS, nuclear magnetic resonance, and elemental analysis techniques. The enthalpy of formation of TNBA was measured using a specialized calorimeter that is specially used in testing of explosives and powders. The thermal decomposition performance of TNBA was tested by DSC technology. Meanwhile, the combustion performance of TNBA was also tested. The results of characterizations showed that the prepared sample was indeed TNBA. The enthalpy of formation of TNBA was determined as ΔHf,TNBA=+48.5 kJ/mol. At a heating rate of 20 °C/min, the thermal decomposition peak of TNBA is at TP=285.3 °C, and the activation energy is EK=91 kJ/mol, which is higher than the Tp and EK values of TNT. This indicates that TNBA is a relatively easy to decompose explosive, but the decomposition rate is not fast. The critical temperature for thermal explosion of TNBA reached Tb=247 °C, which is higher than the Tb value of TNT, slightly lower than the Tb value of DNAN, and significantly higher than the Tb value of DNTF, TNAZ, and MTNP. The combustion performance test results showed that the TNBA sample has the highest combustion pressure and the highest pressurization rate; and the TNBA sample has the highest combustion temperature; however, due to the high oxygen balance, the combustion heat of TNBA samples in excess pure oxygen is not the highest. [ABSTRACT FROM AUTHOR]

Abstract Co-combustion is a technology that enables the simultaneous and efficient utilization of biomass and coal gangue (CG). Nevertheless, the factors that affect the combustibility of co-pyrolytic char, which represents the rate-determining step of the entire co-combustion process, remain unclear. This study investigates the impact of the physicochemical properties of co-pyrolytic char, including pore structure, carbon structure, and alkali metals, on the combustion characteristics. The TGA analysis indicates that the ignition and burnout temperatures of the co-pyrolytic char increase as the CG mixing ratio increases, resulting in a prolonged combustion. This is due to the fact that the carbon structure of the co-pyrolytic char becomes increasingly aromatic, accompanied by a reduction in aliphatic hydrocarbons and oxygen-containing groups as the CG mixing ratio increases. Furthermore, the high ash content of the CG is another significant factor contributing to the observed reduction in combustibility. The reaction between mullite, quartz in CG, and alkali metals in biomass results in the formation of aluminosilicate, which reduces the catalytic ability of alkali metals. Furthermore, the char combustion kinetics are analyzed by the KAS method, and the results indicate that the introduction of CG increases the activation energy of the entire char combustion process. The activation energy of the 80RS20CG is within the range of 102.22–164.99 kJ/mol, while the RS char is within the range of 89.87–144.67 kJ/mol.

In this study, the combustion characteristics and kinetics of cotton straw (CS) particles mixed with polyethylene (PE) film and coal gangue (CG) were investigated. The co-combustion characteristics of CS mixed with PE and CG at different heating rates were revealed by the thermogravimetric method and differential thermogravimetric method. The ignition temperature, burnout temperature, and maximum weight loss rate were measured, and the comprehensive combustion and flammability indexes were calculated. The results showed that the composite combustion characteristic index and flammability index increased with the increase in heating rate. The addition of PE and CG additives could effectively extend the combustion time. The Coats-Redfern (C-R) reaction model and N-order reaction model were used to evaluate the kinetic parameters of the blends. The results showed that 12.5% PE + 12.5% CG particles had the lowest activation energy (Ea = 103.73 kJ·mol−1) at the volatile combustion stage. The dynamics conform to the third-order dynamics model. In addition, the applicability of C-R model, Flynn-Wall-Ozawa (FWO) model, and Starink model in the calculation of activation energy was explored, and it was found that the FWO model is not suitable for the calculation of activation energy of biomass pellet combustion kinetics. This study provides a new method for the development and utilization of mixed fuel particles of cotton stalk and solid waste and expands the application prospect of biomass. [ABSTRACT FROM AUTHOR]

Reactive Molecular Dynamics (MD) and Density Functional Theory (DFT) computations are performed to provide insight into the effects of external electrostatic fields on hydrocarbon reaction kinetics. By comparing the results from MD and DFT, the suitability of the MD method in modeling electrodynamics is first assessed. Results show that the electric field-induced polarization predicted by the MD charge equilibration method is in good agreement with various DFT charge partitioning schemes. Then, the effects of oriented external electric fields on the transition pathways of non-redox reactions are investigated. Results on the minimum energy path suggest that electric fields can cause catalysis or inhibition of oxidation reactions, whereas pyrolysis reactions are not affected due to the weaker electronegativity of the hydrogen and carbon atoms. MD simulations of isolated reactions show that the reaction kinetics is also affected by applied external Lorentz forces and interatomic Coulomb forces since they can increase or decrease the energy of collision depending on the molecular conformation. In addition, electric fields can affect the kinetics of polar species and force them to align in the direction of field lines. These effects are attributed to energy transfer via intermolecular collisions and stabilization under the external Lorentz force. The kinetics of apolar species is not significantly affected mainly due to the weak induced dipole moment even under strong electric fields. The dynamics and reaction rates of species are studied by means of large-scale combustion simulations of n-dodecane and oxygen mixtures. Results show that under strong electric fields, the fuel, oxidizer, and most product molecules experience translational and rotational acceleration mainly due to close charge transfer along with a reduction in their vibrational energy due to stabilization. This study will serve as a basis to improve the current methods used in MD and to develop novel methodologies for the modeling of macroscale reacting flows under external electrostatic fields. [ABSTRACT FROM AUTHOR]

The combustion of hydrogen and carbon-monoxide mixtures, so-called syngas, plays an increasingly important role in the safety context of non-fossil energy generation, more specifically in the risk management of incidents in process engineering plants for ammonia synthesis and in nuclear power plants. In order to characterize and simulate syngas/air combustion on industrially relevant scales, subgrid modelling is required, which is often based on a reaction progress variable. To understand the influence of different fuel compositions, turbulence intensities and flame topologies on different possible definitions of reaction progress variable, detailed chemistry direct numerical simulations data of premixed, lean hydrogen/air and syngas/air flames has been considered. A reaction progress variable based on normalized molecular oxygen mass fraction has been found not to capture the augmentation of the normalized burning rate per unit flame surface area in comparison to the corresponding 1D unstretched premixed flame due to preferential diffusion effects. By contrast, reaction progress variables based on other individual species, such as hydrogen, can capture the augmentation of the rate of burning well, but exhibit a pronounced sensitivity to preferential diffusion effects, especially in response to flame curvatures. However, a reaction progress variable based on the linear combination of the main products can accurately represent the temperature evolution of the flame for different mixtures, turbulence intensities and varying local flame topology, while effectively capturing the augmentation of burning rate due to preferential diffusion effects. However, its tendency to assume values larger than 1.0 in the regions of super-adiabatic temperatures poses challenges for future modeling approaches, whereas the reaction progress variable based on hydrogen mass fraction remains bound between 0.0 and 1.0 despite showing deviations in comparison to corresponding variations obtained from the unstretched laminar flame depending on flame curvature variations. [ABSTRACT FROM AUTHOR]

With the development of hydrogen fuel cell vehicles, hydrogen refuelling stations are required to operate at a higher pressure. However, the safety issue of high pressure hydrogen is always considered as the barrier of the wide application of such transportation infrastructures. In this paper, the safety evaluation is performed on a 70 MPa hydrogen dispenser, as one of the most vulnerable equipment to safety events in hydrogen refuelling stations. The numerical simulations are conducted for the hydrogen leakage and combustion for the prototype of the dispenser. The results show the high radiation during the combustion, and the environmental wind can reduce it by promoting the diffusion of hydrogen. Accordingly, the lethal ranges in different cases are manifested by radiation heat flux at the concerned height for the safety of humans. Furthermore, an improved design of the hydrogen dispenser is proposed to cancel the lower ventilation holes based on the analysis. As a result, the radiation heat fluxes due to the hydrogen combustion after leakage is significantly reduced and consequently lead to smaller lethal ranges, indicating the enhanced safety performance of the hydrogen dispenser. • A numerical study is conducted for the hydrogen combustion from a 70 MPa hydrogen dispenser. • The safety distance is evaluated for hydrogen leakage and combustion of dispensers under different wind conditions. • An improved design of the hydrogen dispenser is proposed and proved to be effective in enhancing the safety performance. [ABSTRACT FROM AUTHOR]

The secondary combustion between unburnt fuel in rocket plume and ambient air significantly affects the stealth characteristics of rocket motors. In order to reveal the effect of secondary boundary layer combustion of hydrogen on rocket plume heat release characteristics, a two-dimensional axisymmetric model for boundary layer combustion between the rocket plume and air is established. The results identifies significant exothermic effect due to secondary combustion reaction between the plume and air. Compared to the nozzle plume without considering secondary combustion, the average temperature of the plume with secondary combustion increases by 47%. As hydrogen content in the nozzle plume increases from 2.7% to 4.2%, the average temperature of the nozzle plume increases by 17.2% due to enhanced combustion heat release. The secondary combustion process is weakened with the increase of flight altitude. The average temperature of the nozzle plume decreases by 11.8% from 2 km to 8 km of flight altitude. This is because both the pressure and temperature of the ambient air decrease when the flying altitude rises, which leads to lower secondary combustion reaction and heat release rate. Moreover, as the ambient pressure decreases, the hydrogen concentration in the plume decreases due to plume expansion effect. The results indicate that hydrogen content and flight altitude affect secondary combustion by different mechanisms. The hydrogen content directly affects the concentration term of the reaction rate of secondary combustion. However, the flight altitude affects the kinetic rate of secondary combustion by changing both the temperature and partial pressure of oxygen. The present study provides better insight into the interaction mechanism between nozzle plume and ambient air. • Established numerical model for secondary combustion of rocket plume. • Higher hydrogen content enhances secondary combustion process. • Secondary combustion heat release is weakened as flight altitude increases. • Secondary combustion is controlled by shear mixing and heat transfer. [ABSTRACT FROM AUTHOR]

Hydrogen (H 2) has been regarded as the most promising sustainable energy. Reliable numerical prediction of its combustion is one of the vital steps towards an ultra-clean energy system. This work was intended to examine the preferential diffusion (PD), which is a major feature of the H 2 fuel, using the Flamelet-Generated Manifold (FGM) combustion model. The major focuses were on the reduced treatment of the PD effects and the impacts on turbulent flame modelling with and without H 2 addition. It is found that the PD hardly influences the velocity prediction even with H 2 enrichment, which can be well modelled merely using a unity L e assumption. The quick burning of H 2 can be captured only when the PD effects are included, which is observed to reinforce the burning intensity near the flame root. The PD terms in the control variable equations are found to be less dominant and the by-effects are twofold: (1) the performance of different reduced PD models is validated to be close; (2) ignoring the PD terms and including the PD effects only in the flamelet-tabulation are acceptable. Nevertheless, for scalar predictions in the recirculation zone, preserving the PD terms is found to be essential. It is observed that a more complete PD model can increase the computation cost up to 11%, but a reduced method can save nearly a half of the cost increment. These observations are significant for accurate and efficient treatment of the PD effects in the turbulent flame simulation. • Different reduced preferential diffusion models in FGM are compared. • Preferential diffusion effects influence little on velocity prediction. • Preferential diffusion is essential to model the quick burning of H 2. • Preferential diffusion terms are negligible if without recirculation zone. • Including preferential diffusion only in flamelet-tabulation is acceptable. [ABSTRACT FROM AUTHOR]

Oil shale is a critical strategic resource with enormous reserves. In-situ combustion technology offers great potential for the development of oil shale reserves. In this study, the combustion behavior and kinetics of Domanik oil shale were investigated using High Pressure Differential Scanning Calorimetry. Additionally, the thermal behavior of the oil shale during combustion was studied by using a self-designed Porous Medium Thermo-Effect Cell. Furthermore, the stability of the combustion front and the upgrading effect of the combustion process were investigated with Visual Combustion Tube, and the produced oil was analyzed to evaluate its quality. The results showed that the combustion process of oil shale is characterized by two reaction stages. The oil shale was found to form enough coke residue during the oxidation reactions to allow for stable propagation of a combustion front. The produced oil was of better quality compared to the naturally produced bitumen in oil shale, which indicates that the combustion process had a good upgrading effect. The findings of this study provide a better understanding of the in-situ upgrading process of kerogen and provide significant knowledge about the combustion mechanism of oil shale for its potential development using the in-situ combustion technology. [ABSTRACT FROM AUTHOR]

DAP-4(C6H18N3Cl3O12) is a novel molecular perovskite energetic materials compound that is characterized by high energy, high thermal stability and high oxidation stability. The properties of DAP-4 were enhanced by preparing mixtures of 5%, 10%, 15%, 20%, and 30%SnO2/Al/DAP-4 using the solvent evaporation method. The morphology and structure of the samples were characterized using scanning electron microscopy and energy dispersive spectroscopy. The thermal decomposition characteristics of the samples were analyzed using differential scanning calorimetry and thermal reconnection techniques. The combustion performance test device was used to comparatively analyze the burning pressure, flame temperature, and heat of combustion of the samples. The optimal preparation ratio was determined, and the thermal decomposition mechanism of the SnO2/Al/DAP-4 mixture was deduced. The findings suggest that: The SnO2 and Al powders can be uniformly mixed with DAP-4, leading to the creation of a SnO2/Al/DAP-4 composite that displays outstanding dispersion properties. At the optimal preparation ratio of 20%SnO2/Al, the activation energy required for the thermal decomposition of SnO2/Al/DAP-4 is the lowest, at 106 kJ mol−1. This leads to a significant decrease in the peak temperature of the exothermic decomposition of DAP-4. During the combustion process, the addition of 20%SnO2/Al significantly increased the combustion intensity of DAP-4. This resulted in an increase in the combustion pressure up to 1.1 MPa and a rise in the flame temperature up to 3136 ℃, releasing more combustion heat compared to the feedstock and other proportions of the SnO2/Al/DAP-4 mixtures. [ABSTRACT FROM AUTHOR]

One strategy for utilizing ammonia as an energy vector is to replace conventional hydrocarbons with hydrogen-enriched ammonia in existing or retrofitted combustors. However, the strong differential diffusion effect of hydrogen can significantly alter the combustion properties and cause challenges in combustor operability. Therefore, this numerical study performs a systematic investigation on the effect of differential diffusion on fundamental combustion properties of ammonia/hydrogen fuel blends. The investigated combustion properties span from the initiation of combustion, i.e., ignition, to stretched flame propagation and ultimately to flame stabilization mechanisms. The objective is to evaluate the feasibility of hydrogen/ammonia/air mixtures as substitutes for methane/air particularly considering the implications of differential diffusion effects. To this end, four fuel blends with similar unstretched burning properties are selected: fuel lean ammonia/hydrogen (AH-L), fuel rich ammonia/hydrogen (AH-R), fuel lean methane (M-L) and fuel lean methane/hydrogen (MH-L). First, the forced ignition and stretched flame propagation are evaluated. It is found that the AH-L (AH-R) mixture has a large negative (positive) Markstein length, and thereby among the selected fuel blends, AH-L (AH-R) has the lowest (highest) minimum ignition energy. Then flame stabilization mechanisms are investigated. For a stable flame, AH-L (AH-R) has an intensified (weakened) flame base and a weak (strong) flame tip, which shows a higher flashback (blow-off) propensity. Based on the critical gradient theory, a novel stability regime diagram is proposed. With the regime diagram, the flame stabilization limits (central flashback, boundary layer flashback, stable, and blow-off) and flow conditions can be determined for burners of different sizes. [Display omitted] • Feasibility of H 2 /NH 3 as a substitute fuel for CH 4 was evaluated (4 blends with equal s L 0). • A systematic analysis on ignition, flame propagation and stabilization was performed. • The rich (lean) H 2 /NH 3 mixture is more difficult (easier) to ignite than CH 4 mixture. • The rich (lean) H 2 /NH 3 flame is more prone to blow-off (flashback) than CH 4 mixture. • A flame stability regime diagram based on critical gradient theory was proposed. [ABSTRACT FROM AUTHOR]

The next-generation energy economy relies heavily on hydrogen. Handling hydrogen during production, storage, and transportation requires risk mitigation. In this regard, the application of halide-free additives is very crucial. The present study experimentally and theoretically investigates the individual and combined inhibiting effect of propane and propene on hydrogen-air explosions. The experiments are carried out at 298 K and 1 bar, with additives ranging from 0.5 to 5% for the individual and 1–2% each for the combined effect in the 20–50% hydrogen-air mixture. Experimentally, the additive content in the stoichiometric and rich mixture decreases the explosion pressure, maximum pressure rise (MPR) rate, laminar burning velocity (LBV), and flame temperature, while increasing minimum ignition energy. For instance, the addition of 2% propane in a 50% hydrogen-air mixture, reduces the MPR rate by 98%, whereas such an effect is observed with 2.5% propene. Theoretical study shows that 3% equivalent additive augments inhibiting reactions, countering the main flame-promoting reaction R1 (H + O 2 O + OH) and thereby reducing LBV. Due to its low activation energy, propene consumes the active radicals twice the rate of propane, while propane not only scavenges the active radicals but also promotes oxygen consumption in the prior phase of combustion, weakening flame propagation. Overall, this approach exhibits a significant step forward in harnessing the potential of hydrogen while mitigating the safety risks associated with its use. [Display omitted] • The effect of C 3 -Hydrocarbons and their Mixtures on H2-air explosion is explored. • The additives decrease explosion pressure, MPR rate and LBV while increasing MIE. • Propene increases the consumption rate of active radicals in the additive mixtures. • Propane promotes oxygen consumption in the prior phase of combustion, countering R1. [ABSTRACT FROM AUTHOR]

Ammonia is considered one of the most promising fuels, and mixing ammonia with hydrogen as fuel can achieve zero carbon emissions for engines. In this study, an experimental platform for an ammonia/hydrogen rotary engine was constructed, and successful ignition combustion was performed, demonstrating the possibility of the ammonia/hydrogen rotary engine. A 3-dimensional computational model of the ammonia/hydrogen rotary engine coupled with chemical reaction mechanisms was established, and the dependability of the model was confirmed using experimental data. Using numerical simulations, the impact of hydrogen injection position and time on the distribution of the fuel-air mixture, the propagation of flames, and the emissions of NO X in the cylinder under direct hydrogen injection have been studied. The research shows that the injection position and timing of hydrogen can affect airflow movement by changing the impingement angle and cylinder swirl intensity to alter hydrogen distribution in the cylinder under the guidance of the cylinder wall. Furthermore, with a delay in hydrogen injection timing, the turbulence kinetic energy in the cylinder gradually increases and is consistently more significant than that under premixed conditions, with turbulence kinetic energy in Case B-190 approximately 60% higher than that under premixed conditions. When more hydrogen is around the spark plug, the initial flame kernel is formed faster, resulting in a notable acceleration of the fuel-air mixture's combustion rate within the cylinder. In contrast to alternative hydrogen injection strategies, the injection strategy that employs nozzle A and an injection timing of 230°CA (BTDC) can achieve the highest cylinder pressure and lower NO X emissions. • A CFD computational model of ammonia/hydrogen rotor engine was established and validated. • Hydrogen has a greater impact on the flame development compared to ammonia. • Direct injection of hydrogen enhances the turbulent kinetic energy within the cylinder. • Optimizing the direct injection method of hydrogen can effectively reduce the emission of NOx. [ABSTRACT FROM AUTHOR]

Drop-in fuels for aviation gas-turbine engines have been introduced recently to mitigate global warming. Despite their similarity to the fossil fuel Jet A-1, their combustion in traditional combustors should be thoroughly analyzed to maintain engine health and low emissions. The paper introduces criteria for assessing the impact of the chemical composition of fuels on combustion in the DEGN 380 turbofan. Based on previous emission-test results, the power functions of carbon monoxide and its emission index were adopted as the model of combustion. Based on the general notation of chemical reactions leading to the production of CO in combustion, the regression coefficients were given a physical meaning by linking them with the parameters of the kinetic equations, i.e., the reaction rate constant of CO and CO2 formation expressed as exponential functions of combustor outlet temperature and the concentration of O2 in the exhaust gas, as well as stoichiometric combustion reactions. The obtained empirical functions show that, in the entire range of engine operating parameters, synthetic components affect the values of the rate constants of CO and CO2 formation. It can be explained by the change in activation energy determined for all chain-of-combustion reactions. The activation energy for the CO formation chain changes in the range between 8.5 kJ/mol for A0 and 24.7 kJ/mol for A30, while for the CO2 formation chain between 29.8 kJ/mol for A0 and 30.8 kJ/mol for A30. The reactivity coefficient lnαiCOACODCO changes between 2.29 for A0 and 6.44 for A30, while lnαiCO2ACO2DCO2 changes between 7.90 for A0 and 8.08 for A30. [ABSTRACT FROM AUTHOR]

The simulation of engine combustion processes, such as autoignition, an important process in the co-optimization of fuel-engine design, can be computationally expensive due to the large number of thermo-chemical scalars needed to describe the full chemical system. Yet, the inherent correlations between the different chemical species during oxidation can significantly reduce the complexity of representing this system. One strategy is to select a subset of representative species that accurately captures the combustion process at a fraction of the computational cost of the full system. In this study, we compare the performance of four different techniques to select these species. They include the two-step principal component analysis (PCA) approach, directed relation graphs (DRGs), the global pathway selection (GPS) approach, and the manifold-informed species selection method. A parametric study of the representative species selection is carried out on data from the simulation of homogeneous and perfectly stirred reactors by investigating seven cumulative variances and 47 different cut-off percentages for the two-step PCA, and 65 and 51 thresholds for the DRGs and GPS, respectively. Results show that these selection methods capture key important species that can accurately describe the chemical system and track each stage of oxidation. The two-step PCA is sensitive to the cumulative variance, and DRGs and GPS are sensitive to the choice of target variables. By selecting key representative species and reducing the number of thermo-chemical scalars, these three methods can be used to develop computationally efficient hybrid chemistry schemes. [ABSTRACT FROM AUTHOR]

The usage of renewable energy is a mitigation phenomenon majorly impacting the power sectors, with biomass being one of the sources directly replacing coal in various applications. This leads to the portrayal of biomass having the potential to be a carbonaceous material, namely the Empty Fruit Bunch (EFB) of oil palm. To increase the characteristics of EFB, it can be converted into carbon-based products through thermochemical processes, such as hydrothermal carbonization. Therefore, this study aimed to compare the characteristics of feedstock and biochar EFB using the TGA method. The heating rate used in this study is 10 - 30°C/min at five °C/min intervals. The effect of heating rate on kinetic parameters and thermal (DTG, TGA) and combustion (T ignition, T burn out) characteristics was also determined. This study carried out the HTC process at temperatures of 210°C and 230°C. The results showed that biochar EFB had a higher ignition, burnout temperature, and activation energy than raw EFB. Ignition temperatures for EFB-HT210°C and EFB-HT230°C were 297°C and 298°C; burnout temperatures for EFBHT210° C, EFB-HT230°C were 407°C and 450° C; and the activation energy for EFB-HT°210C, EFB-HT°230C were 58.84 kJ/mol and 62.16 kJ/mol. Besides the characteristics of biomass, the heating rate also affects combustion. This proved that increased heating rate caused higher ignition and burnout temperature and decreased activation energy. The results also indicated that the difference in heating rate influenced the peak temperature in DTG. [ABSTRACT FROM AUTHOR]

Methylcyclohexane (MCH) is the simplest alkylated cyclohexane, and has been widely employed in surrogate models to represent the cycloalkanes in real fuels. Thus, extensive experimental and kinetic modeling studies have been performed to understanding the combustion chemistry of MCH. However, through a detailed literature analysis, there still lack a systematic theoretical study on the abstraction reactions of MCH, which are the main initial oxidation pathway of MCH. Herein, this work reports a systematic ab initio chemical kinetic study on the abstraction reactions of MCH with different radicals/species. Specifically, reaction rate constants of 30 abstraction reactions of MCH with H/O/OH/O2/HO2/CH3 at different sites are computed using transition state theory (TST) by using quantum chemistry calculation results at DLPNO‐CCSD(T)/CBS//M06‐2X/cc‐pVTZ level. The computed results are incorporated into a detailed mechanism to simulate newly measured ignition delay times (IDTs) of MCH in this work at equivalence ratios of 0.5, 1.0, and 2.0, pressures of 2 and 5 bar, temperatures ranging from 1140 to 1640 K. The updated detailed mechanism demonstrates improvement in the prediction of IDTs, especially at fuel‐rich conditions. The fuel concentration and dilution effect on the IDTs are discussed, and a general Arrhenius expression is adopted to fit the IDTs from both this work and literature work. This work should be valuable for further optimization of detailed kinetic mechanisms and also for gaining insight into the combustion chemistry of MCH. [ABSTRACT FROM AUTHOR]

Studying the relationship between electronic structure and activity helps to understand the catalytic mechanism since the catalytic combustion is a redox reaction dominated by electron transfer. Herein, we regulated the electron energy and O p-band center of La-based perovskite catalysts by a facile method of changing the B-site ion (B = Co, Mn, Fe). The crystal structure, morphology, reducibility, element valence distribution, and catalytic properties of prepared catalysts were characterized. Combining with DFT calculation, it was found that the low electron energy in (110) facets of LaCoO3/SiO2 catalyst contributes to the formation of reactive oxygen species and high-valence Co3+ ions. The highest oxygen adsorption activation capacity of LaCoO3/SiO2 originates from a moderate location of the O p-band center with respect to the Fermi level. As expected, the LaCoO3/SiO2 sample shows higher n-butylamine oxidation activity than that of LaMnO3/SiO2 and LaFeO3/SiO2. This work provides different insights into understanding the activity of La-based perovskite catalysts for oxidation reactions. [ABSTRACT FROM AUTHOR]

Process design critically depends on the characterization of fuels and their kinetics under process conditions. This study steps beyond the fundamental methods of thermogravimetry to modulated (MTGA) and Hi-Res™ (high resolution) techniques to (1) add characterization detail and (2) increase the utility of thermal analysis data. Modulated TGA methods overlay sinusoidal functions on the heating rates to determine activation energy as a function of temperature with time. Under devolatilization conditions, Hi-Res™ TGA maintains a constant mass loss with time and temperature. These two methods, run independently or overlaid, offer additional analysis in which multiple samples at different heating rates are run to different final temperatures. Advanced methods allow researchers to use fewer samples by conducting fewer runs, targeting practical experimental designs, and quantifying errors easier. The parameters of the studies included here vary the heating rate at 10, 30, and 50 °C/min; vary gas-phase oxygen for pyrolysis or combustion conditions; and particle size ranges of 100–125 µm, 400–425 µm, and 600–630 µm. The two biomass fuels used in the studies are pinewood from Northern Sweden and wheat straw. The influence of torrefaction is also included at temperatures of 220, 250, and 280 °C. Apparent activation energy results align with the previous MTGA data in that combustion conditions yield higher values than pyrolysis conditions—200–250 kJ/mol and 175–225 kJ/mol for pine and wheat combustion, respectively, depending on pre-treatment. Results show the dependence of these parameters upon one another from a traditional thermal analysis approach, e.g., the Ozawa-Flynn-Wall method, as well as MTGA and Hi-Res™ thermogravimetric investigations to show future directions for thermal analysis techniques. [ABSTRACT FROM AUTHOR]

This study explores the transition in combustion technologies from dry micro-mix hydrogen-air to wet micro-mix hydrogen-oxygen configurations. The investigation involves a comprehensive analysis of the combustion processes currently being considered for converting methane gas turbines to methane-hydrogen mixtures and hydrogen, including wet premixed, dry low emission, sequential combustion, and micro-mix, examining key parameters such as efficiency, emissions, and overall performance. Then, the work considers the shift from utilizing air as an oxidizer to oxygen. Wet micro-mix hydrogen-oxygen combustion is then discussed for its impact on combustion dynamics and the potential for achieving zero emissions, cancelling NOx emissions in addition to CO 2 emissions. The findings contribute valuable insights into the feasibility and advantages of transitioning from conventional hydrogen-air combustion to innovative wet hydrogen-oxygen combustion, paving the way for more sustainable and environmentally friendly combustion technologies. Scheme of a hydrogen energy storage system comprising one electrolyser, two tanks for the hydrogen and the oxygen, and an O 2 /H 2 /H 2 O gas turbine power system. The system could be able to receive non-dispatchable electricity and release dispatchable electricity working as a battery but without any limitation on the amount of energy storable, or the time of the storage. [Display omitted] [ABSTRACT FROM AUTHOR]

The development of nano-energetic materials has significantly advanced, leading to enhanced properties and novel applications in areas such as aerospace, defense, energy storage, and automobile. This research aims to engineer multi-dimensional nano-energetic material systems with precise control over energy release rates, spatial distribution, and temporal and pressure history. In this context, sol–gel processing has been explored for the manufacture of nanocomposite aluminum thermites using aerogels. The goal is to produce nano-thermites (Al/Fe2O3) with fast energy release rates that are insensitive to unintended initiation while demonstrating the potential of sol–gel-derived aerogels in terms of versatility, tailored properties, and compatibility. The findings provide insightful conclusions on the influence of factors such as secondary oxidizers (KClO3) and dispersants (n-hexane and acetone) on the reaction kinetics and the sensitivity, playing crucial roles in determining reactivity and combustion performance. In tandem, ignition systems contribute significantly in terms of a high degree of reliability and speed. However, the advantages of using nano-thermites combined with hot bridge-wire systems in terms of ignition and combustion efficiency for potential, practical applications are not well-documented in the literature. Thus, this research also highlights the practicality along with safety and simplicity of use, making nano-Al/Fe2O3-KClO3 in combination with hot bridge-wire ignition a suitable choice for experimental purposes and beyond. [ABSTRACT FROM AUTHOR]

A nanostructure of lithium-zinc copper ferrite (LiZnCu-Ferrite) prepared experimentally by the auto-combustion method depends on different parameters. The auto-combustion method operates at a temperature (160 °C) suitable for preparing the required nanostructure ferrite phase. The dependent composition was [Li 0.5-x Zn x Cu x Fe 2.5-x O 4 at (x = 0, 0.05, 0.15, 0.25, 0.35, and 0.45)]. A pre-firing at temperature (650 °C) was applied during the calcination process that was suitable to remove unwanted products. The sintering at temperature (800 °C) was suitable for a pelletized shape of ferrite samples. The X-ray diffraction (XRD) pattern showed a spinel structure of ferrite phase produced for all samples under study with the lattice constant in the range (8.345–8.368 Å) as a function of (x). The crystallite size was in the range (18.41–30.27 nm) calculated by the Scherrer method. The transmission electron microscope (TEM) showed a production of nanorods in the size range (10–45 nm) and nanoparticles in the size range (10–40 nm). There was a coincidence between the results of the XRD and TEM analyses. On the other hand, the scanning electron microscope (SEM) showed the surface morphology and the nature of grain size, which was a sign of the presence of nanostructure; it agreed with the XRD analysis. FTIR spectra showed evidence that the system Li0.5-xZnxCuxFe2.5-xO4 had spinal ferrite nanoparticles successfully prepared by sol-gel auto-combustion. A vibrating sample magnetometer (VSM) showed a change in magnetic parameters as compensation factor (x) increased for all composites of LiZnCu-ferrite such as saturation magnetization (Ms), initial magnetic permeability (μi), remanence (Mr), and coercive force (Hc) that measured from M − H loops. A saturation magnetization increased as a function of (x) and recorded a maximum value at (x = 0.15). While the coercivity, initial magnetic permeability (μi), and remanence magnetization enhanced as a function of (x) and recorded a maximum value at (x = 0.45). [ABSTRACT FROM AUTHOR]

Spontaneous combustion of coal gangue (CG) hills has caused varieties of secondary disasters that seriously endanger the ecological environment of the world. The emission law of index gases and their oxidation kinetics during the secondary oxidation process of CG with different ranks of oxidation were studied by using the temperature programmed device and online mass spectrometer (MS). Fourier transform infrared spectroscopy (FTIR) was used to reveal the changes of the CG internal active functional groups. The results showed that the energy required for the combustion of CG with low rank of pre-oxidation was significantly lower than that of the raw sample. However, as the oxidation rank increased, due to amounts of volatile components were released in the process of oxidation reaction, the CG in the combustion process of the emission of index gases and its oxygen consumption rate gradually reduced; the rapid oxidation stage shifted to the direction of the high temperature. In this study, the risk of spontaneous combustion of CG after oxidation at 80 ℃ under 3% oxygen concentration was the strongest. The results of this paper are of great guiding significance for exploring the spontaneous combustion characteristics of CG hills and their prevention by traditional covering method. [ABSTRACT FROM AUTHOR]

It is common knowledge that in-situ combustion is highly promising method for improving heavy oil recovery. The present research explores the effects of Cobalt-ligated catalysts derived from sunflower oil (CoSFO) and tall oil (CoTO) on heavy oil oxidation, aiming to enhance in-situ combustion process. Through differential scanning calorimetry (DSC) we assessed the oxidation kinetics of heavy oil in the presence and absence of these catalysts. Our findings indicate that both CoSFO and CoTO significantly improve the oxidation process, particularly in the high-temperature oxidation (HTO) phase crucial for combustion front stabilization. Notably, CoTO demonstrated superior efficacy in reducing oxidation times across all conversion levels, suggesting its potential to optimize the efficiency of EOR techniques. This research highlights the promise of Cobalt-ligated catalysts in advancing heavy oil recovery and suggests directions for future studies to further investigate their industrial applications. [ABSTRACT FROM AUTHOR]

Liquid rocket engines equipped with LOx/GCH4 pintle injectors represent a promising technology when a large throttling capability is required. Still, limited amounts of data are available in the literature about the numerical characterization of pintle injector configurations under reacting conditions, with the entirety of these studies resorting to global or quasi-global reaction mechanisms. To this end, the objective of the present work is to assess the impact of chemical kinetic modeling on the prediction of major combustion observables, thermal flow field, and gas–liquid interaction in a pintle configuration of interest. Specifically, we carry out three unsteady Reynolds-averaged Navier–Stokes simulations under an Eulerian–Lagrangian fashion through variable-fidelity kinetic schemes, namely, one quasi-global scheme and two skeletal schemes derived from the high-pressure Zhukov's detailed mechanism. On the one hand, employing quasi-global chemical kinetics delivers an inconsistent flame topology. On the other hand, the overall combustion characteristics remain unaltered regardless of the skeletal mechanism complexity, while significant discrepancies can be envisaged in the flame dynamics. Moreover, the computational burden exponentially increases with mechanism size, preventing high-fidelity skeletal schemes from being leveraged in design-oriented computational fluid dynamics. Based on these findings, quasi-global chemical kinetics should be discarded when targeting high-pressure rocket engine conditions, while ad-hoc optimized skeletal mechanisms should be developed. This way, the present study provides an insightful contribution to identifying the optimal complexity of chemical kinetic modeling to ensure reliable, still cost-effective numerical simulations of liquid rocket engine combustion devices. • Chemical kinetics modeling impacts LOX/GCH4 combustion predictions in pintle injectors. • Semi-global mechanisms overestimate mixture reactivity in oxidizer-rich regions. • Too compact skeletal schemes may predict local extinction in ultra-oxidizer-rich regions. • Optimal complexity in skeletal mechanisms should be pursued to restrain CPU cost. [ABSTRACT FROM AUTHOR]

Due to the semi-enclosed space of underground coal seams and the implementation of nitrogen injection measures, most coalfield fires occur in multi-atmosphere environments. At present, there is little research on the combustion situations and kinetics of coal under multi-atmosphere conditions. In this paper, simultaneous thermal analysis experiments were conducted to investigate the combustion behaviors of bituminous coal and anthracite in O2-CO2-N2 atmospheres with different volume fractions. A new index for quantitative characterization of coal combustion situation in multi-gas mixing atmospheres was proposed based on the combustion situation intensity index and heat release rate. Furthermore, a method to predict the coal combustion situation using artificial neural network (ANN) was proposed. The results showed that the combustion rate decreased with the increase in CO2 volume fraction and the decrease of N2 volume fraction under multi-gas mixing atmospheres. The volume fraction changes in inert gases had little effect on the ignition temperature or burnout temperature and had a greater effect on the combustion reactivity of bituminous coal. In a 15% O2-5% CO2-80% N2 atmosphere, the combustion could be inhibited for bituminous coal, while being promoted by anthracite. The combustion situation of bituminous coal in a 15% O2-25% CO2-60% N2 atmosphere was greater than that in air. Based on the proposed coal combustion situation index and the selected optimal ANN model, the coal combustion situation in O2-CO2-N2 atmospheres could be well predicted. This paper provides a reliable theoretical basis for judging the coal combustion spread in the coalfield fire area. [ABSTRACT FROM AUTHOR]

Fugitive methane emissions account for a significant proportion of greenhouse gas emissions, and their elimination by catalytic combustion is a relatively easy way to reduce global warming. New and novel reactor designs are being considered for this purpose, but their correct and efficient design requires kinetic rate expressions. This paper provides a comprehensive review of the current state of the art regarding kinetic models for precious metal catalysts used for the catalytic combustion of lean methane mixtures. The primary emphasis is on relatively low-temperature operation at atmospheric pressure, conditions that are prevalent in the catalytic destruction of low concentrations of methane in emission streams. In addition to a comprehensive literature search, we illustrate a detailed example of the methodology required to determine an appropriate kinetic model and the constants therein. From the wide body of literature, it is seen that the development of a kinetic model is not necessarily a trivial matter, and it is difficult to generalize. The model, especially the dependence on the water concentration, is a function of not only the active ingredients but also the nature of the support. Kinetic modelling is performed for six catalysts, one commercial and five that were manufactured in our laboratory, for illustration purposes. [ABSTRACT FROM AUTHOR]

To realize the utilization of peanut shell, this study investigates the combustion behavior, chemical kinetics and thermodynamic parameters of peanut shell using TGA under atmospheric air at the heating rates of 10, 20, and 30 K/min. Results indicate that increasing the heating rate leads to higher ignition, burnout, and peak temperatures, as observed in the TG/DTG curves shifting to the right. Analysis of combustion performance parameters suggest that higher heating rates can enhance combustion performances. Kinetic analysis using two model-free methods, KAS and FWO, shows that the activation energy (Eα) ranges from 93.30 to 109.65 kJ/mol for FWO and 89.72 to 103.88 kJ/mol for KAS. The data fit well with coefficient of determination values (R2) close to 1 and the mean squared error values (MSE) less than 0.006. Pre-exponential factors using FWO range from 2.19 × 106 to 8.08 × 107 s−1, and for KAS range from 9.72 × 105 to 2.25 × 107 s−1. Thermodynamic analysis indicates a low-energy barrier (≤±6 kJ/mol) between activation energy and enthalpy changes, suggesting easy reaction initiation. Furthermore, variations in enthalpy (ΔH), Gibbs free energy (ΔG), and entropy (ΔS) upon conversion (α) suggest that peanut shell combustion is endothermic and non-spontaneous, with the generation of more homogeneous or well-ordered products as combustion progresses. These findings offer a theoretical basis and data support for the further utilization of agricultural biomass. [ABSTRACT FROM AUTHOR]

Integrating hydrogen with CNG is crucial for carbon neutrality and environmental goals, as it enhances flame temperature, reduces emissions, and combats global warming. This study employs the CHEMKIN tool to examine combustion characteristics, including adiabatic flame temperature, mole fraction, normalization, and production rate, in H2-CNG mixtures under various atmospheric and operating conditions. Blending 50% hydrogen with CNG results in significant changes, including a temperature increase from 2322 to 2344 K when the hydrogen content is at 50%. The introduction of hydrogen causes a notable 30–35% reduction in CH4 mole fraction and a simultaneous 26.6% increase in C-normalized CH4 production. Free radicals play a role in affecting CO2 production, with the normalization of CO species increasing from 0.068 to 0.087. Through NSGA-II multi-objective optimization methods, the study identifies a 50% H2-50% CNG blend as the optimal choice for thermal and environmental performance. The study explores the energy and environmental impacts of incorporating hydrogen into CNG-air combustion, with a specific focus on the effects of 50% H2 blending with CNG. Hydrogen blending benefits from elevated adiabatic flame temperature and increased free radical formation, ultimately leading to emission reduction. These findings firmly establish H2-CNG mixtures as promising environmentally friendly alternatives with superior combustion characteristics. Their potential paves the way for significant progress towards achieving carbon neutrality and combating climate change through cleaner, more efficient fuel options. [ABSTRACT FROM AUTHOR]

Alkaline water electrolysis represents a fundamental method for hydrogen generation, offering simplicity and cost-effectiveness. Operating at a standard voltage of 1.23 V, electrolyzers efficiently split water molecules into hydrogen and oxygen. Central to this process are the electrodes within the electrolytic cell, where the cathode serves as the site for hydrogen production via reduction reactions. To enable the integration of hydrogen into conventional spark-ignition (SI) engines, a blend of liquefied petroleum gas (LPG) and hydrogen at a 4:1 ratio is utilized, strategically adjusting combustion characteristics. This blended fuel undergoes meticulous preparation through a vaporizer unit to ensure precise mixing ratios before introduction into the engine's combustion chamber via a bypass line on the input manifold. Here, controlled air mixing at a stoichiometric ratio of 17:1 ensures optimal combustion. The combustion of this LPG-hydrogen mixture is marked by the distinct blue flame characteristic of hydrogen combustion, signifying complete combustion. Leveraging vaporized fuel delivery enhances fuel-air mixing within the combustion chamber, promoting thorough combustion and reducing emissions of nitrogen oxides and hydrocarbons in the exhaust gas, thereby contributing to cleaner combustion processes in conventional SI engines. Furthermore, hydrogen gas demonstrates rapid combustion tendencies, presenting a potential hazard with its flammability range spanning from 4% to 75% concentration in the atmosphere. These inherent characteristics highlight the necessity for rigorous safety protocols and engineering innovations to effectively manage the challenges inherent in utilizing hydrogen as a vehicle fuel source. [ABSTRACT FROM AUTHOR]