Combustion Kinetics Research Articles

TG-FTIR/MS study on the combustion kinetics and gas emission characteristics of forest duff under different oxygen concentrations

TG-FTIR/MS study on the combustion kinetics and gas emission characteristics of forest duff under different oxygen concentrations

Flameless venting characteristics and design model of micro-nano PMMA dust explosion

The effects of Fe–Ni foam thickness and dust size on flame propagation, reduced overpressure, and venting efficiency in 30 μm and 150 nm polymethyl methacrylate (PMMA) dust explosions were investigated. The flame quenching mechanism was revealed by coupling the heat transfer and flow of the dust flame within the Fe–Ni foam. It is found that micron dust is more prone to quenching than nano dust, and the differences in the quenching process of micro-nano dust are explained by combining the dust combustion kinetics and the theory of inter-particle heat transfer. The pressure venting mechanism of micro-nano dust was analysed under different thicknesses of Fe–Ni foam, and the thermal expansion effect of the flame passing through the Fe–Ni foam and its flow resistance significantly increased the reduced explosion overpressure. The flow continuity of the micro-nano dust was classified by means of the Knudsen number (Kn), which elucidates the effect of dust size differences on the pressure evolution. A prediction model for the maximum reduced explosion overpressure is proposed based on the explosion pressure venting of micro-nano dust. Changes in vented pressure have a direct impact on the efficiency of flameless venting. Nano-dust has an efficiency of more than 20 % lower than that of micron dust.

Effect of grain boundary on the ignition and flame propagation mechanisms of TC11 alloy in oxygen-enriched environment

Grain boundaries (GBs) were known as a kind of common defects, but their impact on metal combustion was unclear. This study discovered that when the TC11 alloy's grain size reduced, the critical temperature and oxygen pressure for ignition dropped and the burning velocity accelerated. A modified Frank-Kamenetskii model demonstrated a well match to the relationship between grain size and ignition temperature, and the GBs showed a lower activation energy for ignition than the intragrain. The primary processes via which GBs influenced the kinetics of combustion were the peritectic reaction between Ti and O and the intergranular diffusion of alloying elements.

Structure characteristics and combustion kinetics of the co-pyrolytic char of rice straw and coal gangue

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.

Quasi-CJ rotating detonation with partially premixed methane-oxygen injection: Numerical simulation and experimental validation

The efficiency gain of rotating detonation depends on several loss factors related to the chamber geometry, the injection principle, the propellants and their mass flow rates, and the equivalence ratio. Numerical simulation can help quantify these losses, and this work presents a Large Eddy Simulation (LES) of rotating detonation in an annular chamber and its validation against experiments. The simulation captured the mixing processes, the overall dynamics of the detonation, the deflagration, and the burnt gas expansion. The injection device was numerically designed to ensure partial premixing of the propellants before injection into the chamber. The chamber had a length of 110 mm, an outer diameter of 80 mm, and a radial width of 10 mm. The mixture consisted of gaseous CH4 and O2 with an equivalence ratio of 1.2 and a mass flow rate of 160 g/s. Combustion kinetics was modeled using a skeletal mechanism with 62 reactions and 16 species. The boundary conditions were adiabatic slip walls. The results reproduce well the detonation velocity (within 1% deviation) and the pressure variation behind the wave. The simulated OH* chemiluminescence compares well with experimental high-speed imaging of the outlet and side of the chamber. The simulation results indicate that 65% of the propellant mass is well mixed in front of the wave whereas 15% of the mixture is burned by deflagration. They show that CH4 and O2 do not axially stratify because they have similar injection dynamics between periodic perturbations induced by the rotating detonation. Good propellant mixing and low deflagration losses explain the high experimental detonation velocity, about 90% of DCJ, and a high combustion efficiency of 98%. These agreements between the computational and experimental results indicate that the simulation is capable of capturing the physical scales relevant to RDC operation and producing reliable results for RDC design.

Integrated catalytic systems for simultaneous NOx and PM reduction: a comprehensive evaluation of synergistic performance and combustion waste energy utilization.

The global transition towards sustainable automotive vehicles has driven the demand for energy-efficient internal combustion engines with advanced aftertreatment systems capable of reducing nitrogen oxides (NOx) and particulate matter (PM) emissions. This comprehensive review explores the latest advancements in aftertreatment technologies, focusing on the synergistic integration of in-cylinder combustion strategies, such as low-temperature combustion (LTC), with post-combustion purification systems. Selective catalytic reduction (SCR), lean NOx traps (LNT), and diesel particulate filters (DPF) are critically examined, highlighting novel catalyst formulations and system configurations that enhance low-temperature performance and durability. The review also investigates the potential of energy conversion and recovery techniques, including thermoelectric generators and organic Rankine cycles, to harness waste heat from the exhaust and improve overall system efficiency. By analyzing the complex interactions between engine operating parameters, combustion kinetics, and emission formation, this study provides valuable insights into the optimization of integrated LTC-aftertreatment systems. Furthermore, the review emphasizes the importance of considering real-world driving conditions and transient operation in the development and evaluation of these technologies. The findings presented in this article lay the foundation for future research efforts aimed at overcoming the limitations of current aftertreatment systems and achieving superior emission reduction performance in advanced combustion engines, ultimately contributing to the development of sustainable and efficient automotive technologies.

Chemical reaction network analysis on N2O emissions control strategies of ammonia/ methanol Co-combustion

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 N2O, 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 N2O and NO. Increasing the combustion pressure weakens the chain reactions, thereby reducing the formation of both NO and N2O; the increase in initial temperature raises NO emissions, but also promotes the decomposition of N2O due to the abundance of H in the post-combustion phase. Optimizing post-combustion efficiency and controlling the formation of NO are crucial for N2O emission control. Thus, a staged methanol injection strategy is proposed, where early injection reduces NO emissions and late injection facilitates the decomposition of N2O.

A shock-tube experimental and kinetic simulation study on the autoignition of methane at ultra-lean and lean conditions

Coalbed methane represents an important kind of natural gas resource in many countries. However, the low-concentration property of coalbed methane limits its applications. To gain insight into the combustion kinetics of coalbed methane and facilitate its combustion utilization, this work reports an experimental and kinetic simulation study on the autoignition properties of methane at ultra-lean and lean conditions. A shock-tube (ST) facility is used for ignition delay time (IDT) measurements with equivalence ratios at 0.5, 0.1, and 0.05 with pressure at 2 and 10 bar under the temperature ranging from 1320 to 1850 K. The measured IDTs can be correlated into a general Arrhenius expression, and the equivalence ratio effect on IDTs is then analyzed. Seven detailed chemical kinetic mechanisms are employed to predict the IDTs and statistical error indicators are used to evaluate their performance. Detailed kinetic analysis via sensitivity and reaction path analysis is performed to uncover the kinetic differences among the seven mechanisms. It is shown that some of the reaction paths only exist in the NUIGMech1.3 mechanism, while the other detailed mechanisms do not consider them. Reaction path analysis indicates that the reactions related to O2, OH and O species become more important compared to the reactions involving CH3 and H radicals as the equivalence ratio decreases from lean to ultra-lean conditions. Detailed chemical kinetics analysis is also conducted to demonstrate the uncertainty of key reactions. The present work should be valuable to gain insight into the methane ignition characteristics and to facilitate kinetic mechanism optimization of methane combustion.

Modeling of a heat-integrated biomass downdraft gasifier: Influence of feed moisture and air flow

A model for a heat-integrated biomass downdraft gasifier is developed and used to study the influence of changes in biomass moisture content and gasifier air flow. This one-dimensional steady-state model accounts for pyrolysis, combustion and gasification reaction kinetics as well as transport phenomena occurring within the gasifier and heat integration system. The gasifier is divided into four zones for solving the ordinary differential equations (ODEs), because each zone has different geometry for the reactor or heating system. The material and energy balance ODEs are solved as a boundary value problem (BVP), ensuring that conditions for the producer gas at the bottom of the reactor match the conditions of the countercurrent annulus gas, which is used for heating. The model also accounts for the preheating of the biomass using exhaust gas from an associated engine used to generate electricity from the producer gas. The model predicts the process gas temperature, flow rate and composition and was validated using two experimental runs with different control inputs. The model predictions show good agreement with the data. Simulations with the highest feed moisture result in lower reactor temperatures and simulations with the highest air flow result in the highest reactor temperatures.

Experimental study on ammonia-diesel co-combustion in a dual-fuel compression ignition engine

Ammonia, as a carbon-free renewable fuel and a potential hydrogen carrier, is gaining increasing interest in addressing greenhouse gas emissions in industrial applications and transportation. This paper presents experimental studies on the co-combustion of ammonia with diesel fuel in a single-cylinder industrial compression ignition engine operating in dual-fuel mode. The energy share of ammonia ranged from 0 to 60%. Increasing the proportion of ammonia compared to diesel fuel in the compression ignition engine leads to a change in the combustion process character, increasing the kinetic combustion phase at the expense of diffusive combustion. However, it does not result in an increase in the peak pressure rise (PPR) beyond the permissible value of 1 MPa/deg for piston engines. It increases ignition delay and shortens the combustion duration, while also increasing thermal efficiency and decreasing specific energy consumption. An increase in the NH3 share results in a decrease in combustion efficiency, a reduction in unit emissions of NO, CO2, and soot, and an increase in CO emissions. Beyond 42% ammonia share, it reduces unit THC emissions. At a 42% ammonia share, the dual-fuel engine achieves the highest indicated thermal efficiency (ITE), lowest specific energy consumption (SEC), shortest combustion duration, and lowest unit soot emissions.

Influence of O2 on structural evolution of biochar in oxidative pyrolysis of cellulose

Oxidative pyrolysis could mitigate energy requirement in endothermic pyrolysis, but evolution of pyrolytic products might be impacted in oxidative atomosphere. This was investigated herein at 300–600 °C in a carrier gas of 11 vol% of oxygen with cellulose as a research object for the pyrolysis, as cellulose-derived aliphatic structures are prone to oxidization. The results indicated that O2 reacted with organics on cellulose/biochar even from 300 °C, decreasing biochar production while enhancing bio-oil formation. Oxidation of the organics on the biochar increased CO/CC ratio but did not increase oxygen content, as formation of the oxygen-containing aliphatic structures and their elimination via cracking took place in parallel, which in overall formed the biochar of higher C/O and C/H ratios, but not necessarily higher thermal stability. The abundance of the thermally unstable aliphatic structures was responsible for this, but it was also the reason for the improved comprehensive combustion characteristic index and combustion kinetics. Additionally, pyrolysis at 600 °C in presence of O2 formed the biochar with a specific surface area of 426.2 m2/g (mainly micropores), which was significantly higher than that of counterpart in nitrogen (28.9 m2/g). The in-situ IR characterization of the pyrolysis suggested that O2 favored formation of oxygen-containing species such as -OH, CO of varied forms, *CO2, olefinic CC but not aromatic CC.

Modeling on rapid prediction and cause diagnosis of boiler combustion efficiency

Presently, a method for determining pulverized coal burnout rate (PCBR) was developed on kinetics combustion model. Proposed method can promptly track influence of air coal ratio (ACR), boiler load, uniformity index (UI), coal powder fineness (CPF), particle size, and air powder mixing uniformity (PMUC) on PCBR. Moreover, developed method with fewer computations, time-saving, simplicity and low-cost can be exploited to diagnose decreasing causation of combustion efficiency.Results indicate, for anthracite and lean coal, ACR should be maintained near optimal value with 9.39–11.59 kg/kg to achieve consummate combustion efficiency. Correspondingly, higher and appropriate ACR with 10.87–12.0 kg/kg and 7.18–7.94 kg/kg should be maintained for bituminous coal and lignite. 0.1 UI improving achieves 0.18 % upgrading in PCBR. PCBR is more sensitive to UI variation above 75 % BMCR. More significant effect is presented for lean coal and lignite with changing PMUC especially below 50 % BMCR. Basically 0.1 PMUC improving achieves 0.55 enhancement in PCBR below 50 % BMCR. Concurrently 0.7 increment is delivered for anthracite and lean coal. Coal with high volatile content causes larger particle sizes of coal powder to burn out at furnace outlet. Investigation result can predict potential financial savings from unburnt carbon (UC) reduction.

Plasma-assisted NH3/air flame: Simultaneous LIF measurements of O and OH

In the emerging field of plasma-assisted ammonia (NH3) combustion, the evolution of key intermediate species has rarely been reported. This work establishes a simultaneous measurement system of laser-induced fluorescence (LIF) for hydroxyl (OH) and quantitative two-photon-absorption LIF for atomic oxygen (O), to explore the OH and O dynamics in an NH3/air flame affected by a nanosecond (ns) pulsed plasma discharge. Firstly, with the plasma on, the molar fraction of O is quantified to reach 8.7 × 10–3 in the burnt zone, about two orders of magnitude higher than that without plasma. In addition, the OH LIF signal intensity is four times higher, indicating a significant kinetic enhancement. Then, the spatial characteristics of OH and O are discussed and compared, showing remarkable discrepancy. The discrepancy between them indicates that O production is dominated by plasma kinetics, however, the OH production, primarily stemming from reactions between O and NH3/H2O, still depends on parameters associated with combustion kinetics. We further study the temporal dynamics of O and OH. It is concluded that O and OH peaks at 1.75 μs are mainly attributed to the pathway of quenching of the excited species. After that, O and OH start to decay but show significant differences between unburnt and burnt zones, which are characterized by a single-exponential decay and a bi-exponential decay, respectively. In the unburnt zone, the OH decay is much slower than the O decay due to the diverse pathways for OH production. In the burnt zone, the bi-exponential decay of O and OH can essentially be regarded as a process in which the NH3/air reactive system reaches chemical equilibrium. At this stage, the impacts of the excited species from the plasma gradually diminish and combustion kinetics dominates alone.

Experimental and chemical kinetics study on the flammability limit of CO2/C3H6 mixture working fluid at variable initial temperature

CO2/C3H6 mixture has a wide range of applications in refrigeration systems, heat pumps and Organic Rankine Cycle (ORC) systems, but its flammability safety needs to be considered. An experimental and computational investigation has been conducted on the determination of the flammability limits of CO2/C3H6 and on the understanding of associated limit phenomena in general. We tested the flammable zone of CO2/C3H6 at variable initial temperature. The accuracy of the prediction model of calculation adiabatic flame temperature were verified based on the experimental data. Meanwhile, a high-speed camera was used to record the process of CO2 suppression of flame propagation near flammability limit. Furthermore, based on kinetic numerical calculation, the effect of CO2 chemical and thermal on the flammability limit of C3H6 were analyzed. The results show that the thermal effect of CO2 is greater than that of chemical effect near the flammability limit. The theory of chemical reactivity inhibition reduces the yield and molar ratio of key radicals. The addition of CO2 can inhibit the activity of the dominant chain and increase the activity of the dominant chain termination reaction in the global combustion kinetics. Results of this study provide theoretical guidance for the safe application of CO2/C3H6 mixture.

Combustion Characteristics, Kinetics and Thermodynamics of Peanut Shell for Its Bioenergy Valorization

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.

Methane Combustion Kinetics over Palladium-Based Catalysts: Review and Modelling Guidelines

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.

Experimental study on co-combustion of domestic garbage and sewage sludge: Evaluation of synergistic effect and thermo-kinetic behavior

A persistent increase in domestic garbage (DG) has become a significant worldwide issue due to its negative impact on the ecosystem. The co-combustion way of DG and sewage sludge (SS) in a garbage incineration plant has been deemed a viable option. The study aims to quantify co-combustion behaviors, interaction effects, and thermo-kinetic properties between DG and SS at isothermal conditions by a thermogravimetric analyzer. The results showed that co-combustion of DG with 20 % SS could boost the combustion performance indices, and exhibit the synergistic effect. In addition, at the various SS blending ratios (10, 20 and 35 %) under an air atmosphere, combustion performance indices gradually decreased with an increased SS blending ratio but the synergistic effects were inhibited with a 35 % SS blending ratio. Coat-Redfern method was used to determine the combustion kinetics and thermodynamic properties. The apparent activation energy in the DG-SS (80 %/20 %) blend exhibited a non-linear relationship but increased proportionally with higher SS blending ratio. The lowest activation energy (34.70 kJ/mol) was obtained at the DG-SS (90 %/10 %) blend. The results suggest that the co-combustion of DG and SS can improve the overall combustion performance with an optimal blending ratio of 20 % SS for the co-combustion application.

CONTROL OF PARAMETERS AND STRUCTURE OF DETONATION WAVE IN A DUAL-FUEL METHANE-HYDROGEN MIXTURE

A generalized model of chemical kinetics of detonation combustion of stoichiometric dual-fuel methane-hydrogen mixture is proposed. It allows calculating the molar mass and internal energy of a mixture without calculating its detailed chemical composition. The model was verified within the framework of a numerical calculation of the cellular multifront structure of a detonation wave. The calculated size of the detonation cell, as well as the qualitative structure of detonation (irregularity of the cellular structure due to the formation of both primary and secondary transverse waves, and incomplete combustion of gas in the detonation wave) are in good agreement with experiment.

The Influence of NH3 on Coal Combustion Kinetics during Coal/NH3 Cocombustion: Experiments and ReaxFF MD Simulations

The Influence of NH₃ on Coal Combustion Kinetics during Coal/NH₃ Cocombustion: Experiments and ReaxFF MD Simulations

The Oxidation Performance of a Carbon Soot Catalyst Based on the Pt-Pd Synergy Effect

Pt-Pd-based noble metal catalysts are widely used in engine exhaust aftertreatment because of their better carbon soot oxidation performance. At present, the synergistic effect of Pt and Pd in CDPFs, which is the most widely used and common doping method, in catalyzing the combustion of carbon smoke has not been reported, and it is not possible to give an optimal doping ratio of Pt and Pd. This paper investigates the carbon soot oxidation performance of different Pt/Pd ratios (Pt/Pd = 1:0, 10:1, 5:1, 1:1) based on physicochemical characterization and particle combustion kinetics calculations, aiming to reveal the Pt-Pd synergistic effect and its carbon soot oxidation law. The results show that Pt-based catalysts doped with Pd can improve the catalyst dispersion, significantly increase the specific surface area, and reduce the activation energy and reaction temperature of carbon soot reactions, but excessive doping of Pd leads to the enhancement of the catalyst agglomeration effect, a decrease in the specific surface area, and an increase in the activation energy and reaction temperature of the carbon soot reaction. The specific surface area and pore capacity of the catalyst are the largest, and the activation energy of particle oxidation and the pre-exponential factor are the smallest (203.44 kJ∙mol−1 and 6.31 × 107, respectively), which are 19.29 kJ∙mol−1 and 4.95 × 108 lower than those of pure carbon soot; meanwhile, the starting and final combustion temperatures of carbon soot (T10 and T90) are the lowest at 585.8 °C and 679.4 °C, respectively, which are 22.1 °C and 20.9 °C lower than those of pure carbon soot.