Combustion Research Articles

Investigation of tetrazole- and bistetrazole-based lithium salts as colorants in environmentally friendly pyrotechnics

ABSTRACT Due to the harmful effects of chlorinated combustion products and strontium in currently used red-burning pyrotechnics on human health and the environment, new substitutes have to be found. A promising alternative could be using lithium-salts. While it is a literature-known problem that the generation of a lithium-based red flame color is a challenging task due to the diverse requirements of the Li(0) color species, a promising alternative could be using lithium-heterocycle salts. In this context, nitrogen-rich lithium tetrazole and bistetrazole salts, namely, lithium tetrazolate, lithium 5-aminotetrazolate, dilithium 5,5’-bistetrazolate dihydrate and dilithium 5,5’-bis(tetrazolate-1-oxide) have been investigated as potential replacements. To evaluate the performance of the salts a variety of mixtures were prepared and their pyrotechnic parameters were analyzed. Furthermore, application-specific pyrotechnic clusters and parachute flares were produced and these were also tested for burning time, dominant wavelength, spectral purity and luminous intensity. Observations on the use of lithiated nitrogen-rich salts in pyrotechnic mixtures showed a red color impression, indicating the potential of these mixtures. Further research opportunities can be pursued by refining nitrogen-rich compounds.

Unlocking the Value of Phosphogypsum Waste: Steam Calcination for Efficient Decomposition and Resource Recovery

ABSTRACT Phosphogypsum is a waste by-product of phosphate fertilizer production. It contains calcium sulfate (CaSO4.xH2O), which can be decomposed to produce calcium oxide (CaO) and sulfur dioxide (SO2). Steam calcination is a process that uses steam to decompose CaSO4. This study represents the first comprehensive investigation of steam calcination applied to phosphogypsum, comparing its performance to pure CaSO4 at various temperatures (1050–1200 °C) and steam molar ratios (0, 4%, and 30%). The results showed that steam calcination can significantly lower the calcination temperature of both CaSO4 and phosphogypsum. The presence of steam can significantly accelerate the decomposition reaction of pure CaSO4 and phosphogypsum when compared to decomposition in nitrogen or air. It was found that the decomposition reaction in steam follows the contracting cylinder reaction model in the case of CaSO4 and the first-order reaction model for the phosphogypsum. Additionally, the activation energy for the steam calcination of CaSO4 and phosphogypsum were found to be 421.2 kJ/mol and 418.6 kJ/mol, respectively, which are lower than the activation energy for the calcination in oxyfuel combustion products (O2, CO2, SO2, and H2O gases) 531.4 kJ/mol demonstrating its potential for enhanced energy efficiency. As a result, steam calcination emerges as a promising sustainable solution for valorizing phosphogypsum while reducing energy consumption and greenhouse gas emissions.

Explosion Load Characteristics of Fuel—Air Mixture in a Vented Chamber: Analysis and New Insights

The advances in research on the explosion load characteristics of the fuel–air mixture in vented chambers are reviewed herein. The vented explosion loads are classified into three typical types based on this comprehensive literature research. These models are the accumulation load model, attenuation load model, and interval jump load model. The characteristics of the three different typical vented explosion load models are analyzed using Fluidy-Ventex. The research results show that overpressure is largely determined by methane concentrations and vented pressure. The turbulent strength increased from the original 0.0001 J/kg to 1.73 J/kg, which was an increase of 17,300 times, after venting in the case of a 10.5 v/v methane concentration and 0.3 kPa vented pressure. When the vented pressure increased to 7.3 kPa, the turbulent strength increased to 62.2 J/kg, and the overpressure peak correspondingly increased from 69 kPa to 125 kPa. In the case of the interval jump load model, the explosion overpressure peak tends to ascend when the intensity of the fluid disturbance rises due to the venting pressure increasing at a constant initial gas concentration. When the venting pressure reaches tens of kPa, the pressure differential increases sharply on both sides of the relief port, and a large amount of combustible gas is released. Therefore, there is an insufficient amount of indoor combustible gas, severe combustion is difficult to maintain, and the explosion load mode becomes the attenuation load model.

Metal Acetate-Enhanced Microwave Pyrolysis of Waste Textiles for Efficient Syngas Production

The production of waste textiles has increased rapidly in the past two decades along with the rapid development of the economy, the majority of which has been either landfilled or incinerated, resulting in energy loss and environmental pollution. Microwave pyrolysis, which can transform heterogeneous and complex waste feedstocks into value-added products, is considered one of the most competitive technologies for processing waste textiles. However, achieving selective product formation during the microwave pyrolysis of waste textiles remains a significant challenge. Herein, sodium acetate, potassium acetate, and nickel acetate were introduced into waste textiles through an impregnation method as raw materials to improve the pyrolysis efficiency. The optimized process parameters indicated that nickel acetate had the most favorable promotional effect of the three acetates. Notably, the waste textiles containing 1.0% Ni exhibited the highest gas production rate, with the hydrogen-containing combustible gas reaching 81.1% and 61.0%, respectively. Using X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy to characterize the waste textiles before and after pyrolysis, it was found that nickel acetate was converted into metallic nickel (Ni0) during microwave pyrolysis. This active site significantly enhanced the pyrolysis process, and as the gas yield increased, the disorder of the resulting pyrolytic carbon also rose. The proposed Ni0-enhanced microwave pyrolysis mediated by nickel acetate offers a novel method for the efficient disposal and simultaneous resource recovery of waste textiles.

Effect of Nozzle Type on Combustion Characteristics of Ammonium Dinitramide-Based Energetic Propellant

The present study explores the influence of diverse nozzle geometries on the combustion characteristics of ADN-based energetic propellants. The pressure contour maps reveal a rapid initial increase in the average pressure of ADN-based propellants across the three different nozzles. Subsequently, the pressure tapers off gradually as time elapses. Notably, during the crucial initial period of 0–5 μs, the straight nozzle exhibited the most significant pressure surge at 30.2%, substantially outperforming the divergent (6.67%) and combined nozzles (15.5%). The combustion product variation curves indicate that the contents of reactants ADN and CH3OH underwent a steep decline, whereas the product N2O displayed a biphasic behavior, initially rising and subsequently declining. In contrast, the CO2 concentration remained on a steady ascent throughout the entire combustion process, which concluded within 10 μs. Our findings suggest that the straight nozzle facilitated the more expeditious generation of high-temperature and high-pressure combustion gases for ADN-based propellants, expediting reaction kinetics and enhancing combustion efficiency. This is attributed to the reduced intermittent interactions between the nozzle wall and shock waves, which are encountered in the divergent and combined nozzles. In conclusion, the superior combustion characteristics of ADN-based propellants in the straight nozzle, compared to the divergent and combined nozzles, underscore its potential in informing the design of advanced propulsion systems and guiding the development of innovative energetic propellants.

Green synthesis of a novel P/N/S containing bio-based flame retardant and its applications in poly(lactic acid): rapid self-extinguish, anti-dripping, and excellent mechanical performance

Poly(lactic acid) (PLA), which is recognized as a potential biodegradable material, brings serious fire concern because of its flammability with heavily molten drips. In this investigation, a bio-based flame retardant named CS@ATMP@MI (CAM) consisting of chitosan (CS), amino trimethylene phosphonic acid (ATMP), and methionine (MI) was developed through a simple and environmental-friendly synthesis approach. CAM provided effective flame retardancy and anti-dripping ability without compromising mechanical properties. PLA/CAM composites achieved a UL-94 V-0 rating with 1.0 wt% CAM and a limited oxygen index value of 28.4 % with 3.0 wt% CAM. The high efficiency is due to the high phosphate content in ATMP and the strong coordination between CS, ATMP, and MI. The cone calorimetry tests showed that adding 2.0 wt% CAM increased the total smoke production from 0.2 to 0.6 m2, and thermogravimetric analysis/infrared spectrum analysis indicated that combustible gas production was reduced over 50 % with 3.0 wt% CAM, demonstrating that phosphorus-nitrogen synergy in CAM could effectively capture free radicals and released inert gases. Char analysis showed that the PLA/CAM composites could form a thicker and denser char layer during combustion due to phosphorus-sulfur synergy, which promoted char formation to shield mass transfer. PLA/CAM composites maintained excellent mechanical performance, with a 3.0 wt% CAM increasing tensile strength from 53.9 to 57.3 MPa and Young's modulus from 1782 to 2262 MPa. This study presented a sustainable method for synthesizing an effective bio-based flame retardant and a strategy for producing eco-friendly, fire-resistant PLA composites for industrial applications.

Research on the Calculation Method and Diffusion Pattern of VCE Injury Probability in Oil Tank Group Based on SLAB-TNO Method

Accidental leakage from oil–gas storage tanks can lead to the formation of liquid pools. These pools can result in vapor cloud explosions (VCEs) if combustible vapors encounter ignition energy. Conducting accurate and comprehensive consequence analyses of such explosions is crucial for quantitative risk assessments (QRAs) in industrial safety. In this study, a methodology based on the SLAB-TNO model to calculate the overpressure resulting from a VCE is presented. Based on this method, the consequences of the VCE accident considering the gas cloud concentration diffusion are studied. The probit model is employed to evaluate casualty probabilities under varying environmental and operational conditions. The effects of key parameters, including gas diffusion time, wind speed, lower flammability limit (LFL), and environment temperature, on casualty diffusion are systematically investigated. The results indicate that when the diffusion time is less than 100 s, the VCE consequences are significantly more severe due to the rapid spread of the gas cloud. Furthermore, increasing wind speed accelerates gas dispersion, reducing the spatial extent of casualty isopleths. The LFL is shown to have a direct impact on both the mass and diffusion of the flammable gas cloud, with higher LFL values shifting the explosion’s epicenter upward. The environmental temperature promotes gas diffusion in the core area and increases the mass of the combustible gas cloud. These findings provide critical insights for improving the safety protocols in oil and gas storage facilities and can serve as a valuable reference for consequence assessment and emergency response planning in similar industrial scenarios.

Experimentation of Grate Combustion of Municipal Solid Waste in Ouagadougou: Influence of Primary and Secondary Air Flow on Thermal Potential

The present work concerns the study of the influence of combustion air flows on the thermal potential during the combustion of a 2 kg mixture of solid model waste from the city of Ouagadougou. This mixture consists primarily of wood, cardboard and plastic. The prototype model is a natural laterite internal-walled grate furnace. During these investigations, we were interested in the temperature variation measured by 4 thermocouples K1 to K4 placed respectively from the waste bed to the top of the furnace. These variations are considered according to a variable primary and secondary air flow. The maximum primary and secondary airflow is 3000 L/min. Measurements are taken throughout the experiment at a step of 18 seconds and a maximum duration of 3 minutes for each case of flow considered. Maximum temperatures reaching 450oC are observed following the injection of secondary air only. This is explained by the supply of oxygen making the combustion more complete. The results show that the injection of primary and secondary air at a flow rate of 1500 L/min gives a more stable temperature result, i.e. 362,18oC 186,82oC 109,27oC 72,41oC respectively for the thermocouples K1, K2, K3, K4. An increase in the primary and secondary air flow to a maximum of 3000 L/min leads to a drop in temperatures due to the dilute internal atmosphere. These results allow to set the optimal operating parameters of the furnace in order to produce more heat for its recovery into electricity through a heat exchanger and a steam turbine.

A centrifuge modelling setup for dewatering, rewetting, and characterizing soil deposits

Dewatering in soils serves various purposes in the field of geotechnical engineering as well as other disciplines. In geotechnical engineering, dewatering is effective for improving stability, reducing settlements, and limiting seepage of contaminated pore fluid. This study details the development of an experimental setup that enables dewatering and rewetting soil deposits in-flight in a geotechnical centrifuge while the pore pressures/suctions and moisture contents are measured. Cone penetration tests and shear wave velocity measurements are also used to characterize the material in-flight. Detailed discussion is provided regarding the construction of the tensiometers and calibration of the moisture content probes. Tests are performed on two coal combustion products (CCPs) to exemplify the capabilities of the equipment. Illustrative test results provide time histories and profiles of soil suction and water content at different depths, agreeing well with measurements from laboratory soil-water retention curves. The results also show that dewatering of the CCP deposits leads to significant increases in strength and stiffness, and that after subsequent rewetting, the material maintains a permanent increase in stiffness. The developed system enables an economical and reliable study of the impacts related to dewatering and rewetting cycles to fulfill research purposes in a broad range of engineering disciplines.

Modeling of network public opinion communication based on social combustion theory under sudden social hot events.

Sudden social hot events spread rapidly in the Internet era, which can easily cause group behaviors. Therefore, studying the law of public opinion communication has important theoretical and practical significance for controlling public opinion. This paper constructs the DBUS (Divorced-Burning-Unburning-Stable) model according to the social combustion theory deduced from the analogy of natural combustion phenomena. This paper comprehensively considers the influence of individual characteristics and external environment on the dissemination of online public opinion, introduces indicators such as individuals' self-awareness ability, authority to reflect individual differences, and takes the surrounding individual influence as an external environment factor. Through simulations, we find that (1) the speed of public opinion communication and the dissipation speed are related to cognitive ability, conformity and the network structure; (2) the credibility of the government and the media and the transparency of the information released are the most important factors affecting the scale of public opinion communication; In addition, the rationality and effectiveness of the model established in this paper are verified by an example.

Why Do Things Burn? Elizabeth Fulhame's Challenge to the Antiphlogistic Theory of Combustion.

Motivated by her interest in fabric arts, late-eighteenth-century British chemist Elizabeth Fulhame experimentally investigated whether cloths of gold, silver, and other metals could be made by chemical rather than mechanical processes. In contrast to other women studying science at this time, she not only published an original monograph under her own name that challenged both the phlogistic and antiphlogistic views of combustion but also proposed an alternative explanation for oxidation and reduction. Although her contemporaries widely cited her innovative research, her history is not well known, yet a careful analysis of her work provides further insights into the reception of the antiphlogistic theory and the challenges and limitations experienced by women in chemistry during this period.

Current recycling innovations to utilize e-waste in sustainable green metal manufacturing.

The ever-increasing market demand and the rapid uptake of the technologies of electronics create an unavoidable generation of high-volume electronic waste (e-waste). E-waste is embedded with valuable metals, alloys, precious metals and rare earth elements. A substantial portion of e-waste ends up in landfills and is incinerated due to its complex multi-material structure, creating loss of resources and often leading to environmental contamination from the release of landfill leachates and combustion gases. Conversely, due to the ongoing demand for valuable metals, global industrial and manufacturing supply chains are experiencing enormous pressure. To address this issue, researchers have put multifaceted efforts into developing viable technologies and emphasized right-scaling for e-waste reclamation. Several conventional and emerging recycling technologies have been recognized to be efficient in recovering metal alloys, precious and rare earth metals from e-waste. The recovery of valuable metals from e-waste will create an alternative source of value-added raw materials, which could become part of supply chains for manufacturing. This review discusses the urgency of metal recycling from e-waste for sustainability and economic benefit, up-to-date recycling technologies with an emphasis on their potential role in creating a circular economy in e-waste management.This article is part of the discussion meeting issue 'Sustainable metals: science and systems'.

DOWN DRAFT GASIFIER TO PRODUCE SYNGAS BY BIO WASTE

Biowaste is a valuable resource for sustainable energy production. Through combustion, it generates thermal energy, while gasification a thermo chemical process which transforms solid fuel into gaseous fuel. This process, specifically through a downdraft gasifier, converts biowaste into a combustible gas known as producer gas. Utilizing biowaste as a fuel source plays a crucial role in reducing dependency on fossil fuels, providing a renewable, low-carbon energy alternative. Combining biowaste with other renewable sources like wind and solar power is an effective solution for small-scale, decentralized power generation. This approach not only meets local electricity needs but also supplies heat for rural development. Optimizing operating conditions and methodologies for maximum syngas production in biomass gasification is essential. The gasification system designed here includes a downdraft biomass thermo chemical conversion gasifier, a gas transport line with tar removal, and a fully enclosed combustion chamber—together, forming a robust setup for efficient, clean energy production. KEY WORD: Downdraft gasifier, biowaste, gasification, pyrolysis, syngas

Hydrodynamic theory of premixed flames propagating in closed vessels: flame speed and Markstein lengths

A hydrodynamic theory of premixed flame propagation within closed vessels is developed assuming the flame is much thinner than all other fluid dynamic lengths. In this limit, the flame is confined to a surface separating the unburned mixture from burned combustion products, and propagates at a speed determined from the analysis of its internal structure. Unlike freely propagating flames that propagate under nearly isobaric conditions, combustion in a closed vessel results in continuous increases in pressure, burning rate and flame temperature, and a progressive decrease in flame thickness. The flame speed is shown to depend on the voluminal stretch rate, which measures the deformation of a volume element of the flame zone, and on the rate of pressure rise. Both effects are modulated by pressure-dependent Markstein numbers that depend on heat release and mixture properties while capturing the effects of temperature-dependent transport and stoichiometry. The model applies to flames of arbitrary shape propagating in general flows, laminar or turbulent, within vessels of general configurations. The main limitation of hydrodynamic flame theories is the assumption that variations inside the flame zone due to chemistry or turbulence, which could potentially alter its internal structure, are physically unresolved. Nonetheless, the theory, deduced from physical first principles, identifies the various mechanisms involved in the combustion process as demonstrated in detailed discussions of planar flames propagating in rectangular channels and spherically expanding flames in spherical vessels. It also enables the construction of instructive models to numerically simulate the evolution of multi-dimensional and corrugated flames under confinement.

Experimental Investigation of Thermal Runaway Behaviour and Inhibition Strategies in Large-Capacity Lithium Iron Phosphate (LiFePO4) Batteries for Electric Vehicles

Large-scale lithium-ion batteries play an important role in the electric vehicle market and the thermal runaway (TR) behaviour of batteries is one of the significant threats to the passengers. In this study, we conducted a series of thermal abuse tests concerning single battery and battery box to investigate the TR behaviour of a large-capacity (310 Ah) lithium iron phosphate (LiFePO4) battery and the TR inhibition effects of different extinguishing agents. The study shows that before the decomposition of the solid electrolyte interphase (SEI) film, temperature consistency within the battery were maintained and it was advisable to use temperature detectors. With the destruction of the internal structure of the battery and the uneven temperature distribution at the subsequent battery reaction stage, a large amount of combustible gas was released when the safety valve was opened. The combustible gas fire detector is used to improve alarm reliability and provided a stable early warning response time. Based on this TR behaviour, a LiFePO4 battery box with a standard size of 1060 × 660 × 250mm was constructed. The TR inhibition effect of two different extinguishing agents (heptafluoropropane and perfluorohexanone) were investigated using a metal tube spraying method with a spraying dose of 1.8kg (spraying rate of 0.06kg/s) and a spraying pressure of 2.5MPa. The results showed that using either of these, satisfy the requirements for TR inhibition in large-capacity LiFePO4 batteries and the flames could be completely extinguished without any reignition, and the chain reaction of the surrounding batteries was effectively prevented. Moreover, heptafluoropropane was proven to have a shorter fire-extinguishing time, whereas perfluorohexanone had the advantage of inhibiting temperature rise. This study provides valuable experimental results for early warning and inhibition of TR in large-capacity LiFePO4 batteries for electric vehicles.

Analytical study of rotating detonation and engine operating conditions

In this paper, the mechanism of rotating detonation is analytically discussed using a two-dimensional sheet model. Two ratios are employed in this discussion: the ratio of the sonic point width to the detonation front width, and the ratio of the effective mixture injection area to the injection area. In the rotating detonation, the unconfined boundary can increase the width at the sonic point and decrease the detonation wave speed. Although the high detonation pressure hinders mixture injection, effectively preventing some injectors from functioning, the high pressure acting on the injection end wall produces thrust. Mass, momentum, energy, and angular momentum conservations are used to determine these ratios. The calculated results are in reasonable agreement with past experimental and numerical findings. The present model succeeds to clarify the features, parameter relationships, and overall mechanism of the rotating detonation analytically and to specify flow field of the rotating detonation under given boundary conditions, e.g., the velocity deficit and the effective injection area ratio. The specific impulse of a rotating detonation engine was lower than that of an ordinary rocket engine due to the lower combustion gas pressure when the combustion gas expanded to 1 atm. The thrust coefficient and the specific impulse of an air-breathing rotating detonation engine were shown to be lower than those of a ramjet engine, respectively, primarily because of the smaller airflow rate into the engine.

Generation characteristics and molecular reaction dynamics mechanism of PAHs during oxygen-lean combustion of jet coal

Severe coalfield fires occur in China, mainly in the northwest provinces of Xinjiang, Inner Mongolia, and Ningxia. Among the organic pollutants produced by oxygen-lean combustion, PAHs are considered one of the most dangerous pollutants due to their environmental contamination and “carcinogenic, teratogenic, and mutagenic” effects on human beings. In this paper, to address the problems of PAHs generation and reaction mechanism in coalfield fire, the jet coal from Xinjiang Zhundong Coalfield was selected to conduct the experiments, and the combustion products were detected using GC–MS and FTIR. The molecular dynamics method based on the reaction force field was also used to calculate the reaction process of 17 single molecules (5083 atoms) of jet coal combusted from 300 K to 4000 K at 0.5 oxygen equivalent ratio. The experimental results show that the generation of PAHs increased roughly from 573 K to 773 K at the three oxygen concentrations, and an increase in oxygen content can enhance PAHs generation to some degree. The structural evolutions and product changes in the system have been traced, and it is also clarified that the reaction history of oxygen-lean combustion mainly experiences two stages: thermal decomposition of coal structure and transformation of aromatic structure. The generation mechanism of PAHs is proposed from the perspective of molecular reaction dynamics. On the one hand, it is due to the breakage of active sites such as C-S, C-O, and O-H during the decomposition of coal structure. On the other hand, it originates from the polycondensation reaction triggered by the dehydrogenation of aromatic structure that enlarges the aromatic dimension The research results reveal the generation characteristics and reaction pathways of PAHs in the oxygen-lean combustion of low-rank coal in the fire zone and provide certain references for coal fire management and pollutant control.

Performance evaluation on the chemical looping combustion of the chromium-containing leather waste and the fate of chromium using thermodynamic analysis

Leather waste (LW) consistently contains a high content of chromium (Cr), which significantly limits its utilization due to the toxicity of hexavalent chromium formed through oxidation. To prevent this oxidation, chemical looping combustion (CLC) is employed to dispose of the chromium-rich LW. First, the gaseous and solid pollutants generated during air combustion and CLC are compared when LW is used as fuel. The results indicate that CLC is an effective way to significantly decrease the oxidation of chromium (Cr(VI)/Crtotal) at typical operating temperatures. Subsequently, various operating parameters, namely the equivalence ratio of oxygen carrier to leather waste (αOC/LW), the equivalence ratio of steam to leather waste (αS/LW), and air reactor (AR) temperature, are changed to investigate their effects on the CLC combustion and pollutant behaviors. The findings reveal that no chromium is oxidized in the fuel reactor. The oxidation in AR is associated with the presence of Na in the AR, which can react with chromium to form Na2CrO4. Increasing αOC/LW from 0.8 to 1.2 reduces the oxidation of chromium in the AR from 11.68% to 1.76%, while increasing αS/LW from 0.2 to 1.6 has the opposite effect, improving the oxidation of chromium in the AR from 3.16% to 5.18%.

Performance response analysis and optimization for integrated renewable energy systems using biomass and heat pumps: a multi-objective approach

The focus of this study is to optimize the exploration of biomass-driven multi-energy systems, which include combined heat, power, and gas generation. The objective is to enhance the thermal, environmental, and economic performance indicators of the system. The optimization objectives encompass the quantities of internal combustion engines and air source heat pumps, as well as the dimensions of tanks utilized for anaerobic fermentation. A mathematical model was developed to optimize multiple objectives for combined heat, power, and gas generation systems by employing multi-objective intelligent optimization algorithms. The validation and analysis were conducted using rural residences in Lanzhou, Gansu Province, China, as a case study. The sensitivity analysis of biomass gasification combined heat and power systems was conducted from both technical and cost perspectives, examining the dynamic impact characteristics on the outcomes of multi-objective optimization. The findings indicate that the annual energy-saving rate of the optimized combined generation system decreased from 3.62% to -6.78%, while the growth in carbon emissions reduction rate increased from 76.05 to 81.38%, and the annual cost-saving rate grew from 0.97 to 14.96%. The power generation efficiency of the cogeneration station and hydraulic retention time were found to have a significant impact on the multi-objective optimization results of the combined generation system among the technical parameters. The unit cost of anaerobic fermentation tanks had a more significant impact on the multi-objective optimization results in terms of cost parameters, compared to the price of biogas residue.

Effect of CO2 on the explosion limit parameters and kinetic characteristics of ammonia-hydrogen-air mixtures

To explore the effect of CO2 on the explosion limit parameters and kinetic characteristics of the NH3-H2-air mixtures, the standard combustible gases explosion limits device was utilized to test and analyze the explosion limit, critical oxygen concentration, and explosion triangle. Based on the CHEMKIN software, the suppression mechanism of CO2 on NH3-H2-air mixtures explosion with 0.4 R (hydrogen ratio) and a near-inerting critical concentration was simulated and analyzed. The results indicated that increasing F (volume fraction of CO2) led to a decrease in the upper explosion limit (UEL) of NH3-H2-air mixtures and an increase in the lower explosion limit (LEL). When F increased to 36%, the explosion of the NH3-H2-air mixtures with 0.4 R was completely suppressed. As R increased, the UEL and LEL decreased and increased linearly, respectively, the critical explosion-suppression concentration of CO2 increased, the critical oxygen concentration decreased, and the explosive zone area also increased. In addition, based on the analysis of the changing characteristics of the UEL and LEL, prediction models for the UEL and LEL of NH3-H2-air mixtures with different hydrogen ratios under the effect of CO2 were provided. Reaction kinetics analysis found that less CO2 had a more pronounced impact on ·H and ·OH. However, when F increased to 20-30%, the maximum mole fraction of ·O decreased the most. At this point, the sensitivity of·NH2 towards decreasing oxygen concentrations became comparable to that of ·H and ·OH. When F increased to a near-critical explosion-suppression concentration of 30%, ·H, ·OH, ·O, and ·NH2 were in a critical state of disappearing, and the chain initiation of the explosion was destroyed. Sensitivity analysis indicated that ·H+O2(+M)<=>HO2(+M) and ·NH2+·NH=N2H3 performed a more significant inerting effect on ·H and ·NH2, which ultimately led to the termination of the explosive chain reactions.