Numerical Study on the Explosion Reaction Mechanism of Multicomponent Combustible Gas in Coal Mines

Abstract

Combustible gases, such as CO, CH₄, and H₂, are produced during spontaneous coal combustion in goaf, which may cause an explosion under the stimulation of an external fire source. It is of great significance to study the influence of combustible gases, such as CO and H₂, on the characteristics of a gas explosion. In this study, CHEMKIN software (Version 17.0) and the GRI-Mech 3.0 reaction mechanism were used to study the influences of different concentration ratios between CO and H₂ on the ignition delay time, free radical concentration, and key reaction step of a gas explosion. The results show that the increase in the initial CH₄ and CO concentrations prolonged the ignition delay time, while the increase in the H₂ concentration shortened the time and accelerated the explosion reaction. The addition of H₂ promoted the generation of free radicals (H·, O·, ·OH) and accelerated the occurrence of the gas explosion. CO generated ·OH free radicals and dominated the methane consumption through the R119 and R156 reactions. As the concentrations of CO and H₂ increased, the R38 reaction gradually became the main driving factor of the gas explosion.

1. Introduction

Gas explosions occur due to intense chemical reactions between methane and oxygen when ignited by an external source. The concentration range for methane explosions in air is generally between 5% and 16%. Sources of ignition for gas explosions in coal mines can include the spontaneous combustion of coal, electrical sparks, and heat generated by the friction of rock impacts [1,2,3]. The conditions conducive to gas explosions are not constant; they vary with environmental factors, such as the temperature and the addition of different gas mixtures [4,5]. Research showed that in addition to the CH₄ concentration, the presence of other combustible gases, such as CO and H₂, can also significantly alter the characteristics of explosions [6,7]. Especially hydrogen, due to its low ignition energy and high explosion rate, can significantly enhance the explosiveness of mixed gases, even in small amounts [8]. Research on the characteristics of gas explosions under various conditions not only aids in identifying the hazards associated with gas explosions but also facilitates the scientific development of explosion prevention measures [9,10]. In recent years, with the advancement of experimental techniques and numerical simulation methods, significant progress has been made in the study of gas explosion characteristics and their influencing factors. Numerical simulation methods, especially those based on chemical reaction kinetics models, such as GRI-Mech 3.0, have been able to simulate the explosion process of multi-component gases under different environmental conditions and reveal the generation and reaction pathways of free radicals. These studies provide an important theoretical basis for the development of explosion prevention and control measures, especially for the study of gas explosion characteristics in complex coal mine environments, which helps to more scientifically evaluate and prevent the occurrence of gas explosions.

In experimental studies of gas explosion characteristics, Cashdollar et al. [11] examined the impact of the reactor size, turbulence intensity, and ignition energy on the explosion limits of methane (CH₄). Cammarota et al. [12] collected data on the explosive behavior of CH₄-O₂ mixtures using photodiodes, finding that the combustion speed of the mixtures ranged from 0.7 to 10 m/s. Salzano et al. [13] conducted tests in a 5 L sealed cylindrical container to study the effect of hydrogen (H₂) on methane explosion characteristics, noting a significant impact when the H₂ content in the mixture exceeded 50%. Pekalski [14] and Gieras et al. [15] revealed through their experiments the influence of the initial temperature on the gas explosion limit parameters. Tang et al. [16] identified how methane explosion characteristic parameters change with the initial environmental pressure, demonstrating that these parameters decrease as the initial pressure is reduced. Huang et al. [17] investigated the explosion limits of methane–air mixtures under high-pressure conditions, determining that the explosion limits ranged from 2.93% to 60.75% at 30 MPa and proposed a high-pressure explosion limit model for methane–air mixtures. Takahashi et al. [18] studied the effects of different ignition materials on the explosion limits, finding that metals with higher melting points and higher voltages were more suitable for measuring explosion limits. To predict the explosion limits of combustible gas mixtures, some researchers derived formulas based on combustion kinetics or the heat and mass transfer relationships between reacting gases, which can predict the explosiveness of combustible gases to some extent [19,20,21].

In numerical simulation studies of gas explosion characteristics, Kobiera et al. [22] developed a model describing the explosion process in enclosed pipelines that is capable of simulating explosions under different flame front and turbulence intensity conditions. Maremonti et al. [23] simulated the explosion characteristics of gas in interconnected containers, identifying turbulence effects caused by the connection as the main factor enhancing explosions. Salnazo et al. [24] used computational fluid dynamics to simulate the flame acceleration behavior of gas in pipelines, validating the numerical model by comparing it with experimental results and finding it was well suited for slower turbulent deflagration states. Zhang et al. [25] studied the effect of ignition energy on the characteristics of gas explosions by establishing a three-dimensional geometric model, concluding that ignition energy only has a certain impact on the process of gas explosions. Yang et al. [26] used the OpenFOAM code to study the characteristics of gas explosions with non-uniform concentration gradients in mine tunnels and found that non-uniform gas explosions are more destructive than uniform gas explosions. Qiu et al. [27] studied the effects of different elbows on the propagation characteristics of methane–air premixed explosions through a combination of numerical simulation and experimental comparison and found that the attenuation of the explosion shock wave is affected by the bending angle.

In terms of the reaction mechanisms of gas combustion and explosions, researchers conducted in-depth studies and developed various mechanisms, including GRI-Mech 3.0 [28,29,30]. The conclusions drawn under laboratory conditions cannot fully simulate the complex situations of actual mines, and due to the limitations of experimental conditions and resources, the small sample size of data leads to low accuracy in the research results. Numerical simulation methods have revealed deeper insights into the process and intrinsic mechanisms of gas explosions, somewhat compensating for the limitations of experimental research. Although there was some research on the impact of gases, such as CO and H₂, on gas explosions, there has been a lack of systematic studies on the comprehensive effects of multi-component gas mixtures. Therefore, the research in this study is of certain significance for preventing coal mine gas explosions.

In this work, CHEMKIN and GRI-Mech 3.0 were used to analyze the impact of different concentration ratios of CO and H₂ on the ignition delay time, free radical concentration, and key reaction step of the gas explosion. The sensitivity coefficient was calculated to explain the effects of various gas concentrations on the reaction. It is of great importance to illustrate the influence of different gas concentrations on gas explosions.

2. Methodology

2.1. Selection of Reaction Mechanism

Gas explosions occur through a series of elementary reactions. In the environment of a coal mine goaf where spontaneous coal combustion occurs, combustible gases, such as CO, CH₄, and H₂, are produced, necessitating the selection of a reaction mechanism suitable for the explosion of multi-component mixed gases in the goaf. So far, the chemical mechanisms of combustion for gases like CO, CH₄, and H₂ have been extensively studied and the established reaction mechanisms are relatively mature. For this simulation, the GRI-Mech 3.0 reaction mechanism was employed, which includes 53 components and 325 elementary reactions. This mechanism is applicable to reaction systems within a temperature range of 1000–2000 K, a pressure range of 10 torr to 10 atm, and an equivalence ratio range of 0.1 to 5. This mechanism encompasses a detailed array of elementary reactions and has a broad applicability, enabling the analysis of combustion reaction kinetics for CH₄, CO, H₂, and mixed gases [31]. Here, a zero-dimensional constant-volume combustion reactor model was used for the simulation. This model represented a constant-volume adiabatic reaction system, where the combustible components and oxygen could mix completely and sufficiently, and were in a static, non-turbulent state. The technology roadmap of this study is shown in Figure 1.

2.2. Initial Computational Conditions

The influence of different CO and H₂ concentration ratios on the reaction kinetics during the gas explosion process was investigated using the CHEMKIN software. The simulation assumed that the air composition was solely composed of O₂ and N₂. The gases selected for the simulation included O₂, N₂, CH₄, CO, and H₂. The initial conditions were set at a temperature of 1000 K and a pressure of 0.1 MPa, with a reaction duration of 2.0 s. To maintain consistency with experimental setups, the reactor was configured as a 20 L constant volume environment. The simulation was designed with two sets of experiments: one involved a mixture of gas and CO, with concentration ranges from 0 to 5%, and the other involved a mixture of gas, CO, and H₂, also with concentrations ranging from 0 to 5%. The specific parameters are outlined in

Table 1. Parameters of the initial calculation conditions.

CH4 Concentration (%)	Concentration of CO and H2 (%)	Ratio 1 (Excluding H2)			Ratio 2
		CO (%)	O2 (%)	N2 (%)	CO (%)	H2 (%)	O2 (%)	N2 (%)
7	0	0	19.53	73.47	0	0	19.53	73.47
	1	1	19.32	79.68	1	0	19.32	79.68
	2	2	19.11	78.89	1.9	0.1	19.11	78.89
	3	3	18.9	78.1	2.8	0.2	18.9	78.1
	4	4	18.69	77.31	3.5	0.5	18.69	77.31
	5	5	18.48	76.52	4	1.0	18.48	76.52
9.5	0	0	19.005	71.495	0	0	19.005	71.495
	1	1	18.795	70.705	1	0	18.795	70.705
	2	2	18.585	69.915	1.9	0.1	18.585	69.915
	3	3	18.375	69.125	2.8	0.2	18.375	69.125
	4	4	18.165	68.335	3.5	0.5	18.165	68.335
	5	5	17.955	67.545	4	1.0	17.955	67.545
11	0	0	18.69	70.31	0	0	18.69	70.31
	1	1	18.48	69.52	1	0	18.48	69.52
	2	2	18.27	68.73	1.9	0.1	18.27	68.73
	3	3	18.06	67.94	2.8	0.2	18.06	67.94
	4	4	17.85	67.15	3.5	0.5	17.85	67.15
	5	5	17.64	66.36	4	1.0	17.64	66.36

.

2.3. Sensitivity Analysis

Sensitivity analysis was employed to elucidate the extent to which the rate constants of the chemical reactions influenced the concentration variations of reactants within a system. This was achieved by calculating the first-order sensitivity coefficients of each elementary reaction rate constant with respect to the system parameters, such as the temperature, concentrations of the intermediate products, and concentrations of the final products. Suppose the governing equation for a variable Z is given by

$${\displaystyle \frac{\mathrm{d}\mathrm{Z}}{\mathrm{d}\mathrm{t}}}=\mathrm{F}\left(\mathrm{Z},\mathrm{t},\mathrm{a}\right)$$

(1)

where Z (Z₁, Z₂, …, Z_i) is the mass fraction of each component in the system, %; a (a₁, a₂, …, a_i) is the pre-exponential factor of each primitive reaction step.

The first-order sensitivity coefficient can be calculated as follows:

$${\mathrm{W}}_{\mathrm{l},\mathrm{i}}={\displaystyle \frac{\partial {\mathrm{Z}}_{\mathrm{i}}}{\partial {\mathrm{a}}_{\mathrm{i}}}}$$

(2)

Taking the derivative of this yields

$${\displaystyle \frac{\mathrm{d}{\mathrm{w}}_{\mathrm{l},\mathrm{j}}}{\mathrm{d}\mathrm{t}}}={\displaystyle \frac{\partial {\mathrm{F}}_{\mathrm{l}}}{\partial \mathrm{Z}}}{\mathrm{W}}_{\mathrm{l},\mathrm{j}}+{\displaystyle \frac{\partial {\mathrm{F}}_{\mathrm{l}}}{\partial {\mathrm{a}}_{\mathrm{i}}}}$$

(3)

3. Results and Analysis

3.1. Impact of Coal Self-Combustion Environmental Mixed Gas on the Ignition Delay Time of Gas Explosions

The ignition delay time is the duration before combustion wherein a flammable gas and air mixture remains unignited under specific temperature and pressure conditions. This metric reflects the physicochemical characteristics of a mixed gas fuel. Simulations were conducted to determine the changes in the ignition delay time when CO or a CO and H₂ mixed gas was added to methane gas concentrations of 7%, 9.5%, and 11%. The results are presented in

Table 2. Data of gas explosion ignition delay time (initial temperature 1000 K).

CH4 Concentration (%)	Combustible Gas Concentration (%)	Ignition Delay Time (s)
		Add CO Gas	Add CO and H2 Gas Mixture
7	0	0.902	0.902
	1	1.106	1.106
	2	1.281	0.806
	3	1.436	0.600
	4	1.577	0.246
	5	1.707	0.092
9.5	0	1.067	1.067
	1	1.307	1.307
	2	1.527	1.060
	3	1.733	0.868
	4	1.929	0.428
	5	2.116	0.181
11	0	1.162	1.162
	1	1.418	1.418
	2	1.659	1.200
	3	1.890	1.020
	4	2.113	0.544
	5	2.328	0.246

.

Figure 2 illustrates the relationship between the ignition delay times and varying concentrations of added combustible gases. For pure methane gas at concentrations of 7%, 9.5%, and 11%, the ignition delay times were recorded at 0.901 s, 1.067 s, and 1.161 s, respectively. This indicates that higher methane concentrations correlated with increased ignition delay times. In the systems that contained methane mixed with CO, the addition of CO consistently resulted in a linear increase in the ignition delay times. Moreover, higher initial methane concentrations amplified the increase in the ignition delay times, as depicted by the steeper slope of the curve in Figure 1. The analysis suggests that both the increase in the initial methane concentration and the addition of the CO gas extended the ignition delay times of the methane explosions, which exerted a suppressive effect on the initial ignition phase.

For the combustible gas system comprising methane mixed with CO and H₂, the ignition delay times initially increased and then rapidly decreased as the concentration of the mixed gas rose. For example, at a mixed gas concentration of 2%, the presence of H₂ significantly reduced the ignition delay time from 1.281 s to 0.806 s for the system with a 7% methane concentration. As the H₂ content in the mixed gas concentration increased from 2% to 5%, the reductions in the ignition delay times were 37.1%, 58.2%, 84.4%, and 98.3%, respectively. Similarly, the ignition delay times for the methane explosions at concentrations of 9.5% and 11% also demonstrated consistent trends. These results indicate that the presence of H₂ in the gas mixture substantially reduced the ignition delay times, accelerating the process of the gas explosion reactions.

3.2. Effect of Gas Mixture in Coal Spontaneous Combustion Environment on Concentration of Key Free Radicals in Gas Explosion

The effects of CO on H·, O·, and ·OH in the gas explosion process of different concentrations were simulated, and the 7% concentration of gas was taken as an example for analysis, as shown in Figure 3. As can be seen from Figure 2, for the gas with a 7% concentration, the peak molar fractions of three key free radicals showed a similar change relationship with the addition amount of CO, that is, with the increase in the CO concentration, the peak molar fractions of H·, O·, and ·OH all showed an increasing trend, in which the H· radical increased the fastest, while the O· and ·OH radicals increased relatively little. By comparing the molar fractions of H·, O·, and ·OH, it can be found that the residual concentration of the ·OH radical was higher than that of H· and O· in the same reaction system. For example, in the reaction system of the 7% pure gas, the molar fractions of the H· and O· free radicals that remained in the explosion reaction were 0.0012 and 0.003, and the molar fractions of the ·OH free radicals that remained in the explosion reaction were 0.011. This was because more H· and O· free radicals that remained in the chain reaction system could combine to produce ·OH free radicals, which resulted in a higher ·OH free radical concentration after the gas explosion. In addition, it can also be seen from Figure 3 that with the increase in the CO concentration, the peak time of the three key free radicals gradually moved backward. For example, when the concentration of CO increased from 1% to 5%, the time for the H· radical to reach its peak concentration increased from 1.106 s to 1.707 s, indicating that the addition of CO delayed the reaction time of the gas explosion, which was consistent with the above simulation results on the ignition delay time of the gas explosion.

The effect of the gas mixture on the concentration of key free radicals in the gas explosion process with a 7% concentration is shown in Figure 4. Similar to the effect of CO on the gas explosion free radicals, the peak molar fractions of H·, O·, and ·OH also showed an increasing trend with the increase in the mixed gas concentration, in which the H· radical increased the fastest, while the O· and ·OH radicals increased relatively little. Different from the effect of CO on the free radicals in the gas explosion, H₂ was mixed in the experimental group when the concentration of the gas mixture was 2%, which resulted in earlier peak molar fractions of H·, O·, and ·OH free radicals. In addition, with the increase in the H₂ concentration in the mixed gas, the advance of the peak time of free radicals became more significant. This phenomenon also demonstrated that the H₂ served as an accelerator gas capable of markedly accelerating the process of the gas explosion.

Figure 5 shows the comparison of H·, O·, and ·OH free radicals in the gas explosion process by adding CO mixed with CO and H₂. As can be seen from the figure, for the 7% gas, the addition of combustible gas could promote the generation of three kinds of free radical concentrations of H·, O·, and ·OH, and their molar fractions gradually increased with the increase in the combustible gas concentration. At the same concentration, the promoting effect of mixed gas on the formation of H· and ·OH was stronger, but the promoting effect on the formation of O· was weaker than that of CO. For the 9.5% gas, the H· free radical showed an increasing trend with the increase in the combustible gas concentration, O· showed a first increasing and then decreasing trend, and ·OH showed a decreasing trend. Comparing the effect of the mixed gas and CO gas on the gas explosion, it can be found that the mixed gas had a stronger promoting effect on the generation of the H· free radical.

For the 11% gas, the addition of combustible gas significantly promoted the formation of the H· free radical, but significantly inhibited the formation of the O· and ·OH free radicals. Comparing the effects of the mixed gas and CO gas on the gas explosion, it can be found that the mixed gas had a strong promotion effect on the generation of the H· free radicals, a relatively strong inhibition effect on the reduction of the O· free radicals, and the change in the mole fraction of the ·OH free radicals was similar to that of CO. In addition, it can also be found from Figure 5d that the peak total molar fraction of three key free radicals, H·, O·, and ·OH, in the gas mixture was larger than that in the explosive reaction with only CO added, indicating that the addition of H₂ in the gas mixture accelerated the generation of key free radicals in the gas explosion reaction, which promoted the gas explosion process.

3.3. Influence of the Environmental Mixed Gas from Coal Self-Ignition on the Key Reaction Steps of Methane Consumption

Figure 6 illustrates the impact of CO on the sensitivity of key elementary reactions in a 7% methane environment. As shown in Figure 6a, the elementary reactions that influenced the methane generation and consumption included R32, R53, R119, R156, R158, and R161. Among these, reactions R53 and R158 exhibited positive sensitivity coefficients, indicating that they inhibited the methane consumption. Conversely, reactions R32, R119, R156, and R161 displayed negative coefficients, suggesting that they accelerated the methane consumption and facilitated the progression of the system’s reactions. With the increased CO concentration in the methane reaction system, the sensitivity of these elementary reactions to methane was significantly enhanced, suggesting that the addition of CO intensified the influence of these reactions on methane. The introduction of CO in the system altered the elementary reactions that affected the methane consumption and generation. As the CO concentration increased from 1% to 5%, the elementary reactions that impacted the methane generation shift from R53 and R158 to R53, R120, and R158, and finally to R98, R120, and R158. Reaction R158, crucial for chain scission, impedes methane explosions by destroying chain carriers. Reactions R53 and R98, which consume H· and ·OH radicals, respectively, inhibit methane explosions by depleting reactive radicals. Although reaction R120 generates ·OH radicals, its overall influence on CO consumption and the interaction with various elementary reactions result in a suppressive effect on methane consumption.

In this study of elemental reactions that affected the gas consumption, it was observed that with an increased CO concentration, the key elemental reactions influenced the gas consumption transition from R32, R119, R156, and R161 to R32, R119, R155, and R156, and eventually to R32, R119, and R156. The introduction of CO shifted the primary elemental reactions that promoted gas explosions from R32 and R156 to R119 and R156. Notably, R119, characterized by the reaction HO₂ + CH₃ <=> OH + CH₃O, facilitates the production of ·OH radicals. Similarly, R156, described by the reaction CH₃ + O₂ <=> OH + CH₂O, also generates ·OH radicals. Consequently, for the gas mixture with a 7% gas content, the addition of CO made R119 and R156 the most critical reactions that impacted the gas consumption by promoting gas explosions through the increased generation of ·OH radicals.

Figure 7 and Figure 8 illustrate the impact of CO on the gas sensitivity of the critical elementary reactions for the gas concentrations of 9.5% and 11%. The figures indicate that for both concentrations, the elementary reactions R32, R53, R119, R156, R158, and R161 significantly influenced the gas generation and consumption. Notably, reactions R53 and R158 had the most substantial impacts on the gas generation, while reactions R32, R119, R156, and R161 predominantly affected the gas consumption. A comparison with the primary elementary reactions in a 7% gas explosion revealed that as the concentration of gas increased, the major elementary reactions that affected the gas consumption remained unchanged; however, their sensitivity coefficients increased. For a 9.5% gas mixture, when the CO concentration was increased from 1% to 5%, the key elementary reactions that influenced the gas consumption remained consistent with those in the absence of CO, but their corresponding sensitivity coefficients increased, indicating that the higher CO concentrations progressively amplified the impacts of these reactions on the gas consumption. For an 11% gas mixture, increasing the CO concentrations in the reaction system also significantly heightened the sensitivity of the elementary reactions that affected the gas consumption, suggesting that the addition of CO intensified the influence of these reactions on the gas consumption at this concentration. Similar to the conditions at 7% and 9.5% gas concentrations, the addition of CO shifted the primary elementary reactions that facilitated the gas explosion from R32 and R156 to R119 and R156.

Simulations of the sensitivity effects of a CO and H₂ mixed gas on the gas consumption under different initial computational conditions are depicted in Figure 9, Figure 10 and Figure 11. The sensitivity analysis results for the mixed gas concentrations of 0% and 1% were identical to those for CO’s impact on the gas, hence only the results for the 3% and 5% mixed gas concentrations are presented here. This analysis particularly focused on the influence of H₂ in the mixed gas on the key reaction steps in the gas consumption.

As shown in Figure 9, the critical elementary reactions that affected the gas consumption were reactions R32, R38, R119, R120, R156, and R158, where R120 and R158 had positive sensitivity coefficients, indicating their major roles in the gas production. Conversely, reactions R38, R119, R120, and R156, with negative coefficients, significantly influenced the gas consumption. By comparing the elementary reactions influenced by the pure CO gas, it is evident that the principal elementary reactions affected by the mixed gas shifted from R156 to R38. Reaction R38, represented by H + O₂ <=> O + OH, produces highly reactive O· and ·OH radicals that promote the branched chain reactions leading to gas explosions, accelerating the explosion process. As the concentration of mixed gas in the reaction system increased, the sensitivity of these critical elementary reactions to gas consumption showed a general trend of weakening, suggesting that the addition of mixed gas reduced the influence of these reactions on the gas consumption.

In the suppression of the gas consumption, the elementary reactions R158, R120, and R98 dominated as the concentration of the mixed gas increased from 3% to 5%. However, the extent of their impact on the gas consumption changed with increased gas concentrations. For the reactions that promoted the gas consumption, the relevant elementary reactions shifted from R119, R38, and R156 to R38, R119, and R84 as the concentration increased from 3% to 5%. Notably, the most influential reaction changed from R119 to R38, indicating that higher concentrations of mixed gases altered the key reaction steps that affected the gas consumption, where R38 had the greatest impact. In comparison with the main reactions at the 5% CO concentration that influenced the gas consumption, the R38 reaction, which produces O· and ·OH radicals, had a more pronounced effect on enhancing the gas explosions, making it the most significant contributor to gas explosion enhancement within the mixture.

Figure 10 and Figure 11 illustrate the impact of a mixed gas on the key elementary reactions sensitive to the 9.5% and 11% concentrations of gas, respectively. From the diagrams, it is evident that for the 9.5% gas mixture, as the concentration of the mixed gas increased, the key elementary reactions that influenced the gas formation and consumption underwent changes. Specifically, the reactions critical to gas production shifted from R120 and R158 to R98, R120, and R158. Meanwhile, those vital for gas consumption changed from R32, R156, R38, and R119 to R36, R119, and R38. Additionally, the increase in the mixed gas concentration enhanced the influence of reaction R38 on the gas consumption, indicating an elevated impact of this reaction step. For the 11% gas mixture, the key elementary reactions that affected the gas formation and consumption remained identical to those in the 9.5% scenario; however, the degree of influence of each reaction on the gas consumption varied slightly. Moreover, as the concentration of the mixed gas rose to 5%, reaction step R38 progressively became the most influential in terms of the gas consumption.

4. Conclusions

This study used CHEMKIN software and the GRI-Mech 3.0 reaction mechanism to simulate in detail the explosion characteristics of methane–air–CO–H₂ mixed gas in a coal spontaneous combustion environment. Through simulation experiments, the specific effects of different concentrations of CO and H₂ on the ignition delay time, free radical generation, and reaction mechanism were analyzed. The following were the main conclusions:

(1)

At the CH₄ concentrations of 7%, 9.5%, and 11%, the ignition delay time was significantly prolonged as the CO concentration increased from 1% to 5%. The presence of CO suppressed the initial ignition stage of the explosion and delayed the start of the combustion chain. When H₂ was added, the result was completely the opposite, with a significant reduction in the ignition delay time. H₂ had a significant acceleration effect in the mixed gases, where it greatly reduced the ignition time and increased the risk of explosion.

(2)

As the concentration of the mixed gas increased, the peak molar fractions of three critical free radicals—H·, O·, and ·OH—also showed an increasing trend, with their occurrence times advancing. The total peak molar fractions of these critical free radicals—H·, O·, and ·OH—in the mixed gas were greater than in the reactions that involved only CO, indicating that the integration of H₂ into the mixed gas promoted the generation of key free radicals, which facilitated the occurrence of gas explosions.

(3)

As the concentration of CO increased, R119 and R156 became the dominant reaction steps, which promoted the gas explosion by generating more ·OH radicals. The addition of H₂ changed the main reaction pathway, and the sensitivity of various elemental reactions that affected the gas consumption showed a general trend of weakening. R38 became the most critical reaction step. This reaction accelerated the explosive chain reaction by generating O· and ·OH radicals, which significantly enhanced the explosiveness of the mixed gas.

(4)

The explosive behavior of the multi-component mixed gases was significantly influenced by the concentrations of CO and H₂. In actual coal spontaneous combustion zones, the presence of CO prolongs the reaction time of the explosion, and the addition of H₂ significantly shortens the ignition delay time, accelerating the generation of free radicals and the explosion chain reaction. This discovery has important guiding significance for the prevention and control of gas explosions in actual coal mines. In practical applications, special attention must be paid to the presence of H₂, as even small concentrations of H₂ may significantly increase the risk of explosion.