Research on Gas Plasma Ionization Characteristics Based on Methane/Air/K₂CO₃ Mixed Combustion Scheme

Abstract

A high-temperature gas plasma scheme using methane/air/K₂CO₃ mixed combustion is proposed for the application background of hypersonic aircraft. The actual combustion temperature was calculated by ANSYS Chemkin Pro software; the various components of the combustion reaction were determined; and the function between temperature and electrical conductivity was established, revealing the variation law of ionization decomposition of K₂CO₃ ionized seeds with gas temperature. At 1500 K, K₂CO₃ ionized seeds are close to complete ionization. Increasing the mass fraction of K₂CO₃ ionized seeds will enhance the endothermic effect of K₂CO₃ seed ionization decomposition. Under the same residual gas coefficient conditions, the combustion equilibrium temperature will correspondingly decrease. The increase in initial combustion temperature results in an approximately linear increase in equilibrium temperature and conductivity. With the increase in initial pressure, the equilibrium temperature of gas shows a logarithmic growth trend, while conductivity gradually decreases and the gradient of change gradually slows down. This study provides a new method for evaluating the ionization characteristics of high-temperature gas plasma formed by potassium carbonate (K₂CO₃) as ionization seed, and hydrocarbon fuel (CxHy) combined with air.

1. Introduction

Plasma is an ionized gas composed of free electrons and ions, known as the fourth state of matter, and divided by temperature into high-temperature and low-temperature plasmas [1,2]. When an applied voltage reaches the ignition voltage of a gas, the gas molecules are punctured, creating a mixture of electrons, ions, atoms, and free radicals [3]. Although electron temperature is high during discharge, the temperature of heavy particles is very low, and the whole system presents a cryogenic state, so-called cry plasmas, also called non-equilibrium plasmas [4,5,6].

Plasma has been used in many fields such as aviation, energy, and industrial combustion systems [7,8]. In the field of combustion, non-equilibrium plasma combustion technology has been paid more and more attention due to its advantages, such as improving ignition performance, increasing flame propagation speed, improving combustion efficiency, and reducing emissions of pollutants [9]. Ionization effects in turbulent conditions include increased or fluctuating ionization rates, increased non-uniformity in electron density distribution, changes in plasma stability, and complex dynamical behavior due to non-linear interactions. In studies, Inomata et al. has revealed the positive role of plasma in combustion. Klimov et al. used a plasma generator to internally combust C₃H₈ fuel in experiments, demonstrating that plasma enhances combustion stability.

Plasma is electrically conductive, and its trajectory will deflect under the action of an electromagnetic field, which can be used to achieve the thrust vectoring aspects of a power plant. It is found that the effect of a plasma thrust vector controlled by a magnetic field is greatly influenced by electrical conductivity [10,11]. However, temperature is affected by the properties of hydrocarbon fuels, and the range of controllable combustion temperature is limited. Therefore, higher electrical conductivity can be obtained by adding ionized seeds to gas, thereby enhancing flow ionization characteristics.

When adding a small amount of alkali metal salts with low ionization potential to high-temperature gases, the alkali metal seeds ionize and release free electrons, causing the gas flow to exhibit ionization characteristics at lower temperatures [12]. K₂CO₃ is used as ionization seeds in the Hypersonic Vehicle Electric Power System (HVEPS) program. At 1718 K, the conductivity reached 16.78 S/m. NaK alloy is used as ionization seeds; at 2200 K, the conductivity is in the range of 4.8~12 S/m [13]. The following rule has been found in some of the computational studies we have conducted: adding ionized seeds reduces the temperature of the gas. With an increase in ionized seed mass, the conductivity of the K₂CO₃ seed scheme presented a bell-shaped distribution, while that of the CS₂CO₃ seed scheme presented a monotonic increasing trend, but the increasing gradient decreased gradually. At the same mass of ionized seeds, the electrical conductivity of the CS₂CO₃ scheme was better than that of the K₂CO₃ scheme. Compared to the K₂CO₃ seed scheme, the conductivity of the NaK seed scheme showed a monotonic increasing trend.

However, the scheme did not provide the relationship between conductivity and the initial temperature and pressure of combustion.

In a study of plasma thrust vectors, the purpose of using electron beam-induced ionization is to enhance and maintain the ionization characteristics of the working fluid in the irradiated area of the high-energy electron beam, which is called “local” plasma [14,15]. However, the effect of adding ionized seeds to gas is related to the spatial dispersion of ionized seeds. This method excites plasma with a larger distribution range, called “integrated” plasma [16,17], with a wider magnetron acting area, and an energy management solution is also more feasible.

Based on the engineering application background of a hypersonic aircraft thrust vector, this paper will explore the influence of K₂CO₃ ionization seeds on conductivity in methane/air combustion schemes. High-temperature gas working fluid is obtained by mixing and burning the hydrocarbon fuel methane and air, and adding potassium carbonate (K₂CO₃) as ionization seeds to high-temperature gas to obtain combustion plasma. The ionization characteristics of the combustion plasma are revealed, and experimental research is carried out to verify the correctness of theoretical calculations. This provides a basis for the engineering application of magnetic-controlled gas plasma thrust vectoring.

2. Methods

2.1. Description of Gas Plasma Ionization Characteristics

There are three main ways to quantitatively describe the ionization characteristics of plasma, namely electron number density ne, ionization degree α, and conductivity σ. And conductivity α is directly applied to the macroscopic characteristic parameters of plasma calculated by the Navier Stokes and Maxwell coupled equations [18].

For calculation of the ionization characteristics of plasma in a completely thermodynamic equilibrium state, the electron number density ne and ionization degree can be directly solved using the Saha equation and its variants [19] as shown in Formula (1). Among them, n_e is the electron number density; n_i is the ion number density; n₀ is the neutral particle number density; m_e is the electron mass; k is the Boltzmann constant; T is the equilibrium ionization temperature; h is the Planck constant; g_i is the statistical weight of the ion ground state; g₀ is the statistical weight of the neutral particle ground state; and E_i is the particle ionization potential [20].

$$\left\{\begin{array}{l}{n}_e=\sqrt{{\displaystyle \frac{p{(2\pi m_e)}^{3/2}{(kT)}^{1/2}}{h^3}}·{\displaystyle \frac{2g_i}{g_0}}\exp (-{\displaystyle \frac{e{E}_i}{kT}})}\\ \alpha ={\displaystyle \frac{n_e}{n_0}}=\sqrt{{\displaystyle \frac{{(2\pi m_e)}^{3/2}{(kT)}^{5/2}}{p{h}^3}}·{\displaystyle \frac{2g_i}{g_0}}\exp (-{\displaystyle \frac{e{E}_i}{kT}})}\end{array}\right.,$$

(1)

Conductivity σ can be calculated using the Spitzer formula as shown in Formula (2). Among them, ε₀ is the vacuum dielectric constant; k is the Boltzmann constant; T_e is the electron dynamic temperature (in K); e is the electron element charge; Z is the ion charge number (i.e., Zn_i = n_e; n_i is the ion number density); m_e is the electron mass; ln∧ is the Coulomb logarithm; and n_e is the electron number density [20].

$$\left\{\begin{array}{l}{\sigma }_s={\displaystyle \frac{51.6{\epsilon }_0^2}{e^{2}Z}}{({\displaystyle \frac{\pi }{m_e}})}^{1/2}{\displaystyle \frac{{(k{T}_e)}^{3/2}}{\ln \Lambda }}\\ \ln \Lambda =\ln ({\displaystyle \frac{12\pi {({\epsilon }_{0}k{T}_e)}^{3/2}}{Z^2{e}^3{n}_e^{1/2}}})\end{array}\right.,$$

(2)

For the calculation μ of the conductivity of low-temperature non-equilibrium plasma μ, there are mainly Frost’s method based on electron mobility calculation, Chernov’s method based on collision cross-section calculation, and the superposition method. Frost’s method represents conductivity as a function of mobility, i.e., σ = n_eμe, and mobility is obtained from the Boltzmann equation as shown in Formula (3), where N is the particle number density, and ∑ v is the collision frequency between electrons and other particles, and is expressed as a power function of electron energy. The Chernov method is similar to the Frost method, except that it uses collision cross-sections to represent the collision frequency ∑ v.

$$\mu ={\displaystyle \frac{\sqrt{2}e{m}_e^{1.5}N}{3{\pi }^{0.5}{(kT)}^{2.5}}}{\displaystyle {\int }_0^{\infty }\exp (-\frac{m_e{v}^2}{2kT})\frac{v^4}{{\displaystyle \sum \nu }}dv},$$

(3)

The text uses the superposition method to calculate conductivity σ. Consider the low-temperature non-equilibrium plasma resistance 1/σ as the superposition of resistance under two types of limit conditions. The first type of limit is to consider its resistance as the resistance 1/σ_L of a weakly ionized gas, calculated using Chapman and Cowling formulas. The second type of limit is to consider its resistance as equivalent to 1/σ_S of the plasma resistance in the “complete thermodynamic equilibrium state”, and calculate it using the Spitzer formula as shown in Formula (4) [21].

$$\left\{\begin{array}{l}{\displaystyle \frac{1}{\sigma }}={\displaystyle \frac{1}{{\sigma }_L}}+{\displaystyle \frac{1}{{\sigma }_s}}\\ {\sigma }_L={\displaystyle \frac{n_e{e}^2}{m_{e}nQ\sqrt{8kT/(\pi m_e)}}}\\ {\sigma }_s={\displaystyle \frac{51.6{\epsilon }_0^2}{e^2{Z}_i}}{({\displaystyle \frac{\pi }{m_e}})}^{1/2}{\displaystyle \frac{{(kT)}^{3/2}}{\ln \Lambda }}\end{array}\right.,$$

(4)

Taking potassium carbonate K₂CO₃ as an example, the parameter nQ used to solve the limit conductivity σ_L is calculated by the following formula:

$$nQ=(n_n{Q}_n+n_k{Q}_k+n_i{Q}_i),$$

(5)

Among them, Q_n, Q_k, and Q_i represent the effective collision cross-sectional area of ions, atoms, and molecules in gas, respectively. While n_n, n_k, and n_i are the spatial number densities of neutral molecules, atoms, and ions in gas.

$$Q_k=4\times {10}^{-18},$$

(6)

$$Q_n=23{(2800/T)}^{0.15}\times {10}^{-20},$$

(7)

$$\left\{\begin{array}{l}{Q}_i=2.8\pi {(p_i)}^2\ln ({\lambda }_D/p_i)\\ {\lambda }_D=\sqrt{{\epsilon }_{0}kT/(n_e{e}^2)},p_i=e^2/(12\pi {\epsilon }_{0}kT)\end{array}\right.$$

(8)

By applying Formulas (4)–(8), the electrical conductivity of gas (σ) can be calculated.

2.2. Calculation of Combustion Components

Below 3000 K, the ionization degree of an ordinary gas is only in the order of 10⁻⁸, with no capability to apply electromagnetic characteristics. From the definitions of ionization degree and electrical conductivity, it can be found that it is important to calculate the concentration of chemical components in gas plasma, which closely links the internal microscopic processes of gas plasma with the macroscopic characteristics of the system. From the definitions of ionization degree and conductivity, it can be found that calculating the concentration of chemical components in gas plasma is very important as it closely links the internal microscopic processes of gas plasma with the macroscopic characteristics of the system.

Gas temperature is mainly determined by the combustion reaction. β is used to characterize the excess air coefficient, which is the ratio of the actual airflow to the theoretical airflow during combustion. When the coefficient of excess air is equal to one, it means that the amount of air in the mixture is exactly the theoretical amount needed for the fuel to burn completely. Excess air reduces the combustion temperature when the excess air coefficient is greater than one, resulting in increased exhaust heat loss. When the excess gas coefficient is less than one, the lack of air causes the fuel to not burn fully, creating CO and unburned hydrocarbons, and the combustion efficiency drops dramatically.

The residual gas coefficient is characterized by α, and the combustion temperature is controlled by adjusting the residual gas coefficient β. The main reaction processes involved in gas plasma are shown in

Table 1. K₂CO₃ gas plasma reaction process.

Reaction Process	Reaction Process
(1) ${\mathrm{C}}_{\mathrm{x}}{\mathrm{H}}_{\mathrm{y}}+{\displaystyle \frac{4\mathrm{x}+\mathrm{y}}{4}}{\mathrm{O}}_2{=\mathrm{xCO}}_2+{\displaystyle \frac{\mathrm{y}}{2}}{\mathrm{H}}_2\mathrm{O}$	(2) ${\mathrm{CO}}_2\rightleftharpoons \mathrm{CO}+{\displaystyle \frac{1}{2}}{\mathrm{O}}_2$
(3) ${\mathrm{H}}_2+{\displaystyle \frac{1}{2}}{\mathrm{O}}_2\rightleftharpoons {\mathrm{H}}_2\mathrm{O}$	(4) ${\displaystyle \frac{1}{2}}{\mathrm{H}}_2+{\displaystyle \frac{1}{2}}{\mathrm{O}}_2\rightleftharpoons \mathrm{OH}$
(5) ${\displaystyle \frac{1}{2}}{\mathrm{H}}_2\rightleftharpoons \mathrm{H}$	(6) ${\displaystyle \frac{1}{2}}{\mathrm{N}}_2+{\displaystyle \frac{1}{2}}{\mathrm{O}}_2\rightleftharpoons \mathrm{NO}$
(7) ${\displaystyle \frac{1}{2}}{\mathrm{N}}_2\rightleftharpoons \mathrm{N}$	(8) ${\displaystyle \frac{1}{2}}{\mathrm{O}}_2\rightleftharpoons \mathrm{O}$
(9) ${\mathrm{K}}_2{\mathrm{CO}}_3\rightleftharpoons {\mathrm{K}}_2{\mathrm{O}+\mathrm{CO}}_2$	(10) ${\mathrm{K}}_2\mathrm{O}\rightleftharpoons 2\mathrm{K}+{\displaystyle \frac{1}{2}}{\mathrm{O}}_2$
(11) $\mathrm{KOH}\rightleftharpoons \mathrm{K}+\mathrm{OH}$	(12) $\mathrm{KO}\rightleftharpoons \mathrm{K}+{\displaystyle \frac{1}{2}}{\mathrm{O}}_2$
(13) $\mathrm{K}\rightleftharpoons {\mathrm{K}}^{+}+\mathrm{e}$	(14) ${\mathrm{OH}}^{-}\rightleftharpoons \mathrm{OH}+\mathrm{e}$
(15) ${\displaystyle \frac{1}{2}}{\mathrm{O}}_2+\mathrm{e}\rightleftharpoons {\mathrm{O}}^{-}$	(16) ${\displaystyle \frac{1}{2}}{\mathrm{H}}_2+\mathrm{e}\rightleftharpoons {\mathrm{H}}^{-}$
(17) $\mathrm{K}+{\displaystyle \frac{1}{2}}{\mathrm{H}}_2\rightleftharpoons \mathrm{KH}$	(18) ${2\mathrm{K}+\mathrm{O}}_2{+\mathrm{H}}_2\rightleftharpoons {\left(\mathrm{KOH}\right)}_2$

. The reaction involves C, H, O, N, and K elements, 24 components (i.e., CxHy, O₂, CO₂, H₂, CO, H₂O, O, N, OH, N₂, H, NO, K₂CO₃, K₂O, K, KO, K⁺, KOH, OH⁻, O⁻, H⁻, KH, (KOH)), and 18 chemical reactions. By observing these reactions, it can be inferred that the ionized seed K₂CO₃ dissociates at high temperatures and appears in various forms, such as K₂O, K, KOH, etc. Among them, only the potassium atom K can ionize free electrons e, achieving gas flow conductivity [22,23]. The combustion temperature in the study was calculated using the chemical equilibrium module in ANSYS Chemkin Pro software, while determining the various components of the combustion reaction. This module accesses the chemical equilibrium calculation library named STANJAN through interface functions to solve the chemical equilibrium of the system, minimizing the Gibbs free energy of the chemical reaction system.

Taking “methane/air/K₂CO₃ (ionized seeds account for 1% of the total mass of gas)” as an example, methane and air (residual gas coefficient is α) start a combustion reaction in an environment with an initial temperature T₀ = 300 K and an initial pressure p₀ = 101,325 Pa; while adding 1% mass fraction of K₂CO₃ seeds to the gas, as the combustion temperature increases, the K₂CO₃ seeds absorb heat and begin ionization. When the combustion reaction and ionization heat absorption effect reach equilibrium, the seeds induce the gas plasma to exhibit conductivity α. Figure 1 shows the molar relative concentration distributions of 24 components in order of magnitude.

Figure 2 shows the distribution of ionization characteristics of gas plasma under different conditions. As the residual gas coefficient β increases, the temperature of the gas plasma shows a bell-shaped distribution β. Around the residual gas coefficient β = 1, the temperature peak of the gas plasma reaches 2206.3 K. When the excess air coefficient is greater than one, the actual air quantity is greater than the theoretical air quantity, and the oil–gas mixture comprises more air but less fuel; the excess air will also lower the gas temperature. The electron number density n_e and conductivity both show peaks around the σ residual gas coefficient β = 0.9~1. As the temperature of the gas plasma increases, the degree of ionization and decomposition of K₂CO₃ ionized seeds gradually increases. When the temperature of the gas plasma exceeds 1500K, the ionization and decomposition ratio of K₂CO₃ ionized seeds exceeds 99%, approaching complete ionization.

Figure 2d shows the conductivity of gas plasma (with 1% K₂CO₃ ionization seed added) under different temperature conditions. When the residual gas coefficient β increases from 0.6 to 0.9 (Points A to D in Figure 2d), the gas temperature increases accordingly, and the conductivity rapidly reaches the peak value of 1.26 S/m. When the residual gas coefficient β increases from 0.9 to 1 (Points D to E in Figure 2d), although the gas temperature reaches 2206.3 K, the conductivity σ slightly decreases to 1.18S/m. Subsequently, as the residual gas coefficient β continues to increase from one (Points E to I in Figure 2d), the conductivity of the gas plasma σ rapidly decreases with decreasing temperature. The above analysis shows that the ionization characteristics of gas plasma depend on a high-temperature environment.

3. Results and Discussion

3.1. Influence of Ionized Seed Mass Fraction on Gas Plasma Characteristics

3.1.1. Results and Analysis

Based on the “methane/air_/K₂CO₃” scheme, the mass fractions of K₂CO₃ ionized seeds were 1%, 5%, and 10%, respectively. Figure 3 compares the effects of K₂CO₃ seeds with different mass fractions on the characteristics of gas plasma. Overall, increasing the mass fraction of K₂CO₃ ionized seeds will enhance the endothermic effect of K₂CO₃ seed ionization decomposition. Under the same residual gas coefficient α conditions, the equilibrium temperature of gas plasma will correspondingly decrease. Corresponding to the 2000 K high-temperature region near the residual gas coefficient α = 1, K₂CO₃ seeds have been in a highly decomposed state, with a decomposition ratio of over 99%. However, contrary to the expected enhancement of conductivity α, when the mass fraction of K₂CO₃ ionized seeds increased from 5% to 10%, there was a significant decrease in conductivity α, and the peak conductivity of the 10% K₂CO₃ seed scheme was even lower than that of the 1% K₂CO₃ seed scheme.

For the convenience of practical applications, it is necessary to quantitatively determine the relationship between conductivity σ and temperature T [24]. Set temperature T as a variable and conductivity α as a function, and fit the functional relationship between them. That is, σ (T) = a₁T + a₂T² + a₃T³ +⋯+ a_nTⁿ, where a₁, a₂, a₃,⋯, a_n are undetermined coefficients, and n is the polynomial order. Perform polynomial fitting of different orders using K₂CO₃ ionization seed mass fractions of 1%, 5%, and 10%. The left side of Figure 4 shows the polynomial fitting residual sum of squares (RSS) and adjusted correlation coefficient ARS (Adj. R-Square).

3.1.2. Qualitative Relationship Between Conductivity and Temperature

As shown in Figure 4a,c,e, the fitting order increases from three to five; the square sum of squares of the fitting polynomial residuals gradually decreases; the adjustment correlation coefficient ARS gradually increases; and the increase in the fitting order improves the fitting accuracy. Afterwards, the fitting order continues to improve, and RSS and ARS remain at a stable level, indicating that the improvement of the fitting accuracy of the continued increase in the order is limited [25]. For different quality fraction K₂CO₃ seed schemes, the fifth-order fitting polynomial shows good accuracy. The fifth-order polynomial is selected to fit the functional relationship between temperature and conductivity as shown in Figure 4.

Table 2. Conductivity fitting results of gas plasma (methane/air/K₂CO₃).

K2CO3 Seeds Mass Fraction	σ (T) = a1T + a2T2 + a3T3 + a4T4 + a5T5
	a1	a2	a3	a4	a5
1%	0.00374	−1.19856 × 10−5	1.40541 × 10−8	−7.15634 × 10−12	1.33864 × 10−15
5%	0.00489	−1.61065 × 10−5	1.94334 × 10−8	−1.01970 × 10−11	1.96759 × 10−15
10%	0.00344	−1.17463 × 10−5	1.47230 × 10−8	−8.03843 × 10−12	1.61580 × 10−15

presents the fitting results for different schemes of “methane/air/K₂CO₃” gas plasma (mass fractions of 1%, 5%, and 10%, respectively).

3.2. Influence of Initial Reaction Conditions on the Ionization Characteristics of Gas Plasma

3.2.1. Determination of Initial Conditions

The ionization characteristics of gas plasma were preliminarily analyzed using the “methane/air/K₂CO₃” scheme as an example. For the reactions involved in gas plasma, assuming an initial temperature T₀ = 300 K and an initial pressure p₀ = 101,325 Pa, the entire reaction process is maintained under constant pressure conditions. The assumption of constant pressure is closer to the combustion process of the engine, but the initial temperature T₀ and initial pressure p₀ of the airflow at the inlet of the combustion chamber vary with the actual operating conditions of the engine [26,27]. Therefore, this section investigates the effects of initial temperature T₀ and initial pressure p₀ on the ionization characteristics of gas plasma. Considering the rapid response of gas plasma ionization characteristics to combustion equilibrium temperature, the high-temperature regions corresponding to residual gas coefficients of 0.9, 1, and 1.1 are mainly selected for comparative analysis. The “methane/air/1% K₂CO₃” scheme was selected, and Figure 5 and Figure 6 compared the effects of different initial temperature T₀ and initial pressure p₀ conditions on gas plasma characteristics, respectively.

3.2.2. Effects of Initial Temperature

As the initial temperature T₀ increases, the equilibrium temperature and conductivity of the gas plasma approximately show a linear growth trend. Under different residual gas coefficient conditions, the residual gas coefficient scheme of 0.9 can enable gas plasma to balance the high equilibrium temperature and strong conductivity.

3.2.3. Effects of Initial Pressure

As the initial pressure p₀ increases, the equilibrium temperature of the gas plasma shows a logarithmic growth trend [28], while the conductivity α gradually decreases, and the gradient of change slows down. Under different residual gas coefficient conditions, the scheme with residual gas coefficient α = 1 can maintain the gas plasma at a higher equilibrium temperature. The gas plasma formed by schemes with residual gas coefficient β = 0.9 and β = 1 has a higher conductivity and is basically the same. From an engineering perspective, the combination of gas plasma technology and flow control in engines, especially in the combustion chamber/tailpipe section, has great potential for development. The compression process of the engine increases the initial temperature and pressure of the airflow, and introduces ionization seeds during the combustion process. The higher initial temperature increases the conductivity of the gas plasma, while the higher initial pressure ensures the stability of the conductivity changes of the gas plasma.

3.3. Experimental Verification

To verify the effectiveness of theoretical calculations, experiments were conducted on a combustion and flow control test bench. The experimental platform, experimental methods, and steps are the same as those in Ref. [1]. The experiment chose a methane/air/K₂CO₃ mixed combustion scheme. The experimental conditions are shown in

Table 3. Experimental conditions.

Case	Initial Temperature K	Pressure Pa	Conductivity S/m	Excess Air Coefficient	Percentage of Ionized Seeds	Magnetic Field Intensity T
1	600	101,325	2.9	0.9	5%	0
2	600	101,325	2.9	0.9	5%	0.6
3	900	101,325	7.5	0.9	5%	0.6
4	1200	101,325	11.8	0.9	5%	0.6

. Figure 7 shows the combustion flame morphology at different initial temperatures.

From Figure 7a, it can be seen that the residual gas coefficient is equal to 0.9, and the flame does not deflect in the absence of a magnetic field. As shown in Figure 7b–d, the degree of flame deflection is minimal at an initial temperature of 600 K. At an initial temperature of 1200 K, the degree of flame deflection is maximal. Because the initial temperature of the chemical reactants increases, the chemical equilibrium temperature also increases. The ionization decomposition rate of K₂CO₃ seeds increases; the number of ionized particles in the gas increases; and the conductivity increases. Under the control of a magnetic field, charged ions undergo deflection under the Lorentz force, exhibiting the flame deflection phenomenon shown in the figure at a macroscopic level. The experimental results confirmed the consistency of the conductivity variation pattern shown in Figure 5b. The external electromagnetic field significantly improves combustion efficiency through ionization regulation and combustion dynamics optimization, which, in turn, improves ionization; K₂CO₃ is fused at high temperatures to form ionic conductors, which combine with electromagnetic fields to construct an electrical reaction. The electromagnetic field achieves dynamic management of the combustion process by regulating the degree of ionization.

4. Conclusions

This article introduces the calculation method of seed-induced gas plasma ionization characteristics, and analyzes gas plasma ionization characteristics based on a methane/air/1% K₂CO₃ mixed combustion scheme. The main conclusions are as follows:

(1)

Based on the same initial reaction conditions, a high-temperature environment is beneficial to the ionization characteristics of gas plasma. Above 1500 K, after adding K₂CO₃ ionization seeds into the gas, it gradually shows ionization characteristics, and these characteristics become more pronounced as the combustion temperature increases.

(2)

For alkali metal salt ionization seeds, their ionization process requires absorbing of the heat released by combustion reactions and releasing free electrons. As a result, ionized seeds endow gas with certain conductive properties, forming seed-induced gas plasma.

(3)

For combustion reactions, increasing the initial temperature of reactants is beneficial for improving the ionization characteristics of seed-induced gas plasma.

(4)

Alkali metal salt K₂CO₃ is a powdery crystal at room temperature, easily soluble in water, and can be sprayed with fluidized solid powder using a fluidized bed device. Alkali metal salts have lower costs and higher safety during manufacturing, storage, and use, even in high overload environments. From the perspective of seed characteristics, alkali metal salts are more suitable for use in the field of open air flow control.