Research on gas sensitive mechanism of low concentration methane threshold based on micro-nano ionization sensor

When the concentration of CH4 is low, the current detection methods for CH4 in coal mines have problems such as low sensitivity and slow response. The existing research on micro-nano ionization gas sensors mainly focuses on the detection of high concentration gas, and the simulation model used is a one-dimensional simplified discharge model, ignoring the lateral drift and diffusion of N2 and CH4 molecules and ions generated by ionization. For low-concentration CH4 gas, the accurate detection of the sensors needs to be further verified. In order to solve the above problems, the lateral drift and diffusion of ions are considered on the basis of existing studies and a plasma module is added. A two-dimensional discharge model of CH4-N2 mixed gas at room temperature and pressure in the micro-nano field domain is established by using a fluid-chemical dynamics hybrid method. The model analyzes the safe discharge voltage, gas sensitivity and the relationship between the discharge current density and the CH4 concentration of CH4-N2 mixed gas at room temperature and pressure. The analysis results show that the safe discharge voltage of the ionization sensor is 200 V and the signal-to-noise ratio is high. In CH4-N2 mixed gas, CH4 inhibits the ionization process of N2. The output current density of the ionization sensor decreases linearly with the increase of CH4 concentration (0.25%-1.5%), which reflects the sensitive characteristics of the ionization sensor to low concentration of impurity gas. Hence, the detection of low concentration CH4 can be achieved by using the monotonously decreasing linear relationship between CH4 concentration and the current density.