基于微纳电离式传感器的低浓度甲烷阈值气敏机理研究

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

在CH_( 4)浓度较低时,目前煤矿井下CH_( 4)的检测方法存在灵敏度较低、反应较慢等问题。现有微纳电离式气体传感器研究主要针对高浓度气体的检测,且使用的仿真模型为一维简化放电模型,忽略了N_( 2)、CH_( 4)分子与电离产生离子的横向漂移与扩散,对低浓度CH_( 4)气体的准确检测还有待进一步验证。针对上述问题,在现有研究的基础上考虑了离子的横向漂移与扩散,并加入了等离子体模块,采用流体-化学动力学混合方法建立了常温常压下CH_( 4)-N_( 2)混合气体在微纳场域下的二维放电模型,分析了在常温常压下CH_( 4)-N_( 2)混合气体的安全放电电压、气敏性以及放电电流密度与CH_( 4)浓度之间的变化关系。分析结果表明:电离式传感器的安全放电电压为200 V,且信噪比较高;在CH_( 4)-N_( 2)混合气体中,CH_( 4)对N_( 2)的电离过程起抑制作用;电离式传感器的输出电流密度随CH_( 4)体积分数的增加(0.25%~1.5%)而线性递减,体现了电离式传感器对低浓度杂质气体的敏感特性,利用CH_( 4)浓度与电流密度之间单调递减的线性关系,可以实现对低浓度CH_( 4)的检测。

When the concentration ofCH_( 4) is low,the current detection methods forCH_( 4) 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 N_( 2) and CH_( 4) molecules and ions generated by ionization.For low-concentrationCH_( 4) 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 ofCH_( 4)-N_( 2) 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 theCH_( 4) concentration ofCH_( 4)-N_( 2) 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.InCH_( 4)-N_( 2) mixed gas,CH 4 inhibits the ionization process of N_( 2).The output current density of the ionization sensor decreases linearly with the increase ofCH_( 4) 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 concentrationCH_( 4) can be achieved by using the monotonously decreasing linear relationship betweenCH_(4) concentration and the current density.