TDLAS气体检测系统仿真与影响因素分析

Simulation and Influencing Factors Analysis of Gas Detection System Based on TDLAS Technology

船舶运输作为大宗货物的重要流通手段,为我国经济社会发展做出了巨大贡献,但与此同时船用柴油机带来了严重的污染排放问题。在全球排放限制日益严峻的背景下,实现对其排放参数的实时监测,对环境保护、节能减排、优化柴油机控制策略与燃烧性能等都具有重要意义。近年来可调谐半导体激光吸收光谱(TDLAS)技术因其精度高、响应快等优点逐渐受到青睐,该技术的广泛应用对其的研究提出了更高要求,因此利用数学软件对其进行仿真模拟,对测试系统的开发、参数调整都具有一定价值。结合目前的船舶排放检测问题,以其中最具代表性的污染物NO为目标气体,利用软件制作了气体浓度测量仿真模型。检测系统仿真模型主要由光源调制、线型函数拟合、模拟气体吸收、线强函数S(T)拟合、锁相放大器等各部分组成。采用波长调制的方法对浓度测量过程进行仿真,将高频正弦波和低频锯齿波相叠加用以调谐激光,激光经过气室进行模拟吸收后,信号经过锁相放大器调解得到各阶谐波信号。将二次谐波比一次谐波的峰值点作为信号,采用最小二乘法进行浓度-信号幅值曲线拟合并以此进行浓度反演和误差计算,反演误差在2.5%以内。分析了温度、压力等环境因素对信号幅值的影响并绘制了谐波图线,通过引入参考气室来消除环境波动对结果造成的影响,在环境变动时不需要重新拟合浓度-峰值曲线,可直接得到结果。尝试了不同的正弦波频率和调制系数等参数,分析了调制参数对信号幅值的影响,选取了较为合适的参数范围。为柴油机在线排放测试系统的构建和参数选择提供了一定参考。

As a necessary means of circulation of bulk cargo,ship transportation has made significant contributions to our country’s economic and social development.However,at the same,time marine diesel engines have brought severe problems of pollution emissions.In the context of increasingly stringent global emission limits,real-time monitoring of its emission parameters is of great significance to environmental protection,energy conservation,emission reduction,optimization of diesel engine control strategies and combustion performance.In recent years,tunable diode laser absorption spectroscopy(TDLAS)technology has gradually been favored due to its high accuracy and fast response.The wide application of this technology puts forward higher requirements for its research,so using mathematical software to simulate it has a certain value for this test system’s development and parameter adjustment.Combining the current ship emission detection problems,taking the most representative pollutant NO as the target gas,a simulation model of gas concentration measurement was made using software.The simulation model of the detection system is mainly composed of a light source modulation part,a line type function fitting part,a simulated gas absorption part,a line strength function S(T)fitting part,and a lock-in amplifier.The method of wavelength modulation is used to simulate the concentration measurement process.The high-frequency sine wave and the low-frequency saw tooth wave are superimposed to tune the laser.After the gas chamber absorbs the laser,the signal is adjusted by the lock-in amplifier to obtain the harmonic signals.The peak point of the value of the second harmonic divided by the first harmonic is used as the signal.The least-square method is used to fit the concentration-signal amplitude curve,and then the concentration inversion and error calculation are performed.The inversion error is within 2.5%.Analyzed the influence of temperature,pressure and other environmental factors on the signal amplitude and drew the harmonic graph.By introducing a reference gas chamber to eliminate environmental fluctuations on the results,there is no need to refit the concentration-signal curve when the environment changes.The result can be obtained directly.Tried to use different sine wave frequency,modulation coefficient and other parameters.Analyzed the influence of modulation parameters on signal amplitude and selected a suitable parameter range.It provided a certain reference for the construction of a diesel engine online emission test system and the selection of parameters.