基于离轴积分腔输出光谱的燃烧场CO浓度测量研究

CO是碳氢燃料不完全燃烧的重要产物，常常被作为反应燃烧效率的标志物，燃烧场CO组分浓度的精确测量对提高燃烧效率、减少污染物排放具有重要意义。离轴积分腔输出光谱（OA-ICOS）是一种利用物质对激光的特异性吸收，实现对该物质分析和测量的技术，具有非接触、稳定和高灵敏度等优点。针对燃烧场CO浓度低，背景信号干扰强等特点，采用分布反馈式（DFB）激光器搭建基于离轴积分腔输出光谱的CO浓度测量系统，通过直接吸收光谱的测量方法实现对高温燃烧场CO浓度测量。利用仿真模拟的方法，在所用激光器中心波长的附近选出了常温下谱线强度较为突出，高温下不受其他燃烧产物干扰的第一泛频带R(10)吸收谱线。通过固定光程池对比吸光度的方法标定了OA-ICOS系统的有效光程；通过比较不同扫描频率下吸收谱线的信噪比和线型拟合残差标准差，得到最佳波长扫描频率；通过测量不同浓度CO混合气体的吸收信号分析了系统误差。探究了不同燃烧情况下CH₄/Air预混平焰炉上CO的产生情况，根据燃烧场测量区域温度分布情况描述了温度分布不确定度对CO测量结果的影响。当量比为1.0时，在10 ms的测量时间分辨率下，噪声等效灵敏度（NEAS）为3.67×10-7 cm-1·Hz-1，系统测量误差小于4.5%，燃烧场测量区域温度分布不确定度带来的CO浓度测量不确定度为5.6%。改变当量比从0.8到1.2时，得到平均温度变化范围为1 275~1 368 K，CO浓度变化范围为0.041%~1.57%。研究发现随着当量比的提高，燃烧场温度和CO浓度均呈上升趋势。实验结果表明将离轴积分腔输出光谱技术应用于燃烧场气体参数测量具有信噪比高、检测灵敏度高等优点，可以实现痕量气体组分浓度的精确测量。

Research of Carbon Monoxide Concentration Measurement in Combustion Field by Off-Axis Integrated Cavity Output Spectroscopy

Carbon monoxide (CO) is one of the important products of insufficient combustion of hydrocarbon fuels and is often used as a marker of reaction combustion efficiency. The accurate measurement of CO concentration in the combustion field is of great significance to the engine to improve combustion efficiency and reduce pollutant emissions. Off-axis Integrating Cavity Output Spectroscopy (OA-ICOS) is a technology to analyze and measure a material by using the specific absorption of the substance to the laser spectrum. It has the advantages of non-contact, stability and high sensitivity. Aiming at the characteristics of low CO concentration and strong background signal interference in the combustion field, an OA-ICOS system was built with a distributed feedback (DFB) laser to measure the CO concentration in high-temperature combustion field by direct absorption spectroscopy (DAS) method. The first broadband R(10) absorption line, which is more prominent at room temperature and not interfered with by other combustion products at high temperature, was selected near the center wavelength of the DFB laser by absorbance simulation. The effective optical length of the OA-ICOS system was calibrated by comparing the absorbance with the fixed optical path cell. The best wavelength scanning frequency was obtained by comparing the signal-to-noise ratio of the absorption line at different scanning frequencies and the standard deviation of the linear fitting residuals; The system error was analyzed by measuring the absorption signal of CO mixed gas of different concentrations. The production of CO on the CH₄/Air premixed flat flame furnace under different combustion conditions was evaluated. The influence of the temperature distribution uncertainty on the CO measurement results was described by the temperature distribution in the measurement area of the combustion field. A minimum concentration detection limit of 5.83×10-6 was achieved under the time resolution of 10 ms, the system measurement error was less than 4.5%, and the uncertainty of CO concentration measurement caused by the temperature uncertainty of the combustion field was 5.6% when the equivalence ratio is 1.0. The variation ranges of average temperature and CO concentration are 1 275~1 368 K and 0.041%~1.57% when the equivalence ratio changes from 0.8 to 1.2. The experimental results show that the OA-ICOS has the advantages of a high signal-to-noise ratio and high detection sensitivity to measure the gas parameters in the combustion field and can develop an accurate measurement of the concentration of trace gas components.