基于准固定波长TDLAS-WMS的燃烧场温度及碳氧化合物浓度时间演变研究

The temperature and concentration of CO2 and CO are the critical indicators for sufficiency of the fossil fuel combustion. Species time-histories data describing these parameters are especially important for the new concept foundation and development of the latest combustion technologies. There are some defects in DFB diode laser which is usually employed in the tunable diode laser absorption spectroscopy with high scanning frequency. Beside that, the pressure shift of absorption line at high pressure can not be ignored. So it is hard to measure elevated pressure combustion with high time resolution using scanned- or fixed-TDLAS-WMS. In order to overcome this disadvantage, a new technical scheme named quasi-fixed-wavelength Wavelength Modulation Spectroscopy is developed and combined with Tunable Diode Laser Absorption Spectroscopy (quasi-fixed-wavelength TDLAS-WMS). Frequency-Division Multiplexing (FDM) and Cavity-Enhanced Absorption Spectroscopy (CEAS) are also employed in the development to yield the accurate values of the parameters in the same path. In this research, the second harmonic signals of the WMS which is the most commonly employed for gas sensing are replaced by the higher harmonic signals. Due to the utilization of the higher harmonic signals along with the high scanning frequency for the DFB diode laser and the technique for the noise impression, the influence of the background harmonic signal on the measurement at high temperature and pressure can be impressed. The time-history with time resolution of micro-second for temperature and concentration of CO2 and CO can be measured simultaneously in the same way by means of the method. The sufficiency of combustions under different conditions will be analyzed by this method. The obtained time-history rules can be used for development and validation of combustion model and mechanics with high combustion efficiency.

燃烧场中温度及碳氧化合物浓度等参数的时间演变规律是判断燃烧充分性的基本依据，对设计高效燃烧室、发展新型燃烧技术具有重要意义。目前基于TDLAS的燃烧诊断中常用的DFB半导体激光器在高频扫描下波长输出存在缺陷，同时由于高压下谱线压力位移变得明显，因此难以通过传统扫描波长及固定波长的TDLAS-WMS实现对高压燃烧场的高精度时间分辨测量。本项目提出一种准固定波长TDLAS-WMS方法，结合频分复用及腔增强吸收光谱技术，利用高次谐波代替二次谐波探测方式，配合激光器高速扫描和各种噪声抑制手段，开展化石燃料高压燃烧过程中流场参数的时间演变测量研究，实现对温度及CO2、CO浓度在相同时空维度上的微秒量级时间分辨测量；通过分析不同燃烧条件下温度及碳氧化合物浓度的同时空演变规律，得到实现稳定高效燃烧的释热条件，为高热效率燃烧模型的建立提供数据支持，为新型高热效率燃烧技术的开发提供基础数据支持及研究手段。

燃烧是化石燃料进行能源贡献的主要方式，对燃烧温度及燃烧产物的浓度进行在线检测有助于提高燃烧效率，控制污染性气体的排放，对节能减排有着极其重要的作用。.可调谐二极管激光吸收光谱（TDLAS）技术可用于测量燃烧场温度、组分浓度、流场速度等，具有对流场无扰动、高响应速率、高灵敏度、测量系统小巧紧凑等优势，且其分析测量不受测量环境中背景气体、粉尘以及环境温度和压力的影响，近年来被广泛应用到了大气环境监测、工业过程控制、医疗诊断及化学反应过程等领域。随着科技的不断进步，对化石燃料的燃烧诊断技术也在不断的发展，分子位于中红外和近红外波段的吸收光谱被作为传感目标大量运用到了燃烧流场的参数诊断中，本项目就以如何有效降低火焰背景辐射及其他非目标气体分子的干扰、高效率高准确度的实时测量出火焰燃烧产生的CO气体浓度及火焰温度为目标，开展的主要研究包括以下五个方面：.① 利用改进后的高温高压静态气体池，实现对CO及CO2在常温和高温下的谐波信号分析以及部分谱线参数，包括线强、自加宽、氮气加宽等，评估其在本研究中的潜在应用性。.② 基于开放式结构的腔增强吸收光谱测量系统，将波长调制与腔增强技术相结合，实现了对空气中CO2、CO的高灵敏度测量。.③ 发展了一种具有双向探测结构的增强型腔增强吸收光谱技术，实现了对以上两种气体的同时探测。.④ 考虑到火焰对光路的强烈干扰，为了准确得到火焰中的有效光程，以4302.87 cm-1处水的谱线作为目标谱线，通过光谱吸收面积比值法有效的计算出燃烧火焰中的有效光程。.⑤ 搭建了开放式结构的燃烧诊断系统，以乙烯/空气作为燃料，氮气作为保护气，分别利用扫描波长调制和准固定波长调制辅助的腔增强吸收光谱技术，测量了不同当量比下的CO2和CO光谱信号，实现了对火焰中CO浓度的实时测量；通过双线比值法，利用一对CO2谱线信号实现了对火焰温度的实时监测。.上述研究为燃烧诊断提供了新颖可靠的技术手段，有助于极大的推动新型燃烧诊断技术的发展。