Several examples of laser in situ monitoring of combustion processes are presented. Using a frequency modulated (13)CO(2) waveguide laser, in situ concentrations of NH(3) down to 1 ppm were measured at temperatures up to 600 degrees C in waste incinerators and power or chemical plants. Following ignition of CH(3)OH-O(2) mixtures by a TEA CO(2) laser, gas temperature profiles were measured using rapid scanning tunable diode laser spectroscopy of CO molecules. In laminar CH(4)-air counterflow diffusion flames at atmospheric pressure absolute concentrations, temperatures, and collisional lifetimes of OH radicals were determined by 2-D and picosecond LIF and absorption spectroscopy. Two-dimensional LIF and Mie scattering were used to observe fuel injection and combustion in a diesel engine.

https://deepblue.lib.umich.edu/bitstream/handle/2027.42/86767/Sick52.pdf;sequence=1

Laser in situ monitoring of combustion processes

Infrared (IR) spectroscopy is a proven tool for gas analysis, and tunable mid-IR diode laser absorption spectroscopy is a special technique giving optimum sensitivity, selectivity and measurement speed for most molecules of interest. Molecules such as the NOx family (N2O, NO, NO2, HONO, and HNO3) can be detected selectively down to well below part per billion levels. The technique works well with all molecules having line spectra and thus is quite universal. It is conceptually simple and detects gases by repetitively scanning absorption lines, which is possible due to the narrow laser line width and easy laser tuning. The scanning procedures of diode laser spectroscopy optimally reduce background fluctuations. Basic operation principles are explained in the article.



Alternative techniques are well established and often allow detection of single components at lower system cost, but in general need specific sample pretreatment that makes the results often difficult to compare. Mass spectroscopy is an alternative multicomponent technique that reaches comparable selectivity, but only with preselection processes which induce calibration problems of their own, such as matrix-dependent sensitivity. In order to give an insight into the capabilities of tunable mid-IR diode laser absorption spectroscopy, three exemplary systems are treated in detail for air monitoring from airplanes, from rockets, and gas analysis of combustion exhaust. System parameters are explained, and system performance is compared with alternative techniques.

Laser absorption spectroscopy: Air monitoring by tunable mid-infrared diode

Of the various secondary measures taken to reduce NOx emissions from large combustion facilities, the method or catalytic reduction of nitrogen oxides by ammonia has found the widest acceptance.

K. Gregorius

Papers

Stack Gas Control by Diode Laser Spectrometers in Power Plants