Laser-induced fluorescence of NCN in low and atmospheric pressure flames.

The cyanonitrene radical, NCN, is detected by laser-induced fluorescence in laminar, adiabatic, flat phi=1.3 methane-air flames at 200 hPa and atmospheric pressure. Laser excitation of the A approximately 3Piu(020)-X approximately 3Sigmag-(000) band at 317 nm allows off-resonant fluorescence to be detected at 326 nm. Excitation and dispersed fluorescence spectra are presented, as well as profiles of NCN and CH versus height above burner.

Nitric oxide flow tagging in unseeded air.

A scheme for molecular tagging velocimetry is presented that can be used in air flows without any kind of seeding. The method is based on the local and instantaneous creation of nitric oxide (NO) molecules from N(2) and O(2) in the waist region of a focused ArF excimer laser beam. This NO distribution is advected by the flow and can be visualized any time later by laser-induced fluorescence in the gamma bands. The creation of NO is confirmed by use of an excitation spectrum. Two examples of the application of the new scheme for air-flow velocimetry are given in which single laser pulses are used for creation and visualization of NO.

Laser-induced fluorescence of formaldehyde hot bands in flames.

Laser-induced fluorescence and excitation spectra of formaldehyde in the A-X 4(1)(0) band at 370 nm are recorded in the primary flame front of a Bunsen flame. An examination of partition functions shows that this excitation can minimize temperature bias for formaldehyde in situ diagnostic measurements.