Velocity measurements of reactive and non‐reactive flows by NO‐LIF method using NO2 photodissociation

Velocities of reactive and non‐reactive flows, where NO₂ molecules were seeded, were measured by a NO‐based Laser Induced Fluorescence (LIF) method. NO₂ dilute gases were injected from a round tube with an inner diameter of 2 cm and its flow rate was 10 liters/minute or 20 liters/minute. Experiments were performed for 4 conditions—non‐reactive flows of NO₂ dilute gases at two flow rates, an unburnt gas flow of the premixed flame with NO₂ addition, and an unburnt gas flow of the diffusion flame with NO₂ addition. NO molecules were produced in flows by planar emissions of 355 nm laser rays from an Nd:YAG laser system, and NO‐LIF images were taken in a pre‐determined delay. An ICCD camera, a dye laser excited by an excimer laser, and Nd:YAG laser were strictly synchronized by a pulse generator. NO‐LIF signals, which were emitted by photochemically produced NO from NO₂, were strong enough to measure the NO displacements in the case of non‐reactive flows, while with only a few ppm concentrations of NO₂ added it was possible to measure the velocity in detail. Although fluctuations of NO trajectories were observed at the flow rate of 20 liters/minute, instantaneous velocities were measured accurately. In the case of the unburnt gas of the diffusion flame, NO‐LIF signals were also strong, and profiles of NO produced by NO₂ photodissociation were clearly measured. Profiles of NO produced by NO₂ photodissociation in the unburnt gas of the premixed flame were also clearly measured, even in the vicinity of the reaction zone. It can be seen that velocities were measured correctly in the unburnt regions of the premixed and the diffusion flames. With this method, it was possible to measure velocities of both steady and unsteady flows. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(1): 40–52, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20038