Gas-phase velocity field measurements in dense sprays by laser-based flow tagging

It is demonstrated in this work that gas-phase velocity measurements can be performed in dense sprays by using a new 2D laser-based how tagging techni que. Velocity measurements in dense sprays, such as automotive direct injec tion (DI) Otto and Diesel sprays, are difficult with conventional technique s because of the high number densities of droplets, the optical thickness o f the medium, and multiple light scattering effects. The present flow taggi ng technique is performed by two consecutive laser pulses, i.e., 'write' an d 'read' lasers. The write laser creates a grid of tracer molecules (NO) by inducing a photodissociation process. The tracer molecules are convected w ith the flow and probed by the read laser after a certain delay. The instan taneous velocity held is determined by time-of-flight analysis.