Kinetics of I2 and HI photodissociation with implications in flame diagnostics

This paper investigates the application of iodine (I₂) tracer in reactive flows to image the concentration filed by using photodissociation spectroscopy (PDS). The PDS technique first uses a short laser pulse to completely photodissociate iodine-containing species into iodine atoms, and then uses a second laser pulse to image the iodine atoms. Due to the completeness and rapidity of the photodissociation (PD), the concentration of I atoms after PD represents that of the iodine element seeded into the flow, which forms a conserved scalar and can be used to image the concentration field. The feasibility of the PDS technique is evaluated in three steps. First, a multi-level kinetic model was developed to capture the major physics relevant to the PDS technique. Second, controlled experiments were conducted to validate the multi-level kinetic model. Third, the validated model was applied to evaluate the applicable range and accuracy of the PDS technique in representative hydrocarbon flames. The results suggest a simple approach to implement the PDS technique using I₂ seeding in flames, which can provide good accuracy across a wide range of mixture fractions and strain rates.