Induction zone length measurements by laser-induced fluorescence of nitric oxide in hydrogen-air detonations

Abstract

This experimental study aims at presenting a proof-of-concept for induction zone length (Δi) measurements in H2-air detonations by using the laser-induced fluorescence (LIF) of nitric oxide (NO) technique. The proof-of-concept is evidenced on a stoichiometric H2-air detonation, propagating in a mixture initially at 18 kPa and 293 K, by using an excitation wavelength at 225.120 nm and seeding the H2-air mixture with 1900 ppm of NO. Both, experiments in an optical detonation duct with a rectangular section and numerical simulations with an in-house code, KAT-LIF, are conducted. After verifying that the NO seeding has a negligible effect on the detonation structure, the main results are the following. A single correlation between the NO-LIF signal evolution and the Δi is determined numerically, based on the LIF signal decay at the end of the induction zone. The Δi measurements have a satisfactory 2% theoretical accuracy, determined from comparisons between Zeldovich-von Neumann-Döring (ZND) and KAT-LIF simulations, and a ±160−μm experimental uncertainty. An evolution of the induction zone length as a function of the cellular cycle is observed experimentally but, due to line of sight integrated chemiluminescence imaging of the detonation structure, a correlation between induction length and cellular cycle could not be achieved. However, statistical analysis of the results revealed that the evolution of the experimental induction lengths well correlates with the ZND and KAT-LIF simulations.