ID 426

Liquid-Vapor Imaging in Fuel Sprays Using Lifetime-Filtered Planar Laser-Induced Fluorescence

 

Abstract:

The effective dispersion of fuel vapor is critical for the development of novel combustion devices because of the impact on ignition, stability, efficiency, and emissions. An optical technique capable of separating and quantifying the liquid and vapor phases in fuel sprays has been elusive. This is primarily due to the dominance of the liquid phase signals over vapor phase signals that occur in the same spectral range. The liquid intensity can be orders of magnitude more intense due to the higher density. However, fluorescence lifetimes are often shorter for the liquid phase as compared with the vapor phase. This work demonstrates the use of temporal fil-tering as a simple approach to distinguishing the two phases in a planar optical measurement. Images captured immediately after the laser pulse favor the liquid phase, while those captured tens of nanoseconds later favor the vapor phase. The short time delay between the signal from each phase, captured using a two-camera setup, en-sures the flow is essentially frozen in time. Various fuel sprays were imaged under a heated nitrogen co-flow, and the emission spectra and fluorescence decay profiles were characterized. The applicability of this technique for distinguishing liquid and vapor fields in undoped fuels and fuel tracers is investigated, as is the use of tem-poral filtering for reducing the spectral overlap in the liquid and vapor fluorescence of exciplex fuel tracers. The results indicate that the use of temporal filtering can significantly improve the ability to distinguish liquid and vapor phases using laser-induced fluorescence techniques.