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This study focuses on the development of a new laser diagnostic based on Laser Induced Fluorescence by seeding the gas (N2) in which hydrogen is injected with fluorescent tracer. In this paper, three tracers were characterized, two aromatic compounds (toluene and difluorobenzene) and one ketone (acetone). The first part of this study compared the fluorescence of both aromatic compounds without injecting H2 . More particularly the influence of a temperature variation on the quantum yield and cross section absorption was regarded. It appeared that difluorobenzene was more suitable LIF measurement than toluene as it has a higher quantum yield that is less dependent to temperature variation. Then, Negative LIF was tested using two different tracers (difluorobenzene and acetone) and considering three different post-processing methods to consider the temperature variation inside the hydrogen jet: no temperature correction, temperature calculated based on a CFD RANS simulation, temperature calculated via an isentropic expansion and adiabatic mixture hypothesis. Results evidence that the first and the third methods presents respectively a lower and upper limit for the hydrogen mole fraction when the second method is biased by the presence of shock and expansion structures near the injector nozzle. Finally, it appears that, with the proper temperature correction, difluorobenzene and acetone yield similar results, despite the fact the acetone fluorescence needing more amplification to be captured, the signal to noise ratio is lower than for aromatic compounds.
Quintens et al. (Mon,) studied this question.