LIF imaging of species and temperature in technical combustion at elevated pressures

Planar laser-induced fluorescence (PLIF) has been used to measure time-resolved spatial distributions of temperature, fuel and OH in an SI engine, modified for optical access, and a jet engine combustion chamber segment. For temperature measurements, a two-line PLIF scheme was used: Two different rotational lines of the OH radical, which served as indicator molecule, were excited successively using nanosecond pulses from two laser systems operating on different wavelengths. The resulting fluorescence intensity is proportional to the population of the initial rotational state; the ratio of the two fluorescence signals is therefore proportional to the ratio of the populations, which in turn depends on the temperature. The fluorescence signal resulting from excitation by one of the two lasers is proportional to the OH density and provides thus information on flame structure. If the laser is tuned away from an OH resonance, fluorescence resulting from kerosene can be observed. The measurements presented here provide information on flame structure, heat release and mixing properties, which can serve as design aids, as well as for CFD code validation purposes.