PROBE AND OPTICAL DIAGNOSTICS FOR SCALAR MEASUREMENTS IN PREMIXED FLAMES

Procedures which allow the measurement of scalars in premixed recircul ating flames using digitally-compensated thermocouples or, alternative ly, laser-Rayleigh scattering, are described together with the error s ources associated with the use of these techniques. The procedure for the numeric compensation of the thermocouple signals included experime ntal data on the characteristics of the effect of velocity and tempera ture on the time constant of the thermocouple and was optimised to gua rantee the temporal resolution of the system. The Rayleigh system incl uded its calibration in a propane/air flame and was optimised to avoid contamination of Mie scattering from small particles. The effect of t he photomultiplier shot noise on the Rayleigh signal is quantified and used to compensate the results. The two techniques are shown to give rise to results in close agreement and to be suitable to characterise the turbulence nature of strongly recirculating premixed flames.