FINITE RATE CHEMISTRY AND NO MOLE FRACTION IN NON-PREMIXED TURBULENT FLAMES

Finite rate chemistry is investigated in turbulent N-2-diluted H-2 dif fusion flames by means of laser spectroscopic methods and a numerical model of combustion. The major species occurring in these hydrogen fla mes or the temperature are measured with SRS (Spontaneous Raman Spectr oscopy) or Rayleigh spectroscopy. Some minor species, the radical OH a nd the pollutant NO, are simultaneously measured with linear LIF (Lase r Induced Fluorescence). Multidimensional pdfs (probability density fu nction) can be deduced from these measurements. Use is made of a numer ical model with two principal variables, mixture fraction xi and react ion progress variable eta, as a basis for discussion of the experiment al results. A k-epsilon-turbulence model together with a two-dimension al presumed pdf for the coupling of turbulence and chemistry are appli ed. So, experimental two-dimensional pdfs as well as mean values of xi and eta as functions of the position in the flame are deduced from th e simultaneous measurements. The experimental and theoretical spatial maxima of the mean OH molefraction agree well in magnitude, despite th e correlation coefficient between xi and eta of the measured pdf can h e as high as 0.5. The neglect of this covariance for the calculation o f the presumed pdf is quantified. It results in clear deviations for t he OH molefraction. The experimental NO and OH molefractions are bette r simulated by flame calculations carried out with the presented combu stion model than by the also shown calculations based on a single vari able for description of chemistry. (C) 1998 by The Combustion Institut e.