The application of turbulent reaction models to the oxidation of CO in a turbulent flow

Abstract

The oxidation of carbon monoxide in a turbulent flow was investigated separately from the other reactions in flames under conditions where the rates of turbulent mixing and of the chemical reaction are of the same magnitude. For that purpose, CO was admixed into the bot exhaust of a natural gas flame with an excess of air. Measurements of mean values of the CO and O 2 volume fractions, the temperature and the axial velocity were compared with computational simulations using different turbulent reaction models for carbon monoxide oxidation. The k −∈ model could be used to simulate the turbulent mixing processes. The comparison of measurements and calculations demonstrated that a turbulent reaction model with a kinetic expression is necessary to describe carbon monoxide oxidation under these conditions. Simpler models, such as the flamesheet or Eddy-Break-Up-Model, could not explain the clear influence of the temperature on the carbon monoxide profiles. Further, the influence of fluctuations on the effective reaction rate was considered by integration of the rate expressions over different assumed probability density functions (PDF). This procedure resulted in better agreement between measured and calculated carbon monoxide volume fractions, but also differences depending on the PDF used.