Pic Formation during the Combustion of Simple Hydrocarbons in Inhomogeneous Incineration Systems

The formation of products of incomplete combustion (PICs) during incineration processes strongly depends on the influence of mixing on the instantaneous values of the reactant concentrations and the temperature in the combustion chamber. Experiments were performed to illustrate the influence of turbulence intensity on PIC formation in a turbulent plug flow reactor, where C2H4 was injected into an oxygen-rich, high-temperature stream. The intensity of the turbulence and the characteristic eddy size were varied and measured, and the effects of such variations on the burnout rate of the fuel and the byproducts were monitored. A numerical model, the partially stirred plug flow reactor (PaSPFR) model, based on the probability density function (PDF) approach, was able to capture the main effects of the turbulence on the formation of selected byproducts. The PDF model was developed for stationary, isotropic turbulent flow. Due to the simplifying assumptions about the flow field, the model can incorporate detailed chemical mechanisms, a feature that proved to be crucial for the description of the evolution of even a small subset of chemical species. The model was tested versus the experiments for the simple situation of an ethylene/air non-premixed flame. The predicted concentration profiles of ethylene and of the PIC that was present in largest amount (C2H2) showed good agreement with the experimental results. The model calculations allowed a more detailed analysis of the chemical aspects of the combustion process than was possible by the experiments alone. The modeling investigation included the effects on PIC concentrations of the initial temperature of the secondary fuel stream, a parameter that could not be changed during the experiments.