A Comparison of Turbulent Premised Combustion Models

摘要

Lean premixed gas turbine combustors have become the method of choice for ground based power generation. This is due to their ability to reduce harmful pollutants while not sacrificing efficiency. These combustors sustain combustion by inducing strong recirculation and swirl to always keep hot, partially burned products in contact with fresh incoming mixture. On a premixed combustion regime diagram, these combustors are in the distributed reaction zones and well stirred reactor regimes. Detailed models that combine fluid mechanics and chemistry are needed to optimize their design. Here a new turbulent premixed combustion model, the premixed Conditional Moment Closure model (CMC), is compared to several existing models, namely the Laminar 1-D Flamelet (L1DF), the Perfectly Stirred Reactor (PSR) and the 1-step infinitely fast chemistry models. It is shown that these three models can be derived from the premixed CMC, in other words they can be thought of as simplifications of the more general premixed CMC model. The L1DF model assumes the small-scale turbulence does not affect the reaction rates, only the large-scale turbulence affects the reactions through the PDF, Poinsot and Veynante (2001). Chemical reactor models treat the combustor as a series of perfectly stirred and plug flow reactors, allowing detailed chemistry, but significantly simplified fluid mechanics, Nicol (1995). The fast chemistry model simplifies the calculations by assuming the fuel is instantly burned to products, with no intermediate species, Poinsot and Veynante (2001). These models do not account for the affects of the small-scale turbulence on the reaction rates and therefore are limited in their ability to predict emissions. The premixed CMC model is a relatively new method that attempts to account for the affects of the small-scale turbulence through the scalar dissipation (also called micromixing), Martin et al. (2003). Next the premixed CMC model is derived and compared to the three models described above.