Skeletal mechanism construction by entropy production analysis: detailed reaction mechanisms with irreversible reactions

The combustion technologies nowadays adopted to reduce pollutant emissions and increase combustion efficiency are complex and their accurate description requires complex reaction mechanisms consisting of hundreds of species and several thousands of reactions [1]. However, especially in application to practical systems, numerical simulations can be afforded only adopting simplified descriptions of the kinetics. Therefore, the possibility to obtain reduced mechanisms with assessed range of validity is an important topic. Kooshkbaghi et al. [2,3] proposed to identify the most relevant reactions in a detailed chemical mechanism evaluating the entropy generated by the elementary reactions, thus obtaining an attractive approach for mechanism reduction. This approach allows to identify, with a simple analysis of thermodynamic states crossed during the chemical transformation of reactants to products, the most relevant reactions, thus deriving skeletal mechanisms which only include the most significant species for a particular application. Being based on thermodynamic law, the degree of approximation can be selected and verified. In the original formulation [2], the evaluation of the entropy production rate was based on the principle of detailed balance, a property that does not hold in the case of irreversible reactions which are often adopted in the development of detailed mechanisms for complex fuels (e.g. [4]). Therefore, it is advisable to have a more general formulation that holds even in presence of irreversible reactions. In this work the recent advances of this research effort [5,6] are presented: starting from the principles of chemical reaction thermodynamics, an alternative formulation is derived valid for both reversible and irreversible reactions and thus useful for the reduction of a wide set of detailed mechanisms. To illustrate the potentiality of this approach, it has been applied to obtain the reduction of the detailed mechanism developed by the group of CRECK [4], formed prevalently by irreversible reactions, to derive a reduced mechanism for n-dodecane.