- Author
-
Reitz, R. D.
|
Bracco, F. V.
- Title
- Global Kinetics Models and Thermodynamic Equilibrium
- Coporate
- Princeton Univ., N. J.
- Report
-
WSS/CI 83-33,
- Book or Conf
- Combustion Institute/Western States Section. Spring Meeting, 1983. April 11-12, 1983,
Pasadena, CA,
7 p.,
1983
- Keywords
-
kinetics
|
thermodynamics
|
reaction kinetics
|
chemical equilibrium
- Abstract
- Global chemistry models are often used for analytical and numerical studies of combustion due to their simplicity. However, the commonly used one step irreversible reaction mechanism leads to the correct thermodynamic equilibrium only in certain special cases, e.g. when the assumption of complete combustion is appropriate. Multistep irreversible reactions, and even combinations of reversible and irreversible reactions, in general present the same problem unless the irreversible reactions are suitably constrained. However, the option of constraining rates of irreversible reations to get the correct final equilibrium is not available when the final equilibrium is not known a priori, e.g. in applications where the state of the reactants varies in space and/or time. Thus, to obtain the correct equilibrium unconditionally all species must respect the condition that their net rate of change is zero unconditionally at thermodynamic equilbrium. This condition can be achieved in a number of ways and two possible formulations are discussed. The first is a generalization of the equations of chemical equilibrium while the second is based on an expansion about local equilibrium. The advantage of the second method is that it is more flexible and can be used for problems with only one global chemistry timescale and arbitrarily many chemical species.