In some numerical solution algorithms for chemically reacting flow, it is a significant computational savings to separate the temperature-dependent part of the rate expressions (that is, the rate constants in most cases) from the concentration-dependent contribution. In particular, evaluation of Jacobian matrix elements through perturbation of solution variables often relies on numerous function evaluations and hence numerous calls to Gas-phase Kinetics to evaluate rate expressions. The temperature-dependent portion of the rate expression contains an exponential, which is computationally expensive to evaluate. When the temperature variable is not being perturbed, it is unnecessary to repeat this evaluation.

To facilitate a more computationally efficient solution algorithm, Ansys Chemkin provides additional subroutines that either provide the temperature-dependent rate coefficients or, given these rate coefficients, return the species’ net rates of production. The subroutine for evaluating the temperature-dependent rate constant for each reaction is called CKKFRT, while the subroutine that takes the rate constant as input and returns the species net rates of production is called CKWYPK. The use of these subroutines is described in more detail in the Chemkin Application Programming Interface Manual Application Programming Interface Manual, specifically in Chemical Production Rates and Alphabetical Listing of the Gas-phase Kinetics Subroutine Library .