Abstract
<jats:p>A new approach is presented for simulating mixing-sensitive homogeneous chemical reactions between two streams that automatically determines an appropriate infinitely fast reaction bounding limit so that instantaneous species concentrations may be calculated. The method appears to be applicable to any reaction system or set of kinetic parameters or reaction conditions without adaptation. A composite reaction summarizes at any moment the consumption and formation of all reacting species; the stoichiometric coefficients in the composite reaction may be thought of as a mathematical ray indicating the overall direction of the reaction system. The ray is used to calculate the maximum extent of the composite reaction, providing a bounding limit for the instantaneous reactant concentrations. The form of the ray is obtained directly from solution of the chemical species rate equations coupled with the variance of the concentration fluctuations and is determined by the stoichiometric coefficients of the underlying reactions and the extent of each reaction at any moment. Illustrations are provided in which the new closure is applied to several different types of chemistry that exhibit mixing-sensitivity.</jats:p>