Comment on: ‘‘Chaos in the Showalter–Noyes–Bar–Eli model of the Belousov–Zhabotinskii reaction’’

The recent numerical work of Lindberg et al. convincingly demonstrates that chemical chaos in a continuous flow, stirred tank reactor (CSTR) can be reproduced by a spatially homogeneous, accurate model of the kinetics of the Belousov–Zhabotinskii(BZ) reaction. However, some problems remain. The chaos in this model and two others, one using an accurate model of the chemical kinetics in conjunction with spatial inhomogeneity resulting from the finite CSTR mixing time and the other using a flawed model of the BZ chemical kinetics, results from coupling of two cycles coexisting within the complex dynamic model. The second cycle in the case of the homogeneous models involves a product of the main chemical limit cycle which is present at a high average concentration. In the Lindberg et al. model this product is assumed to be HOBr. It is clear, however, that a large [HOBr] does not accumulate in the real system because of its rapid reaction with Br−. We suggest that while the Lindberg et al. results are clearly important, this process still needs to be accounted for. Furthermore, the rate parameter values used by Lindberg et al. are not those currently thought to be correct, and the chaos disappears if the accurate rate constant values are used. We discuss why this is so. It is further argued that the Lindberg et al. results do not eliminate the possibility that at least part of the experimentally observed CSTR chaos results from effects related to incomplete mixing.