1. The work by Merkle et al.25in 1969 on the Merkle-Turk-Summerfield (MTS) transient flame model, developed from granular diffusion flame (GDF) steady-state approach,98is of particular interest for transient burning modeling. The spatial heat release rate distribution in the gas phase was modeled by combining a rectangular pulse (KTSS flame) with a delta function (flame sheet) in the first and only attempt known to this author to account at the same time for both chemical kinetics and mass diffusion effects in transient flames; see the sketch in Fig.3c. In the opinion of this writer, however, the unique contribution of MTS flame isthe introduction of characteristic gas-phase times for both chemical kinetics and mass diffusion. In all other transient flame models, no characteristic time for the gas-phase processes was explicitly considered. In spite of its conceptual sophistication, however, the whole MTS approach depends on some arbitrary assumption asto the resulting total characteristic time and the need to select appropriate constants for the two individual characteristic times (kinetic and diffusive).