International audiencePreviously we have shown how a single species X can be introduced, representing either HO 2 for high-temperature ignition or H 2 O 2 for low-temperature ignition, to develop an algorithm that covers the entire range of ignition, flame-propagation, and combustion conditions, without a significant degradation of accuracy, for hydrogen-air systems. By adding relevant CO chemistry to the hydrogen chemistry, this same approach can be applied to derive a comparably useful four-step reduced-chemistry description for syngas blends that have small enough concentrations of methane, other hydrocarbons , or other reactive species to be dominated by the elementary steps of the H 2 /CO system. The present communication reports the r...