The propagation mechanism of laminar, premixed, DME-fueled flames: The role of the fragmented explosive region

The mechanism by which a premixed laminar DME/air flame front propagates is investigated. It is shown that far from the flame front chemical activity manifests itself via reaction CH 3 + HO 2 → CH 3 O + OH, which is sustained by diffusion of its reactants from the flame towards upstream. Fuel break-up there is dominated by reaction DME + OH → CH 3 OCH 2 + H 2 O and follows the path DME → CH 3 OCH 2 → CH 3 OCH 2 O 2 → CH 2 OCH 2 O 2 H → HO 2 CH 2 OCHO → CH 2 O. Further downstream, when a significant pool of radicals is formed, fuel break-up is dominated by reaction DME + H → CH 3 OCH 2 + H 2 and follows the path DME → CH 3 OCH 2 → CH 2 O. These radicals activate strongly exothermic reactions, so that a strong upstream diffusive heat transfer is generated that sustains chemical activity. The transition of the fuel break-up mechanism from one path to the other causes an interruption of the explosive region that develops ahead of the flame. Fragmented explosive regions have been encountered in homogeneous autoignition of a number of fuels, which were attributed to prevailing NTC conditions. The same feature was also encountered in laminar flames of several fuel/air mixtures, but this is the first time that an explanation is provided for this phenomenon. • Fuel break-up follows in succession two different paths. • The first path initiates with the reaction CH 3 +HO 2 ⇒ CH 3 O+OH. • Diffusion of thermal energy, CH3 and HO2 are crucial in sustaining the first path. • The second path is dominated by the reaction H+O 2 ⇒ H+OH. • The two paths result in a fragmented explosive region.