Pyrolytic and oxidative structures in HDDI mild combustion

The typical structure of un-premixed counter-diffusion flames in standard conditions can be significantly modified when injected flows are diluted and/or pre-heated. The increase of the fuel and/or oxidant flow dilution up to extreme conditions can lead to the formation of nonignitable mixtures. The oxidation processes can be sustained just in case the pre-heating temperature of one flow is high enough to promote self-ignition of the system. A high initial enthalpy of flows and a low fuel and/or oxygen concentration can drastically modify the structure of the oxidative region as well as the physical and chemical kinetics with respect to conventional diffusion flame. Such operating conditions are typical of mild combustion processes. More specifically a combination of both heating and dilution of oxidant and/or fuel yields an un-premixed combustion process named Hot Diluted Diffusion Ignition (HDDI). Numerical simulation was carried out by means of commercial codes and kinetic mechanisms available in the literature in order to analyze the change of the structures of the reactive region induced by pre-heating and dilution of flows in two different configurations.