The effect of pre-heating and dilution level on the combustion field and ‎flue gas composition of an oxy-MILD combustion system in a ‎laboratory‏-‏scale furnace

In this study, oxy-combustion is numerically investigated under MILD conditions. This novel combination is ‎simulated in a laboratory-scale furnace with parallel fuel and oxidant jets and a recirculating flow. With nitrogen ‎removal from the oxidant stream, zero NOx emission for gaseous fuel systems is expected. Combustion field is ‎modelled using a well-stirred reactor and computational fluid dynamics. In the CFD modelling, RANS equations ‎are solved using RNG k-ε and EDC model is employed to model the turbulence-chemistry interaction. The effect ‎of oxidizer preheating and CO2 dilution on the combustion field as well as flue gas composition is investigated. ‎The results indicate that the flame maximum temperature does not experience a significant increase when the ‎preheat temperature rises, positively affecting the temperature distribution at the cost of CO emission which is a ‎direct consequence of higher recirculation and mixing rate. Also, a kinetic study on the chemical effect of CO2 ‎presence reveals that CO production path through CH3O radical is more strengthened compared to the main path ‎through formaldehyde when increasing the dilution level. When diluting the oxidant, methylene’s role become ‎more influential in CO formation than when pure oxygen is used, contributing to higher CO emission. CO2 defeats ‎CH4 and O2 to absorb the free H radicals, causing higher levels of CO production.‎