Numerical study of oxy-fuel MILD (moderate or intense low-oxygen dilution combustion) combustion for CH4–H2 fuel

• The combination of Oxy-Fuel and MILD (moderate or intense low-oxygen dilution combustion) combustions is studied in the present work.
• The OXY-MILD condition shows a decrease in temperature gradient in comparison with the MILD one.
• In comparison with the MILD condition the reaction rates reduce under the OXY-MILD one.
• The OXY-MILD combustion demonstrates a lower Damköhler number respect to the MILD one.

This paper demonstrates a numerical study on the combination of Oxy-Fuel and MILD (moderate or intense low-oxygen dilution combustion) combustions, i.e. OXY-MILD. The N2 of a hot oxidizer was replaced with CO2 and H2O in a MILD combustion test case. The study was conducted using a CFD analysis, a zero-dimensional well-stirred reactor analysis, and a reactors network analysis. In the CFD analysis, RANS equations with modified k−εk−ε equations were solved for a 2D-axisymmetric computational domain. Results showed a decrease in temperature gradient, reaction rate, and Damköhler number under the OXY-MILD condition in comparison with the MILD one. It seems the higher the oxygen level in the preheated oxidizer, the more effective the removal of N2 from the hot oxidizer was on the uniformity and extending of the reaction zone. Under OXY-MILD condition, an increment of inlet oxygen level decreased concentrations of CO, NO, CH2O, and HCO and increased temperature in the reaction zone. Furthermore, the effect of fuel hydrogen content on the reaction zone was investigated. A reduction of fuel hydrogen content led to an increase in both the uniformity of temperature field and the area of the reaction zone, and a decrease in formations of NO and CO for the OXY-MILD combustion.