Direct Numerical Simulation of Methane Turbulent Premixed Oxy-Fuel Combustion

A 3-D DNS (Three-Dimensional Direct Numerical Simulation) study with detailed chemical kinetic mechanism of methane has been performed to investigate the characteristics of turbulent premixed oxy-fuel combustion in the condition relevant to Spark Ignition (SI) engines. First, 1-D (one-dimensional) laminar freely propagating premixed flame is examined to show a consistent combustion temperature for different dilution cases, such that 73% H₂O and 66% CO₂ dilution ratios are adopted in the following 3-D DNS cases. Four 3-D DNS cases with various turbulence intensities are conducted. It is found that dilution agents can reduce the overall flame temperature but with an enhancement of density weighted flame speed. CO₂ dilution case shows the lowest flame speed both in turbulent and laminar cases. Reaction path analysis based on an in-house post-processing tool is performed to show that the chemical effect of dilution agent H₂O leads to an increase of the key elementary reactions; however the total effect is endothermic compared with the counterparts for air condition case. This also results in a lower temperature of the oxy-fuel combustion. Furthermore, weak and strong levels of turbulent intensities 0.8 and 2.4 m/s are studied to show that the higher turbulent intensity leads to higher pressure rise rate, more flame surface wrinkling and higher displacement speed.