Lean Blowout Limits and $NOx$ Emissions of Turbulent, Lean Premixed, Hydrogen-Enriched Methane/Air Flames at High Pressure

Flame stability is a crucial issue in low $NOx$ combustion systems operating at extremely lean conditions. Hydrogen enrichment seems to be a promising option to extend lean blowout limits (LBO) of natural gas combustion. This experimental study addresses flame stability enhancement and $NOx$ reduction in turbulent, high-pressure, lean premixed methane/air flames in a generic combustor capable of a wide range of operating conditions. Lean blowout limits and $NOx$ emissions are presented for pressures up to $14bar$⁠, bulk velocities in the range of 32–$80m∕s$⁠, two different preheating temperatures (⁠$673K$⁠, $773K$⁠), and a range of fuel mixtures from pure methane to 20% $H2∕80%$$CH4$ by volume. The influence of turbulence on LBO limits is also discussed. In addition to the investigation of perfectly premixed $H2$-enriched flames, LBO and $NOx$ are also discussed for hydrogen piloting. Experiments have revealed that a mixture of 20% hydrogen and 80% methane, by volume, can typically extend the lean blowout limit by $∼10%$ compared to pure methane. The flame temperature at LBO is $∼60K$ lower resulting in the reduction of $NOx$ concentration by $≈35%$$(0.5→0.3ppm∕15%$$O2$⁠).