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 14 bar, bulk velocities in the range of 32-80 m/s, two different preheating temperatures (673 K, 773 K), and a range of fuel mixtures from pure methane to 20% H-2/80% CH4 by volume. The influence of turbulence on LBO limits is also discussed in addition to the investigation of perfectly premixed H-2-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 similar to 10% compared to pure methane. The flame temperature at LBO is similar to 60 K lower resulting in the reduction of NOx concentration by approximate to 35% (0.5 -> 0.3 ppm/15% O-2).