Effects of injection position and blending ratio on NOX reduction in methane-ammonia co-combustion via ammonia lancing

Co-firing methane with ammonia can decarbonize high temperature industrial processes, yet the fuel-bound nitrogen in NH 3 introduces a substantial NO X penalty under pre-blended operation. This study examines ammonia lancing, the separate injection of NH 3 into the plume of an established methane flame, in a pilot-scale furnace with a commercial burner. The ammonia fuel fraction ( x NH3 = 0 to 0.38) and axial injection position (L/D b = 0 to 2) were varied at a fixed thermal input of 76 kW and an equivalence ratio of 0.95, with pre-blending as the baseline. Lancing produced a two-zone flame structure, with a methane swirl core anchored at the burner exit and a downstream ammonia reaction zone formed by two opposed jet flames from lances angled at 45° toward the furnace axis. At x NH3 = 0.19, where the pre-blend NO X peaks, lancing reduced NO X by 60, 73, and 88% at L/D b = 0, 0.6, and ≥ 1.5, respectively, with the same position dependence at the other blending ratios. The reduction was accompanied by increases in N 2 O and CO, which were largest at L/D b ≥ 1.5 and the highest ammonia fractions, where N 2 O reached approximately twice the pre-blend value and CO exceeded 1000 ppm. A firing rate sweep at L/D b = 1.5 and x NH3 = 0.28 showed that N 2 O fell by 32% as the near burner temperature rose by 61 K, while NO increased but stayed nearly a factor of 8 below the pre-blend value. Ammonia slip remained below the FTIR detection limit of approximately 1.5 ppm for x NH3 ≤ 0.28 and became significant only at x NH3 = 0.38. A favorable operating window was identified at L/D b ≤ 0.6 with x NH3 ≤ 0.28, in which NO X is reduced by 60 to 73% and the total greenhouse gas emissions remain close to the pure methane baseline.