Impact of non-premixed hydrogen enrichment on soot and emissions of Jet A-1 spray flames in a model aeronautical gas turbine combustor

The effects of non-premixed hydrogen enrichment on the flow field, fuel evaporation, flame topology, soot formation, and exhaust emissions of a swirl-stabilized Jet A-1 spray flame were investigated. Diagnostics included particle image velocimetry, polycyclic aromatic hydrocarbon laser-induced fluorescence, OH ∗ chemiluminescence, soot luminescence, laser-induced incandescence, and exhaust gas analysis. Tests were conducted at a fixed thermal power of 8.83 kW, global equivalence ratios ( 𝜙 ) of 0.50 and 0.64, and hydrogen power fractions ( ℋ 2 ) of 0%–50%. The stagnation point location exhibited non-monotonic and monotonic trends at 𝜙 = 0 . 6 4 and 𝜙 = 0 . 5 0 , respectively, linked to variations in spray size and flame anchoring. At 𝜙 = 0 . 6 4 and ℋ 2 = 0 % , the flame was lifted, with soot concentrated along the shear region and peak mean soot volume fractions ( ̅ ̅ ̅ ̅ ̅ ̅ 𝑓 v ) ∼ 5 0 ppb. At ℋ 2 = 1 0 % , an attached non-premixed hydrogen flame front formed, reducing the peak ̅ ̅ ̅ ̅ ̅ ̅ 𝑓 v to 8 ppb, likely due to enhanced fuel evaporation. At ℋ 2 = 2 0 % – 3 0 % , increased droplet size and flame anchoring near the fuel nozzle potentially led to a high-temperature, fuel-rich zone that raised peak ̅ ̅ ̅ ̅ ̅ ̅ 𝑓 v to 24–40 ppb. At ℋ 2 = 4 0 % – 5 0 % , despite increased droplet size, the peak ̅ ̅ ̅ ̅ ̅ ̅ 𝑓 v reduced to < 5 ppb, below the detection limit, due to hydrodynamic and possibly chemical effects. CO emissions became negligible at ℋ 2 = 2 0 % , relative to ℋ 2 = 0 % , coinciding with flame anchoring closer to fuel nozzle, but increased at larger ℋ 2 as droplet size increased. NO emissions reached a minimum of 28 ppm at ℋ 2 = 1 0 % and increased at larger ℋ 2 , which may be associated with flames anchoring near the fuel nozzle and expected higher temperatures. At 𝜙 = 0 . 5 0 , soot and NO decreased, consistent with leaner operations and hydrodynamic effects, while CO increased, likely due to pronounced flame lift-off. Overall, for this configuration, soot and emissions are governed by competing effects of hydrodynamics, spray, flame topology, and hydrogen chemistry, depending on 𝜙 and ℋ 2 . Novelty and significance statement Hydrogen addition to liquid-fuel spray flames is often viewed mainly as a change in fuel chemistry. This study shows that it also reorganizes the spray, flow, and flame structures. In non-premixed hydrogen/Jet A-1 combustion, hydrogen enrichment can change the H/OH radical pool, while the reduced liquid-fuel flow limits carbon availability and alters droplet size, evaporation, and spray momentum. The attached hydrogen flame front also changes spray flame anchoring and topology. Together, these effects modify recirculation, residence time, local fuel–air mixing, and the spatial overlap between fuel-rich regions and reaction zones. This coupled behavior explains why soot, CO, and NO x do not vary monotonically with hydrogen fraction. The broader contribution is that hydrogen addition alone is insufficient to predict pollutant formation in dual-fuel spray combustion. Instead, soot formation and combustion emissions depend on the competition between spray evolution, flow hydrodynamics, spray flame anchoring, and the chemical effects of hydrogen addition.