Emission response of Jet A-1 and HEFA-SAF blends (50–90 vol% HEFA) in a NexGen burner: equivalence-ratio effects and fuel-normalised indices

• FAA-certified NexGen burner compares Jet A-1, HEFA-SAF and blends (50–90%). • Measured O 2 , CO 2 , CO, NOx and SO 2 across equivalence ratios 0.50–1.44. • HEFA-SAF cut EI-CO from 0.032 to 0.007 g/kg fuel under rich combustion regime. • HEFA-SAF lowers EI-NOx peak from 0.144 to 0.020 g/kg fuel; blends show trade-offs. • GC–MS fingerprints link fuel structure (linear/branched) to emissions and soot. In recent years, the civil aviation industry has encountered growing pressure from the public and regulators to curb air pollutants and climate emissions. Sustainable aviation fuels (SAFs) produced through the Hydroprocessed Esters and Fatty Acids (HEFA) method have been approved as blends with conventional Jet A-1 under ASTM D7566 . However, comparative burner-scale evidence linking composition, gaseous emissions, and emission indices (EI) across lean to rich combustion remains limited, particularly for HEFA-rich blends and SO 2 behaviour. This study employs the FAA-certified Next Generation (NexGen) burner-for the first time applied to HEFA-SAF and HEFA-rich blends to measure O 2 , CO 2 , CO, NOx and SO 2 for Jet A-1 (B0), HEFA-SAF (B100) and their blends (B50J50, B70J30, B90J10) across twelve equivalence ratios (ϕ = 0.50–1.44), compute fuel-normalised EI-CO, EI-CO 2 , EI-NOx and EI-SO 2 , none of which have been reported from this platform for SAF or blends and pair emissions with GC–MS end-member fingerprints. NexGen burner provides a realistic fire conditions, like those encountered in real-life accidents, particularly in areas near aircraft engines. HEFA blending improved key properties (lower density and viscosity, lower freezing point, higher flash point and gravimetric energy density). B100 showed the highest residual O 2 and the lowest CO, NOx and SO 2 ; EI-CO peaked at 0.811 g/kg fuel (B0) but plunged to 0.010 g/kg fuel for B100, while EI-NOx decreased from 0.198 g/kg fuel (B0) to 0.014 g/kg fuel for B100. HEFA-rich blends EI-CO decreased and their EI-CO 2 increased. However, EI-NOx increased non-linearly with HEFA fraction under lean-to-stoichiometric conditions (ϕ = 0.50–1.0). Attributed to the higher gravimetric energy density of HEFA-rich blends increasing local flame temperature and amplifying the thermal Zeldovich NOx pathway; an equivalence-ratio-dependent trade-off that reverses at rich conditions where B100 retains its 80.1% NOx advantage over B0. Non-monotonic EI-SO 2 across the blend series suggested intra-batch sulphur variability in the HEFA-SAF supply. These results provides a single-platform, composition-aware dataset that supports emissions benchmarking and blend optimization for certification. Future work should evaluate non-volatile particulate matter and complement the results with FTIR or GCxGC analysis to reduce co-elution ambiguity. Also, combine emissions with heat release, and fuel-specific energy conversion metrics.