Rapid assessment of jet engine-like soot from combustion of conventional and sustainable aviation fuels using flame spray pyrolysis

Black carbon, or soot, is one of the highest contributors to global warming. The International Civil Aviation Organization (ICAO) has adopted regulatory standards for soot from aircraft engines, also referred to as a nonvolatile particulate matter (nvPM), to limit or reduce the harmful impacts of nvPM on the environment. Sustainable aviation fuels (SAF) offer advantages to reduce soot emissions and overall environmental impact but require extensive testing and evaluation before wider adoption. Typical measurements of soot produced by combustion of aviation fuels require full-sized jet engines and large volumes of fuel, which can be prohibitively expensive. This study investigates flame spray pyrolysis (FSP) as a simple bench-top tool for comparison of soot emissions from the combustion of different liquid jet fuels. A sampling assembly is designed for soot collection and analysis. Morphological analysis follows from transmission electron microscopy (TEM) image analysis and mobility (differential mobility analyzer) classification. Morphologies are compared to previous measurements from aircraft turbines. Soot agglomerate size distributions and elemental to total carbon ratios (EC/TC) are measured for three liquid fuels and flame conditions with Reynolds numbers and burner equivalence ratios ranging from 6100 to 9100 and 7 to 13, respectively. Day-to-day variations in the dilution ratio resulted in up to 20% variability in the measured total agglomerate number-based concentration and mobility diameter. Geometric mean primary particle and mobility diameter values are below 21 and 104 nm, respectively, in excellent agreement with those emitted from jet engines and prior work using FSP. EC/TC remains >0.75 for most flame conditions and fuels and increases with burner equivalence ratio, but values as low as 0.63 are measured from SAF combustion.