Characterization of the Fine Particle Emissions from the Use of Two Fischer–Tropsch Fuels in a CFM56-2C1 Commercial Aircraft Engine

The fine particulate matter (PM) emissions from the use of two types of Fischer–Tropsch aviation fuels and their 50:50 blends with military JP-8 were quantified as part of the first Alternative Aviation Fuel Experiment (AAFEX). Measurements were made 30-m downstream of a CFM56-2C1 engine for PM mass and number, particle size distribution, black carbon (BC), and volatile PM (sulfate + organics) using selected online instrumentation. The PM number emission index (EI_N) ranged from ∼2 × 10¹⁵ to 7 × 10¹⁶ particles/kg fuel burned depending on fuel flow, fuel composition, and sampling temperature with the magnitude of the emissions inversely correlated to fuel flow. The PM mass emissions (EI_M) measured in the study varied from ∼5 to 680 mg/kg fuel, again depending on fuel flow, fuel type, and sampling temperature with a characteristic U-shaped curve of EI_M with respect to fuel flow observed from the data. At low fuel flow (corresponding to low engine power), particle number and volume size distributions contained a single mode, whereas at higher engine power, a bimodal distribution was observed. The BC emissions varied from ∼3 to 415 mg/kg fuel depending on fuel type and were found to exponentially increase with engine power (fuel flow). The volatile PM varied with sample temperature, fuel type, and increasing fuel flow within the range of EIs from ∼0.4 to 11 mg/kg fuel with the highest values being at low fuel flow. Finally, the use of the two neat alternative fuels reduced the EI_N by a median value of 70–73% and the EI_M by ∼94% as compared to JP-8 across all power conditions tested.