Particulate and Gaseous Emissions of an Allison 250-C20B Turboshaft Engine Using FT-SPK

Abstract Aviation is known to be a significant contributor to air pollutant emissions. To minimize aviation’s environmental impact, alternatives to fossil-based kerosene are needed. However, complete decarbonization of aviation by electrification or by switching to carbon-free fuels will not be possible in the short and medium term. One potential solution is, therefore, to use Sustainable Aviation Fuels (SAF). In this paper, a synthetic paraffinic kerosene (SPK) produced using the Fischer-Tropsch (FT) process was tested on an Allison 250-C20B helicopter turboshaft engine to analyze the fuel’s emissions compared to regular Jet A-1. Specifically, three fuel types were tested: conventional Jet A-1, a 50% FT-SPK blend, and 100% neat FT-SPK. The focus of the tests was set to measure the changes in emitted non-volatile particulate matter (nvPM) when using FT-SPK and to compare the results with other alternative aviation fuels, specifically HEFA-SPK. Representative engine load points were selected for the tests, based on the International Civil Aviation Organization’s (ICAO) Landing and Take-off-cycle (LTO-cycle). The nvPM emissions were measured using a condensation particle counter (CPC) and a scanning mobility particle sizer (SMPS). These were employed to characterize the particle number and size distribution. Additionally, an FTIR/O2/FID combination was used to assess key combustion products, including CO2, NOx, CO, and the unburned hydrocarbons (UHC). A resonance-enhanced multiphoton ionization time-of-flight mass spectrometer (REMPI ToF-MS) was employed as a real-time system to monitor the relative variation in the amount of various polycyclic aromatic hydrocarbons (PAH) in the exhaust gas for different fuels and load conditions. This approach allows for a more in-depth analysis of the combustion behavior and the formation processes of nvPM. The particle measurement systems indicate a decrease in particle number of up to −88% at low power settings when FT-SPK is used. This is also in accordance with the reductions of the analyzed aromatic structures. Interestingly, compared to HEFA-SPK, there is also a significant reduction in gaseous emissions, such as CO and UHC when using FT-SPK.