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The aviation industry is increasingly focused on the development of sustainable alternative fuels to augment and diversify fuel supplies while simultaneously reducing its environmental impact. The impact of airport operations on local air quality and aviation related greenhouse * Corresponding author, e-mail address: plobo@mst.edu 2 gas emissions on a life cycle basis have been shown to be reduced with the use of alternative fuels. However, the evaluation of incremental variations in fuel composition of a single alternative fuel on the production of non-volatile particulate matter (nvPM) emissions has not been explored. This is critical to understanding the emissions profile for aircraft engines burning alternative fuels and their impact on air quality and climate change. A systematic evaluation of nvPM emissions from a GTCP85 aircraft auxiliary power unit (APU) burning a 16 different blends of Used Cooking Oil (UCO) derived Hydroprocessed Esters and Fatty Acids (HEFA) type alternative fuel with a conventional Jet A-1 baseline fuel was performed.The nvPM number-and mass-based emission indices for the 16 fuel blends and neat 100% UCO-HEFA were compared against those for the baseline Jet A-1 at the three APU operating conditions. Fuel composition was found to influence nvPM production. The reductions in nvPM were found to be greater with increasing fuel hydrogen content (higher proportion of UCO-HEFA in the fuel blend). For a 50:50 blend of UCO-HEFA and Jet A-1, which would meet current ASTM specifications, the average reduction in nvPM number-based emissions was ~35%, while that for mass-based emissions was ~60%. The nvPM size distributions were found to narrow and shift to smaller sizes as the UCO-HEFA component of the fuel blend increased. This shift has a greater impact on the reduction in nvPM mass compared to the overall decrease in nvPM number, when comparing the blends to the baseline Jet A-1.

The aviation industry is exploring the economic viability and environmental sustainability of the use of alternative fuels to power aircraft main engines and auxiliary power units. The International Civil Aviation Organization is also developing a regulatory standard for aircraft engine non-volatile Particulate Matter (nvPM) emissions to meet the growing public demand for improvement in air quality. This study compared the nvPM emissions in the exhaust stream of a small (<26.7 kN thrust) mixed turbofan aircraft engine burning a conventional Jet A fuel as well as a Sasol Iso-Paraffinic Kerosene (IPK) fuel derived from coal, using a standardized sampling and measurement system. The goal of the study was to demonstrate the regulatory system on a small mixed turbofan engine and to assess the suitability and limitations of using such systems for turbofan engines burning fuels with different fuel properties. Significant reductions in both nvPM number-and mass-based emission indices were observed with the IPK fuel across the full spectrum of engine thrust settings. The percent reduction in nvPM mass-based emissions was higher than the reduction in nvPM number-based emissions for the corresponding engine thrust settings because smaller and fewer particles were generated with IPK fuel combustion. PM size distribution mean diameters for the IPK fuel were found to be smaller than that for Jet A. The composition of the organic PM emissions for the two fuels was almost identical, and the organic PM was also found to be proportional to the soot concentration. The nvPM mass-based emissions for the mixed turbofan engine measured with the standardized system exhibited a high degree of measurement uncertainty at low engine thrust settings. This limitation was not encountered for nvPM number-based emissions.

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Growing concern over emissions from increased airport operations has resulted in a need to assess the impact of aviation related activities on local air quality in and around airports, and to develop strategies to mitigate these effects. One such strategy being investigated is the use of alternative fuels in aircraft engines and auxiliary power units (APUs) as a means to diversify fuel supplies and reduce emissions. This paper summarizes the results of a study to characterize the emissions of an APU, a small gas turbine engine, burning conventional Jet A-1, a fully synthetic jet fuel, and other alternative fuels with varying compositions. Gas phase emissions were measured at the engine exit plane while PM emissions were recorded at the exit plane as well as 10 m downstream of the engine. Five percent reduction in NO(x) emissions and 5-10% reduction in CO emissions were observed for the alternative fuels. Significant reductions in PM emissions at the engine exit plane were achieved with the alternative fuels. However, as the exhaust plume expanded and cooled, organic species were found to condense on the PM. This increase in organic PM elevated the PM mass but had little impact on PM number.