Characterization of Emissions From the Use of Alternative Aviation Fuels

Abstract

Alternative fuels for aviation are now a reality. These fuels not only reduce reliance on conventional petroleum-based fuels as the primary propulsion source, but also offer promise for environmental sustainability. While these alternative fuels meet the aviation fuels standards and their overall properties resemble those of the conventional fuel, they are expected to demonstrate different exhaust emissions characteristics because of the inherent variations in their chemical composition resulting from the variations involved in the processing of these fuels. This paper presents the results of back-to-back comparison of emissions characterization tests that were performed using three alternative aviation fuels in a GE CF-700-2D-2 engine core. The fuels used were an unblended synthetic kerosene fuel with aromatics (SKA), an unblended Fischer–Tropsch (FT) synthetic paraffinic kerosene (SPK) and a semisynthetic 50–50 blend of Jet A-1 and hydroprocessed SPK. Results indicate that while there is little dissimilarity in the gaseous emissions profiles from these alternative fuels, there is however a significant difference in the particulate matter emissions from these fuels. These differences are primarily attributed to the variations in the aromatic and hydrogen contents in the fuels with some contributions from the hydrogen-to-carbon ratio of the fuels.

Impact of Alternative Jet Fuels on Engine Exhaust Composition During the 2015 ECLIF Ground-Based Measurements Campaign

“…One particle number mode features a peak at ∼10 nm (nucleation mode) while the second peaks at 40–50 nm (accumulation mode). This particle size distribution has been reported in several other publications. − The sulfur content in the fuel has a direct impact on the nucleation particle mode at sufficient distance from the engine exhaust (>15 m) . This is in good agreement with the particle number size distributions in the present measurements (Figure and SI Figure S7–S14) but the impact of the particle mode at 10 nm on the total emitted particle mass is–of course–negligible (Figure B and D).…”

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

“…Published literature is limited for the emissions performance and atmospheric PM evolution of aircraft engines running on sulfur- or aromatic-free jet fuels. ,,, Most other data were collected near the engine exit using a sampling protocol which does not capture the volatile sulfur and organic particles formed in the downstream plume. − ,− ,− , In addition, some data sets only provide normalized EIs rather than actual emissions, thus further restricting their usefulness for comparison to other work. Table S4 in the Supporting Information shows the emissions reductions associated with the use of the FT jet fuels and blends evaluated in our study as compared to other alternative fuel measurements reported in the literature.…”

“…These fuels include synthetic paraffinic kerosene (SPK) manufactured by the Fischer–Tropsch (FT) process from coal and natural gas as well as hydroprocessed esters and fatty acids (HEFA) made from various types of biomass and other sources, all of which have similar molecular distributions . Although a number of studies have been conducted on these fuels, limited PM emissions data are available. − These studies generally show a decrease in PM mass, number, and size with the use of FT fuel, the magnitude of which depends on engine power, the proportion of alternative fuel used, and the sulfur, aromatics, and napthalene content of the conventional fuel used in the blends. , …”

Assessment of the Fuel Composition Impact on Black Carbon Mass, Particle Number Size Distributions, Solid Particle Number, Organic Materials, and Regulated Gaseous Emissions from a Light-Duty Gasoline Direct Injection Truck and Passenger Car

“…Similar to the PMI, fuels containing a higher aromatic content have higher TSI values as these compounds generate more BC during combustion when compared to aliphatic hydrocarbons. The higher emission rates of particles could lead to more coagulation resulting in particles with larger diameters, consistent with the particle number size distributions observed with high fuel aromatic content. − One study suggested that operating an engine at the same conditions with fuels containing nearly identical fuel aromatic content but substituting the monoaromatics with naphthalenes (from 0.78% to 1.19% by volume) could increase BC and nonvolatile PM emissions by 40% and 30%, respectively . Multiple NASA studies also suggest that the fuel sulfur and aromatic content affects the volatile PM emissions and contribute to measurement variability.…”

“…Early observations showed that different hydrocarbons have different tendencies to generate BC. − Many studies often compared petroleum-based jet fuel to renewable jet fuel containing significantly less or even the absence of aromatic hydrocarbons. Observations suggested that low fuel aromatic content, high hydrogen to carbon ratio, and low iso-to-normal paraffin ratio are factors to explain the lowered particulate matter mass (PMM) emissions from aviation turbine engines. − Some studies reported that particle size distributions could shift to larger diameter with increasing fuel aromatic content and thus produce higher BC emissions. − These studies have implied the possible existence of relationships between BC formation and fuel composition.…”