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. 2020 Apr 16;34(4):4958-4966.
doi: 10.1021/acs.energyfuels.0c00094.

Impact of Biofuel Blends on Black Carbon Emissions from a Gas Turbine Engine

Raju R Kumal  1 , Jiawei Liu  1 , Akshay Gharpure  1 , Randy L Vander Wal  1 , John S Kinsey  2 , Bob Giannelli  3 , Jeffrey Stevens  3 , Cullen Leggett  3 , Robert Howard  4 , Mary Forde  4 , Alla Zelenyuk-Imre  5 , Kaitlyn Suski  5 , Greg Payne  6 , Julien Manin  6 , William Bachalo  6 , Richard Frazee  7 , Timothy B Onasch  8 , Andrew Freedman  8 , David B Kittelson  9 , Jacob J Swanson  9
Affiliations

Impact of Biofuel Blends on Black Carbon Emissions from a Gas Turbine Engine

Raju R Kumal et al. Energy Fuels. .

Abstract

Presented here is an overview of non-volatile particulate matter (nvPM) emissions, i.e. "soot" as assessed by TEM analyses of samples collected after the exhaust of a J-85 turbojet fueled with Jet-A as well as with blends of Jet-A and Camelina biofuel. A unifying explanation is provided to illustrate the combustion dynamics of biofuel and Jet-A fuel. The variation of primary particle size, aggregate size and nanostructure are analyzed as a function of biofuel blend across a range of engine thrust levels. The postulate is based on where fuels start along the soot formation pathway. Increasing biofuel content lowers aromatic concentration while placing increasing dependence upon fuel pyrolysis reactions to form the requisite concentration of aromatics for particle inception and growth. The required "kinetic" time for pyrolysis reactions to produce benzene and multi-ring PAHs allows increased fuel-air mixing by turbulence, diluting the fuel-rich soot-forming regions, effectively lowering their equivalence ratio. With a lower precursor concentration, particle inception is slowed, the resulting concentration of primary particles is lowered and smaller aggregates were measured. The lower equivalence ratio also results in smaller primary particles because of the lower concentration of growth species.

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Figures

Figure 1.
Figure 1.
HRTEM image of an aggregate showing primary particle and nanostructure.
Figure 2.
Figure 2.
Schematic representation of soot formation process highlighting the effect of aromatic content in Jet-A fuel in combustion kinetics compared to biofuel having primarily paraffinic molecules.
Figure 3.
Figure 3.
Representative HRTEM images of soot emitted from J-85 turbojet with Jet-A and blends with Camelina biofuel at 100% thrust. The aggregate size decreases with decreasing fuel aromatic content. (a) Jet-A (b) 30% camelina blend, and (c) 70% camelina blend.
Figure 4.
Figure 4.
(a)Variation of aggregate size as a function of engine thrust for Jet-A, 30% and 70% camelina blend fuels and (b) correlation between primary particle size and aggregate size irrespective of fuel and thrust.
Figure 5.
Figure 5.
High resolution TEM images showing nanostructures of soot particles formed at 100% thrust from three different fuels; (a) Jet-A, (b) 30% camelina blend and (c) 70% camelina blend.
Figure 6.
Figure 6.
(a) Variation of fringe tortuosity of soot particles emitted at 100% thrust from three different fuels; Jet-A, 30% camelina blend and 70% camelina blend, and (b) skeletonized image of corresponding HRTEM image for Jet-A fuel illustrating fringe tortuosity.
Figure 7.
Figure 7.
Schematic representation of fuel-rich pockets with time and fuel type. Darker and larger region indicate a fuel-rich pocket with higher fuel-air equivalence ratio (ϕ). With turbulence, the fuel content of rich regions is reduced as is the corresponding growth species concentration – slowing particle inception and rate of surface mass addition.
Figure 8.
Figure 8.
Mole ratio plot of C5/C6 as a function of ϕ at 1600 K
See this image and copyright information in PMC

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