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.
Bibliographical noteFunding Information:
The authors acknowledge Naneos for lending a Naneos Partector TEM sampler on which some of the TEM grids were sampled with. HRTEM characterization was done using the microscopy facilities of the Materials Research Institute at The Pennsylvania State University. HRTEM guidance from Dr. Jennifer Gray and Dr. Ke Wang is gratefully acknowledged. The VARIAnT 3 field campaign and tests were supported by the U.S. EPA and Arnold Air Force Base.
© 2020 American Chemical Society.