Pulsed laser heating of diesel engine and turbojet combustor soot: Changes in nanostructure and implications

Abstract

Carbonaceous particulate produced by a diesel engine and turbojet engine combustor are analyzed by transmission electron microscopy (TEM) for differences in nanostructure before and after pulsed laser annealing. Soot is examined between low/high diesel engine torque and low/high turbojet engine thrust. Small differences in nascent nanostructure are magnified by the action of high-temperature annealing induced by pulsed laser heating. Lamellae length distributions show occurrence of graphitization while tortuosity analyses reveal lamellae straightening. Differences in internal particle structure (hollow shells versus internal graphitic ribbons) are interpreted as due to higher internal sp³ and O-atom content under the higher power conditions with hypothesized greater turbulence and resulting partial premixing. TEM in concert with fringe analyses reveal that a similar degree of annealing occurs in the primary particles in soot from both diesel engine and turbojet engine combustors—despite the aggregate and primary size differences between these sources. Implications of these results for source identification of the combustion particulate and for laser-induced incandescence (LII) measurements of concentration are discussed with inter-instrument comparison of soot mass from both diesel and turbojet soot sources.

Graphical Abstract

Editor:

• Jason Olfert

Acknowledgements

Dr. Robert Howard and Arnold Engineering Development Complex, (AEDC) TN, U.S. Air Force are gratefully acknowledged for supporting Artium Technologies, Inc.’s participation in the VARIAnT 3 campaign, the laboratory experiments, and analyses. The authors acknowledge Naneos for lending a Naneos Partector TEM sampler with which some of the TEM grids were sampled. HRTEM characterization was conducted using the microscopy facilities of the Materials Research Institute at The Pennsylvania State University. HRTEM guidance from Drs. Jennifer Gray and Ke Wang is gratefully acknowledged.

The following VARIAnT 3 team members are acknowledged for their contributions:

John Kinsey¹, Bob Giannelli², Jeffrey Stevens², Cullen Leggett², Robert Howard³, Brandon Hoffman³, Mary Forde³, Alla Zelenyuk-Imre⁴, Kaitlyn Suski⁴, Richard Frazee⁵, Tim Onasch⁶, Andrew Freedman⁶, David Kittelson⁷ and Jake Swanson⁷

¹Formerly with the US Environmental Protection Agency, Office of Research and Development, Center for Environmental Measurement and Modeling, Research Triangle Park, NC 27711, USA, currently retired. ²US Environmental Protection Agency, National Vehicle and Fuel Emissions Laboratory (NVFEL), Ann Arbor, MI 48105, USA. ³US Air Force, Arnold Engineering Development Complex (AEDC), Arnold AFB, TN 37389, USA. ⁴US Department of Energy, Pacific Northwest National Laboratory (PNNL), Richland, WA 99352, USA. ⁵Singularity Scientific Consulting Services, LLC, Whitmore Lake, MI 48189, USA. ⁶Aerodyne Research Inc., Billerica, MA 01821, USA. ⁷Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455, USA.

Disclosure statement

The U.S. Environmental Protection Agency collaborated in the research described herein. This work has not been subject to administrative review and does not necessarily reflect the views of the Agency. No official endorsement should be inferred. EPA does not endorse the purchase or sale of any commercial products or services.

The authors declare no competing financial interests.

Additional information

Funding

The authors are grateful to the U.S. EPA who funded the VARIAnT 3 field campaign and invited our participation.