posted on 2019-01-09, 00:00authored byAnton
D. Sediako, Anthony Bennett, William L. Roberts, Murray J. Thomson
Airborne
soot is a product of incomplete combustion from engines
and industrial processes. Unburnt soot is carcinogenic, a major contributor
to climate change, and detrimental to combustor lifespan and efficiency.
An understanding of how high-pressure combustion affects the oxidation
properties of soot is crucial for the design of clean-burning, high-pressure
engines and downstream soot filtration technologies. This paper presents
the first real-time look at the oxidation of soot particles formed
at high pressure and demonstrates that the oxidation pathway changes
as combustor pressures increase. Soot particles were formed in an
ethylene-fueled diffusion flame, with pressures ranging from 1 to
25 bar, and were subsequently sampled and oxidized inside an ETEM
allowing for the nanoscale, real-time observation of oxidation pathways.
The high-pressure generated soot grew larger in diameter, formed larger
aggregates, and developed graphitic outer shells, protecting the reactive
amorphous carbon core. The graphitic shell structure fundamentally
changed the oxidation pathway of soot from diffusion driven internal
oxidation at lower pressures to highly nonreactive surface oxidation
reactions at high pressures. This work demonstrates that as combustor
pressures increase to achieve higher thermodynamic efficiencies, highly
resilient oxidation-resistant soot is produced.