Soot Size Distribution & Structure during Enclosed Spray Combustion of Jet Fuel

UNA TRIVANOVIC, Georgios A. Kelesidis, Sotiris Pratsinis, ETH Zurich, Switzerland

     Abstract Number: 19
     Working Group: Carbonaceous Aerosol

Abstract
Aircraft engines are significant sources of soot that have inflammatory and cytotoxic responses [1] and contribute to global warming through direct radiative forcing [2] and indirectly by facilitating formation of ice nuclei and contrail cirrus clouds [3]. The characteristics of aircraft soot vary drastically with the applied thrust [4]. So, understanding the relation between combustion conditions, soot primary particle diameter, d_p and nanostructure is essential to quantify and mitigate the impact of such emissions on climate change and public health. Here, the evolution of soot d_p and nanostructure is monitored during enclosed spray combustion (ESC) of jet A1 fuel at various Effective eQuivalence Ratios (EQR) for ESC’s capacity to match the size and composition characteristics of soot from aircraft engines [4]. The soot nanostructure can be characterized by the Raman ratio of the soot disorder (D) over graphitic (G) band, as well as the crystallite length, L_c, and interlayer distance, d₀₀₂, of soot from X-Ray diffraction. As EQR increases from 1.46 to 1.88, the soot d_p increases from 14 to 23 nm due to enhanced surface growth [5], while D/G decreases from 0.9 to 0.8. This indicates that small soot nanoparticles have a more disordered structure than larger ones, consistent with such soot data from an inverted burner [6] and a laboratory gas flare [7]. As soot d_p increases, its d₀₀₂ (circles) decreases while the L_c (triangles) increases. This confirms that small soot nanoparticles have fewer layers per crystal which are also less densely packed than larger ones resulting in a more disordered structure, corroborating Raman measurements, for the first time to the best of our knowledge [8]. Additionally, the ordered nanostructure of the large particles lowers their oxidation rate increasing their light absorption [9] that affects both of their cytotoxicity and radiative forcing of soot as stated above.

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