High-throughput generation of aircraft-like soot

Figures & data

Figure 1. Schematic of experimental set-up with spray combustion (not to scale) enclosed in two 30 cm long quartz glass tubes with 20 L/min of nitrogen added between the tubes with a torus ring (Teleki et al. 2009). Particles are sampled (Goudeli, Gröhn, and Pratsinis 2016) after the second glass tube and diluted with nitrogen. Most of the flow is then sent through a glass fiber filter for offline N₂ adsorption analysis, thermogravimetric analysis (TGA) and transmission electron microscopy (TEM) of the collected soot. The remaining flow is further diluted with a rotating disk dilution system and sent through an X-ray neutralizer followed by a differential mobility analyzer (DMA) and condensation particle counter (CPC), which typically make up a scanning mobility particle sizer (SMPS). Broken lines represent tubing which was added only temporarily for tandem aerosol particle mass (APM) APM–SMPS measurements.

Figure 2. Normalized soot number concentration, dN/dlog(d_m)/N_tot, as a function of mobility diameter, d_m, at various equivalence ratios (EQR). The shaded areas represent one standard deviation between, at least, 9 measurements.

Figure 3. (a) The geometric mean mobility, ${\overline{d}}_m$ (open circles), and PP diameter, ${\overline{d}}_p$ (open triangles), as well as (b) the geometric standard deviation of the mobility, σ_g,m (filled circles), and PP size distributions, σ_g,p (filled triangles), as a function of EQR. Error bars represent the standard deviation between, at least, 9 measurements.

Figure 4. The number of soot PPs per agglomerate, n_p, as a function of their normalized mobility diameter, d_m/${\overline{\mathrm{d}}}_{\mathrm{p}}$ produced at various EQR and measured by APM-SMPS (symbols and double dot-broken line). Power laws derived for aggregates (Kelesidis, Goudeli, and Pratsinis 2017b; solid line) and agglomerates of monodisperse PPs in point contact (Sorensen 2011; dotted line) or aggregates of polydisperse and chemically bonded PPs (Kelesidis, Goudeli, and Pratsinis 2017a; dot-broken line) are shown also. The inset shows an exemplary TEM image of soot made at EQR = 1.29.

Figure 5. Effective density, ρ_eff, as a function of d_m of soot from enclosed spray combustion at EQR = 1.59 (circles), 1.46 (triangles), 1.34 (diamonds) and 1.29 (squares) in comparison to data from an airplane (Johnson et al. 2015; open inverse triangles) and a helicopter engine (Olfert et al. 2017; filled inverse triangles). The measured soot ρ_eff are compared also to those obtained from a power law derived by DEM for surface growth and agglomeration (Kelesidis, Goudeli, and Pratsinis 2017b; red dot-broken line and red shaded area), as well as an empirical power law extracted from engine data (Olfert and Rogak 2019; black solid line and gray shaded area).

Figure 6. The present OC/TC of soot from TGA (open symbols) and TOA (filled symbols) as a function of EQR.

Table 1. The OC/TC of soot from various aircraft engines, as well as from enclosed spray combustion at EQR = 1.25 – 1.34 measured by TOA and/or TGA.

	OC/TC (%)
	by TOA	by TGA
Turbofan engine (Delhaye et al. 2017)	14 − 25	–
// // (Elser et al. 2019)	14 − 25	–
Powerjet // (Marhaba et al. 2019)	12 − 24	–
Turbojet // (Klingshirn et al. 2019)	8 − 19	15 − 40
This work: Enclosed spray combustion at EQR = 1.25 − 1.34	17 − 19	22 − 36

Figure 7. The mass concentration, M, of soot produced from enclosed (circles) and open spray combustion units (Kholghy and DeRosa 2021; squares) as a function of ${\overline{\mathrm{d}}}_{\mathrm{m}}$ as well as a 5201 miniCAST (Ess and Vasilatou 2019; triangles) with its data corrected with a realistic MAC.

Figure 8. Specific pore surface area concentration, dA/dlog(w), as a function of pore width, w, of soot made at EQR = 1.59 (solid line), 1.46 (broken line), 1.34 (dot-broken line) and 1.29 (dotted line) using the Barrett-Joyner-Halenda (BJH) method.

Table 2. The specific surface area spray combustion soot at four EQR by the N₂ adsorption, SSA, and with transmission electron microscopy (TEM), SSA_TEM. The ${\overline{d}}_p$ from the literature is used to estimate the SSA_TEM of aircraft soot from ${\overline{d}}_p$ = 10 (Boies et al. 2015) to 18 nm (Liati et al. 2014).

	SSA [m^2/g]	SSATEM [m^2/g]
EQR = 1.59	258	233
// 1.46	282	233
// 1.34	239	251
// 1.29	160	245
Aircraft soot	–	185 − 333

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