Bipolar Diffusion Charging of Soot Aggregates

Figures & data

FIG. 1 Schematic diagram of experimental apparatus.

FIG. 2 Typical soot size distributions used in this work: premixed ethylene flame at Φ = 2.1, sampled at 20 mm above the burner and allowed to coagulate for 1 and 20 s. Arrows illustrate the preferred relationship between size distribution and selected size for the examples of ∼ 70 nm and ∼ 250 nm particles.

FIG. 3 Charging efficiency versus aerosol flow rate through ²¹⁰Po neutralizer (ADI housing) for 45 nm PAO oil droplets.

FIG. 4 Bipolar charging of PAO oil droplets. Upper panel: z = ± 1. Lower panel: z = ± 2. Solid symbols represent experimental data from this work; open symbols are data from Wiedensohler et al. (1986). Solid lines represent best log-log fits of the data to third order polynomials. Dashed lines depict Fuchs model predictions.

TABLE 1 Bipolar charging efficiency parameterizations: f _z = 10^{∑limits _k a _z,k log (d _m ) k}

Measurement	z	a z,0	a z,1	a z,2	a z,3	a z,4	a z,5
Soot—present work	+3	−27.6243	19.9539	−3.7776	—	—	—
	+2	−21.2905	22.0034	−7.9597	0.9574	—	—
	+1	−3.2328	2.2417	−0.3731	−0.0553	—	—
	−1	−3.3612	2.9226	−0.8317	0.0380	—	—
	−2	−20.3678	21.1106	−7.5141	0.8845	—	—
	−3	−28.3714	21.3038	−4.1282	—	—	—
Oil—combined fits ^1	+3	−25.4373	17.8044	−3.2907	—	—	—
	+2	−13.1680	9.5095	−1.8950	0.0118	—	—
	+1	−3.2412	2.3299	−0.5102	−0.0106	—	—
	−1	−3.0127	2.1972	−0.4483	−0.0197	—	—
	−2	−15.3056	13.1212	−3.6374	0.2869	—	—
	−3	−26.4814	19.1064	−3.5878	—	—	—
TSI/Wiedensohler 1988 ^2	+1	−2.3484	0.6044	0.4800	0.0013	−0.1553	0.0320
	−1	−2.3197	0.6175	0.6201	−0.1105	−0.1260	0.0297

FIG. 5 Triply charged particles. Top panel: PAO oil droplets. Solid lines depict Fuchs model predictions. Dashed lines are polynomial best fits. Bottom panel: flame generated soot. Solid lines are from the Fuchs model. Dashed lines show predictions from the charging theory for fibrous aerosols of Wen et al. (1984a) using d ₀ = 17 nm.

FIG. 6 Bipolar charging of flame generated soot aggregates. Upper panel: z = ± 1. Lower panel: z = ± 2. Symbols represent experimental data. Solid lines depict the best fits to the spherical particle data from Figure 4. Dashed lines show predictions from the charging theory for fibrous aerosols of Wen et al. (1984a) using d ₀ = 17 nm.

FIG. 7 TEM images of mobility size selected soot particles. (a) d _m = 200 nm. (b) d _m = 100 nm. (c) d _m = 50 nm. (d) d _m = 25 nm.

FIG. 8 Bipolar charging of diesel engine exhaust particulate matter. Upper panel: z = ± 1. Lower panel: z = ± 2. Symbols represent experimental data. Solid lines depict the best fits to the spherical particle data from Figure 4. Dashed lines show predictions from the charging theory for fibrous aerosols of Wen et al. (1984a) using d ₀ = 17 nm.

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