Volatile PM and Coatings of Volatile Material on Solid Core Particles
DEKATI EDD
4.4 Volatile Coated Solid Core Particle Removal
Recognising that volatile compounds can exist not only as stand-alone particulates but also as agglomerates and coatings on solid particles (e.g. soot) should be an important consideration when evaluating the effectiveness of a volatile removal system. Figure 4.15 shows of a TEM image of such a particle formation in which a volatile particle (ammonium sulphate) has combined with an agglomerated soot particulate in a diesel automotive exhaust.
Figure 4.15: Aggregate of an ammonium sulphate particle and an agglomerated soot particle, reproduced from [44].
Volatile PM and Coatings of Volatile Material on Solid Core Particles
To examine how the removal efficiency of a VPR may be affected by such particle formations soot particles produced by the PALAS GFG 1000 soot generator were coated with a surface of volatile material (tetracontane) prior to their entry into the VPR system. The same two VPRs were used for this experimentation, those being the DEKATI EED and the GRIMM ESS.
Using a DMA three original soot particle diameters were investigated; 100, 50 and 30nm. At the flow rate and sample conditions required sufficient qualities of 15nm soot particles were not achievable and have therefore not been considered. Each soot size distribution was individually passed through Cardiff University VG within the crucible airflow ensuring the particles were exposed to a region saturated with a high concentration of tetracontane vapour. To detect if a coating had been applied to the soot particles a SMPS was used to provide a size distribution upstream of the VPR, downstream SMPS measurements were then subsequently made to gauge what impact the VPR had on the ‘challenge’ aerosol. In addition to particle size assessment number concentration measurements were also taken upstream and downstream of the VPR using a CPC. A schematic diagram of the experimental setup is shown in Figure 4.16.
Figure 4.16: Schematic diagram of volatile removal experiment using volatile coated solid core ‘challenge’ aerosol.
Volatile PM and Coatings of Volatile Material on Solid Core Particles
122
Results gathered when evaluating the performance of the DEKATI EED system and GRIMM ESS VPR systems will again be presented dependent on the ‘challenge’ aerosol being supplied (100, 50, and 30nm solid core volatile coated particles).
4.4.1 Results: 100nm Volatile Coated Solid Core ‘Challenge’ Aerosol
From the upstream size spectrum of the ‘challenge’ aerosol it is clear that there is significant growth of the ≈100nm solid particles after they have passed through the VG. On exiting the DEKATI EDD the number concentration of the challenge aerosol has been reduced from 2.60x105 to 9.68x104 N/cm3. The size spectral analysis of this new aerosol composition shows that the remaining particle distribution consists mainly of particles in the ≈60nm size region (GMD of 64nm).
Figure 4.17: (a) Number concentrations recorded up and downstream of the DEKATI EDD, (b) SMPS particle size spectra recorded up and downstream of the DEKATI EDD when supplying 100nm volatile coated solid core particle ‘challenge’ aerosol.
The upstream and downstream number concentrations measured when delivering 100nm volatile coated particle to the GRIMM ESS were of approximately the same magnitude. The upstream PM size distribution is unlike that observed during all other volatile coated PM test conditions apart from that of the 50nm GRIMM ESS ‘challenge’
aerosol test condition. These two VPR validation experiments were performed on at a
0.00E+00
Volatile PM and Coatings of Volatile Material on Solid Core Particles
later time period than the others present and this is considered to be the reason for the variability. The final result of the PM coating was that much larger particles are produced across a size range of 150 to 350nm. The downstream PM size distribution indicates that particles of a similar size were being introduced into the VG however it appears that an increased level of agglomeration occurred (larger particles). Input parameters were identical for the PALAS soot generator and VG however ambient conditions may have occurred
Figure 4.18: Number concentrations recorded up and downstream of the GRIMM ESS (left), SMPS particle size spectra recorded up and downstream of the GRIMM ESS (right) when supplying 100nm volatile coated solid core particle challenge aerosol.
4.4.2 Results: 50nm Volatile Coated Solid Core ‘Challenge’ Aerosol
Consistent with the 100nm challenge aerosol when ≈50nm solid particle were introduced through the supply air of the VG, the resulting aerosol size distribution showed considerable particle growth. The DEKATI EDD was again successful at removing the majority of the coated volatile material and the suspended volatile material with a reduction in the measured aerosol of 99.9%.
0.00E+00
Volatile PM and Coatings of Volatile Material on Solid Core Particles
124
Figure 4.19: (a) Number concentrations recorded up and downstream of the DEKATI EDD, (b) SMPS particle size spectra recorded up and downstream of the DEKATI EDD when supplying 50nm volatile coated solid core particle ‘challenge’ aerosol.
As was earlier discussed the upstream size distribution of the 50nm volatile coated solid core ‘challenge’ aerosol is different from that seen in other conditions. The end result of appraisal with this aerosol is consistent though previous test conditions in that the downstream size distributions indicate that the volatile coating has been removed and the solid core particle remain.
0.00E+00
Volatile PM and Coatings of Volatile Material on Solid Core Particles
Figure 4.20: (a) Number concentrations recorded up and downstream of the GRIMM ESS, (b) SMPS particle size spectra recorded up and downstream of the GRIMM ESS when supplying 50nm volatile coated solid core particle ‘challenge’ aerosol.
4.4.3 Results: 30nm Volatile Coated Solid Core ‘Challenge’ Aerosol
The up and downstream size spectra show that following the DEKATI EDD the particle size distribution has returned to approximately that of the solid 30nm particles which were introduced into the VG.
Volatile PM and Coatings of Volatile Material on Solid Core Particles
126
Figure 4.21: (a) Number concentrations recorded up and downstream of the DEKATI EDD, (b) SMPS particle size spectra recorded up and downstream of the DEKATI EDD when supplying 30nm volatile coated solid core particle ‘challenge’ aerosol.
The PM size distribution measured downstream of the GRIMM ESS when supplied with the 30nm volatile coated solid core particle aerosol show that the volatile PM coating and only particle of ≈35nm remain.
Figure 4.22: (a) Number concentrations recorded up and downstream of the GRIMM ESS, (b) SMPS particle size spectra recorded up and downstream of the GRIMM ESS when supplying 30nm volatile coated solid core particle ‘challenge’ aerosol.
0.00E+00
Volatile PM and Coatings of Volatile Material on Solid Core Particles
Table 4.2: Summary of the volatile coated solid core particle ‘challenge’ aerosol number concentrations and GMDs measured up and downstream of the test VPR.
Sample position relative to tested VPR
Concentration (N/cm3) GMD (nm) DEKATI EDD
100nm
Upstream 2.60x105 138
Downstream 9.68x104 64
50nm
Upstream 8.32x104 110
Downstream 1.27x102 38
30nm
Upstream 9.62x104 104
Downstream 2.63x101 27