Certificate of Nanoparticles

DiSC Particle Sensor Comparison Measurements from 2011, August 11

Particle Number and Size Measurements and Mass Estimation

Customer: E-FUEL TECHNOLOGY SA

c/o: DOMINFID SA

PO Box 5477

Via Pioda 8

CH-6901 Lugano

Reference: Ing. Enrico Fumagalli

Contractor: Matter Aerosol AG

Bremgarterstr. 62

CH-5610 Wohlen

Responsible: dipl. Ing. Thomas Mosimann, Head of Research & Development

[email protected]

Author: dipl. Ing. Adrian Hess, Corporate Researcher

[email protected]

2

DiSC Particle Sensor Comparison Measurements from 2011, August 11

Introduction

Different nanoparticle sensors were arranged to analyze the exhaust of a light duty vehicle equipped

with a Diesel engine and Diesel Particle Filter. Several Diffusion Size Classifier (DiSC) sensors were set

up in parallel in order to compare the detected values to each other and to reference sensors i.e.

condensation particle counters.

A DiSC sensor provides on line information about the particle number concentration, and mean

particle size. The detected particle number concentrations have been compared to the values

provided by condensation particle counters (CPC). The mean particle size was used to estimate

particle volume and therewith particle mass concentration.

Since the DiSC sensors do not provide a detailed particle size spectrum but only a total particle

number and mean size, these calculations permit rough particle mass estimations but not accurate

mass concentration information.

Materials and Methods

The sensors were arranged as shown in Fig. 1. A NanoMet (NM3, NM2) dilution and conditioning unit

was placed as well directly at the vehicle exhaust as behind the constant volume sampler (CVS). The

NanoMet system dilutes the raw aerosol and removes volatile particle components therewith only

solid particles are fed to the particle sensors.

Fig. 1: Sensor arrangement

While the sensors set directly at the vehicle exhaust did detect the particle concentrations in the

exhaust gas volume, the constant volume sampler dilutes exhaust gas to a constant gas flow which

allows to determine the emitted particle number per cycle or per kilometer respectively.

A number of nanoparticle sensors were connected to both NanoMet units. The Engine Exhaust

Condensation Particle Counter EECPC TSI 3790 and Condensation Particle Counter CPC TSI 3772 were

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used as reference particle number counters to which the DiSC sensors could be compared. The

EECPC is a device specifically designed for PMP compliant engine exhaust particle measurements. It

counts only particles with a size larger than about 23 nm. Smaller particles are intercepted at the

device inlet and therewith not counted. The standard CPC is not equipped with this small particle

separator and counts all particles down to about 10 nm.

Different Diffusion Size Classifier (DiSC) sensors were attached in parallel to the reference CPCs.

DiSC mini is a downsized handheld version of the standard DiSC. Both types provide number

concentration and mean particle size as aerosol characteristics. Their calculation algorithm bases on

the assumption that nanoparticles emitted by combustion processes are log-normal distributed. So

the sensors are not able to detect bimodal or multi modal particle size distributions.

In order to estimate the emitted particle mass instead of the particle number, a simple calculation

was applied. The volume of a spherical particle with a given size can easily be calculated by

=

with d as particle diameter. If there was only one particle size, this single particle volume

could be multiplied by the particle density and the number concentration to determine the particle

mass concentration. Since the DiSC calculation algorithm assumes a log-normal particle size

distribution and larger particles contribute much stronger to the total particle volume than smaller

ones, this expression has to be added by a specific particle size distribution shape coefficient.

For a log-normal distribution with a standard deviation =1.8 this shape coefficient is cs=4.73. With a

unit factor of 10-9

the total particle volume and mass concentration can be estimated:

This estimation bases on different assumptions like spherical particle shape, log-normal size

distribution with =1.8 and constant particle density. In reality the particles are not spherical but

consist of even smaller primary particles which are combined to fractal agglomerates. The estimation

may be adequate for a relative comparison between aerosols generated under similar conditions, but

their absolute values are not very accurate.

Since the particle emissions during the NEDC cycles are very unsteady and especially peaks during

acceleration phases or gear shifting significantly varied between the different cycles, the total

particle mass emissions were calculated based on the average particle number concentrations and

average particle sizes of the single cycles. This allows to compare the emissions of the different

cycles.

Results and Discussion

Some DiSC sensors turned out to run instable. So only the signals of 4 DiSC sensors were used for this

particle mass emission estimation: DiSC mini Goldy and DiSC std Testo on NanoMet 3 for raw gas

measurements and DiSC mini Demo AK and DiSC std FHNW on NanoMet 2 for measurements

behind the constant volume sampler allowing to determine the particle emissions per kilometer.

The bar diagram in Fig. 2 shows the particle mass concentration estimation of the raw gas detected

by the sensors DiSC mini Goldy and DiSC std Testo. The total particle mass concentration

calculated based on particle number concentration and mean size detected by DiSC sensors is

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reduced by a factor of about 5 during the cycles run using emulsion fuel (E-F) compared to the first

cycles when the vehicle was fired with standard fuel.

2 1.8 1.6 1.4 1.2

1 0.8 0.6 0.4 0.2

0

Sensors Behind NM3 - PM per Exhaust Gas Volume DiSC mini Goldy 101'261

DiSC std Testo 101'052

Ref - Cycle 1 Ref - Cycle 2 Ref - Cycle 3 E-F Cycle 1 E-F Cycle 2 E-F Cycle 3

Fig. 2: Particle mass concentration during different driving cycles

The values determined behind CVS shown in Fig. 3 look less optimistic. The different ratio of the

particle mass concentration per exhaust volume and total particle mass per kilometer can probably

be explained by a different exhaust volume amount when the vehicle was driven with different fuels.

2 1.8 1.6 1.4 1.2

1 0.8 0.6 0.4 0.2

0

Sensors Behind CVS / NM2 DiSC mini Demo AK 101'263

DiSC std FHNW 100'876


Fig. 3: Total particle mass per kilometer during different driving cycles

Fig. 4 shows the particle number average values of the different elementary cycles during the first

NEDC cycle when reference fuel was used.

Fig. 4: Comparison of DiSC and EECPC/CPC number concentration values with standard fuel

5

The left plot shows some DiSC number concentration values compared with the EECPC which was

attached to the same dilution system and so had the same particle characteristics. On the right plot

the corresponding DiSC values are compared with the standard CPC values, both attached to the

second dilution system. It can easily be seen that the DiSC values correspond quite well to both CPC

values when standard fuel is used.

In Fig. 5 the same comparison is made for the first cycle which was driven with emulsion fuel. Besides

the number concentration is clearly higher with this fuel, it is obvious that the standard CPC still

correlates very vell to the specific DiSCs while the EECPC significantly underestimates the particle

number concentration.

Fig. 5: Comparison of DiSC and EECPC/CPC number concentration values with emulsion fuel

The EECPC only counts particles with diameters over about 23nm while the standard CPC measures

all particles down to around 10nm. The very much lower particle number values of the EECPC mean

that significantly more very small particles are emitted when emulsion fuel is used instead of

standard diesel fuel.

This is also also affirmed by the particle size information recorded by the DiSC sensors. The average

mean particle diameters around 60nm recorded during the first NEDC cycle with reference fuel are

shown in Fig. 6 the ones recorded with emulsion fuel in Fig. 7.

The comparison of the concentrations measured by the two CPC types and the DiSC measurements

indicate that there might be a bimodal particle size distribution where the most significant fraction of

the particle number is in a very small size range below 23 nm when emulsion fuel is used.

The influence of this very small particle fraction on the emitted particle mass should be further

investigated, e.g. by gravimetric mass analysis and maybe SMPS measurements which could give

detailed size distribution information.

Fig. 6: Average particle size during elementary cycles of NEDC cycles with emulsion fuel

Fig. 7: Average particle size during elementary cycles of NEDC cycles with emulsion fuel

Conclusions

Particle number and size measurements were done using different DiSC sensors. These data were

used to estimate particle mass concentrations, and total particle mass emissions per kilometer.

Significant particle mass reductions were observed when emulsion fuel was

used instead of standard Diesel fuel.

The achieved particle mass information do base on spherical particle shape. The single particle

density was constant under both conditions. The particle size distribution was assumed to be log-

normal.

Adrian Hess, 07. September 2011

Page 6

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Appendix: Excel Sheet Showing Calculated Particle Mass Emission Data

Average Mass Concentration during NEDC Cycle [mg/m3] - estimated using SPHERICAL particle shape theory

model device id S/N sensor position Reference Fuel Emulsion Fuel


DiSC mini Goldy 101'261 NanoMet3

1.26 0.94 0.75 0.21 0.22 0.21

DiSC std Testo 101'052 NanoMet3

0.44 0.56 0.58 0.09 0.09 0.08

DiSC mini Demo AK 101'263 NanoMet behind CVS 0.09 0.08 0.07 0.05 0.05 0.04

DiSC std FHNW 100'876 NanoMet behind CVS 0.07 0.05 0.04 0.03 0.03 0.03

Total Particle Mass per kilometer NEDC Cycle [mg/km] - estimated using SPHERICAL particle shape theory

DiSC mini Demo AK 101'263 NanoMet behind CVS 1.3224 1.1428 0.9942 0.6822 0.6911 0.6507

DiSC std FHNW 100'876 NanoMet behind CVS 1.0212 0.7675 0.6425 0.4904 0.4897 0.3897

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Sensors Behind NM3 - PM per Exhaust Gas Volume DiSC mini Goldy 101'261 1.8

1.6 DiSC std Tes to 101'052

1.4

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Sensors Behind CVS / NM2 DiSC mini D em o AK 101'263 1.8

1.6 DiSC std FH NW 100'876

1.4

1.2

1

0.8

0.6

0.4

0.2

0


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