Instruments Based on Electrical Detection of Aerosols

Dhaniyala, Suresh; Fierz, Martin; Keskinen, Jorma; Marjamäki, Marko

doi:10.1002/9781118001684.ch18

Cited by 18 publications

(11 citation statements)

References 97 publications

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“…Figure 3b also shows the Fuchs model computations for the TC configuration. The experimental data were found to be within the range of charging efficiencies calculated for N i t products of 2 and 3 × 10 12 m −3 s. The slope of the calculated charging efficiency curves is less steep, exhibiting an exponent of~1.05, which is close to what similar calculations for unipolar chargers predict at such N i t products [6]. The steeper curve in the experimental data is anticipated owing to the fractal-like structure of graphite particles [20].…”

Section: Tandem Negative Positive Corona (Tc)supporting

confidence: 80%

“…The key element of a DC-based detector is a unipolar charger that electrically charges the particles. The charging efficiency follows a power-law dependence on particle diameter with an exponent that is typically around 1.1-1.6 [6]. The EU regulation 2017/1154 [7] requires a much tighter size dependence, thus necessitating the use of advanced DC-based sensor concepts to reduce the size influence [8,9].…”

Section: Introductionmentioning

confidence: 99%

“…The actual effect will depend on the charge level and size of the particles as well as the design characteristics of the corona. The charging efficiency of commercial corona chargers is typically less than one for neutral particles smaller than 30 nm [6]. Therefore, when highly charged particles of the same polarity in this size range (like those produced in the SCR) pass through them, their charge level can only increase and will thus be much higher than if they were neutral.…”

Section: Introductionmentioning

confidence: 99%

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Experimental Assessment of an Electrofilter and a Tandem Positive-Negative Corona Charger for the Measurement of Charged Nanoparticles formed in Selective Catalytic Reduction Systems

Schwelberger

Mamakos

Fierz³

et al. 2019

Applied Sciences

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Onboard measurement of non-volatile particle number (PN) emissions with portable emissions measurement systems (PEMS) was introduced for the type-approval of passenger cars in Europe since 2017 and is foreseen for heavy-duty (HD) vehicles in 2021. First studies on the performance of PN-PEMS with HD engine exhaust revealed larger differences between established PN-PEMS techniques than what was observed for passenger cars. Particles forming in selective catalytic reduction (SCR) systems for NOx of late technology HD engines have recently been identified as a potential reason for the observed differences. The formed particles have a size distribution peaking below the regulatory limit of 23 nm and most importantly acquire high (more than one) positive charges at the elevated exhaust temperatures. Precise measurement of such highly charged nanosized particles with PN-PEMS instrumentation utilizing diffusion charger (DC) based counters requires proper conditioning of these charges. Two approaches were investigated in this study: (a) an electrofilter (EF) to completely remove charged particles below the regulated size and (b) a tandem negative-positive corona (TC) charger to directly condition pre-charged particles. The two technical solutions were tested alongside the unmodified DC-based PN-PEMS, a PN-PEMS utilizing a condensation particle counter (CPC) and a reference stationary PN system using exhaust of two SCR-equipped HD engines. The results confirmed that the particles forming in such SCR systems are responsible for the observed inconsistencies and that both technical solutions efficiently address the interferences of these pre-charged nanoparticles.

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Section: Tandem Negative Positive Corona (Tc)supporting

confidence: 80%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Experimental Assessment of an Electrofilter and a Tandem Positive-Negative Corona Charger for the Measurement of Charged Nanoparticles formed in Selective Catalytic Reduction Systems

Schwelberger

Mamakos

Fierz³

et al. 2019

Applied Sciences

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“…In the case of instruments utilizing unipolar corona chargers, the effect can be significant, especially considering that positive coronas are preferred owing to the reduced ozone formation. This is because their cutoff size characteristics are controlled from the charger efficiency curve which typically lies below þ1 e for neutral particles smaller than 50 nm (Dhaniyala et al 2011). When sampling particles carrying more charges of the same polarity, the charge will remain largely unchanged leading to an overestimation.…”

Section: Discussionmentioning

confidence: 99%

Effect of selective catalytic reduction on exhaust nonvolatile particle emissions of Euro VI heavy-duty compression ignition vehicles

Mamakos

Schwelberger

Fierz³

et al. 2019

Aerosol Science and Technology

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The nonvolatile particle number (PN) emissions of late technology diesel heavy-duty vehicles (HDV) are very low due to the introduction of Diesel Particulate Filters (DPF). Nevertheless, a large fraction (50%) of particles below the current lower regulated size (23 nm) was recently reported. Moreover, large differences between laboratory and PN Portable Emission Measurement Systems (PN-PEMS) have been observed. In order to better understand such differences, the physical properties of the exhaust aerosol from two Euro VI technology diesel heavy-duty engines were studied. It was found that urea injection leads to formation of nonvolatile particles. The produced particles covered a wide size range spanning from below 10 nm to above 100 nm. As such, they contribute to the regulated PN emissions, with measured concentrations corresponding to as high as 2 Â 10 11 #/kWh over a World Harmonized Transient Cycle (WHTC). However, a large fraction of them was undetected owing to their small particle size. Low-cutoff size (10 nm) Condensation Particle Counters (CPCs) (which are under discussion to be included in the regulations) measured up to twice as high concentrations. Considering the large particle losses in the sampling systems at this size range, the true concentrations can be two times higher from what the low-cutoff CPCs reported. When the temperature of the SCR system exceeded a threshold of 300 C, the produced particles were found to be positively charged, increasing the average exhaust aerosol charge up to þ3 elementary charges per particle. Scanning Mobility Particle Sizer (SMPS) measurements of non-neutralized samples revealed that even the smallest of them can carry more than one positive charge. The findings of this study can explain the differences reported between PEMS and laboratory systems and especially those based on diffusion charging. They also provide insight for a refinement of technical requirements prescribed in the European PEMS regulation to more accurately quantify the PN emissions from such technologies.

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“…The measurement scheme in diffusion charging-based sensors involves the use of attachment of unipolar ions to particles by diffusion followed by detection of particle current. Ions undergoing Brownian motion attach to particle surface, imparting an electrical charge to the particles (Dhaniyala et al, 2011). Subsequently, the charged particles are trapped on a particle filter where the total charge of the particles is measured by an aerosol electrometer, which is related to particle surface area as follows (Matter Engineering AG, 2001):…”

Section: Approaches Used For Measurement Of Surface Areamentioning

confidence: 99%

Comparison of diffusion charging and mobility-based methods for measurement of aerosol agglomerate surface area

Kulkarni

2012

Journal of Aerosol Science

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We compare different approaches to measure surface area of aerosol agglomerates. The objective was to compare field methods, such as mobility and diffusion charging based approaches, with laboratory approach, such as Brunauer, Emmett, Teller (BET) method used for bulk powder samples. To allow intercomparison of various surface area measurements, we defined 'geometric surface area' of agglomerates (assuming agglomerates are made up of ideal spheres), and compared various surface area measurements to the geometric surface area. Four different approaches for measuring surface area of agglomerate particles in the size range of 60-350 nm were compared using (i) diffusion charging-based sensors from three different manufacturers, (ii) mobility diameter of an agglomerate, (iii) mobility diameter of an agglomerate assuming a linear chain morphology with uniform primary particle size, and (iv) surface area estimation based on tandem mobility-mass measurement and microscopy. Our results indicate that the tandem mobility-mass measurement, which can be applied directly to airborne particles unlike the BET method, agrees well with the BET method. It was also shown that the three diffusion charging-based surface area measurements of silver agglomerates were similar within a factor of 2 and were lower than those obtained from the tandem mobility-mass and microscopy method by a factor of 3-10 in the size range studied. Surface area estimated using the mobility diameter depended on the structure or morphology of the agglomerate with significant underestimation at high fractal dimensions approaching 3.

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Instruments Based on Electrical Detection of Aerosols

Cited by 18 publications

References 97 publications

Experimental Assessment of an Electrofilter and a Tandem Positive-Negative Corona Charger for the Measurement of Charged Nanoparticles formed in Selective Catalytic Reduction Systems

Experimental Assessment of an Electrofilter and a Tandem Positive-Negative Corona Charger for the Measurement of Charged Nanoparticles formed in Selective Catalytic Reduction Systems

Effect of selective catalytic reduction on exhaust nonvolatile particle emissions of Euro VI heavy-duty compression ignition vehicles

Comparison of diffusion charging and mobility-based methods for measurement of aerosol agglomerate surface area

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