Centrifugal Particle Mass Analyzer Research Articles

Demonstration of the CPMA-Electrometer System for Calibrating Black Carbon Particulate Mass Instruments

In an effort to improve regulations for particulate emissions from aircraft engines, the Aircraft Exhaust Emissions Measurement Committee, SAE E-31, is investigating instruments to measure black carbon mass concentration in real time. The current candidates are a laser-induced incandescence instrument (LII 300) and a photo-acoustic Micro-Soot Sensor (MSS). However, both of these instruments use indirect techniques, measuring parameters other than the actual mass of particulate in the exhaust, and therefore require calibration. Previously, it has been shown that a centrifugal particle mass analyzer (CPMA) can be used in conjunction with an aerosol electrometer to traceably generate an aerosol with known mass concentration. This system can be used to rapidly calibrate particle mass instruments (on the order of minutes), without the time-consuming process of filter sampling, which is often used for calibration and prone to sampling artifacts. Here, we demonstrate the feasibility of the CPMA-electrometer syst...

Effective Density and Mass-Mobility Exponent of Aircraft Turbine Particulate Matter

A centrifugal particle mass analyzer and a modified differential mobility spectrometer were used to measure the mass and mobility of particulate matter emitted by CFM56-5B4/2P, CFM56-7B26/3, and PW4000-100 gas turbine engine sources. The mass-mobility exponent of the particulate matter from the CFM56-5B4/2P engine ranged from 2.68 to 2.82, whereas the effective particle densities varied from 600 to , depending on the static engine thrust and sampling methodology used. The effective particle densities from the CFM56-7B26/3 and PW4000-100 engines also fell within this range. The sample was conditioned with or without a catalytic stripper and with or without dilution, which caused the effective density to change, indicating the presence of condensed semivolatile material on the particles. Variability of the determined effective densities across different engine thrusts, based on the scattering about the line of best fit, was lowest for the diluted samples and highest for the undiluted sample without a catalytic stripper. This variability indicates that the relative amount of semivolatile material produced was engine thrust dependent. It was found that the nonvolatile particulate matter, effective particle density (in kilograms per cubic meter) of the CFM56-5B4/2P engine at relative thrusts below 30% could be approximated using the particle mobility diameter ( in meters) with .

Particle effective density and mass during steady-state operation of GDI, PFI, and diesel passenger cars

Particle effective density is an important physical property of vehicle exhaust, and is required for estimating particulate matter (PM) mass emissions using the Integrated Particle Size Distribution (IPSD) method. In this study, we measure particle effective density of five light-duty vehicles with PM emissions below the Low Emission Vehicle (LEV) III PM standards of 1 or 3mg/mi (0.62 and 1.86mg/km) using the Differential Mobility Analyzer (DMA) – Centrifugal Particle Mass Analyzer (CPMA) approach. Test vehicles included two gasoline direct injection (GDI) vehicles without particulate filters, and for the first time reported in the literature, two port-fuel injected (PFI) vehicles and a turbocharged direct injection (TDI) light-duty diesel vehicle with a diesel particulate filter (DPF). The particle effective density functions generally resemble previous work on GDI and diesel engines without particulate filters but, for many size ranges, the PFI and TDI vehicles produced emissions with higher particle effective densities than GDI vehicles. Good linear correlation was found between the gravimetric and IPSD methods when applying the new particle effective density functions to size distribution measured by the TSI Engine Exhaust Particle Sizer (EEPS, 5.6–560nm, R2=0.84); however, the IPSD method underestimated gravimetric mass by 64%. When using a TSI Aerodynamic Particle Sizer (APS, 0.54–2.5µm) to measure the contribution of larger particles, underestimation bias was virtually eliminated and the correlation improved dramatically (R2=0.96). Even stronger correlation between IPSD and gravimetric methods was achieved when using a Scanning Mobility Particle Sizer (SMPS, 8.7–365nm) and the APS (R2=0.97). A procedure for correcting EEPS measurements using the SMPS is presented and evaluated.

Determination of PM mass emissions from an aircraft turbine engine using particle effective density

Inventories of particulate matter (PM) emissions from civil aviation and air quality models need to be validated using up-to-date measurement data corrected for sampling artifacts. We compared the measured black carbon (BC) mass and the total PM mass determined from particle size distributions (PSD) and effective density for a commercial turbofan engine CFM56-7B26/3. The effective density was then used to calculate the PM mass losses in the sampling system. The effective density was determined using a differential mobility analyzer and a centrifugal particle mass analyzer, and increased from engine idle to take-off by up to 60%. The determined mass-mobility exponents ranged from 2.37 to 2.64. The mean effective density determined by weighting the effective density distributions by PM volume was within 10% of the unit density (1000 kg/m3) that is widely assumed in aircraft PM studies. We found ratios close to unity between the PM mass determined by the integrated PSD method and the real-time BC mass measurements. The integrated PSD method achieved higher precision at ultra-low PM concentrations at which current mass instruments reach their detection limit. The line loss model predicted ∼60% PM mass loss at engine idle, decreasing to ∼27% at high thrust. Replacing the effective density distributions with unit density lead to comparable estimates that were within 20% and 5% at engine idle and high thrust, respectively. These results could be used for the development of a robust method for sampling loss correction of the future PM emissions database from commercial aircraft engines.

Steady-state measurement of the effective particle density of cigarette smoke

The steady-state effective particle density of mainstream smoke from a University of Kentucky 3R4F reference cigarette was determined using a Differential Mobility Analyser (DMA) and Centrifugal Particle Mass Analyser (CPMA). The cigarette smoke was generated using a smoking machine under ISO puffing parameters (35ml puff of 2s duration, every 60s) and collected in a Tedlar® bag. This smoke generation process resulted in the first puff of the smoking cycle aging approximately 7min longer than the last puff. The effective particle density (measured immediately upon completion of the last puff) was found to be independent of the particle mobility size, indicating the particles have a spherical morphology, with an average density of 1180±113kg/m3. Particle coagulation was also found to occur within the Tedlar® bag by comparing particle mobility size distributions, measured with a Scanning Mobility Particle Sizer (SMPS), against an analytical model. This model showed that particle coagulation dominated the particle number concentration decay within the Tedlar® bag compared to particle diffusion or settling losses. Therefore cigarette smoke particles must have a liquid component to maintain a constant effective particle density function in the presence of coagulation. After the 7min filling process, the effects of particle aging time and initial particle number concentration in the Tedlar® bag on the effective particle density were found to be small and indistinguishable within the bias uncertainty of the measurement system.

Mass–Mobility Measurements Using a Centrifugal Particle Mass Analyzer and Differential Mobility Spectrometer

Mass–mobility measurements using a centrifugal particle mass analyzer (CPMA) and differential mobility spectrometer (DMS) are demonstrated. The CPMA, which classifies an aerosol by mass-to-charge ratio, is used upstream of a DMS, which measures the mobility size distribution of the mass-classified particles in real-time. This system allows for mass–mobility measurements to be made on transient sources at one particle mass or an entire effective density distribution for steady state sources in minutes. Since the CPMA classifies particles by mass-to-charge ratio and multiply charged particles are present, particles of several different masses will be measured by the DMS. Therefore, a correction scheme is required to make accurate measurements. To validate this measurement scheme, two different CPMA-DMS systems were used to measure the known density of di(2ethylhexyl) sebacate (DEHS). The first system consisted of a CPMA and standard DMS500 (Cambustion). This system measured an average effective density of 1...

Effects of volatile coatings on the laser-induced incandescence of soot

We have measured time-resolved laser-induced incandescence (LII) from combustion-generated mature soot extracted from a burner and (1) coated with oleic acid or (2) coated with oleic acid and then thermally denuded using a thermodenuder. The soot samples were size selected using a differential mobility analyzer and characterized with a scanning mobility particle sizer, centrifugal particle mass analyzer, and transmission electron microscope. The results demonstrate a strong influence of coatings on the magnitude and temporal evolution of the LII signal. For coated particles, higher laser fluences are required to reach signal levels comparable to those of uncoated particles. The peak LII curve is shifted to increasingly higher fluences with increasing coating thickness until this effect saturates at a coating thickness of ~75 % by mass. These effects are predominantly attributable to the additional energy needed to vaporize the coating while heating the particle. LII signals are higher and signal decay rates are significantly slower for thermally denuded particles relative to coated or uncoated particles, particularly at low and intermediate laser fluences. Our results suggest negligible coating enhancement in absorption cross-section for combustion-generated soot at the laser fluences used. Apparent enhancement in absorption with restructuring may be caused by less conductive cooling.

Effective density of Aquadag and fullerene soot black carbon reference materials used for SP2 calibration

Abstract. The mass and effective density of black carbon (BC) particles generated from aqueous suspensions of Aquadag and fullerene soot was measured and parametrized as a function of their mobility diameter. The measurements were made by two independent research groups by operating a differential mobility analyser (DMA) in series with an aerosol particle mass analyser (APM) or a Couette centrifugal particle mass analyser (CPMA). Consistent and reproducible results were found in this study for different production lots of Aquadag, indicating that the effective density of these particles is a stable quantity and largely unaffected by differences in aerosol generation procedures and suspension treatments. The effective density of fullerene soot particles from one production lot was also found to be stable and independent of suspension treatments. Some differences to previous literature data were observed for both Aquadag and fullerene soot at larger particle diameters. Knowledge of the exact relationship between mobility diameter and particle mass is of great importance, as DMAs are commonly used to size-select particles from BC reference materials for calibration of single particle soot photometers (SP2), which quantitatively detect the BC mass in single particles.

Soot Particle Studies—Instrument Inter-Comparison—Project Overview

An inter-comparison study of instruments designed to measure the microphysical and optical properties of soot particles was completed. The following mass-based instruments were tested: Couette Centrifugal Particle Mass Analyzer (CPMA), Time-of-Flight Aerosol Mass Spectrometer—Scanning Mobility Particle Sizer (AMS-SMPS), Single Particle Soot Photometer (SP2), Soot Particle-Aerosol Mass Spectrometer (SP-AMS) and Photoelectric Aerosol Sensor (PAS2000CE). Optical instruments measured absorption (photoacoustic, interferometric, and filter-based), scattering (in situ), and extinction (light attenuation within an optical cavity). The study covered an experimental matrix consisting of 318 runs that systematically tested the performance of instruments across a range of parameters including: fuel equivalence ratio (1.8 ≤ φ ≤ 5), particle shape (mass-mobility exponent ( D fm ), 2.0 ≤ D fm ≤ 3.0), particle mobility size (30 ≤ d m ≤ 300 nm), black carbon mass (0.07 ≤ m BC ≤ 4.2 fg) and particle chemical composition. I...

The effective density and fractal dimension of particles emitted from a light-duty diesel vehicle with a diesel oxidation catalyst

A differential mobility analyzer (DMA) and a Couette centrifugal particle mass analyzer (Couette CPMA) were used to measure the effective density and fractal dimension of particles emitted from a light-duty diesel vehicle fitted with a diesel oxidation catalyst (DOC). It was found that at high engine loads, the DOC increased in temperature, sulphate levels in the particulate matter increased, and a transient nucleation mode was observed. The increase in sulphate levels resulted in a drastic increase in the effective density and fractal dimension of the particles. At low engine loads (8–15%), sulphate levels were much lower, no nucleation mode was present and the fractal dimension varied from 2.22 to 2.48, which is in good agreement with previous studies. At 40% load, sulphate levels were much higher and the fractal dimension was 2.76.

The experimental transfer function of the Couette centrifugal particle mass analyzer

The Couette centrifugal particle mass analyzer (CPMA) classifies particles by their mass-to-charge ratio. Unlike the aerosol particle mass (APM) analyzer, the Couette CPMA uses a stable system of forces to improve the transfer function of the classifier. A prototype Couette CPMA has been built and tested. The experimental results from the prototype agree well with theory and it is found that indeed the transfer function of the Couette CPMA is better than the APM's. Experimental work is shown using a differential mobility analyzer (DMA) and Couette CPMA to classify polystyrene latex (PSL) and di-2-ethylhexyl sebacate (DEHS) particles. By measuring the mass of PSL particles the absolute uncertainty of the Couette CPMA was found to be 6.7–38% higher in terms of mass (or 2.2–11% higher in terms of equivalent diameter) than the expected value. However, when the DMA–CPMA system was calibrated with PSL particles the density of DEHS particles was measured to within approximately 3% of the expected value.

A Numerical Calculation of the Transfer Function of the Fluted Centrifugal Particle Mass Analyzer

A new particle mass classifier called the Fluted Centrifugal Particle Mass Analyzer (CPMA) is presented and compared to the Aerosol Particle Mass (APM) Analyzer and the Couette CPMA. These particle mass classifiers use electrostatic and centrifugal forces to classify particles by their mass-to-charge ratio. The Fluted CPMA uses reversed ‘scooped’ sections to create a stable system of forces in the radial direction but not in the angular direction. The stable forces in the radial direction improve the transfer function of the classifier. A Lagrangian model (neglecting diffusion) of the Fluted CPMA is derived from which the transfer function of the classifier is found. The model shows that, like the APM and Couette CPMA, a single non-dimensional number determines the shape of the transfer function. The comparison of the classifiers shows that the Couette CPMA outperforms the Fluted CPMA and APM. However, the Fluted CPMA outperforms the APM over a wide range of operating conditions and may be easier to manuf...

New method for particle mass classification—the Couette centrifugal particle mass analyzer

A new particle mass classifier, the Couette centrifugal particle mass analyzer (CPMA), is described and compared to the existing aerosol particle mass (APM) analyzer. The Couette CPMA and APM use centrifugal and electrostatic forces to classify particles according to their mass-to-charge ratio. The APM consists of two rotating coaxial electrodes, rotating at the same angular velocity, between which charged particles pass. Depending on the voltage and rotational speeds of the electrodes, particles of different mass-to-charge ratios will be classified. The Couette CPMA uses a similar operating procedure, but the inner electrode rotates slightly faster than the outer. This produces a stable system of forces that dramatically improves the transfer function of the classifier. Two theoretical models of the classifiers are developed. One model neglects the effects of diffusion and the other model does not. The models show that the shape of the transfer function for both devices is determined by two non-dimensional constants. The models also show that the Couette CPMA has better performance characteristics than the APM when transfer functions are compared.