A Portable Ultrafine Particle Sizer for In-Situ Engine Exhaust Monitoring

Andrew Vize, Matt Casari Faculty Advisors - Britt Holmén and Jeff Frolik

School of EngineeringUniversity of Vermont (UVM)

Transportation Research Center Expo 5 / 6 / 2009

Background

Preliminary Design System Layout Theory of Operation: We are attempting to quantify particulate size based on the particles electric mobility, which is

proportional to the aerodynamic diameter of the particle. In the proposed system particles will be charged, passed through a normalizing region and then directed into a static electric field where they will be separated and quantified based on particle electric mobility. This type of system is currently leveraged on large laboratory instruments. Our approach utilizes modern electronics and fabrication techniques to greatly reduce the size of the instrument.

Charging the Particles: We are proposing the use of a coronaionizer to charge particles in our system. A corona is a region of extremely high electric field, which causes a breakdown in the local atmosphere and a small region of plasma is formed. (1)This high region of electric field is generated by setting a high potential (in the kilovolt range) across a set of electrodes with contrasting dimensions, in this case a cylindrical electrode (2) around a pin. The resulting plasma forms around the pin andproduces a cloud of free electrons which drift outwards toward the outer electrode. The particulate drifts perpendicularly throughthis region and collects some of these free electrons, thus developing a negative charge. (3)

Particulate Flow: To promote laminar flow, the particleswill be passed though a flow straightener and / or ion optics.This will ensure that particles enter the analyzer in a narrow band, thus improving the resolution of the measurement.

Injecting Sheath Gas: (4) Sheath gas is clean, charged particulate free gas whichenvelopes the particulate stream. The sheath gas provides the resistance tothe particulate flow which makes the differences in particle mobility measurable.

Monodisperse Particulate Bands: Particles entering the mobility analyzer encounter a static electric field induced by a center electrode (5) which is negatively charged and thus repels the particles toward the outer diameter of the analyzer. Particles with a smaller cross sectional area have a higher mobility, are deflected more quickly, and impact the outer wall of the

analyzer further up stream than do larger particles.

It is in this manner that particles are separated.

Quantifying Particles: Particles striking the outer wall of the analyzer will impact a flexible printed circuit board. (6) The charged particle will be neutralized by the metallic surface of

the printed circuit board as the charge is transferred into the metal. Many particle strikes will result in a small current flow

which can be measured and correlated to a particulate count.

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Definition: Particulates are a complex mixture of extremely small particles and liquid droplets. Ultrafine Particulates are comprised of particles which have a diameter of 100 nano-meters or less. Our study is primarily concerned with ultrafine particulate generated in engine exhaust.

Health Effects: Ultrafine particulate can penetrate the alveolar-capillary barrier and be transported through the blood to be deposited in organs and possibly cause long-term fatal effects such as asthma and inflammatory diseases.

NOTE: EPA DOES NOT CURRENTLY REGULATE ULTRAFINE PARTICULATE

Particulate Measurement: Measuring ultrafine particulate is typically done in a laboratory setting. Particulate monitoring instruments are bulky and not designed for in-situ (i.e., on-board) monitoring. Therefore, particulate sizing instruments are connected to engine dynamometers which are run at loads equivalent to on-road conditions. By eliminating in-situ data-taking, it is possible that some particulate generating events may be missed.

Project Goals: To build a low-cost, low-power system capable of discriminating particle size in the ultrafine range. The system, the Portable Ultrafine Particulate Sizer (PUPS), can be integrated on a standard vehicle in order to measure engine exhaust particulates in-situ. Additionally, the system will be capable of 1 Hz resolution (1 sample per second) and also have similar capabilities to instruments which are currently used to make in-laboratory measurements.

Ongoing Work

The overall System Layout will be low-power and utilize SD Media for on-board data storage. Amplification circuitry will be designed using discrete low-noise electrometers to accurately measure particulate concentrations.

Picture from Maryland Department of the EnvironmentCurrently we are working on:

• Flexible PCB Layout for detectors.• Amplification Circuitry Layout and Simulation.• Detector structure construction.

Next Steps:• Develop code for embedded controllers.• Build and compare amplifiers to existing solution.• Assemble prototype of system.• Test system and calibrate to set standards.• Integrate GPS for spatial discrimination.

End Goal

Equipping a large fleet of vehicles with PUPS detectors will help to create a large data set to accurately model the generation of Ultrafine Particle concentrations. With better models, this research will help influence the EPA to set strict regulation of Ultrafine Particle emissions.

Diagram of PUPS Assembly