Grantee Research Project Results
2012 Progress Report: Quantifying the Effects of the Mixing Process in Fabricated Dilution Systems on Particulate Emission Measurements via an Integrated Experimental and Modeling Approach
EPA Grant Number: R834561Title: Quantifying the Effects of the Mixing Process in Fabricated Dilution Systems on Particulate Emission Measurements via an Integrated Experimental and Modeling Approach
Investigators: Zhang, Ke Max
Institution: Cornell University
EPA Project Officer: Chung, Serena
Project Period: May 1, 2010 through April 30, 2013 (Extended to October 30, 2013)
Project Period Covered by this Report: May 1, 2012 through April 30,2013
Project Amount: $250,000
RFA: Novel Approaches to Improving Air Pollution Emissions Information (2009) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Air
Objective:
The main objective of this study is to investigate a key uncertainty in PM emissions measurement by examining the following questions: How do the mixing processes in the current constant volume sampler (CVS) systems differ from those in the real-world conditions? How do the mixing processes in the different CVS systems differ from each other? How does the mixing process interact with aerosol dynamics that affect PM measurements in the CVS systems and PM transformation in the atmosphere?
Progress Summary:
The main task for this project period is to compare laboratory emission measurements (i.e., using fabricated dilution systems) and on-road chasing measurement (i.e., using atmospheric dilution) of vehicle emissions through numerical simulations. This is a key step in explaining how the mixing processes in the fabricated dilution systems differ from those in the real-world conditions. We have made significant progress in achieving the objective of research. First, we conducted numerical simulations, the first of its kind in the research community, to represent the chasing measurements, and the simulation results are compared favorably with the experimental results. Second, we developed techniques to simulate the operations of two widely used fabricated dilution systems, i.e., porous and ejector dilutors. Notably, the ejector dilutors have been employed in Portable Emission Measurement System (PEMS).
We employed the Comprehensive Turbulent Aerosol Dynamics and Gas Chemistry (CTAG) to simulate the on-road chasing and laboratory emission measurements described in Rönkkö et al. (2006). Figure 1 illustrates a sample of the simulation results for the on-road chasing experiment.
Figure 1. Simulated instantaneous spatial profiles of (a) particle number concentration, (b) particle nucleation rate for the on-road chasing experiment.
In the on-road chasing environment, the shape of the exhaust plume is changing rapidly in the wake of the vehicle, strongly affected by vehicle-induced turbulence (Figure 1a). New particle formation takes place in the near-wake region (Figure 1b). Sensitivity studies indicate that parameters such as the chasing distances, the velocity of ambient wind (perpendicular to the road), and the location of exhaust pipe affect the on-road chasing emission measurements.
Figure 2 depicts the simulation results for laboratory emission measurements. The exhaust is mixing rapidly with the dilution air inside the porous diluter and near the entrance of the ageing chamber. Then the flow transforms to laminar inside the ageing chamber. The mixture is further diluted inside the ejector diluter, where the supersonic flow is achieved at the orifice. It is found that the formation of new particles can occur in the porous diluter and near the entrance of the ageing chamber.
Figure 2. Simulated spatial, instantaneous profiles of particle number concentration for laboratory emission measurements.
Figure 3 shows the comparisons between simulated and measured particle size distributions (PSDs) for on-road chasing experiments and laboratory emission measurements, indicating the performance of the CTAG model is adequate.
Figure 3. Comparisons of simulated and measured PSDs for driving condition 7 described in Rönkkö et al. (2006).
Future Activities:
We will conduct a large set of sensitivity simulations to generalize our findings, especially in terms of how the mixing process interacts with aerosol dynamics that affect PM measurements.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
| Other project views: | All 5 publications | 2 publications in selected types | All 2 journal articles |
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Wang YJ, Zhang KM. Coupled turbulence and aerosol dynamics modeling of vehicle exhaust plumes using the CTAG model. Atmospheric Environment 2012;59:284-293. |
R834561 (2011) R834561 (2012) R834561 (Final) |
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Wang YJ, Yang B, Lipsky EM, Robinson AL, Zhang KM. Analyses of turbulent flow fields and aerosol dynamics of diesel engine exhaust inside two dilution sampling tunnels using the CTAG model. Environmental Science & Technology 2013;47(2):889-898. |
R834561 (2011) R834561 (2012) R834561 (Final) R834554 (Final) |
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Supplemental Keywords:
emissions, diesel, dilution, ejector dilutor, porous dilutor, ultrafine particles, CTAG, CFD.Relevant Websites:
Aerosol dynamics inside a rotating disk diluter Exit
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.