Dr. Chris Laroo

Environmental Scientist US Environmental Protection Agency Office of Transportation and Air Quality

Assessment and Standards Division

2000 Traverwood Dr. Ann Arbor, MI 48105

Subject: Transient Partial Flow PM Measurement Peer Review

Dear Dr. Laroo:

I have reviewed those parts of the EPA FRM (U.S. EPA, 2009) that relate to the use of partial flow sampling systems (PFSS) for transient PM measurements. These are sections 40 CFR Part 1065,140(e), 1065.170(c)(1)(vi), and 1065.545. Wit h regard to the review I find the following:

1) Clarity/Understandability

– The sections referenced are clear and understandable. 2) Reasonableness of methodology and assumptions

- The methodology associated with use of the partial flow sampling system is reaso nable and given the reference material provided the assumptions on which parameters used in these sections are selected is also reasonable. 3) Appropriateness of data

– The data used in locking down the parameters used in these sections is very appropriate. However, I have some comment on the thoroughness of one of

the references used. See the attached review. 4) Recommendations for any alternate methodologies and/or data

– I have made some

recommendations and comments on the sections reviewed. These are incl uded in the

attached review.

Sincerely,

Dr. Bruce Cantrell BKC Consulting 2504 Lake Crossing Dr. Greenwood, IN 46143

- 8598 Phone: (317) 889

- 6402

e

- mail: BKC Consulting@comcast.net

EnclosureReview of

Use of partial flow systems for transient PM measurement

By

Bruce Cantrell, BKC Consulting September 7, 2007

Summary Comments

This is a review of those parts of the EPA FRM (U.S. EPA, 2009) that relate to the use of partial

flow sampling systems (PFSS) for transient PM measurements. These are sections 40 CFR Part 1065,140(e), 1065.170(c)(1)(vi), and 1065.545. In locking down the parameters used in these sections, the EPA has relied on two published studies; (CRC, 2007 ) and (Sierra Instruments, (2006). Review of the FRM requires comment on each of these studies.

The Sierra Instruments study cited is rather shallow and reads more like an Executive Summary than report of a study. The correlation testing results are skimmed over and the correlations are not cited. Rather two comparison plots are offered. No Regressions are offered and the statistics are simply stated rather than backed up with data. The variance in results of engines running with CCRT devices are attributed to problems in filter gravim etrics that are simply alluded to

, and the impact on the paired

– t and F

- tests is not discussed. Rather, the claim is repeated that the results conform to Part 1065 without substantiation. This leaves the reader in the position of taking their word for the results stated and that is not acceptable

.

The CRC report (CRC, 2007) describing a more complete study of several commercially available PFSS reports the characteristics of each system under a variety of conditions. Sample

flow c orrelations with a fu ll flow CVS are presented and s tandard error is calculated for each

correlation

. Most of these correlations yielded r 2 values greater than 99 percent and standard

error less than 5%. In addition, measured PM concentrations are compared with those obtaine d using the CVS for a range of emission concentrations from <10 to 85% of the 2007standard

. This permitted exploration of particle and filter artifact formation under condition similar to those pertaining when a diesel particulate filter (D P F) is in use. The effect of sample residence

time was also studied. As with the Sierra report (Sierra, 2006) gravimetric analysis of collected samples shows high variability when a DPF is used and PM concentrations are very low, less

than 10% of the 2007 standard. Th is is explored in terms of particle and filter artifact using OC/EC analysis.

Specific Comments

40 CFR Part 1065,140(e)

– This section is a fairly faithful adaptation of the results reported in the CRC report and, taken at face value, the Sierra report. It mixes the traditional dilution

p rocedures with those necessary to accomplish partial flow dilution using the available commercial partial flow sampling systems. Aside from temperature control of the dilution process the most critical parameter here is residence time of the sample before it reaches thesamp le collection device, be it a filter or real

- time monitor. This needs to be as short as possible. Subsection (3) states that the PFSS residence time should be at least 0.5s. I would change this to

read the PFSS residence time should be at most 0.5s. Al so, the assumed flow temperature should

be 47± 5 oC in keeping with the temperature requirement of the collection media . Sample temperature should be measured at the collection media as part of the temperature control

process

.

1065.170(c)(1)(vi)

– Filter m edia is critical for collection of representative PM. All collection media will collect hydrocarbon artifact, including PTFE. Using support bonded to the back of a

PTFE filter will enhance this because of the increase in available surface area. When usi ng filter media other than pure PTFE, which will collect a minimum amount of artifact, this must be taken into account. For example, PTFE

- coated glass fiber filter will collect a substantial amount of

artifact and should be used with a back

- up filter whic h can be used to correct for artifact build

- up on the filter. Corrections on the order of 50 to 80% in this case are not acceptable. This problem is significant when a DPF is used and emission concentration is less than 10% of the 2007

standard ; quite of ten, concentration measurements using filter collection are indistinguishable

from that obtained as a tunnel blank (CDC,2007)

.

Should the subtended angle in the filter holder transition from inlet to the filter be 14o rather than 12.5o ? This is the angl e for minimum loss that has been a rule of thumb reported for turbulent deposition in studies of expansion sections of PM transport lines. Another study (Sparrow, 2009) finds that10o is the angle where flow separation stops. The authors should make a fin al determination of this before the rule is published.

1065.545

– Several commercially available PFSS units can meet the prescribed requirements (CRC, 2007and Sierra, 2006). They exhibit both linearity

, as evidenced by correlation wi th t otal sample flow

, and response times that permit mean sample flow rates to be accurately determined during each component of a transient test cycle. In addition to the specifications listed, I would add the certification of the flow meters using a NIST traceable transfer standard

.

References :

Coordinating Research Council

, (2007). 2007 DIESEL PARTICULATE MEASUREMENT RESEARCH, Report NO. E

- 66

- 3, Alpharetta, GA, 49 pp.

Sierra Instruments, Inc. (2006). Sierra Instruments Model BG

- 3 vs. CVS Multiple Engine

Correlation Study , Monterey, CA, 7 pp.

Sparrow, E.M., Abraham, J.P.,Minkowskycz, W.J. (2009). Flow separarion in a diverging conical duct: Effect of Reynolds number and divergence angle. International journal of Heat and Mass Transfer, vol. 52 (2009), pp. 3079

- 30 83.

U.S. EPA , (2009). 40 CFR

, Part1065 FINAL with Changes from C3 Marine

– FRM. Office of Transportation and Air Quality, Assessment and Standards Division, Ann Arbor, MI , 238 pp.