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Partial Flow + Direct Exhaust Metering for Light Duty Emissions

Put CVS in your rear view mirror, find a better way forward with Partial Flow!

Dynamic Duo

Light Duty Emissions Sampling

Historically, recommending raw sampling methods over CVS for light duty vehicle testing was problematic due to the need for raw exhaust mass flow measurement.  Today, with breakthroughs in direct raw exhaust mass flow measurement, this problem is solved.


The premise of a technically equivalent, commercially available replacement of CVS by partial flow PM and raw or dilute gaseous emissions sampling methods for Light Duty is fully satisfied by the Sierra's BG3 Partial Flow Dilution System and ExhaustTrak Direct Raw Exhaust Flow Meter.  View Diagram...


The Sierra BG3 Partial Flow Dilution System has been in production since 2003, has been involved in official engine certification and DF tests and multiple independent studies since its inception.  Data provided from BG3 was the primary enabler for the inclusion of PFD in 40CFR 1065 for transient cycle certification. Learn more...


The Sierra ExhaustTrak, in production since 2014, is a highly capable and flexible exhaust mass flow meter with flow turndown capability consistent with competitive systems.  It is available in a wide range of sizes and flow capacities.  ExhaustTrak measurement accuracy, as shown during independent studies, is on par with, or better than, competitive units, while possessing significantly higher tolerance to heat.  Learn more...

The Dynamic Duo

When the BG3 and ExhaustTrak work together, great things happen.  BG3 provides the accurate and repeatable Partial Flow Dilution (PFD), but it needs ExhaustTrak to resolve temporal and dispersion flow rate offsets versus intake air by measuring real time mass flow at the emissions sampling zone.  The ExhaustTrak mass flow rate signal enables improved PFD proportional sampling, produces output in engineering units to the host, meets 1065 accuracy and linearity requirements, and has a fuel H/C input while direct O2 measurement allows for real-time exhaust molecular weight compensation. Read more...

The Case for Light Duty Partial Flow PM

PFD systems are allowed in 40 CFR 1065 for use on transient and steady-state certification cycles.  CARB introduced the LEV-3 PM limits in 2013, requiring compliance to a 3mg/mi standard, phase-in starting in 2017 and 1mg/mi phase-in beginning 2025.  There were concerns centered on observed PM signal-to-noise ratio (precision) at the LEV-3 PM emissions limits, contributed in-part through sample-wall interactions (adsorption, desorption, re-entrainment). The comparative difficulty and cost inherent in remediating a contaminated CVS versus using PFD exacerbated these concerns.

Initial Questions/Points:
  • Is mass still a defensible metric for Light Duty particulate?
  • Is CVS still a technically legitimate system for very low PM measurement?
  • Is raw PFD a legitimate/advantageous alternative for Light Duty PM?
  • CRC E-99-1 and -2 research programs focused on solutions to very low LD PM measurement concerns
  • The use of PFD showed significantly lower tunnel blank values

Now completed, Coordinated Research Council (CRC) E-99-1 and -2 research programs focused on solutions to very low LD PM measurement concerns.  The use of PFD showed significantly lower tunnel blank values

Raw vs. Dilute:

Why would an engine test/development organization use CVS?  CVS is a larger, more expensive, less flexible, less precise method for light duty gaseous and PM emissions sampling, whether in-vehicle or bare engine. Partial Flow is a technically superior, legally compliant option, with full technical support. 

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Solid Particle Number System

  • UN-ECE R49 and R83 compliant
  • Ideal for autos, diesels, pre/post aftertreatment, jet engines, and more
  • Measures particulate concentration down to 23nm (10nm pending)
  • Units calibrated independently by SwRI in their ISO-17025 lab
  • Catalytic Stripper Technology (CST) Improves quantification of sub-23nm particles
  • Takes a sample from a full-flow CVS unit or partial flow dilution system

BG3 Elite

Partial Flow Dilution (PFD) System

  • Transient and steady-state sampling
  • Use in place of CVS for emissions and analytical sampling
  • Light-duty and heavy-duty engines
  • Sample any size or type of engine and any fuel
  • US EPA-approved for R&D and certification work
  • BG3 with ExhaustTrak replaces full flow CVS for Light Duty- Learn more
  • Made in the USA
ExhaustTrakTM Venturi Flow Meter

Raw Exhaust Mass Flow Metering

  • Go direct to the sample zone 
  • Patented pressure averaging rings for zero contamination
  • Eliminating need for chemical mass balance methods
  • Meets or exceeds US EPA 40 CFR Part 1065
  • BG3 with ExhaustTrak replaces full flow CVS for Light Duty- Learn more
AirTrak 628S Flow Meter

Intake Air Mass Flow Metering

  • 200 millisecond response time to changes in flow rates
  • High accuracy 1.0% of full scale over a broad range
  • Outstanding 100:1 turndown
  • Minimal flow blockage and low pressure drop
  • High accuracy at low idle conditions
  • Field adjustment of critical flow meter settings
  • Digital electronics, field calibration validation
Automatic Filter Changer (AFC)

Making gravimetric PM emissions sampling easier, faster and safer!

  • 14 and up to 24 filter puck canister capacity
  • 10 second filter indexing time
  • 2D filter barcode reader reads filter number during final indexing 
  • Plug-and-play with any BG3 partial flow system
  • Meets US EPA 40CFR Part 1065 Regulations
Particulate Filter Holders

47mm, 70mm, and 90mm

  • We stock all filters and filter holder sizes
  • Design meets requirements of Federal Register
  • All filter holders are made of 316L stainless steel
  • Plug-and-play with BG3 partial flow sampler
  • Used in manual mode with other devices
Filter Weighing Chambers

Assure High Quality Filter Media Processing

  • Reduce/eliminate errors in filter weight data
  • Dual chamber "Glove Box" style design
  • Filter bar coding and scanning option
  • Designed per regulatory requirements
  • Compact ready-to-run package
Assure clean dilution air during sampling

Air Handling and Scrubbing

  • Eliminate dirt, water and oil from your air
  • High quality air means high quality data results
  • Custom systems available

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