Particulate Partial Flow Sampling System
 

Product Overview
The Model BG-3 Partial Flow Sampling System (PFSS) is a highly flexible engine particulate emissions sampling device protected by nine patents with several other pending.  It can be used for proportional sampling on transient test cycles with any fuel (diesel, gasoline, natural gas, etc.) and can be used on engines of any size in both engine and chassis test cells.  The Model BG-3 can be used equally effectively for steady state test cycle PM measurements.  Steady-state sampling times range from two to five minutes depending on the relative particulate emissions output of the engine and the size of the filter holder used.  Test cycles for any regulation can be easily designated, set up, and run.  The Model BG-3 satisfies all ISO 8178, ISO 16183 and 40CFR 1065 requirements for transient and steady-state equivalency, plus satisfies EPA requirements for non-road steady-state (CFR Part 89), supplemental 13-mode and ramp modal cycle testing.  The system can also be used as a diluter for particle sizing instrumentation and for gaseous emissions measurement systems, while simultaneously and accurately sampling particulate matter.

The fundamental description of the Model BG-3, per ISO8178-1 (5) is as a “partial flow dilution system with flow control and total sampling”, otherwise known as a ‘split, then dilute” methodology.   The operational difference between BG-3 and CVS is that a CVS first dilutes the full flow of raw exhaust and then collects PM from a small fraction of that flow (dilute, then split), while the BG-3 first proportionally extracts and then dilutes a small fraction of the raw exhaust and then collects PM on a gravimetric filter from that flow (split, then dilute).  The BG-3 design premise is to provide equivalent results to CVS by maintaining proportionality of the raw exhaust sample mass flow relative to the exhaust mass flow rate of the engine.

The primary purpose of the Model BG-3 is to control the flow rate of a representative sample of exhaust during an engine test cycle where engine speed, load, airflow and fuel flow values exhibit high rates of change over very short time frames. The magnitude of engine inlet air mass flow excursions can approach 10:1 within less than two seconds. The challenge for any PFSS is to maintain constant proportional flow from an exhaust stream with a highly variable mass flow rate throughout a typical test cycle. In order to ensure that the total mass of particulate trapped at the filter is equivalent to that obtained by the use of a full flow CVS, the sample flow rate must be controlled in real-time to be proportional to the exhaust mass flow. Further, it is necessary to control this sample flow rate to ensure that the filter temperature does not exceed the regulatory defined limit while the dilution air temperature is maintained in the range required by the regulations.  

Equivalency Testing
Since 2005, Sierra has been working with the EPA to become approved as an alternative method to CVS.  EPA granted approval for the Model BG-3 for use by Caterpillar and Sierra Instruments for certification of pre-2007 on-highway truck engines on the FTP test cycle.  In April 2009, we completed a four year equivalency testing effort to have the Model BG-3 approved as an alternative method to CVS for certification of 2007 and Tier IV test cycles.  The testing included three separate test cells, five different engines, and over 200 separate tests.

Zero-Loss Dilution Tunnel
The magic of the Model BG-3 is the patented dilution tunnel which eliminates the major Achilles heel of any PFSS, the deposition of particulate on dilution chamber walls as the diluted exhaust sample is transferred to the filter from the raw exhaust stream. Zero particulate loss in the patented radial inflow partial flow dilution tunnel (Pictured Above)and a very short equilibration zone before the filter set the BG apart from all other PFSS.   Sierra’s patented dilution tunnel technology is a chamber under pres­sure. Conditioned dilution air permeates from the outside of the chamber in through the walls of a sintered metal tube carrying the diluted sample, creating a hydrocarbon-free air barrier. This eliminates the effect of the dilution system’s “history” on the test sample.

The Model BG-3 is an integrated product that incorporates two flow devices supplying and extracting gas from used in the dilution tunnel design.  The mass flow of raw exhaust sampled at the probe is the difference between the flow rates of the dilution and total mass flow meters. This sample flow is calculated as the difference between the total and dilute flow.

Background
In 1991, Caterpillar Inc. and Sierra Instruments formed a joint agreement to commercialize several Caterpillar patents to produce the Model BG-1 Partial Flow Sampling System (PFSS). Sierra followed this effort up with the Model BG-2 PFSS which features advanced software. 

The flagship Sierra Model BG-3 transient PFSS was developed in 2003 in response to pending requirements for transient cycle development and certification of non-road engines.  Due to their expanded power output levels, higher mass flow rates and elevated test cycle exhaust heat content, off-road engines present a unique set of challenges to the continued use of CVS systems.  Further, a need was expressed by after treatment and engine development personnel for a transient particulate sampling system deployable upstream and downstream of after treatment systems for concurrent particulate sampling to enable particle removal device efficiency studies. Read More…