Recommended Practice for Partial Flow Dilution System Measurement of Particulate Matter (PM)
This Recommended Practice establishes test procedures and best practices for particulate matter (PM) measurement under partial flow conditions. Partial flow PM testing and certification is mostly used on heavy duty applications as described in CFR Part 1065 where full flow sampling systems with full dilution tunnel and CVSs can be very bulky for larger heavy duty engines. 40 CFR Part 1066 also allows the use of partial flow systems for light duty applications in lieu of full flow systems. Partial flow does not require the use of a CVS sampling system or a full dilution tunnel. This makes it easier and more convenient to perform PM measurement in smaller test cells that cannot fit a large CVS or a full dilution tunnel. This document will describe the different components / specifications of the LD and HD partial flow systems, the required quality checks needed to ensure the integrity of the sampling system. It also addresses the many sampling options and calculations that are approved by the regulations. Correlation data between partial and full flow systems will also be included.
Rationale: The conventional test method for particulate matter (PM) of vehicle and engine exhaust has been the gravimetric type where diluted exhaust in a full dilution tunnel connected to a constant volume sampler (CVS) is sampled over a pre-weighed 47 mm Teflon filters. At the end of the test, the filters are post-conditioned in an environmentally controlled chamber for a period of time specified in the regulation after which the filter is weighed again. The net mass of PM on the filter is determined by subtracting the pre-weight from the post-weight. The accuracy of the total PM mass of the test depends on many parameters of varying effect but the most significant seems to be the amount of dilution and the magnitude of the net mass of PM collected on the filter. As the PM emission limits have been gradually getting more and more stringent over the last thirty years, the net mass of PM on the filters is becoming so small which makes it very challenging to weigh accurately considering the effect of all the noises affecting the weighing process. This necessitated the need for a very sensitive and precise micro-balance with a resolution of 0.1 microgram. In addition, a detailed regimen is now required to obtain reliable measurement including static charge removal, buoyancy correction, use of reference filters, substitution weighing and very careful handling of filters by the operators running the test and performing the weighing. All the above mentioned steps are now becoming crucial to minimize the variability and improve repeatability / accuracy of the measurement. The PM limit in the US is now at 3 mg/mile for light duty vehicles and 0.01 g/bhp-hr for heavy duty engines. The PM limit will go down to 1 mg/mile in 2025 as the California Air Resources Board (CARB) announced. The CFR Part 1065 and Part 1066 include test procedures and performance requirements for PM measurement but the information is scattered all around in many different sections with numerous references which makes it very hard for the user to track without missing some important detail or requirement. Partial flow PM measurement is now allowed for heavy duty and light duty applications as an alternative to full flow / CVS systems. In addition to the test procedures which will be located in an easy to read and follow document, this document describes in details the components of partial flow systems with specifications and performance characteristics. It will also include best practices for PM measurement in partial flow mode for light duty and heavy duty applications.