SAE J3241_202312

This recommended practice establishes test procedures and best practices for PM measurements under partial flow conditions. PFDS PM testing and certification is primarily used in heavy duty applications as described in 40 CFR Part 1065 because full flow sampling systems with a dilution tunnel and CVS can be very bulky for large 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. PFDS does not require the use of a CVS sampling system or a full flow 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 flow dilution tunnel. This document describes the different components/specifications of LD and HD PFDS as well as the required quality checks necessary to ensure the integrity of the sampling system. It also addresses the many sampling options and calculations that are approved by the regulations. Correlation between partial and full flow systems will also be discussed. The conventional test method for particulate matter (PM) measurement of vehicle and engine exhaust is the gravimetric type where a small fraction of the total diluted exhaust from a full flow dilution tunnel connected to a constant volume sampler (CVS) is sampled over pre-weighed 47 mm PTFE filters at a temperature of 47 °C ± 5 °C. In a full flow dilution tunnel, all the exhaust flow from the engine flows through the tunnel where it is diluted with ambient air. To cover a wide range of vehicle and engine sizes, either single or double dilution systems are permitted for certification. The accuracy of the total PM mass of the test depends on many parameters but the most significant seems to be the amount of dilution and the magnitude of the net mass of PM collected on the filter. Partial flow systems, which are an alternative method to full flow CVS systems, include the additional complexity in that the sample ratio needs to be carefully controlled proportionally to the varying exhaust flow under transient conditions. Partial flow systems have an advantage of allowing more PM mass to be collected on the filter if the sample ratio is optimized correctly for vehicle or engine being tested. The PM limit in the U.S. is set at 3 mg/mile for light duty vehicles and 0.01 g/bhp-hr for heavy duty engines. The California Air Resources Board (CARB) approved a new PM limit of 1 mg/mile for LD applications starting in 2025 as part of the ACC II regulation. At 1 mg/mile, the net mass of PM on the filters in full flow systems will be approaching tunnel background levels making partial flow systems more desirable as the net mass of PM on the filter can be higher. Partial flow PM measurement also has the advantage of using much smaller, lower cost equipment without the need for a large CVS and full flow dilution tunnel system. The aim of this document is to organize the information in an easy to read-and-follow document, describing in detail the components of partial flow systems with specifications and performance characteristics. It also includes best practices for PM measurement in partial flow mode for light duty and heavy duty applications.