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Light-duty vehicle emission measurement test protocols defined in the Code of Federal Regulation (40 CFR Part 1066) allow sampling particulate matter (PM) of all phases of Federal Test Procedure (FTP-75) on a single PM sampling filter by means of flow-weighted sampling in order to increase PM mass loaded on the filter. A technical challenge is imposed especially for partial flow dilution systems (PFDS) to maintain a precise dilution ratio (DR) over such a wide sample flow range due to the subtraction flow determination method of dilution air and diluted exhaust flows, because the flow difference is critical at high DR conditions. In this study, an improved flow weighting concept is applied to a PFDS by installing a bypass line with a flow controller in parallel with the PM sampling filter in order to improve DR accuracy during flow-weighted sampling.

The United States Environmental Protection Agency (EPA) has finalized a reporting rule for the Greenhouse Gases (GHGs) emissions including Nitrous Oxide (N₂O) from all sectors of the economy. In addition, EPA and the National Highway Traffic Safety Administration (NHTSA) have been working together on developing a National Program of harmonized regulations to reduce GHGs emissions and improve fuel economy of light-duty vehicles (LDV). As a consequence, the limiting value for N₂O emission from LDV is set to 0.01 g/mile. Considering this regulatory limit of N₂O emission from LDV, if the exhaust gas is diluted and stored in a sample storage bag, the concentration of N₂O becomes very low which requires a highly sensitive analyzer for accurate measurement. In the previous study, an instrument based on Quantum Cascade Mid-IR Laser (QCL-Mid IR) Spectroscopy has been developed for measuring ultra-low level of N₂O in automobile exhaust gas sampled in a sample storage bag.

Automobile Particulate Matter (PM) Emission regulation requires gravimetric determination of PM collected on filter media under simulated driving conditions in the laboratory traditionally in a full flow Constant Volume Sampling (CVS) dilution tunnel. There have been discussions about whether current sampling and measurement practices are sufficiently accurate in quantifying PM at the upcoming 1mg/mi PM emissions standards of CARB LEV III. Sampling technique alternative to a CVS such as a Partial Flow Dilution (PFD) system has already been developed and is acceptable for certification testing. Lower dilution ratios and higher filter face velocity (FFV) are options to load traceable amount of PM on filter in case of light duty vehicle (LDV) testing. On the other hand higher dilution ratios and lower FFV are required for heavy duty engine (HDE) testing to keep the PM loaded on filter <400μg.