Very low particle matter mass measurements from light-duty vehicles

Abstract

Recently, there are discussions about whether current sampling and measurement practices for the regulated gravimetric PM measurement are sufficiently accurate in quantifying PM at the proposed 3 and 1 mg/mi emission standards for light-duty vehicles. In this study, a series of modifications were made to the existing gravimetric PM measurement method, aiming to preserve the integrity of the method while increasing the robustness and decreasing the testing variability. The experiments were conducted with a Higher (~2 mg/mile) and a Lower (0.1-0.2 mg/mile) PM Source Vehicle over the Federal Test Procedure (FTP) and US06 cycles, providing PM emissions with various solid/semi-volatile compositions and size distributions. The results showed the suggested modifications, i.e., increased filter face velocities (from 100 to 150 cm/s) and combined filters (single filter vs. 3/4 filters), could increase the collected filter mass without introducing statistically significant differences in the measured PM mass emission rates. No statistically significant improvements were seen in the measurement variability with the Higher PM Source Vehicle. For the Lower PM Source Vehicle; however, the 4-phase cumulative filter showed a statistically significant reduction in PM mass measurement variability, while not impacting the measured PM mass emissions, but these improvements must be weighed against the increased testing costs/time required for the longer test time.

Evaluation of Partial Flow Dilution Systems for Very Low PM Mass Measurements

“…The two CVS PM probes (A and B) both agreed well for the FFV = 100 cm/s (within 3.8%) and FFV = 130 cm/s tests (within 2.9%) and did not show statistically significant differences. The lack of differences in averages for the CVS PM measurements suggests the single filter combined method is in good agreement with the individual filter method by phase [15]. The PFD probes showed mixed comparisons relative to the CVS_A probe.…”

“…[19]. Xue et al reported greater sensitivity of gravimetric method to more aggressive US06 cycle than FTP cycle [15]. It is speculated the PM mass on this first test may have been influenced by PM desorption from the tailpipe and transfer line.…”

“…The results of the PFD to CVS evaluation can be compared to those of previous studies. Using a higher PM source vehicle, with an FTP emission rate of~2.0 mg/mi, Xue et al [15] showed a low relative error rate of − 2.7 and − 5.9% between mean emissions for a PFD (DF = 5 FFV = 150) and a CVS system. Foote et al compared two PFDs with CVS PM emission measurements for two gasoline vehicles with a range of PM emissions from 0.1 to 10.0 mg/mile [1].…”

“…Their results also showed that the PFDs had promise for low-level measurements for a wide range of engine sizes and applications. More recently, a comprehensive study of PM mass measurements from LDVs was conducted as part of the Coordinating Research Council's (CRC's) E-99 project to evaluate increasing filter face velocity (FFV) (from 100 to 175), reducing dilution ratio (DR) (from 7 to 3), using cumulative vs. individual filters, and comparing 3-and 4-bag federal test procedure (FTP) tests [15]. A commercially available partial flow diluter (PFD) was also evaluated in that study.…”

A comparison of a mini-PEMS and a 1065 compliant PEMS for on-road gaseous and particulate emissions from a light duty diesel truck

“…It is also worthwhile to evaluate the PM differences in the context of the future 2025 California LEVIII PM emissions standard of 1 mg/mi, as there is considerable interest in how effective gravimetric and other methodologies are in quantifying PM emissions at levels below 1 mg/mi (Xue et al, 2018;Sardar et al, 2015;Swanson et al, 2018). If the comparisons were based on the future 1.0 mg/mi PM standard, the average differences reduce to −2% to +26% for the AVL total PM mass measurements [StdDif_% = (NCEM-[MSS + GFM])/1.0] and to −1% to 43% for the AVL MSS soot measurements.…”