Heavy-Duty Engines Exhaust Sub-23 nm Solid Particle Number Measurements

The measurement of solid particles down to 10 nm is being incorporated into global technical regulations (GTR). This study explores the measurement of solid particles below 23 nm by using both current and proposed particle number (PN) systems having different volatile particle remover (VPR) methodologies and condensation particle counter (CPC) cutoff diameters. The measurements were conducted in dynamometer test cells using ten diesel and eight natural gas (NG) engines that were going under development for a variety of global emission standards. The PN systems measured solid PN from more than 700 test cycles. The results from the preliminary campaign showed a 10-280% increase in PN emissions with the inclusion of particles below 23 nm. In the main campaign of this study, with the utilization of the current PN system and an add-on CPC to measure sub-23 nm particles, results showed the sub-23 nm fraction averaged between 23-58% and 19-51% of the total particles for diesel and NG engines, respectively. Data from one of the NG engines data showed that the sub-23 nm fraction increased with the use of a catalytic stripper (CS) due to a decrease in solid particles >23 nm. Data from the NG engine also suggested slightly lower counts of sub-23 nm particles from PN systems with a CS. Diesel measurements demonstrated that sub-23 nm particles can be mostly urea particles, and their generation is triggered by the combination of diesel exhaust fluid (DEF) injection rate and a selective catalytic reduction (SCR) outlet temperature of 250°C or greater. A few measurements using B20 fuel reported 5% and 8% higher solid particle counts for >23 nm and >sub-23 nm, respectively, compared to ultra-low sulfur diesel (ULSD) fuel. Particulate Matter (PM) data collected showed no correlation with PN as expected.