A PN-Measurement System for Small Engine Applications

Particulates are among the most harmful emission components of internal combustion engines (ICE)). Thus, emission limits have been widely introduced,
e.g., for light- and heavy-duty vehicles. Although there are still engine applications without particulate limitations, the measurement of particulate mass (PM) and particulate number (PN) emissions is therefore of special interest for the development and operation of ICE. For this purpose, a measurement system for PN consisting of a custom-built sample conditioning and dilution system, and a TSI 3790-A10 condensation particle counter (CPC) as particle number counter (PNC) was designed and built. In this work, we present the conditioning and dilution system, the operational parameters, and results from the particle concentration reduction factor (PCRF) calibration. The sampling system was developed in accordance with the current global technical regulations (GTR15) [2] and consists of a heated sampling probe, up to three dilution stages and a catalytic stripper for volatile particle removal (VPR). In order to be able to cover a variety of engines and provide the wide measurement range of eleven orders of magnitude, further dilution stages were implemented in the system. With the help of a variable mixing chamber dilution and an additional ejector diluter, PCRFs between 1:200 and 1:5000 can be used. The primary dilution stage consists of an ejector-diluter calibrated to a dilution ratio of 1:23,4 at 20 °C. The catalytic stripper arranged in the system consists of an oxidation catalyst and a sulphate trap. A PCRF calibration was done using a Jing miniCAST [3] as a particle source, producing a polydisperse combustion aerosol which is passed through a dilution bridge, a VPR and a differential mobility analyzer (DMA). The DMA allows to select monodisperse modes according to mobility diameters of the particles. The PCRF was measured by a reference CPC (TSI 3775). Calibrations were done at 15, 23, 41, 60 and 100 nm for the eight different dilutions, resulting in 40 measurements.