Capture of Automotive Particulate Matter in Open Substrates

Abstract

Open filters (with low pressure drop) have potential for energy-efficient reduction of particulate matter (PM) from engines. In the work reported here, the capture efficiency of PM in open substrates has been investigated using PM from a real engine under various flow conditions and sampling settings. The observed capture efficiency (CE) confirmed the expected trends that increased residence time and increased temperature give better CE. However, the volatile content (assumed to be hydrocarbons, HC) can increase the apparent CE due to rapid evaporation and/or shrinkage of the PM. In order to quantify these effects, a conceptual model has been implemented that can be used as an in situ analyzer of the PM properties. The results show how exhaust treatment (heating and/or dilution) changes the characteristics of the PM. These properties affect CE and can be used for subsequent catalyst optimization. In addition, the method developed here was used to analyze nucleation-mode PM from a special fuel injection strategy. The results revealed that these particles were mainly nonvolatiles, demonstrating the usefulness of this characterization methodology. Furthermore, an equation for diffusion losses in the rotary dilutor for the DMS500 is presented.

Characterization of Particulate Matter and the Capture Efficiency in Open Metal Substrates

“…Besides substrate length and velocity, the temperature was varied. An inert monolith was placed upstream to minimize any effect of condensed hydrocarbons [4]. A schematic picture and a photo is displayed in Fig.…”

“…The DOC removes emissions of CO and hydrocarbons (HC) as well as oxidizes NO to NO 2 , which is beneficial for the soot oxidation in the downstream DPF. Furthermore, it effectively removes volatile components from the PM [4] and thus changes the PM characteristics in terms of both composition and size. The pressure drop over the DPF depends on the particle size distribution (PSD) which determines the ratio of ''deep filtration'' (deposition inside the pores) and ''soot cake filtration'' (deposition on the channel walls) [5].…”

“…In a previous study, we have also shown how the HC part can be isolated from the solid fraction [4]. In this work we have thus placed an open (inert) monolith upstream the substrate in order to remove the effect of volatile components and to assess the capture of the solid part of the PM.…”

Modelling of particulate matter transformations and capture efficiency

“…The PM was measured using a DMS500 (fast particulate spectrometer from combustion) using a primary dilution factor of 4 and a secondary dilution factor (rotating disc dilution) of 16. The PM losses due to deposition in the sampling pipes and to the dilution in the DMS500 were compensated for, so that all PSDs used are independent of such experimental influences . The measured (apparent) size‐resolved particle CE is defined as …”

“…The PSD measured by the DMS500 generated 38 signals (from 4 to 1000 nm), where the signal was different from zero for approximately 20 size bins in the present experiment. From the analysis of many measurements, the uncertainty could also be estimated …”