Comparative Analysis on the Effects of Diesel Particulate Filter and Selective Catalytic Reduction Systems on a Wide Spectrum of Chemical Species Emissions

Abstract

Two methods, diesel particulate filter (DPF) and selective catalytic reduction (SCR) systems,for controlling diesel emissions have become widely used, either independently or together, for meeting increasingly stringent emissions regulations worldwide. Each of these systems is designed for the reduction of primary pollutant emissions including particulate matter (PM) for DPF and nitrogen oxides (NOx) for SCR. However, there have been growing concerns regarding the secondary reactions that these aftertreatment systems may promote, involving unregulated species emissions. This study was performed to gain an understanding of the effects that these aftertreatment systems may have on the emission levels of a wide spectrum of chemical species found in diesel engine exhaust. Samples were extracted using a source dilution sampling system designed to collect exhaust samples representative of real-world emissions. Testing was conducted on a heavy-duty diesel engine with no aftertreatment devices to establish a baseline measurement and also on the same engine equipped first with a DPF system and then a SCR system. Each of the samples was analyzed for a wide variety of chemical species, including elemental and organic carbon, metals, ions, n-alkanes, aldehydes, and polycyclic aromatic hydrocarbons, in addition to the primary pollutants, due to the potential risks they pose to the environment and public health. The results show that the DPF and SCR systems were capable of substantially reducing PM and NOx emissions, respectively. Further, each of the systems significantly reduced the emission levels of the unregulated chemical species, while the notable formation of new chemical species was not observed. It is expected that a combination of the two systems in some future engine applications would reduce both primary and secondary emissions significantly.

Emissions of polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs from heavy-duty diesel vehicles with DPF and SCR

“…The vehicles with after-treatment significantly reduced particle-phase PAHs by greater than 99%, irrespective of the driving cycles. The consistently highly removal efficiency by the after-treatments has been also reported in many recent studies (Liu et al, 2008;Liu et al, 2010;Khalek et al, 2011), suggesting >90% reduction of the measured PAHs. The vehicles with after-treatment were more efficient in reducing the gas-phase PAHs during cruise and during the UDDS cycle than during idling operation.…”

“…Studies have consistently confirmed the significant reduction of particle-associated PAHs by the DPFs via filtration (Heeb et al, 2008;Liu et al, 2008). It has been postulated that the DPF act as a reactor, forcing an extended exposure of the gaseous pollutants to the trapped soot particles (Heeb et al, 2008) which may change the pathway of gas-to-particle formation of the semivolatile compounds.…”

“…Total PM in the exhaust was significantly reduced by the after-treatment (Heeb et al, 2008;Liu et al, 2008;Herner et al, 2009;Khalek et al, 2011). The PM emitted from the baseline vehicle mainly consisted of carbonaceous particles, accounting for more than 99% of total PM (Herner et al, 2011).…”

Review of Recent Advances in Detection of Organic Markers in Fine Particulate Matter and Their Use for Source Apportionment

“…63 The nature of diesel profiles may change as new engine emission control technologies are implemented. 64 Benz[a]anthracene-7, 12-dione has been shown to be a potential particulate tracer for natural gas combustion particles, showing fairly high emissions rates from consumer-owned natural gas-fired home appliances. 65 There is no remarkable difference in the emissions among different kind of coals, but the combustion conditions play a significant role in PAH emission composition and concentration.…”

Analytical Methodologies for the Control of Particle-Phase Polycyclic Aromatic Compounds from Diesel Engine Exhaust

“…The majority of experiments are performed on chassis dynamometers under predetermined engine load; a heated hose transfers the exhaust from the tailpipe to full flow exhaust dilution tunnels, and therefore, the exhaust gases are collected at low temperature after being mixed and homogenised with the ambient air (with moderate dilution ratios ranging from 6 to 14) in the dilution tunnel, which is connected to a constant volume sampling system (CVS technique) [45,46]. Chassis dynamometers can also be equipped with dilution systems such as critical-flow Venturi dilution tunnels [47], ejection dilutors [48], or rotating disk diluters [49], but undiluted exhaust can also be directly collected through a sampling probe inserted inside the tailpipe, which is a less conventional method [50].…”