Evolution of In-Cylinder Diesel Engine Soot and Emission Characteristics Investigated with Online Aerosol Mass Spectrometry

Abstract

To design diesel engines with low environmental impact, it is important to link health and climate-relevant soot (black carbon) emission characteristics to specific combustion conditions. The in-cylinder evolution of soot properties over the combustion cycle and as a function of exhaust gas recirculation (EGR) was investigated in a modern heavy-duty diesel engine. A novel combination of a fast gas-sampling valve and a soot particle aerosol mass spectrometer (SP-AMS) enabled online measurements of the in-cylinder soot chemistry. The results show that EGR reduced the soot formation rate. However, the late cycle soot oxidation rate (soot removal) was reduced even more, and the net effect was increased soot emissions. EGR resulted in an accumulation of polycyclic aromatic hydrocarbons (PAHs) during combustion, and led to increased PAH emissions. We show that mass spectral and optical signatures of the in-cylinder soot and associated low volatility organics change dramatically from the soot formation dominated phase to the soot oxidation dominated phase. These signatures include a class of fullerene carbon clusters that we hypothesize represent less graphitized, C-containing fullerenic (high tortuosity or curved) soot nanostructures arising from decreased combustion temperatures and increased premixing of air and fuel with EGR. Altered soot properties are of key importance when designing emission control strategies such as diesel particulate filters and when introducing novel biofuels.

Investigation of late-cycle soot oxidation using laser extinction and in-cylinder gas sampling at varying inlet oxygen concentrations in diesel engines

“…This volume corresponds to approximately 0.05% of the total cylinder volume. With this flow rate, the minimum step-by-step resolution for the sampling timing can be less than 3.5 crank angle degrees CAD at high in-cylinder pressures [21]. concentration.…”

Formation of secondary organic aerosol coating on black carbon particles near vehicular emissions

“…Note that rBC-rich particles were composed of more oxygenated organic fragments compared to the HOArich factor (Fig. 3a and b), likely due to the presence of refractory ion fragments (i.e., CO + and CO + 2 ) that originated from oxygenated functionalities on the soot surface and in the soot nanostructure (Corbin et al, 2014;Malmborg et al, 2017).…”

Investigation of the absorption Ångström exponent and its relation to physicochemical properties for mini-CAST soot

“…Only parent peak PAHs with mass-to-charge ratios (m/z; Th) in the range of m/z 202-300 Th were included in the PAH analysis. The m/z of the included PAHs and the final quantification of particle bound PAH mass is according to a modified version of that described by Herring et al (2015); Malmborg et al (2017) and is detailed in section S2 in the SI. Refractory carbon cluster ion fragments originating from the soot core were measured between m/z of 12 and 708 Th (C1¡C59).…”