AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Detailed Characterization of Particulate Matter (PM) Emitted by Lean-Burn Gasoline Direct Injection (GDI) Engine
JACQUELINE WILSON, Alla Zelenyuk, Mark Stewart, George Muntean, John Storey, Vitaly Prikhodko, Samuel Lewis, Mary Eibl, Pacific Northwest National Laboratory
Abstract Number: 376 Working Group: Combustion
Abstract Limited fossil fuel resources and upcoming U.S. fuel economy and emission standards are major challenges in current engine development. We present the results of a study in which we characterized the properties of PM emissions generated by a 2.0L BMW lean-burn turbocharged GDI engine operated under different combustion strategies (lean homogeneous, lean stratified, stoichiometric and fuel rich) before and after a three-way catalyst.
In addition to PM number concentrations and size distributions, we characterized the size, mass, composition and effective density of individual exhaust particles emitted under ~20 engine-operating conditions. These measurements were used to calculate fractal dimension, average diameter of primary spherules, number of spherules, void fraction and dynamic shape factors as function of particle size.
We find that most of the particles produced by the GDI engine are fractal agglomerates containing small amounts of oxygenated organics and PAHs. The fraction of Ca-containing particles, originating from the detergent additives to lubricating oil, varies with operating conditions. These are compact particles with vacuum aerodynamic diameters above 200 nm.
Lean stratified operation yielded the most diesel-like PM. The vast majority of these particles are fractal soot agglomerates with a fractal dimension of 2.18 and are composed of primary spherules with an average diameter of 22 nm. The void fraction of these particles increases from 20% for 50 nm soot particles to nearly 80% for particles larger than 200 nm.
Under stoichiometric operation PM number concentrations decrease by an order of magnitude compared to lean stratified condition. While fractal soot particles emitted under either stoichiometric or lean stratified operations are very similar, the stoichiometric PM contains a higher fraction of Ca-dominated non-fractal particles. Comparison between the characteristics of PM before and after a three-way catalyst provides evidence for the removal of the nuclei mode by the catalyst.