Gasoline direct injection engine soot oxidation: fundamentals and determination of kinetic parameters

Current emissions legislation for road transport vehicles, including modern gasoline vehicle fleet limits the mass and the number of Particulate Matter (PM) emitted per kilometre. The introduction of a gasoline particulate filter (GPF) is expected to be necessary, as was the case for diesel vehicles, the traditionally recognised source of PM in transportation. Therefore, for the design of efficient GPFs and the regeneration strategies, soot oxidation characteristics in gasoline must be understood.
Extensive research has been carried out mainly to investigate the oxidation of diesel soot, however, in the most cases soot were collected on microfiber filters and the activation energy was calculated with the logarithm method assuming mass and oxygen reaction orders equal to one. Identified limitations that lead to inconsistent and inaccurate trends and results are presented in this paper. As a consequence, a novel methodology to accurately obtain the oxidation kinetic parameters for soot emitted from a Gasoline Direct Injection (GDI) engine has been developed and presented in this paper. The particles collected in a silicon carbide wall-flow particulate filter are directly exposed to oxidation conditions in a thermogravimetric analysis (TGA) without the use of microfiber filter.
The significance of more accurate and consistent calculations of soot oxidation kinetic parameters as a result of this methodology will aid modelling and experimental work of the aftertreatment systems and will lead in improving the GPF regeneration process in modern GDI vehicles. Avoiding high peak temperatures during regeneration and large thermal stress gradients and thus increasing the operating life of the filters is amongst the benefits can be seen.