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Walter, Stefanie ; Dietrich, Markus ; Hagen, Gunter ; Moos, Ralf:
Simulative Modelling of the Location Dependent Soot Distribution in Gasoline Particle Filters and their Influence to the Soot Mass Determination by Radio Frequency and Differential Pressure Sensors.
2019
Veranstaltung: 23rd ETH-Conference on Combustion Generated Nanoparticles
, June 17-20, 2019
, Zurich, Switzerland.
(Veranstaltungsbeitrag: Kongress/Konferenz/Symposium/Tagung
,
Poster
)
Abstract
Introduction: Up to now, gasoline engines have been able to meet emission standards without particulate filters, as the combustion of petrol produces much smaller and lighter particles compared to diesel engines and only the particulate mass has been regulated. Due to more stringent emission limits and the regulation of particle numbers, gasoline particulate filter (GPF) have been serialized for many vehicles. To control the soot loading of DPFs in serial applications, often the pressure drop over the filter is evaluated. A further option for filter monitoring is a radio frequency-based approach that detects the deposited soot directly via its conductivity (RF sensor). However, a transfer of the existing knowledge to GPFs is limited due to changed soot properties and boundary conditions (e.g., different regeneration procedures). In order to be independent of complex measurements to improve the sensors for GPF applications, a simulation model was developed in this paper. This allows a deeper insight into the behavior of both sensor systems.
Methodology: In order to enable a realistic description of the entire filter system, the areas downstream and upstream of the GPF as well as the GPF itself were FE-modelled with COMSOL Multiphysics. Due to the fine structure of the filter channels it is not possible to simulate them in detail considering the computing time. For this reason, the GPF is treated as a homogeneous porous medium. The description of the location-dependent mass flow through the GPF is based on the pressure difference between inlet and outlet channels using the Darcy law, which considers the permeability of the filter walls and the deposited soot. In order to take into account the local distribution of the soot load, the trajectories of soot particles up to their entry into the GPF channels were simulated. It was shown that due to their low mass, particles follow the gas flow almost perfectly. Therefore, it was assumed in the following simulations that the deposited soot is proportional to the specific mass flow through the GPF.
Results: With the simulation model it is now possible to observe the soot distribution as well as the flow conditions in all operating modes. Figure 1 shows them at the end of a partial regeneration. The simulations clearly show that soot burn-off mainly takes place in a narrow front. This also has a considerable influence on the mass flow through the GPF. Both effects can possibly affect the accuracy of the RF sensor and the differential pressure system.