Held, Florian (2024)
A 3D Computational Study of Soot Formation in Gasoline Direct-Injection Engines during Transient Operation.
Technische Universität Darmstadt
doi: 10.26083/tuprints-00026970
Dissertation, Erstveröffentlichung, Verlagsversion

Kurzbeschreibung (Abstract)

Particulate matter has harmful effects on the environment and human health. A significant share of anthropogenic sources of particulate matter originate from the transport sector. For this reason, legal limits are in place worldwide to limit particulate matter emissions. Since 2017, part of the EU legislation includes testing of real driving emissions (RDE), i.e., emissions measured during real-world driving. Compliance with the limits according to these new standards cannot only be achieved by optimizing particulate emissions during stationary engine operation but also requires consideration of particulate emissions during highly dynamic engine operation. Hence, the focus of current research and development is increasingly shifting toward highly dynamic transient engine scenarios. While 3D Computational Fluid Dynamics (CFD) is an already established design tool for engine development, especially for steady-state operating points, it is rarely or never used for investigating transient engine operation. On the one hand, this is due to the lack of availability of suited models for analyzing the relevant phenomena along the entire engine cause-and-effect chain. On the other hand, the boundary conditions required for 3D-CFD are usually not characterized in sufficient detail. Added to this is the enormously high computational effort required for the calculation of consecutive engine cycles.

Nevertheless, the available methods and models have continuously evolved in recent years. Together with the continuous increase of available computational resources, 3D-CFD simulation of transient engine scenarios is becoming more and more feasible. This paper will therefore demonstrate how, with the currently available models and resources, 3D-CFD simulation can be utilized to analyze particulate emissions in transient engine scenarios. For this purpose, a complete framework for the simulation of soot particle emissions in a gasoline direct-injection engine is presented. The framework, consisting of a number of engine-specific submodels, is extended by a detailed QMOM (Quadrature Method of Moments) soot model to ensure an accurate representation of the particle formation chain. The framework is first evaluated at the steady-state operating point of an optically accessible research engine and on the basis of available soot luminescence and extinction measurements. In a next step, the framework is extended for the simulation of consecutive multi-cycle simulations and the application in transient engine scenarios. The primary emphasis is placed on the accurate characterization of the transient scenario in the virtual engine environment. Parts of this extension are the introduction of a methodology for averaging data from multiple test bench realizations, a modified 1D gas exchange analysis for calculating crank angle resolved boundary conditions and a parallelization strategy for the efficient calculation of consecutive engine cycles. Finally, the extended framework is applied to an RDE-relevant and soot emission-critical transient driving scenario to study particle formation. A cause-and-effect chain analysis on 30 consecutive engine cycles is performed to identify the root causes of increased particulate emissions. The novel insights gained are then used to identify optimization potential. In summary, this thesis presents a comprehensive framework for the investigation of soot particle formation in transient engine operation of gasoline direct-injection engines. Combined with experimental studies, the framework is suitable as a diagnostic tool for identifying and analyzing the root causes of increased soot particle generation and deriving optimization potentials of individual scenarios.

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