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Case Study

Investigation of Particle Emissions During Highly Transient Engine Operation

The internal combustion engine is still considered as the most widely used propulsion system in the mobility sector. Nevertheless, particulates emitted from this method pose a health threat to the human body. They can cause respiratory and cardiovascular diseases, and are therefore strictly limited. Since these limits will likely be even stricter in the future, the design of next-generation engines requires a detailed understanding of the relevant physical and chemical phenomena inside the engine.


Real Driving Emissions (RDE) measurements taken in real road traffic scenarios show that a large proportion of particulates emitted into the atmosphere during driving can be attributed to individual events. These events are characterized by highly transient engine operation and are strongly influenced by engine conditions, the vehicle’s driver, and environmental factors. To further reduce particulate emissions from the vehicle fleet in the future, it is necessary to focus on the emission peaks that occur.

Engineering Solution

To investigate sources for particle emissions during RDE relevant transient engine operation, we worked together with our experimental partners to apply a combined experimental and numerical approach. Provided with detailed boundary conditions of the transient event, we utilized Ansys CFX coupled with our moment-based soot modeling approach to perform 3D computational fluid dynamics (CFD) in-cylinder simulations of consecutive transient engine cycles and collect insights about underlying emission-promoting effects. The tools and models for remeshing, multiphase flows, and combustion, together with additional engine specific models implemented in Ansys CFX, were crucial for this investigation.


The simulation methodology using Ansys CFX allowed us exclusive access to the processes inside a state-of-the-art series combustion engine beyond the possibilities of any conventional measurement technique. We were able to identify several causes for increased soot particle emission in the investigated events. Further simulations suggest that a reduction potential by a factor of eight is possible for selected engine cycles.

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