Simulation dieselmotorischer Verbrennung
Modeling and Simulation of Compression Ignition Engines
A large fraction of today’s energy consumption is attributable to the transportation sector, which is expected to grow further in the foreseeable future. While substantial effort is being directed towards electrified propulsion systems, internal combustion engines are expected to provide the majority of this transportation energy demand. Therefore, further development of internal combustion engines has a huge potential to reduce environmental impact through emission reduction.
Compression Ignition (CI) engines achieve high thermal efficiencies and thus emit less carbon dioxide compared to Spark Ignition (SI) engines. However, current CI engines suffer from high engine-out pollutant emissions and require expensive exhaust gas after-treatment. Optimizing the combustion process or engine design is extremely challenging and requires detailed fundamental understanding of this multi-scale and multi-physics problem. Hence, high fidelity numerical models are developed at the ITV that provide detailed insight and help gaining a deeper understanding of combustion and pollutant formation processes.
High-Fidelity Spray Simulations
Compression ignition engine combustion involves a wide range of time and length scales that cannot be fully resolved in a single simulation even on current supercomputers. Hence, a three step simulation approach has been developed at the ITV, which decomposes the physical process into three one-way coupled simulations. This simulation framework consists of high-fidelity simulations of the nozzle internal flow, the primary breakup in the vicinity of the nozzle orifice, and reactive spray simulations further downstream.
Direct Numerical Simulation of a scaled-up Diesel injector
The nozzle internal flow is computed using a Large-Eddy Simulation (LES) that resolves the actual nozzle geometry and accounts for cavitation effects and hydraulic flip. The flow field at the nozzle orifice is used as a boundary condition in an interface resolving Direct Numerical Simulation (DNS) of the fuel jet disintegration. Statistics of the liquid structures are recorded and used as initial conditions for an LES of the entire combustion chamber that employs a Lagrangian spray model combined with turbulent combustion and soot models.
Video: Dodecane spray flame (ECN - Spray A)
Top) High-speed schlieren measurements kindly provided by 
Sandia National Laboratories. Reference: S.A. Skeen, J. Manin, L.M. Pickett: Simultaneous Formaldehyde PLIF and High-Speed Schlieren Imaging for Visualization in High-Pressure Spray Flames (Proceedings of the Combustion Institute, Volume 35, Issue 3, 2015, Pages 3167-3174, DOI for Paper)
Bottom) Large-Eddy Simulation using CIAO (in-house code). Visualization of liquid fuel droplets (blue) and temperature iso-contour of 1800 K (red).
Alternative Fuels
Using alternative fuels, which are synthesized using biomass or renewable energy, in internal combustion engines have a huge potential in reducing green-house gas and pollutant emissions. At the ITV, detailed numerical models are developed for studying the effect of chemical and physical fuel properties on the in-cylinder combustion and pollutant formation processes.
Large-Eddy Simulation of a compression ignition engine operated with a novel bio fuel (Dibutyl ether). Visualization of liquid fuel droplets (dark green), fuel vapor iso-contour (light green), and carbon monoxide iso-contour (red).
Engine Combustion Network
The Engine Combustion Network (ECN) is an international collaboration among experimental and computational researchers in engine combustion. For more information, please visit https://ecn.sandia.gov.