Variability phenomena

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The TCC III Collection

LES Working Group

Traditional scientific and engineering approaches have taken us far – efficiencies have been increased and pollutant release has been decreased. However, it is known that, in principle, combustion can be even more efficient and cleaner. We are now at a point where we must utilize simulation-based optimization strategies to find the best possible combustion strategies; combustion strategies that we cannot find without the targeted use of predictive simulation tools. And such tools are, unfortunately, not yet quite ready, especially when stochastic events need to be described.

A concerted experimental and numerical effort is undertaken to understand and describe the nature of stochastic processes in internal combustion engines. The overall goal is to develop physics-based computational tools for a more effective design of combustion engines of the future.

The nature and cause of cyclic variability in engines is not yet fully understood but their importance in developing advanced engine concepts keeps increasing. Giving automotive engineers design tools to predict cyclic variability, and more generally unsteady engine phenomena like warm-up or engine transients, can be viewed as a major challenge for a more effective design of combustion engines of the future. Experimental efforts alone are not sufficient to fully explore the many facets of cycle-to-cycle fluctuations, and therefore Computational Fluid Dynamics (CFD) simulations appear as the best candidate for providing such a design tool. A suitable candidate is the Large Eddy Simulation (LES) technique. Identifying and solving the underlying fundamental flow physics will be the key to success in understanding the stochastic nature of in-cylinder flow – this, in turn, is required to develop practical first-principles-based predictive computational LES design tools for robust and reliable industrial use.In this study, low-, medium-, and high-resolution LES approaches are being pursued in parallel to address these needs. High-resolution LES (minimal subgrid-scale modeling, approaching DNS; >108 cells per cylinder) is being used for physics discovery and model development/validation. Low-resolution LES (RANS-like resolution; currently 105-106 cells per cylinder) is being used for engineering development and applications. Medium-resolution LES (currently 106-107 cells per cylinder) bridges these two extremes. Mesh sizes and the number of cycles that are simulated will increase with time. Optical single-cylinder engines were specifically designed, built, and characterized for LES model development and validation. Optical, including laser-based, imaging tools are available to measure flow and scalar quantities with high spatial and temporal resolution. In particular, the use of high-speed imaging tools enables recording of the evolution of flow structures through a cycle and from cycle to cycle.The intent of this program is to create an interactive collaboration between the modeling and experimental efforts that will identify and execute the experiments and models needed to produce physically based LES models with sufficient fidelity for research and engineering applications.

Tang-Wei Kuo (GM), David Reuss (UM), Volker Sick (UM), Chris Rutland (UW-Madison), Dan Haworth (Penn State)

A comprehensive experimental data base from the TCC III engine is available for free download.

Data include PIV flow measurements, combustion imaging data for a wide range of equivalence ratios, and two fuels -propane and methane.

Schiffmann, P., Reuss, D. L. and Sick, V., TCC-IIII Data Repository. 2017, University of Michigan: Ann Arbor, MI, USA.

Schiffmann, P., Reuss, D. L. and Sick, V., TCCIII Motored Full View. 2017, University of Michigan.

Schiffmann, P., Reuss, D. L. and Sick, V., TCCIII Fired Full View. 2017, University of Michigan.

Schiffmann, P., Reuss, D. L. and Sick, V., TCCIII Fired Spark Plug Region. 2017, University of Michigan.

Schiffmann, P., Reuss, D. L. and Sick, V., "Empirical investigation of spark-ignited flame initiation cycle-to-cycle variability in a homogeneous charge reciprocating engine," International Journal of Engine Research (2017) 10.1177/1468087417720558

Check out also the following review that includes a lot of our work on cycle-to-cycle variability in direct-injection gasoline engines.

  • Fansler, T. D., Reuss, D. L., Sick, V. and Dahms, R. N., "Invited Review: Combustion instability in spray-guided stratified-charge engines: A review," International Journal of Engine Research 16 (3), 260-305 (2015) 10.1177/1468087414565675