A major focus of research at the CRF is advancing toward a predictive modeling capability for combustion processes associated with energy use and related national concerns. Reaching this goal requires an accurate yet concise representation of combustion chemistry, fluid flow, and various heat- and mass-transfer mechanisms within a computational model. Challenges confronting this undertaking include developing a sufficiently detailed understanding of each part of the combustion process and formulating and numerically implementing models that capture the essentials and yet are computationally affordable.
CRF research addresses many facets of these challenges. Needed chemical knowledge is developed through experimental, computational, and theoretical research performed in the Combustion Chemistry Department at the CRF. Within the reacting flows research program, laboratory studies of flames in various flows provide insights into the couplings among flow, combustion chemistry, and other relevant processes that inspire new modeling approaches and enable validation of models that are developed. The laboratory studies are highlighted by the use of state-of-the-art laser diagnostic and imaging techniques, including advancing these techniques, which has been a long-standing focus of CRF efforts. Direct Numerical Simulation (DNS), which is time advancement of the governing equations at full resolution with no physical model simplifications, likewise provides novel insights and is used to validate less costly models. Additionally, advancements in computational hardware and algorithmic capabilities are enabling simulations directly comparable to laboratory experiments.
All of these activities provide understanding and information needed for predictive modeling. The CRF effort to synthesize these and other inputs within a comprehensive modeling framework uses the Large Eddy Simulation (LES) approach. In LES, the smallest scales of fluid motion and flame structure are not resolved on the computational grid, so it is necessary to model unresolved processes. The LES activity is closely coordinated with the reacting flow experiments and with engine research at the CRF.
Reducing the scientific knowledge of combustion processes to a form usable within such a comprehensive modeling framework poses theoretical, mathematical, and computational challenges that are being addressed at the CRF, such as quantifying model uncertainty and reducing multistep chemical-kinetic mechanisms to simpler yet sufficiently accurate schemes. In some instances, these efforts are leading to fundamental advances whose impacts extend over a wide range of disciplines and applications. These and the other activities described here have spawned fruitful collaborations with research programs throughout Sandia National Laboratories and with the worldwide academic community on a diverse range of topics.