Sandia Researchers Are Creating Benchmarks for Combustion Strategy

Two Sandia National Laboratories scientists at the Combustion Research Facility are using NERSC resources to create a benchmark data set for modeling combustion physics relevant to the next generation of internal combustion engines, an undertaking that will benefit the development of efficient engines running on alternative fuels.

Ed Richardson and Jackie Chen will develop three-dimensional simulations of combustion representing the stratified conditions that may be useful when developing engines for anticipated fuels and improved fuel consumption. Despite the continuing development of strategies to improve combustion performance, there is still a need to create a benchmark set of fundamental simulation data for understanding this combustion regime.

Complementary to experimental measurements, direct numerical simulation is a valuable tool for isolating and revealing the interactions among reactants and turbulent mixing in the stratified combustion regime, Richardson said.

“Probing the smallest scales of highly turbulent flames tests our computational limits. With the NERSC resources, we are gaining highly detailed data that currently is unobtainable experimentally.”

Modern combustion devices have been highly optimized for the range of fossil fuels currently available. However, the proposed use of hydrogen, bio-matter or synthetic fuels requires different conditions for effective and clean burning. Stratified combustion is a leading strategy for control of the combustion process in applications ranging from internal combustion engines to the largest power plants.

In stratified combustion, the fuel and the oxidizer are not completely mixed or separated prior to combustion. As a result, conventional combustion models that assume a premixed or non-premixed mode don’t apply. Models for partially pre-mixed modes still require considerable development and validation.

Because of the high computational expense, Richardson and Chen are looking specifically at laboratory-scale flows of several centimeters in scale, which exhibit underlying turbulence–flame interactions also found in combustion engines. The micro-scale mixing and reaction coupling are uniquely captured in high-fidelity direct simulations which resolve all turbulence and flame scales. The researchers’ goal is to determine the combustion efficiency and emissions of compounds, such as carbon monoxide and nitrogen monoxide, that result from the stratified distribution of fuel and oxidizer.

“The flame structures and burning velocity under stratified conditions will be compared to the equivalent uniformly pre-mixed case,” Richardson. “The benchmark simulation data resulting from this study will provide a unique testbed for predictive engineering models in the challenging partially premixed regime.”

The scientists are building on previous research for the current study. A three-dimensional, direct numerical simulation they already have constructed includes a reduced methane and nitrogen chemistry component developed by Tianfeng Lu and C.K. Law at Princeton University. The simulation, a stratified turbulent Bunsen flame, allows for intense turbulence to interact with the flame in a computationally efficient manner.

Richardson and Chen will carry out further calculations by setting different parameters, such as the range of fuel-air ratios, in order to analyze the flame regime.

The researchers have enlisted the help of Kwan-Lui Ma and Hongfeng Yu at the SciDAC Institute of Ultra-Scale Visualization to render their calculations into images for better data analyses.