INCITE ignites combustion simulation

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The results question some basic assumptions about combustion.  The researchers found:

• The simulation revealed that how reactive molecules mix in combustion is different from how non-reactive molecules mix.  The process depends not just on the balance between how turbulence moves molecules and how those molecules diffuse on their own, but also on how the molecules react.  That was surprising, because scientists usually have assumed that the time it takes to mix is the same for all kinds of molecules and corresponds to how turbulence changes over time.  The simulation also found this dependence was present even at high rates of turbulence.
• Greater turbulence causes greater intermittency – small fluctuations in which combustion stops and restarts – and a longer lag time for reignition.
• Locally extinguished portions of the flame most often are reignited when turbulence folds burning flame sections onto non-burning ones, rather than by the slower process of smooth, nonturbulent flame propagation along the edges of the extinction holes.

This fundamental understanding could lead to new, more accurate combustion models and better engine designs, says Evatt Hawkes, a Sandia postdoctoral researcher who worked on the simulation.  “The biggest impact will be felt if this will translate into a model that can be used at an engineering level,” he adds.

The researchers continue to analyze mountains of data the simulation generated, seeking clues to local extinction and reignition. They’re also focusing on fundamentals of the turbulence-chemistry interaction.  Because of the amount and complexity of the data, the researchers are working closely with computer scientists to:

• Automatically find and focus on interesting details in the simulation
• Analyze events in the simulation across multiple scales of time and space – from billionths of a second to minutes and from atoms to whole flames
• Create images to understand the simulation results
• Manage the huge amounts of data these simulations produce.

It couldn’t be done without INCITE and DOE’s world-class computers, says Ramanan Sankaran, another Sandia postdoctoral researcher on the team.

“Leadership computing is enabling this kind of science,” Sankaran says.

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