INCITE ignites combustion simulation
Posted April 16, 2007
 A simulated planar CO/H2 jet flame Click image to enlarge |
Next time you’re presented with a birthday cake, try blowing gently on the candles before giving the big, out-they-all-go puff.
If you do it right, they should burn more intensely. But blow too hard, of course, and the candles go out.
That light puff of air is a form of turbulent mixing. Turbulent mixing produces more power from combustion, but – like blowing hard on a candle – too much causes problems, says Jacqueline Chen, a researcher at Sandia National Laboratory’s Livermore, Calif., site. Sandia is a Department of Energy facility.
“Key chemical reaction rates can’t keep up with the mixing rate, and local quenching occurs” – pockets where fuel remains unburned, Chen says. “If it’s pervasive enough, total blowout may occur” – a bad thing if it happens in an airplane engine. Even local quenching cuts efficiency and increases pollution as unburned fuel goes out the exhaust.
Designers are turning to turbulent mixing and combustion at lower temperatures as they strive to make more efficient and cleaner-burning engines. That’s “pushing combustion to the ragged edge,” Chen says, where flames are nearly unsupportable and combustion occurs by other means, such as autoignition – ignition without an external source like a flame or spark. Combustion at these limits is poorly understood.
