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The adjective cool is relative: the cool flame burns at less than 1,150 degrees Kelvin (1,610 degrees Fahrenheit), about half the typical flame burning temperature of 2,200 degrees Kelvin. While cool flames were first observed in the early 1800s, their properties and usefulness for diesel engine design have only recently been investigated.
"We're trying to quantify the influence of cool flames in stratified turbulent jets during the ignition and flame stabilization processes. The insights gleaned will contribute to more efficient, cleaner burning engines," Chen said. "Our holy grail is to understand the physics of turbulent mixing coupled with high-pressure ignition chemistry, to aid in developing predictive computational fluid dynamics models that can be used to optimize engine design."
Team - Research - Autoignition - Ignition - Fuel
The team's research has shown that during autoignition (the spontaneous ignition of injected fuel in a combustion engine), cool flames accelerate the formation of ignition kernels -- tiny localized sites of high temperature that seed a fully burning flame -- in fuel-lean regions. The work was performed at Sandia's Combustion Research Facility using Direct Numerical Simulations, a powerful numerical experiment that resolves all turbulence scales, and was published in the Proceedings of the Combustion Institute with Krisman as the lead author. The work was supported by the Department of Energy's (DOE's) Office of Basic Energy Sciences.
Borghesi further extended the cool flame study by performing a three-dimensional study on n-dodecane, a diesel surrogate fuel that has been the recent focus of Sandia's Engine Combustion Network on spray combustion in diesels (the study that Krisman authored with dimethyl ether, a simpler fuel, was in two dimensions). Borghesi's paper is pending publication. Taken together, both Krisman's and Borghesi's papers will form a comprehensive study of low-temperature chemistry in autoignitive flames at different stages of ignition.
Details - Engine
The details of starting an engine are often taken for granted. Unlike a...
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