Slo-Mo Flow: Modeling Combustion to Pump Up Engine Efficiency

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BUILDING A BETTER ENGINE Modern engine design relies on a variety of simulation software programs, including Reaction Design's ENERGICO, that model not just the engine itself but also the chemical reactions taking place within the engine.

Pressure from the government to cut emissions of greenhouse gases and toxins has engine-makers taking a closer look at how new fuels combust

By Larry Greenemeier

Despite decades of fine-tuning, the average internal combustion engine still converts only about 20 percent of its fuel into power and spews a variety of emissions harmful to people and the environment.

With customers and government more interested than ever in energy efficiency and pollution, engine designers are feeling the heat. So engineers are turning to sophisticated simulation software to design and test ideas long before they build engine prototypes.

Low emissions, in particular, have become a key technical requirement for large industrial turbines, especially those that run continuously, says Joe Citeno, manager of combustion and emission technology at GE Energy, a division of General Electric Co. based in Greenville, S.C., and a maker of engines and turbines. The growing use of new and largely unproved biofuels, liquefied natural gas, synthetic gases derived from coal, and hydrogen complicates the design challenge, he says.

Better simulation software is helping engineers do a better job. Developing low-emission combustion engines requires "a fundamental understanding of combustion kinetics, or very fast chemistry, as well as fluid flow," Citeno says. "You need to understand the mixing that occurs in one of these gas turbines."

GE Energy uses several different software programs to create models of new engines. Computational fluid dynamics (CFD) software performs millions of calculations to simulate in 3-D the interaction of liquids and gases in the combustor (the part of the engine where fuel ignition takes place). Citeno says he and his team then use ENERGICO and CHEMKIN-PRO software from San Diego–based Reaction Design to simulate the complex chemical reactions, including the emissions they are likely to produce.

Before computer modeling and data crunching software were available, engineers relied on a slower, trial-and-error approach of designing, building and testing new engines, which did not allow them to sample the many different conditions that the software simulates.

The software that Reaction Design sells was first developed by Sandia National Laboratories in Albuquerque, N.M., as a way for engineers to see "phenomena that otherwise couldn't be observed," says chief executive Bernie Rosenthal. "You need to know how something will work before you invest in building it."

In 1997 the company bought the rights from Sandia for software that would become CHEMKIN. (ENERGICO debuted in September.) NASA uses Reaction Design's software to simulate the operation of jet engines using biofuels and other alternative fuels, whereas the U.S. Department of Energy uses the software as part of its Freedom-CAR initiative (kicked off in 2002) to promote the development of hydrogen for fuel-cells as a primary energy source for cars and trucks.

The simulation software cuts in half the time it takes to model the reactions that turn fuel into power, Citeno says, freeing up "the design engineer for the more important mental task of understanding what's physically happening inside the combustor."

http://www.scientificamerican.com/article....gine-combustion

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