Gas-diesel engine combo under development
It may be hard to believe, but the beloved gasoline engine that powers more than 200 million cars across America every day didn’t get its status because it’s the most efficient engine.
Diesel engines can be more than twice as efficient, but they spew soot and pollutants into the air.
Could researchers at the U.S. Department of Energy’s Argonne National Laboratory engineer a union between the two — combining the best of both?
Steve Ciatti, a mechanical engineer at Argonne, is heading a team to explore the possibilities of a gasoline‐diesel engine. The result, so far, is cleaner than a diesel engine and almost twice as efficient as a typical gasoline‐powered engine. (To see how the engine works, go to http://www.anl.gov/Media_Center/News/2011/news110504_gas-diesel.html.)
The basic designs for both kinds of engines actually date back to the 19th century.
German engineer Nikolaus Otto is credited with the gasoline‐fueled four‐stroke design still used today, but Rudolf Diesel noticed the inefficiency of the engine and came up with a design of his own in 1893. The problem is that while diesel engines are more efficient, their emissions are noxious — full of soot and smog‐forming nitrogen oxides, or NOX gases.
Gasoline engines are cleaner, but a typical gas engine is only about 20 percent efficient—that is, only 20 percent of the energy in the fuel actually moves the car, while 80 percent is lost to friction, noise, engine functions or goes out as heat in the exhaust. Many diesel engines reach 40 percent efficiency and higher.
Today, the United States has more stringent emissions requirements than anywhere else in the world. “In fact, as of 2007, in some parts of the country the air coming out of a car is cleaner than the air that went in,” Ciatti said, and engineers haven’t been able to get diesel emissions low enough to meet those standards.
Ciatti and colleagues wanted to clean up diesel’s dirty exhaust, but keep the high efficiency and better gas mileage. To do this, they headed to the dynamometer lab at Argonne’s Transportation Technology R&D Center.
The dynamometer is a machine built to test engine performance. Essentially, it’s just an electric motor to provide resistance to fool the engine into thinking it has a car attached.
Dynamometer test cells can be heavily instrumented and accurately controlled, significantly improving data quality.
“If you’re trying to test out a new engine, the last thing you want to do is put it in a car,” Ciatti explained. “An entire car system introduces all sorts of variables, and you can’t get a truly accurate comparison between engines. What you really want to start with is a dynamometer.”
Combine a dynamometer with the engine you’re testing, and you have an engine test cell: an arrangement that lets you control the tiniest variables, so that engineers can tinker with the engine to see if they can improve its performance. They can simulate how an engine would perform in different cars — a hybrid car, an electric car, a gas‐powered car — and can also measure emissions.
With a diesel engine installed in the test cell, Ciatti and his team were ready to explore the possibilities.
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