The one-cylinder test engine in a UW-Madison research lab is connected to a life-support system of pipes, tubes, ducts, and cables. You might think the engine resembles a patient in intensive care, but in this case, the patient is not sick.
Instead, the elaborate monitoring system shows the engine can convert 59.5 percent of the chemical energy in its fuel into motion — significantly better than the 52 percent maximum in modern diesel truck engines. After being doctored by a group led by Wisconsin Distinguished Professor of Mechanical Engineering Rolf Reitz, this is the most efficient diesel engine in the engine-research world.
“This process is 10 to 15 percent more efficient than the best commercial diesel engines, which are the most efficient internal combustion engines,” Reitz says.
But the test engine is not, strictly speaking, a diesel engine. Instead, it burns diesel and gasoline in a ratio that is precisely controlled to exploit each fuel’s strong points.
Reitz calls the system “reactivity controlled compression ignition,” or RCCI. A group of students in the Engine Research Center at UW-Madison have installed an engine using these principles into a hybrid-electric version of a 2009 Saturn, and are conducting road tests.
High efficiency is only one benefit of the RCCI system. The high temperature operation of conventional gasoline and diesel engines forms nitrogen oxides — the key source of smog. “With the low-combustion temperature, we produce insignificant amounts of nitrogen oxides,” Reitz says. “And if you can run with the ideal mix between fuel and air, you don’t have regions in the combustion chamber that make soot. Soot and nitrogen oxides — the two biggest problems for diesel — are eliminated.”
As road testing of RCCI proceeds, Reitz wants to push the limits of efficiency. “Our study demonstrated 59.5-percent efficiency in a truck-size engine. The theoretical efficiency is 64 percent, so we have reached 95 percent of the theoretical maximum,” he says. “But why is that theoretical level there? What would it take to make it even higher?”