Major Overhaul . . .
by Marcia Goodrich
Internal combustion engines have been around since the seventeenth century, and they have been powering cars since Karl Benz built his first automobile in 1885. But even in the Information Age, we still don't truly know what goes on inside these workhorses of the Industrial Revolution.
That's not surprising, considering that most of the action occurs when a mist of volatile fuel mixes with air and combusts inside a sealed cylinder. "We have been able to harness that process, but we don't fully understand what's happening," says Jeff Naber, an associate professor of mechanical engineering–engineering mechanics.
To find out, Naber and his research team have put together a glittering array of equipment, paid for in part by a $1.4 million grant from the National Science Foundation. It funds one of four major projects that Naber has a hand in, ranging from this fundamental study of how engines work to graduate education in advanced hybrid vehicles for Detroit's auto engineers.
The NSF-funded lab in the Alternative Energy Research Building includes a laser powerful enough to vaporize carbon and a camera that takes a million frames per second. "This allows us to do some pretty cool stuff," he says.
The laser passes through a clear-sapphire window the diameter of a softball, made from a single, perfect crystal that took a year to grow and polish. The camera captures images of fuel mixing with hot gases and igniting and combusting, courtesy of the laser, within one-thousandth of a second inside the custom-made chamber.
"We have numerous models of the processes that occur, but many are based on empirical correlations," says Naber. "This laboratory allows us to dive deep inside the cylinder and understand what's happening in this dynamic process under extreme pressures and temperatures."
During experiments, the engineers control what's going on in an adjacent control room, where they preprogram the entire process on computers and watch the action on a number of video monitors.
The experimental setup offers huge advantages over a stock internal combustion engine. "It's much more fundamental," explains PhD student Jaclyn Nesbitt. "We can isolate variables and gain a better understanding of individual processes."
Naber expects to apply that understanding to another project: developing engines that continuously adapt to changing fuels, environmental conditions, and engine variability and wear.
"It's pretty exciting," he says. "It would transform how engines operate."
Combustion control systems are now calibrated according to what Naber calls "the worst case scenario," which works OK on nearly all engines but not perfectly on any. An adaptable engine would sense those difference and respond throughout the life of the engine. "We could continuously monitor and control combustion to maximize efficiency and minimize emissions" he says. "The goal is to sense what an engine is doing and adjust to it continuously, even as it fires fifty times a second in each cylinder."
Controls are also key in a $2.8 million research project to reduce diesel engine emissions while improving fuel economy, supported in part by $1.8 million from the Department of Energy. In response to government regulations, diesel emissions have plummeted in the past decade, to the point that the exhaust coming out a tailpipe is often cleaner than the surrounding air. However, those gains have been paid for in increased fuel consumption. If the emissions aftertreatment and engine systems were better integrated, fuel economy could be improved.
"A significant impact of this work will be with respect to biofuels," says Naber. Mixing biodiesel and petroleum-based diesel fuel can reduce emissions, but only so far. Once biodiesel exceeds 20 percent, the aftertreatment system performance can deteriorate. "We need to make a system that works together," says Naber, especially as the industry moves away from petroleum.
Naber leads another project on a different kind of internal combustion engine: a hybrid that runs on flex fuel and meets the world's most stringent emissions standards. "There is no ethanol flex-fuel hybrid available because it's a big challenge to meet these emissions standards," he says.
That work is being funded by a $1.5 million grant from the Michigan Public Service Commission and over $1 million in support from General Motors, Sensors Inc. of Saline, Argonne National Laboratory's Transportation Technology R&D Center, and Michigan Tech.
Flex-fuel engines can burn anything from pure gasoline to E85—a blend of 85 percent ethanol and 15 percent gas. Ethanol contains only 63 percent of the stored energy of gasoline and requires about three times the energy to vaporize. Straight gasoline, however, can cause engine knock in a high-performance engine that would run smoothly on ethanol.
The researchers are addressing ethanol's benefits and rough spots. "Under most conditions, gasoline and ethanol behave similarly," says Naber. "But there are differences under high load—when you put the pedal to the metal—where the ethanol provides a significant benefit—and during cold start, when emissions go up significantly with ethanol blended fuels."
No matter what the vehicles of the future looks like, one thing is certain. They won't get any simpler.
"Today's vehicles are extremely complicated already. With hybrids we've added a whole new dimension, and with plug-in hybrids, we're going to interconnect two large systems, transportation and the electrical grid." Naber says.
With that in mind, he has led two graduate classes for automotive engineers in Detroit, most recently with funding from the Michigan Academy for Green Mobility, and is spearheading a new Master of Engineering degree program that focuses on hybrid vehicle technologies. The aim is to create a trained workforce that can handle the vehicle design and development challenges and recognize the opportunities arising in a shifting energy landscape.
"We are focusing on developing their technical knowledge in these new areas, so the auto industry can transition from petroleum," says Naber.
Wherever that transition leads, Naber looks forward to being in the thick of it. "For me, the interesting thing about these projects is getting to work on problems that are important and challenging, and doing things that need to be done."