Revving up the Internal Combustion Engine
In the quest for smarter cars of the future, Hunter Mack (M.S.’04, Ph.D.’07 ME) is putting a new spin on the internal combustion engine.
Mack’s focus as a postdoctoral researcher at Berkeley Engineering is an innovative system called HCCI that behaves like a cross between a gas and a diesel engine.
HCCI, shorthand for homogeneous charge compression ignition, delivers up to 30 percent better fuel economy than gas engines, emits far fewer emissions than a typical diesel and isn’t fussy about what’s pumped in its tank. And because HCCI is a modification of a conventional engine, the system as a whole or elements of it could be installed in new cars within 5 to 10 years.
“Take something that already exists and make it better,” says Mack, part of an eight-member HCCI research team at Berkeley headed by Professor Robert Dibble. “It’s the fastest way to make an immediate impact.”
Though Mack thinks a variety of next-generation technologies are required to address the global need for more sustainable forms of personal transportation, he’s confident that HCCI will figure in that mix. Already, General Motors and Mercedes-Benz have built demonstration cars that operate with HCCI engines.
But development of the HCCI has hit its share of obstacles. The system, first developed by Japanese researchers in the late 1970s, works by premixing fuel and air outside the cylinders like a gas engine. The fuel is then auto-ignited as in a diesel engine under high compression, rather than with a spark plug. The biggest challenges are controlling the precise timing of combustion and boosting the engine’s power output. “HCCI is sort of a cantankerous auto engine,” Mack says.
Onboard computer technology and advanced sensing devices are helping to resolve those problems, Mack says, and HCCI “will be applied to future generations of engines.” In the ground-floor Combustion Analysis Laboratory at Hesse Hall, Mack and fellow researchers study and modify experimental HCCI systems on a pair of single-cylinder engines and a four-cylinder VW diesel engine.
In tandem with that effort, Mack is identifying the cleanest and most efficient blends of fuels to pump into tanks of the not-too-distant future. In one study, he deployed atomic mass spectrometry at Lawrence Livermore National Laboratory (LLNL) to perform carbon-14 tracing on exhaust samples, a novel approach to understanding how an HCCI engine burns a blend of ethanol and diethyl ether. Mack’s list of potential fuels is long—and exotic. It includes an array of mixed alcohols from such biological sources as algae and wood waste, and ethanol mixed with heavy concentrations of water. “We’re trying to make an engine that doesn’t care what it sees,” he explains.
Berkeley’s work on HCCI dates back to 1998, when Dibble began testing the system on a research engine as part of a study taking place at LLNL. Dibble was intrigued by how little pollution-generating nitric oxide the engine produced. “Never before did we have an engine that reduced pollution by a factor of 100 overnight,” he says. Today, the Berkeley researchers are part of a multi-university HCCI consortium funded by the U.S. Department of Energy.
A native of Arkansas, Mack calls his research a “fortuitous choice.” He’d never heard of HCCI before coming to Berkeley in the summer of 2002 to work with Dibble and start his graduate studies. Mack earned undergraduate degrees in physics and mechanical engineering from Hendrix College in Arkansas and Washington University in Missouri, respectively, and knew he wanted to pursue engine research in some form. “I didn’t tinker with cars or have a muscle car. I just liked the science behind it.”
With so much high-profile work taking place on electric, fuel cell, solar and other new-car technologies, Mack is often asked why he studies the internal combustion engine.
“There’s still room for improvement,” he responds. Mack, 30, doesn’t expect to witness the demise of that engine in his lifetime. Instead, he says, “I think they’ll be used less and less and they’ll be used smarter.” One early step might be manufacturing engines that feature dual-spark ignition and HCCI operations, he says.
“Ideally, the goal of all this research is to find a way to sustainably produce fuels and also develop engines that will operate at efficiencies that do no harm to the environment.”