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  5. Focus on new faculty: Sage Kokjohn, tackling the mysteries of internal-combustion engines

Focus on new faculty: Sage Kokjohn, tackling the mysteries of internal-combustion engines

Sage Kokjohn. Photo: Scott Gordon.

Sage Kokjohn’s fascination with the internal-combustion engine began when he took up motocross racing while growing up in Iowa. Today, Kokjohn focuses on helping the next generation of engines keep up with tightening emissions standards and changes in the ever-volatile energy landscape. 

Making those crucial improvements in efficiency comes down to some pretty fundamental questions about what goes on inside the combustion chamber itself, says Kokjohn, who recently began work as an assistant professor of mechanical engineering

“You would think that after 100 years of developing the internal-combustion engine, we’d completely understand what’s going on inside of the combustion chamber, but really we don’t,” he says. “That’s partially because it’s hard to do experiments in the harsh, high-pressure, high-temperature environment inside of the engine. 

Kokjohn began tackling these questions while earning his master’s and PhD in mechanical engineering at UW-Madison. As a grad student, he worked in Wisconsin Distinguished Professor Rolf Reitz’s research group, where he helped develop remarkably efficient techniques for blending diesel fuel and gasoline in an engine’s combustion chamber. He continued to collaborate and co-publish with Reitz even while spending a year and a half as a combustion-research engineer at Cummins Inc. That working relationship, along with the diverse resources of the UW-Madison Engine Research Center, helped to draw Kokjohn back to academic life.

“There are people doing every aspect of engine, spray, and combustion research here,” he says, noting the research spans from diagnostics to sophisticated computer simulations. 

As he builds on his graduate work, Kokjohn’s current goals include applying previous engine-research advances to natural-gas engines, and addressing the obstacles that stand in the way of cleaner, more efficient engines.

“We can often use some type of aftertreatment to reduce emissions of nitrogen oxides or soot, but when we’re talking about converting fuel energy to work, that has to be done in-cylinder,” he says. 

The novel solutions might include a range of lower-temperature combustion strategies, something the ERC has long specialized in. Kokjohn wants to “decouple” some of the factors that tend to hinder greater fuel efficiency. “Typically, things we do to reduce nitrogen oxides have tended to negatively impact fuel efficiency,” he says.

A key problem is that, outside of controlled experimental conditions, many high-efficiency engines perform inconsistently, and it’s not always clear why. With help from high-throughput supercomputers at UW-Madison, Kokjohn and his grad students hope to piece together a more sophisticated understanding of the factors controlling engine combustion. Current computing resources aren’t nearly powerful enough to create a total picture of the combustion chamber, but what researchers can do is create a number of models representing pieces of the combustion process.

His hope is that if he can better understand the relationships between those variables, he can create engines that both emit fewer pollutants and waste less energy in the form of heat.

As the newest ERC faculty member, Kokjohn sees great opportunity for UW-Madison to guide engines into a more efficient future. Most importantly, he hopes that researchers can take a step back from the engines themselves to craft a physics-driven approach to modeling.

“The overall goal is to be able to accurately simulate all of the details of the combustion process in a time frame that’s feasible for use in engine development,” he says.

Scott Gordon
12/12/2013