Award supports study of internal-combustion diagnostic tool

For the past several decades, engineers have been investigating low-temperature combustion as a means of creating engines with diesel-like efficiency and no pollutant emissions.

Optimizing low-temperature combustion to produce the most efficient engine possible also means considering a lot of variables. In fact, the very nature of low-temperature combustion involves a reaction with little active control: You inject the fuels, mixing occurs and then, some time later, combustion starts.

“We’re always on the edge of doing something bad,” says David Rothamer, an assistant professor of mechanical engineering who has received the National Science Foundation’s 2011 Faculty Early Career Development Award (CAREER) to investigate a new technique for measuring the temperature of a low-temperature combustion reaction through the entire process.

That “something bad,” Rothamer says, could result in the engine not starting, running at a temperature that is too high (which produces toxic nitric oxide) or a fuel-to-oxygen ratio that is too high (which produces soot). “Lots of times we don’t know where we are relative to those bounds,” he says. “We need to be perfect within a small range.”

With his $405,000 award, Rothamer will research the use of phosphors — substances that emit light — to measure the temperature of gases in combustion reactions for a variety of practical purposes, including gas turbines for jet engines and internal combustion engines for vehicles.

Specifically, Rothamer is looking at the properties of ions of rare-earth metals such as praseodymium and dysprosium. The ions are embedded in a crystalline ceramic material to create a phosphor that does not melt at high engine temperatures. By analyzing the electromagnetic spectra of the light these phosphors emit at different temperatures, Rothamer can create a diagnostic tool that maps this light to the exact temperature of a combustion reaction.

Phosphors are a useful tracking tool because they are not consumed in a combustion reaction. In addition, their spectral lines are easy to detect in contrast to those of combustion products, which sometimes emit at ultraviolet frequencies that cannot be detected except in a vacuum.

By adding other elements to the ion crystal structure, Rothamer can change the phosphors’ exact properties. Ultimately, he hopes to create a material that will emit distinct spectral lines between 800 and 1800 kelvins, without emitting too much energy as heat instead of light.

Such a tool would help engineers see what’s happening inside the cylinder, which has so far been difficult. “Knowing the distribution of temperature throughout the combustion process, we can start to manipulate other things outside to optimize the reaction,” Rothamer says.

For example, he says, understanding the way the reaction evolves and why unwanted byproducts form as the fuels mix can help engineers to fine-tune the mixing process to prevent or minimize these byproducts.

Rothamer’s CAREER award includes funding for an outreach component. He plans to set up a summer program through the Great Lakes Bioenergy Research Center at UW–Madison, which runs research experiences for teachers. The new program would allow teachers to explore the combustion process, with a biofuels focus.