NSF Early Career Award supports investigation of technique to measure temperature of low-temperature combustion reactions
11 January 2012
David Rothamer, an assistant professor of mechanical engineering at the University of Wisconsin-Madison, recently received a $405,000 National Science Foundation 2011 Faculty Early Career Development Award (CAREER) to investigate a new technique using nanoparticle thermographic phosphors for measuring the temperature of a low-temperature combustion reaction through the entire process.
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 requires considering a lot of variables. Further, the very nature of low-temperature combustion involves a reaction with little active control.
“We’re always on the edge of doing something bad,” says Rothamer, which could result in the engine not starting; running at a temperature that is too high (producing NOx) 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.”
The primary objective of the proposed work is to develop and implement a new temperature imaging technique for combusting flows. The technique utilizes the laser-induced emission from nanoparticle phosphors whose emission is highly temperature dependent. The nanometer sized phosphors act as microscopic temperature sensors embedded in the flow. The measurement technique will fill a significant gap in current temperature imaging capabilities. It enables measurements in the temperature range from 700 to 1800 K [427 to 1,527 °C] which is of critical importance for designing the next generation of clean, efficient, combustion technologies. The technique will be capable of measurements where current diagnostics are intractable, making simultaneous temperature imaging measurements of both the reactants and products in practical combustion devices a reality.
The proposed measurement technique will be optimized for the temperature range of interest by studying the fundamental temperature dependence of the phosphor luminescence. This knowledge will be applied to develop a robust technique for temperature measurements in practical devices. In collaborations with researchers at Universities and National Laboratories we will apply this technique to study fundamentals of turbulence-chemistry interactions and low-temperature combustion strategies in piston IC engines.
—Award abstract
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 the specified temperature range, 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.
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