Modeling biofuel fitness for the sea

With the help of a $2 million grant from the U.S. Office of Naval Research, mechanical engineers at the University of Wisconsin–Madison will develop a tool to characterize the performance of a new class of alternative fuels that could be used in maritime vehicles such as submarines and aircraft carriers.

With fossil fuels a limited resource largely controlled by other nations, the U.S. Navy-the largest user of diesel fuel in the country-understandably is interested in alternative fuels that can be produced in the United States.

However, the Navy has some unique needs for powering its fleet of ships, submarines, aircraft carriers, and other marine vessels: The fuels can’t mix with water, nor can they be readily flammable. This excludes most existing biofuels.

A new type of diesel biofuel, called hydro-treated vegetable oil (HVO), could be the answer for maritime vessels. It’s just a matter of determining which, of many possible blends, performs best in an engine. Every fuel has a unique combination of traits, including how hot it burns, how its different components interact, and how quickly the combustion reaction starts.

And as an alternative to expensive, time-consuming tests of each of these traits for every candidate fuel, Rolf Reitz, Wisconsin Distinguished Professor of mechanical engineering at UW–Madison, will lead a project to create a tool for modeling fuel properties.

In fact, Reitz and his colleagues in the UW–Madison Engine Research Center will use the distribution of components in the fuel themselves to predict a fuel’s performance in an engine. For example, all fuels contain different proportions of various types of chemicals, such as aromatic compounds. While each is slightly different, aromatics as a group behave similarly in combustion experiments, and Reitz’s team will characterize how the proportion of aromatic compounds in a fuel affects its behavior in the Engine Research Center suite of test engines.

With rigorous experimentation on a variety of fuels, Reitz says the team can create a world-class model that predicts a fuel’s behavior based solely on its chemical breakdown, allowing the Navy-and eventually, anyone else-to more easily select the best HVO blend for its needs.

“This tool can help them assess whether that fuel makes sense without having to do laborious extensive testing,” Reitz says. “They’ll still have to do some testing, but this lets them eliminate certain classes right off the bat.”