Seafaring Biofuels: Finding the Right Fuel for the Fleet

19 january 2013

As the largest user of diesel in the U.S., the Navy is vulnerable to disruptions in fuel supply. To help in the search for alternative fuels, the Navy has awarded a $2 million grant to a University of Wisconsin engineering professor to find the right fuel for the fleet.

For the next two years, Rolf Reitz and his team will be developing a model to work out the right mix of biofuel for the Navy’s fleet. Reitz’s work is critical because Navy Secretary Ray Mabus has committed to cutting the fleet’s petroleum use in half by 2015, but ships can’t run on just any oil substitute.

The fuels can’t be water soluble, for example.

“The Navy maintains the ballast on ships by pumping water into the fuel tanks as the fuel level decreases. This keeps them floating properly,” Reitz explains. “Some alternative bio-derived fuels are somewhat soluble in water, and hence are not suitable for the Navy.”

The fuel also can’t be readily flammable. On board a ship or submarine, a fire “is a much bigger deal than on land, because there is nowhere to escape to,” Reitz says. “Therefore, maritime fuels must have higher ‘flash points’, or temperature at which they will ignite.”

This strikes a few more alternative fuels off the list.

One fuel that may fit the bill: hydrotreated vegetable oil (HVO), also called renewable diesel.

Renewable diesel is chemically similar to diesel, but is produced using recently living biomass. It can be processed in the same facilities as petroleum, and mixed with diesel for use as a transportation fuel. This makes it more attractive to the Navy than biodiesel, which according to Reitz, is somewhat water soluble, turns rancid like cooking oil and can leave deposits on fuel injectors.

The challenge, says Reitz, is finding the right “proportion of diesel and HVO fuel that would give satisfactory performance in existing Navy engines.”

Since the HVO/diesel recipe can vary, the model Reitz and his team are developing simulates each blend’s performance in an engine – a process requiring thousands of lines of computer code.

Even though it is being developed for the Navy, the model has broader application. According to Reitz,  “any diesel engine or heavy oil combustion system, like furnaces, can use HVOs blended with diesel.”

It can take several days to run just one engine cycle so the modeling will likely not be completed until 2014, according to Reitz.

Top image: The aircraft carrier USS George Washington during a fueling at sea, courtesy U.S. Navy.