MechSE professor studies optimized biofuels for combustion in existing engines

7/7/2014 Meredith Staub

Biofuels have existed for almost as long as cars; Henry Ford in the early 1900s planned to fuel his first cars with ethanol, and some very early diesel engines ran on peanut oil.

Written by Meredith Staub

Biofuels have existed for almost as long as cars; Henry Ford in the early 1900s planned to fuel his first cars with ethanol, and some very early diesel engines ran on peanut oil. Gasoline and diesel are also “biofuels” of a sort, as they come from decomposed plant and animal matter—but while they come from ancient biomatter, the biofuels being studied today by Associate Professor Tonghun Lee and scientists around the world come from more recent plant life.

Today’s biofuels come from plants that typically have a high fat or oil content. These plants then undergo a process called hydro-reforming, which separates them into large hydrocarbons that can then be broken up into smaller pieces depending on what fuel is needed—hydrocarbons in jet fuels have between 7 and 14 carbon atoms, while diesel fuels can have up to 20. The process of refining a biofuel gets more complicated when there are multiple shapes the molecule can take, as chemical structure can influence the performance of a fuel. This makes the processing of a biofuel a crucial step in making them “drop-in fuels,” or fuels that will be compatible with current engines.

Lee’s research specializes in combustion, with a focus on laser and optical diagnostics. These laser and optical diagnostics help him quantify what occurs in the combustion of these biofuels, which gives insight into how exactly different processing methods affect the performance of the biofuel. “Until biofuels become mainstream, nobody is going to build a new engine for biofuels,” Lee said. “We need to make these fuels work in our engines. So we want to provide information about how to process these fuels so that they can become drop-in fuels, and give them design guidelines for an optimized biofuel. ”

The two main properties that Lee is studying in biofuels are ignition and low-temperature chemistry. Each biofuel can have a different ignition delay, which is the 1-50 milliseconds before ignition when the molecules disintegrate and prepare to burn. This delay dramatically influences engine control. Also important is the performance of the fuel at low temperatures.

“So when it’s really hot, high-temperature combustion, all fuels behave kind of the same way,” Lee said. “When it’s cold combustion, fuels behave very differently. So we want to make sure that the fuel performs adequately in terms of the ignition but also in terms of the low-temperature combustion.”

As one of his main projects, Lee is helping the U.S. Navy and Air Force reach their goal of having a biofuel fleet by 2016 and using 50% biofuel in all of their fleets by 2020. Although petroleum-derived fuels are the most widely used fuels, the U.S. generates very little of the petroleum it uses. A desire to ease the country’s dependence on fuel it cannot produce, as well as to use fuels that have less of an impact on the environment, has sparked interest in biofuels created from organic matter.

“It’s driven by the military because the military does not care too much about how much the fuel costs,” Lee said. “The military is concerned about energy independence and increase of warfighting capabilities. Once the technology is mature in that sector, it will trickle down.”

Biofuels are not widely used in the commercial sector today because of their high costs and lower efficiencies compared to petroleum fuels. But Lee has faith that this will change.

“Biofuels are expensive right now,” Lee said, “but you have to keep in mind that we are still in the preliminary experimental phase. Whether we like it or not, biofuels may take over—it may not completely take over petroleum, but it will become a huge portion of our infrastructure. It is ripe for innovation.”

 


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This story was published July 7, 2014.