2005 Year in Review

New Tool Could Help Biodiesel Gain Acceptance

Biodiesel is one step closer to being adopted as an environmentally safe alternative fuel, thanks to an innovative new tool from University of Illinois researchers.

Biodiesel, an alternative fuel that combines diesel fuel with a vegetable oil derivative, has raised environmental concerns because of its questionable levels of nitrogen oxides (NOx). So University of Illinois engineers have developed a sophisticated, three-dimensional combustion model to analyze and understand the mechanisms that cause NOx emissions in the combustion process when using biodiesel.

"NOx emissions occur with just about any fuel, but biodiesel tends to generate more NOx emissions than others," said Al Hansen, a U of I professor of agricultural and biological engineering.

Nitrogen oxides result when temperatures in the combustion chamber of an engine get high enough to cause the nitrogen (which is normally inert) to oxidize.

"Because the composition of biodiesel affects emissions, we realized early on that we needed to first compute the properties of biodiesel as accurately as possible," said Hansen.

To do this, Hansen and graduate student Wenqiao Yuan developed a program that takes into account the proportion of fatty acids in the fuel mixture. This enabled them to identify some of the key properties of the biodiesel fuel mixture, such as viscosity and surface tension.

Using this information in the combustion model they developed, Hansen and Yuan have been able to identify or verify a number of strategies that can be used to help reduce NOx emissions.

"Some of these strategies have already been identified and are well understood," said Hansen. "But others may not be quite so clear."

One strategy is to change the injection timing to alter the engine's start of combustion, said Hansen.

"You want to retard it, actually," he said, "because this moves the combustion process to a point in the cycle where the temperatures aren't quite as high. The combustion can take place in slightly cooler conditions, and that will help to reduce the NOx emissions."

However, Hansen realizes this strategy might meet with resistance among engine manufacturers.

"A manufacturer might be willing to use biodiesel in a regular, unmodified engine, but now we're telling him to change the timing. That's a hurdle, but I think it can be taken."

Hansen believes one way to meet this challenge is with a sensor that will be able to detect how much biodiesel is in the fuel. The sensor will send a message to the unit that controls the injection, telling it the percentage of biodiesel to fuel and signaling a change in the timing.

"There are already sensors that can do this," said Hansen. "So I think the technologies are there to be able to overcome the issue of NOx emissions."

Hansen's and Yuan's research has been funded by a University of Illinois Research Board grant, and the USDA Hatch Act.

by  Editor, theCity1.com
April 4, 2005