Engine Tech Knocks Back the NOx

Biodiesel has advantages over diesel, but one drawback is higher nitrogen oxide emissions. Fortunately, researchers at Purdue University created an engine framework that cleans up.

Greg Shaver, assistant professor of mechanical engineering and a member of the Purdue Energy Center at Discovery Park, walked me through his work. Nitrogen oxide, or NOx, is a common emission from gas and diesel engines and a precursor to smog. Engines that were designed and calibrated for regular diesel don't work the same way with biodiesel, which contains more oxygen. The result: an increase in noxious NOx emissions.

Shaver and his team at Purdue came up with a technique to reduce them to levels back on par with conventional fuel. First, oxygen sensors in the exhaust pipe help determine the biodiesel blend, whether it's 5 percent, 40 percent, or even 100. Other researchers used in-tank sensors, Shaver says, but his approach takes advantage of sensors already in the vehicle to reduce costs. Then, new algorithms in the vehicle's software take the sensor information and guide the decision-making of a 6.7-liter, six-cylinder diesel engine. The system adjusts the fuel-injection timing, the flow of exhaust, and the air-to-fuel ratio to minimize emissions and fuel consumption. Details of this closed-loop control technique were published recently in the journal Energy & Fuels.

"I think we’ve discovered something clever, and a strategy that’s generalize-able," Shaver says of this real-time fuel combustion optimization. Noting how far diesel engine technology has come, he'd like to see automakers adopt the framework and run--cleaner--with it.

Photo: Greg Shaver, right, prepares a diesel engine for biodiesel testing in the lab with grad students Gayatri Adi and Mike Bunce. Credit: David Umberger, Purdue News Service.