Researchers at Purdue University have developed
a new advanced
closed-loop control system which prevents biodiesel fuel blends
from producing more nitrogen oxides that conventional diesel fuels.
Nitrogen oxides are the component of burnt diesel fuel that
contributes to smog. According to the researchers, vehicles burning
biodiesel can produce as much as 40% more nitrogen oxides at some
operating conditions and fuel economy declines by as much as 20%
compared to conventional diesel fuel.
The reason biodiesel
produces more nitrogen oxides during the combustion process is
because the fuel has oxygen in it whereas conventional diesel fuel
doesn't. One key innovation that the new engine control system uses
to help reduce nitrogen oxides produced when burning biodiesel is
exhaust gas recirculation. The technique reroutes a portion of the
exhaust gases back into the cylinders of the engine to reduce the
amount of emissions that are released. Using the exhaust gas
recycling method the researchers were able to reduce the amount of
nitrogen oxides produced and increase fuel economy.
were able to improve the fuel economy with a biodiesel blend while
reducing nitrogen oxides to where they were with conventional
diesel," Gregory Shaver, assistant professor of mechanical
engineering said. "At the same time, we were able to maintain
the customary biodiesel reductions in particulate matter emissions
compared to ordinary diesel fuel while not increasing noise
Using the closed-loop control system and
exhaust gas recirculation the team was able to reduce the nitrogen
oxide emissions produced by the vehicles burning biodiesel to the
same level produced by vehicle burning conventional diesel. However,
while the new techniques did improve the fuel economy of biodiesel
vehicles, the fuel economy is still not as great as that of
traditional diesel fuel.
"This means you get lower
mileage for biodiesel compared to ordinary diesel fuel," Shaver
said. "We improved the combustion efficiency and were able to
get better mileage than before, but still not as good as conventional
The reason that fuel economy with biodiesel
is lower than that of conventional diesel is because biodiesel has 10
to 12% lower energy density than conventional diesel when burned
during the combustion process. The closed-loop control technique uses
advanced models to adjust the engine automatically as it senses what
blend of fuel I being used in the engine. The software in the control
system adjusts fuel injection timing and the air-to-fuel ratio along
with the amount of exhaust gasses returned to the cylinders depending
on the type of fuel being used in the vehicle.
to be able to estimate what the blend ratio is so you know what's
going on in the engine," Shaver said. "Is it 20 percent
biodiesel fuel mixed with 80 percent regular fuel? Then we can do
something to reduce the nitrogen oxides to levels consistent with a
conventional fuel that didn't have oxygen in it."
technology needed to implement the new control system into existing
diesel vehicles is already here. Shaver says that it only adds an
"extra wrinkle or two" to what is already used inside a
vehicles control module. The future of biodiesel production itself is
in question as companies producing the fuel have gone out of business
credits supporting the industry were ended.