GM and Oak Ridge National Laboratory are jointly developing new emissions-cleaning technology that promises better fuel economy for future heavy-duty diesel truck buyers, according to a presentation given during the U.S. Department of Energy's 2011 Merit Review in Washington, D.C.
In 2007, the EPA cracked down on the amount of soot diesel engines could produce, cutting allowable emissions by 90 percent from 2006 levels. In response, truck makers and their powertrain partners created diesel particulate filters to trap soot, a byproduct of diesel’s lean combustion process because not all the fuel is burned.
While cleaning soot from diesel exhaust is great for the environment, it comes with a price. After a while, depending on workload and driving distance, the DPF becomes full and needs to be cleaned out, like a self-cleaning oven. In today's HD pickups, extra diesel fuel is injected into the exhaust stream to boost temperatures in the DPF to more than 1,000 degrees, incinerating the trapped soot. That process can require up to six-tenths of a gallon of diesel – an amount large enough to dent fuel economy and drivers' wallets. It can also take five to 10 minutes, depending on trapped soot levels.
Fuel economy has long been the advantage of diesel over gas engines, returning up to 20 percent to 30 percent better mileage, but DPFs have eaten away at this advantage.
GM and ORNL have created a solution to the mileage problem that could reduce the fuel economy penalty of DPF regeneration by at least 25 percent by 2015 relative a 2008 baseline, according to the presentation.
Instead of using diesel fuel, an electric heater placed at the front of the DPF is used to raise temperatures to the point where the trapped soot is incinerated, at around 1,112-degrees.
So far, an experimental electric heater has been tested on a small-displacement 1.9-liter four-cylinder GM diesel engine, but a project member from ORNL says the solution is scalable to heavy-duty pickups with large-displacement oil burners, like GM's 6.6-liter Duramax V-8.
With the 1.9-liter engine, the electrically assisted DPF has been shown to remove up to 95 percent of soot and cuts regeneration times by 75 percent.
Improved fuel economy using an EA-DPF should also please the EPA, which is getting tough on diesel engines again. Heavy-duty pickups, currently excluded from federal fuel economy standards, will have to meet the first mileage regulations by 2016.
The electrically assisted diesel particulate filter project is being financed with $1.3 million split evenly between GM and ORNL. It runs through September 2012.
[Source: U.S. Department of Energy]