TransForum Vol. 9, No. 2

Low-Temperature Combustion Knocks Out NOx, Saves Fuel and Money

One of the hottest concepts in clean diesel technology is low-temperature combustion (LTC).

Engineers from Argonne’s Transportation Technology Research and Development Center (TTRDC) are exploring LTC as a means to reduce nitrogen oxide (NOx) and particulate matter (PM) emissions, and lessen the need for expensive aftertreatment devices.

Mechanical engineer Steve Ciatti readies an endoscope to capture diesel emissions images.

The idea behind LTC is to avoid creating harmful diesel emissions by reducing the combustion temperature from 3,000 degrees Kelvin to less than 2,000 degrees Kelvin.

“NOx formation is exponentially dependent upon flame temperature,” said Steve Ciatti, a mechanical engineer in Argonne’s TTRDC.

With stringent U.S. Environmental Protection Agency regulations in place for diesel engine emissions, automakers have a particular interest in innovative solutions like LTC.

Low-temperature combustion is not an entirely new concept, but most approaches come with engine performance problems. Ciatti and his fellow researchers are defining optimal LTC conditions that will result in very low outputs of NOx and PM, while retaining high engine efficiency and a reasonably high power density.

“This project definitely has the potential to be game-changing because the fuels being considered are not much different from what refineries currently produce. The potential to eliminate, or at least significantly reduce, the need for NOx aftertreatment is very high,” Ciatti said.

Current aftertreatment tools—diesel particulate filtration systems for PM and catalysts for NOx—use fuel as the working chemical to clean the PM filter and fuel or urea to reduce NOx. Therefore, LTC will also have a positive impact on fuel efficiency.

“This will result in a large cost savings compared to current aftertreatment devices and will improve efficiency because the fuel will not be needed as a feedstock to regenerate PM or NOx aftertreatment devices,” Ciatti said.

Argonne is developing a low-temperature combustion system that will enable Premixed Charge Compression Ignition (PCCI). In this approach, injection timing is used in combination with fuel properties, so ignition timing and combustion can be controlled more easily.

Detailed combustion information is needed to arrive at optimal LTC conditions. Ciatti and his colleagues are using endoscopes, advanced cameras and fiber-optic tools to obtain images and videos of fuel spray characteristics and combustion reactions and temperatures. In the future, researchers plan to use the powerful X-ray beams at Argonne’s Advanced Photon Source to capture even more detailed images of fuel sprays.

Ciatti is also validating engine and test cell hardware and software to ensure proper engine operation and control when using gasoline-like fuels. He expects to have some preliminary results this fall.

Argonne is working with General Motors, BP, ConocoPhillips, the University of Illinois at Chicago and the U.S. Air Force to develop this technology into a usable system for automobiles.

Research funding is provided by the U.S. Department of Energy’s Office of Vehicle Technologies under Gurpreet Singh.

October 2009