Featured Research

from universities, journals, and other organizations

Up in flames: Evidence confirms combustion theory

Date:
July 1, 2014
Source:
DOE/Lawrence Berkeley National Laboratory
Summary:
Researchers have uncovered the first step in the process that transforms gas-phase molecules into solid particles like soot and other carbon-based compounds. The finding could help combustion chemists make more-efficient, less-polluting fuels and help materials scientists fine-tune their carbon nanotubes and graphene sheets for faster, smaller electronics. In addition, the results could have implications for the burgeoning field of astrochemistry, potentially establishing the chemical process for how gaseous outflows from stars turn into carbon-based matter in space.

Graphical representation of the chemistry in the early stages of soot formation. The mechanism to the right was demonstrated by experiment, while the one on the left was not.
Credit: Dorian Parker, University of Hawaii

Researchers at the Department of Energy's Lawrence Berkeley National Lab (Berkeley Lab) and the University of Hawaii have uncovered the first step in the process that transforms gas-phase molecules into solid particles like soot and other carbon-based compounds.

The finding could help combustion chemists make more-efficient, less-polluting fuels and help materials scientists fine-tune their carbon nanotubes and graphene sheets for faster, smaller electronics. In addition, the results could have implications for the burgeoning field of astrochemistry, potentially establishing the chemical process for how gaseous outflows from stars turn into carbon-based matter in space.

"When you burn a flame, you start with a gas-phase reactant and then analyze the products, which include soot," says Musahid Ahmed, scientist in the Chemical Sciences Division at Berkeley Lab. "But there is no direct evidence for the chemical bonds that break and form in the process." For more than 30 years, scientists have developed computational models of combustion to explain how gas molecules form soot, but now Ahmed and his colleagues have data to confirm one long-standing theory in particular. "Our paper presents the first direct observation of this process," he says.

While the research is relevant to a number of disciplines -- combustion science, materials science, and astrochemistry -- it's combustion science that could see the most direct impact the soonest, says Ahmed. Specifically, the fundamental chemistry discovery could be used to find or design fuels that burn cleaner and don't produce as much soot.

Think about your car engine. If the combustion process were perfect, only carbon dioxide and water would come out of the tailpipe. Instead, we see fumes and particulates like soot, a visible macromolecule made up of sheets of carbon.

Theoretically, there are hundreds of different ways molecules can combine to create these dirty emissions. But there has been one popular class of mechanisms that outlines possible early steps for bond making and bond breaking during combustion. Called hydrogen abstraction-acetylene addition, or HACA, it was developed by Michael Frenklach professor of mechanical engineering at the University of California Berkeley in 1991.

One version of HACA works like this: during the high-temperature, high-pressure environment of combustion, a simple ring of six carbon and six hydrogen atoms, called benzene, would lose one of its hydrogen atoms, allowing another two-carbon molecule called acetylene, to attach to the ring, giving it a kind of tail. Then the acetylene tail would lose one of its hydrogen atoms so another acetylene could link up in, doubling the carbon atoms in the tail to four.

Next, the tail would curl around and attach to the original ring, creating a double-ring structure called naphthalene. Link by link, ring by ring, these molecules would continue to grow in an unwieldy, crumpled way until they became the macromolecules that we recognize as soot.

To test the first step of the theoretical HACA mechanism, Ahmed and collaborators from the University of Hawaii used a beamline at the Advanced Light Source (ALS) at Berkeley Lab specifically outfitted to study chemical dynamics. The ALS, a DOE Office of Science user facility, produces numerous photons over a wide range of energies, allowing researchers to probe a variety of molecules produced in this chemical reaction with specialized mass spectrometry analysis.

Unique to this experimental setup, Ahmed's team used a so-called hot nozzle, which recreates combustion environment in terms of pressure and temperature. The group started with a gaseous mix of nitrosobenzene (a benzene ring with a molecule of nitrogen and oxygen attached) and acetylene, and pumped it through a heated tube at a pressure of about 300 torr and a temperature of about 750 degrees Celsius. The molecules that came out the other end were immediately skimmed into a mass spectrometer that made use of the synchrotron light for analysis.

The researchers found two molecules predominantly emerged from the process. The more abundant kind was the carbon ring with a short acetylene tail on it, called phenylacetylene. But they also saw evidence for the double ring, naphthalene. These results, says Ahmed, effectively rule out one HACA mechanism -- that a carbon ring would gain two separate tails and those tails would bond to form the double ring -- and confirm the most popular HACA mechanism where a long tail curls around to form naphthalene.

Ahmed's local team included Tyler Troy, postdoctoral fellow at Berkeley Lab, and this work was performed with long-term collaborator Ralf Kaiser, professor of physical chemistry at the University of Hawaii at Manoa, and Dorian Parker, postdoctoral fellow also at Hawaii. The research was published June 20 online in the journal Angewandte Chemie.

"Having established the route to naphthalene, the simplest polycyclic aromatic hydrocarbon, the next step will be to unravel the pathways to more complex systems," says Kaiser.

Further experiments will investigate these follow-up mechanisms. It's a tricky feat, explains Ahmed, because the molecular possibilities quickly multiply. The researchers will add infrared spectroscopy to their analysis in order to catch the variety of molecules that form during these next phases of combustion.

This research was funded by the DOE Office of Science and the National Science Foundation.


Story Source:

The above story is based on materials provided by DOE/Lawrence Berkeley National Laboratory. The original article was written by Kate Greene. Note: Materials may be edited for content and length.


Cite This Page:

DOE/Lawrence Berkeley National Laboratory. "Up in flames: Evidence confirms combustion theory." ScienceDaily. ScienceDaily, 1 July 2014. <www.sciencedaily.com/releases/2014/07/140701101535.htm>.
DOE/Lawrence Berkeley National Laboratory. (2014, July 1). Up in flames: Evidence confirms combustion theory. ScienceDaily. Retrieved October 22, 2014 from www.sciencedaily.com/releases/2014/07/140701101535.htm
DOE/Lawrence Berkeley National Laboratory. "Up in flames: Evidence confirms combustion theory." ScienceDaily. www.sciencedaily.com/releases/2014/07/140701101535.htm (accessed October 22, 2014).

Share This



More Matter & Energy News

Wednesday, October 22, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Thanks, Marty McFly! Hoverboards Could Be Coming In 2015

Thanks, Marty McFly! Hoverboards Could Be Coming In 2015

Newsy (Oct. 21, 2014) If you've ever watched "Back to the Future Part II" and wanted to get your hands on a hoverboard, well, you might soon be in luck. Video provided by Newsy
Powered by NewsLook.com
Robots to Fly Planes Where Humans Can't

Robots to Fly Planes Where Humans Can't

Reuters - Innovations Video Online (Oct. 21, 2014) Researchers in South Korea are developing a robotic pilot that could potentially replace humans in the cockpit. Unlike drones and autopilot programs which are configured for specific aircraft, the robots' humanoid design will allow it to fly any type of plane with no additional sensors. Ben Gruber reports. Video provided by Reuters
Powered by NewsLook.com
Graphene Paint Offers Rust-Free Future

Graphene Paint Offers Rust-Free Future

Reuters - Innovations Video Online (Oct. 21, 2014) British scientists have developed a prototype graphene paint that can make coatings which are resistant to liquids, gases, and chemicals. The team says the paint could have a variety of uses, from stopping ships rusting to keeping food fresher for longer. Jim Drury reports. Video provided by Reuters
Powered by NewsLook.com
China Airlines Swanky New Plane

China Airlines Swanky New Plane

Buzz60 (Oct. 21, 2014) China Airlines debuted their new Boeing 777, and it's more like a swanky hotel bar than an airplane. Enjoy high-tea, a coffee bar, and a full service bar with cocktails and spirits, and lie-flat in your reclining seats. Sean Dowling (@SeanDowlingTV) has the details. Video provided by Buzz60
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins