Researchers at NUI Galway are testing biofuels to see if these might provide an answer to our pressing energy problems, writes Dick Ahlstrom
COMBUSTION is simple - you take fuel, light it with a match and it burns. Or is it so simple?
A research team at NUI Galway's Combustion Chemistry Centre (http://c3.nuigalway.ie) is learning just how complicated the combustion process can be. How a fuel burns depends on pressure, temperature, fuel-air mix and other factors, even down to molecular structure, explains Dr Henry Curran, director of the Science Foundation Ireland-funded centre and a lecturer in chemistry.
His team is mainly interested in simple things, how fast and how well a fuel burns, and after it burns what the emissions contain. But getting at this information is a highly complex business.
The goal is to pick apart the step-by-step reaction process from a chemist's point of view, he explains. "Combustion is usually studied in mechanical engineering departments. We are unique in that we are a chemistry department.
"We understand the chemical reactions and that is where our expertise lies, how fuel burns and applying that to transport and to gas turbines for energy generation. We are trying to study how to optimise gas burning but specifically looking at the chemistry."
The hidden complexity behind the fuel plus match analogy is particularly true for petrol, which has up to 200 separate ingredients, which complicates any chemical description of the burning process. "It is too complicated to solve all the detailed chemistry of each species," says Curran.
It really doesn't get much easier if you choose a simpler fuel, say butane with its simple four carbon atoms, 10 hydrogen atoms structure. "Even with butane you can get 1,200 different reactions."
He likens it to a puzzle.
"A fuel is like a jigsaw puzzle that is complete," he explains. Burning breaks down the puzzle into pieces and they want to be able to study each of the puzzle pieces.
Recent work in the centre has focused on the burning characteristics of a range of biofuels, particularly as these fuels are being touted as an alternative to petroleum-based fuels.
The molecular structure of the biofuel becomes central to understanding their value as a transport or electricity production fuel.
"We are studying how structure influences reactivity," he says. "The idea of the study was there was very little information on how molecular structure affects ignition and emissions."
A complex organic molecule breaks at a certain point first to create new chemical species, and this process continues, varying under different pressure and temperature conditions, he explains. "We take each fuel in isolation and we play games."
Two PhD students, Stephen Dooley (funded by Science Foundation Ireland) and Wayne Metcalfe (funded by the Environmental Protection Agency) set to work looking at two esters, methyl butanoate and ethyl propanoate. These can act as model biofuels to see how such fuels might perform say in a car engine.
Specialised equipment at the centre allows the team to trail each chemical species as it arises, with details of how produced and how consumed. "What we found was the two fuels burn very differently," he says.
The methyl ester proved to be the more promising of the two fuels, Curran says. "Ethyl ester burns faster but also produces more ethylene which produces soot which makes it dirtier."
It also unfortunately produces propanoaic acid as it burns, which can act to destroy car parts in an engine.
Curran worked in the US in the prestigious Lawrence Livermore Laboratory and this helped him develop contacts including links with Princeton University. His two PhD students are both going to Princeton's Department of Mechanical and Aerospace Engineering next month to work with Prof Frederick Dryer.