Greenhouse-absorbing lasers help clear the air

24 November 2006

Greenhouse gases could be made less damaging to the environment by using lasers to "fingerprint" emissions from cars and industry.

"If we continue to use fossil fuels for our energy needs we should ensure that emissions are made as clean and efficient as possible", says Sean O'Byrne, a scientist with the Australian Defence Force Academy (ADFA) who is pioneering the gas-absorbing laser technology.

Dr O'Byrne will shortly be sharing his findings with an Australian car manufacturer but acknowledges that it would need to be installed on a mass scale to be cost effective.

"Gas absorbing laser sensors provide an instantaneous reading on the concentration of greenhouse gases such as carbon dioxide and methane," says O'Byrne, who adds laser diagnostics is a "hardened technology" used to measure fuel combustion flows in hypersonic scramjets, which fly at five times the speed of sound and above (Mach 5).

Dr O'Byrne investigated supersonic combustion at NASA's Langley Research Center in the US prior to working at UNSW.

"By measuring the emission products and their temperature, the fuel and air mixture can be adjusted to provide for more efficient and cleaner burning,” he says.

“Laser sensors can be placed in the exhaust pipe of a vehicle, measuring emissions as the car is being driven. By connecting the sensors to a vehicle computer, the software could change the mix of fuel and air in a vehicle's engine and tell the driver that a tune-up is needed if emissions continue to rise over time.”

The sensors O'Byrne describes use a new type of diode laser, known as vertical-cavity surface-emitting lasers, or VCSELs, to detect the combustion exhaust gases. Dr O'Byrne is one of a handful of researchers worldwide who is using VCSELS for combustion measurements. At certain wavelengths, gases absorb laser light, producing a signal that acts like a fingerprint for each type of molecule that makes up the gas. Several lasers can be combined to measure different gas species simultaneously.

The same technology could be used in power stations to monitor emission fluctuations and alert the operators to sudden changes in emission levels. Such fluctuations may cause safety as well as efficiency problems.

Another potential use for laser technology is its use as an oxygen sensor in aircraft fuel tanks, where oxygen entering the tank can potentially combine with an electrical spark to cause an explosion. Such an explosion is believed to have caused the Boeing 747 crash in New York in 1996 that killed 230 passengers. A diode-laser sensor can continuously monitor the tank to ensure that oxygen levels never become high enough to form a combustible mixture.

Media contacts: Dr Sean O’Byrne, ph 02 6268 8353 (bh), s.obyrne@adfa.edu.au
Dan Gaffney, UNSW Media Office, mob 0411 156 015.