AlliedSignal is developing a laser-based gas-turbine ignition system for improved starting reliability and lower emissions.
The "Photon-Ignition" system is scheduled to be demonstrated in an engine later this year and may also be used, in conjunction with NASA, to develop "smart" fuel injectors.
The photon-ignition system replaces the conventional spark plug in the combustor wall with a laser beam. The beam is generated by a diode laser located "up-engine" of the combustor on the far side of the centrifical compressor. Photons are directed into the combustor via a fibre-optic cable and a mirror.
"Combustion today is achieved by spark plugs igniting fuel on the walls of the combustion chamber," says product-definition and technology-development director Robert Wilson. "This leads to durability and coking problems," he adds. Conventional combustors also suffer from a familiar oxymoron: good operability but environmentally unfriendly, or vice-versa. "A lean priming zone is also a driver of low emissions, but a lean priming zone is harder to start," says Wilson.
"With laser ignition you can run ultra lean. The fibre-optic cable delivering the laser beam can also be used as a pipeline of information out of the combustion zone. This can be used to trim fuel injection, a sort of 'smart fuel injector', which we are pursuing with NASA," he adds.
The most challenging part of the system, interfacing the focusing optics with the engine, has been achieved and a rig demonstration has been completed. An engine demonstration, using an AGT 1500 gas generator, is planned for later this year under US Defense Department funding.
AlliedSignal hopes that the test will demonstrate an expanded ignition envelope, an overall reduction in ignition-system size and weight and the operability of a fuel spray independent of an ignitor. It also hopes to demonstrate lower emissions and better exit-temperature distribution because of the ultra-lean running. The starting system could ultimately be used in turboprops, turbofans and auxiliary power units.
Source: Flight International