Mulitbeam laser aims to improve engine efficiency and emissions

Published on Tue 03 May 2011
Tags: laser, engines

Could the humble spark plug be replaced by a composite laser system?Image courtesy of Takunori Taira, National Institutes of Natural Sciences, Japan

A team of researchers, headed by Takunori Taira, has developed a multibeam laser system small enough to fit into an engine cylinder head, making for a more efficient and economical alternative to traditional spark plugs.

Research into the new laser igniters will be presented at this year's Conference on Lasers and Electro Optics (CLEO) in Baltimore.

Taira believes existing spark plugs prove problematic when addressing the long term goal of improving fuel economy and reducing nitrogen oxides (NOx) produced by engines as a result of combustion.

An engine that ran leaner by burning more air and less fuel could offer a reduction in NOx emissions.

The high voltages needed to ignite leaner air-fuel mixtures are damaging to the electrodes used on traditional spark plugs, which isn't a problem for lasers as they use concentrated optical energy for ignition.

Where conventional spark plugs ignite the air-fuel mixture close to them - with heat lost through the cold metal of the cylinder - lasers focus their beam into the centre of the mixture, ensuring a more symmetrical heat expansion that research shows is up to three times faster than spark plugs.

Taira also believes that lasers make combustion more efficient and fuel economical as they inject energy in nanoseconds, compared with a spark plug's milliseconds.

Using lasers as an alternative to traditional spark plugs is not a new idea, however, lasers capable of igniting the fuel-air mixture have proven too big, inefficient and unstable.

The research to be presented by Taira's team will show how the composite lasers were manufactured from ceramic powders.

These powders are heated to fuse them into optically transparent solids, after which metal ions are embedded to tune their properties.

Ceramics are said to be more durable and thermally conductive than conventional laser crystals, allowing them to dissipate engine heat without breaking down.

Taira's team bonded two yttrium-aluminium-gallium (YAG) segments together to create a laser 11mm long with a 9mm diameter, producing two laser beams that ignite fuel in two locations at the same time, producing a faster and more uniform flame wall.

In order to ignite the leanest air-fuel mixtures completely, the lasers emit several 800 picosecond-long pulses, as a single pulse would not be strong enough.

The dual-beam laser has been tested to a higher Hz level than is required by a commercial engine, although it has yet to be installed in a factory-produced car.

With support from the Japanese Science and Technical Agency (JST), Taira's team is working alongside a large spark plug manufacturer and the DENSO Corporation (a Toyota Group member) to develop the system further.


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