Washington, D.C. – Laser igniters small enough to fit into a cylinder head could one day replace spark plugs and result in cleaner, more efficient and more economical vehicles, according to researchers at Japan’s National Institutes of Natural Sciences.
The researchers presented a new laser system made from ceramics, which they said could be produced inexpensively in large volumes, at the Conference on Lasers and Electro Optics in the U.S.
Takunori Taira, one of the presentation’s authors, said that conventional spark plugs pose a barrier to improving fuel economy and reducing emissions of nitrogen oxides (NOx), a key component of smog. Spark plugs can ignite leaner fuel mixtures, but only by increasing spark energy, and these high voltages erode the spark plug electrodes so quickly that the solution is not economical. By contrast, lasers ignite the air-fuel mixture with concentrated optical energy and are not affected as they have no electrodes.
Conventional spark plugs also sit on top of the cylinder and only ignite the air-fuel mixture close to them. The relatively cold metal of nearby electrodes and cylinder walls absorbs heat from the explosion, quenching the flame front just as it starts to expand. Lasers can focus their beams directly into the centre of the mixture so the flame front expands more symmetrically and up to three times faster than that produced by spark plugs.
Lasers also inject their energy within nanoseconds, compared with milliseconds for spark plugs. “Timing – quick combustion – is very important,” Taira said. “The more precise the timing, the more efficient the combustion and the better the fuel economy.”
Making the small, powerful lasers needed to ignite combustion has been difficult until now. Taira’s research team overcame the problem by making composite lasers from ceramic powders. Ceramics are easier to tune optically than conventional crystals and are much stronger, more durable and thermally conductive, able to dissipate the heat from an engine without breaking down.
The laser ignition system has not yet been installed into actual automobiles made in a factory, but the team is working with a large spark plug company and with DENSO Corporation, a member of the Toyota Group.