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OKAZAKI, Japan – Automakers are now one step closer to replacing spark
plugs for internal combustion engines with laser igniters for cleaner, more
efficient and more economical vehicles.
Lasers have been discussed as a promising alternative ignition source for
efficient internal combustion engines because they promise less pollution and
greater fuel efficiency. Until recently, it was difficult to make small, powerful
lasers that could focus light to ~100 GW/cm² with short pulses of more than
10 mJ each, needed to ignite combustion.
Scientists from Japan’s National Institutes of Natural Sciences overcame
this problem by making composite lasers from ceramic powders. They heated
the powders to fuse them into optically transparent solids, and embedded
metal ions in them to tune their properties. Ceramics are easier to tune optically
than conventional crystals and are much stronger, more durable and
thermally conductive, enabling them to dissipate the heat from an engine
without breaking down.
The research team built its laser from two yttrium aluminum gallium
segments, one doped with neodymium, the other with chromium. The two
segments were bonded together to form a powerful laser only 9 mm in diameter
and 11 mm long. The composite generated two laser beams that could
ignite fuel in two separate locations simultaneously, producing a flame wall
that grows faster and more uniformly than one lit by a single laser.
Not strong enough to light the leanest fuel mixtures with a single pulse,
the laser can, however, inject enough energy to ignite the mixture completely
by using several 800-ps-long pulses. It was tested at 100 Hz – a commercial
automotive engine will require only 60 Hz.
Although promising, the system is not yet being installed into automobiles.
The team is working on a three-beam laser that will enable even faster and
more uniform combustion. Supported by the Japan Science and Technical
Agency, the work was presented at CLEO 2011.