After more than 150 years engine manufacturers are one step closer to being able to replace spark plugs in internal combustion engines with laser igniters. Laser igniters are reputed to enable cleaner, more efficient, and more economical vehicles.

Laser Igniter and Spark Plug Comparison. Click image for more info.

So far lasers strong enough to ignite an engine’s air-fuel mixtures were too large to fit under an automobile’s hood.  At the upcoming Conference on Lasers and Electro Optics in Baltimore on May 1-6, researchers from Japan will describe the first multibeam laser system small enough to screw into an engine’s cylinder head.

Takunori Taira of Japan’s National Institutes of Natural Sciences, one of the presentation’s authors expects the new laser system will be made from ceramics, and could be produced inexpensively in large volumes.

One problem Taira points out with conventional spark plugs is they present a barrier to improving fuel economy and reducing emissions of nitrogen oxides (NOx), a key component of smog.

Spark plugs get the engine ignition job done by sending high-voltage electrical sparks across a small gap between two metal electrodes. The hot spark ignites the air-fuel mixture in the engine’s cylinder producing a controlled air fuel burn that forces the piston down to the bottom of the cylinder, generating the power needed to move the vehicle.

Engines make NOx as a byproduct of combustion burns. If engines ran leaner by burning more air and less fuel, they would produce significantly smaller NOx emissions.

Spark plugs can ignite leaner fuel mixtures, but only by increasing the spark’s energy with more volts and amps, but those high voltages erode spark plug electrodes so fast, the solution is not economical.

Lasers on the other hand ignite the air-fuel mixture with concentrated optical energy, have no electrodes and don’t introduce high voltage and amperage across electrodes inside the cylinder.

Lasers also improve efficiency. Conventional spark plugs sit in or near the top of the cylinder chamber and only ignite the air-fuel mixture right up close to them. The comparatively cold metal of the nearby electrodes and the cylinder walls absorbs heat from the air fuel burn, quenching the flame front just as it starts to expand.  (The why behind the hard cold start explained.)

Taira explains lasers can focus their beams directly into the center of the air fuel mixture. Without being quenched, the flame front expands more symmetrically and up to three times faster than those produced by spark plugs.

Equally important, Taira points out, lasers inject their energy within nanoseconds, compared with milliseconds for spark plugs. “Timing – quick combustion – is very important. The more precise the timing, the more efficient the combustion and the better the fuel economy.”

Laser ignition offers less pollution, greater fuel efficiency, and may not wear out.

Hold on to your seat – making small, powerful lasers has, until now, proven difficult. To ignite combustion, a laser must focus light to approximately 100 gigawatts per square centimeter with short pulses of more than 10 millijoules each.  That multiplied perhaps 3000 times per cylinder and perhaps six or eight cylinders comes to quite a bit of energy.

“In the past, lasers that could meet those requirements were limited to basic research because they were big, inefficient, and unstable,” Taira says. Nor could they be located away from the engine, because their powerful beams would destroy any optical fibers that delivered light to the cylinders.

Taira’s research team overcame this problem by making composite lasers from ceramic powders. The team heats the powders to fuse them into optically transparent solids and embeds metal ions in them to tune their properties, a very clever design.

The ceramic designs are easier to tune optically than conventional crystals. They are also much stronger, more durable, and thermally conductive, so they can dissipate the heat from an engine without breaking down.

It gets better:

Taira’s team built its laser from two yttrium-aluminum-gallium (YAG) segments, one doped with neodymium, the other with chromium. They bonded the two sections together to form a powerful laser only 9 millimeters in diameter and 11 millimeters long (a bit less than half an inch).

The composite generates two laser beams that can ignite fuel in two separate locations at the same time. This would produce a flame wall that grows faster and more uniformly than one lit by a single laser.

This is because one laser is not strong enough to light the leanest fuel mixtures with a single pulse. By using several 800-picosecond-long pulses, however, they can inject enough energy to ignite the mixture completely.

Taira’s research also shows a commercial automotive engine will require 60 Hz (or pulse trains per second). The team has already tested the new dual-beam laser at 100 Hz. The team is also at work on a three-beam laser that will enable even faster and more uniform combustion.

The highly promising laser-ignition system is not yet being installed into actual automobiles made in a factory. Taira’s team is, however, working with a large spark-plug company and with DENSO Corporation, a member of the Toyota Group.  You might note that DENSO broke the ground on the iridium spark plug to rave reviews and tests a few years ago.
Here’s the team: Nicolaie Pavel of Romania’s National Institute for Laser, Plasma and Radiation Physics; Takunore Taira and Masaki Tsunekane of Japan’s Institute for Molecular Science; and Kenji Kanehara of Nippon Soken, Inc., Japan.

Lean burn, a dear goal for gasoline engines for decades may well be on its way.  Cheap enough, and with perhaps kits to apply to older vehicles, spark plug installs could make a big dent in gasoline consumption.  Real payoffs will come when computer controls can exploit the new air fuel mix versatility.  It should offer alternative fuels and mixes better usefulness as well.

This is great news.


7 Comments so far

  1. JP Straley on April 26, 2011 7:44 AM

    Cost and practicality keys. How about the recent idea of supercritical fuel injection. Seen that one around? Great laboratory data, but you cant buy it on a real car.

    Let’s hope the car doesn’t age and burn a little oil, that’s going to be hard on optics!

    Automobiles are a very tough environment, and costs rule manufacturing and sales.

  2. Benjamin Cole on April 26, 2011 1:10 PM

    I hope it works in real life. The USA has plenty of natural gas, and can make methanol from it. I assume such lasers can work on methanol.

  3. BFast on April 26, 2011 8:13 PM

    Seems a bit silly to be putting a lot of R&D into internal combustion engines when they are obsolete. See for a peek into the car of the future. Will it be seen as a nuclear car or a steam car.

  4. Henryk on February 26, 2012 7:13 AM

    The FireStorm Plasma iPlug is a new entry in the formerly mundane area of Spark Plugs. All Spark Plugs produce “sparks” to ignite the Air Fuel Mixture in the combustion Chambers. FireStorm is different, it produces “PLASMA”. By doing that, it eliminates the Catalytic Converter and EGR Systems and can still pass future emission requirements in California.

    Here is a clip:

    Further testing after that clip was shot in Detroit proved a 70% savings in fuel all while affording a 125 More Horsepower.
    It is a Paradigm Shift in Air Fuel Ratio as this plug operates at 30 to 1 Air to Fuel Ratio. All current IC engines operate at 14.7 to 1 and require a Cat and EGR.

    FireStorm can even crack water right in the Combustion_Chamber thereby eliminating so-called HHO Generators. Can I hear fill your car up at the side of your house with the garden hose? YES!!!!

  5. Luke Moore on July 8, 2016 2:57 AM

    thanks for article

  6. Shane Zhang on April 5, 2019 6:16 AM

    really useful information, thanks buddy.

  7. Artizono on April 5, 2019 6:17 AM

    good job.

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