Replacing an Engine’s Spark Plugs with Lasers – That Sounds like the Stuff of Genius

BY Marshall Brain / POSTED April 26, 2011
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The Spark Plugs used in an internal combustion engine have been nearly unchanged since the beginning. The design is very simple – a high-voltage spark jumps a tiny gap and this spark ignites gasoline. Spark plugs are a relatively cheap, reliable way to get the job done.

But spark plugs are not perfect, so now there is a move afoot to replace them with lasers:

Flash of Genius: Lasers Could Replace Spark Plugs Under Your Hood

Scientists are looking to harness the intensely focused light from laser beams to fire the cylinders in combustion engines. And best of all, they claim laser spark plugs will result in better fuel efficiency. Conventional spark plugs only fire the fuel near the top of the cylinder, resulting in a modest amount of fuel wasted with each cycle. And blast after blast, the metal terminal that literally sparks in causing the ignition is slowly worn away.

Clearly it is possible to make a small laser that can burn things, as seen here:

But think about an 4-stroke engine running at 6,000 RPM. The laser has to be able to light the gas 50 times per second in each cylinder at precisely the right time, and it has to do that reliably while sitting atop a hot vibrating engine. To do that, engineers need a 1,000-watt pulsed laser as described here:

Practical internal combustion engine laser spark plug development

If they can create it, the savings can be substantial:

The cost values shown for the natural gas engine laser spark plug are based upon the estimated operational costs of an 800 Kilowatt 16-cylinder Waukesha engine operating at 1200rpm with 16 lasers (one for each cylinder). At 1200 rpm the laser operates 24 hours a day, 365 days a year at 10 Hz (1200 rpm/2 strokes/ 60sec/min) for a total of approximately 315M pulses per year. The natural gas fuel consumption cost estimation for this engine is based upon $10MMBtu, $65.00/hr equal to approximately $569,000 per year [10]. Replacement of a standard spark plug with a laser spark plug provides an estimated 40% increase in fuel efficiency. Under these conditions, the laser spark plug requires $46.00/hr in fuel consumption. This translates into cost savings of approximately $174,000 per year.

A 40% increase in fuel efficiency is an amazing result.

As I read the two articles, it seems like the major advantage of the laser is the larger flame front that it ignites. That leads me to wonder if you could modify the traditional spark system to get a longer spark. For example, could you get a long spark to flow from the plug down to the surface of the piston like a miniature bolt of lightning? Perhaps that is impossible.

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