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September 2000

The Aero-News Network Daily News Brief

SmartPlugs: A Better Idea?
ANN Exclusive Every so often, somebody comes up with a revolutionary idea to change forever the way we do things," and the ideas turn out to be speculative, at best. Mark Cherry, inventor of the SmartPlug, isn't speculating. He's testing, and he's testing independently, and he's testing with some of the best in the business.
The SmartPlug is a device that's about the same size as a regular spark plug, and it screws into the existing spark plug hole in your engine. It performs the same function as the spark plug, that is, it ignites the mixture inside the engine -- but in a totally different way, opening the door to many potential advantages.
The SmartPlug is hollow, with a precious-metal "catalyst" on a ceramic rod running down the middle, and a nearly-sealed bottom end, where a small amount of fuel-air mixture can enter from the area of the combustion chamber of the engine. The catalyst has a tiny wire inside, allowing it to be pre-heated. When the catalyst is sufficiently heated and the engine's fuel-air mix is pumped in, courtesy of the starter motor, the catalyst sets fire to the small amount of charge inside its body, and the flaming charge then blasts out the holes, into the combustion chamber, and, "poof," the piston goes down. Power stroke.
If this sound a lot like the diesel cycle, it should; but with a big difference: the diesel requires very heavy compression for its glow plug to set off the combustion, and the SmartPlug runs at normal compression ratios. It can be used to set off engines running on gasoline, diesel fuel, jet fuel, or an alcohol/water mixture, depending on the engine.
After extensive testing on many different types of engines, and using many different types of fuels, and after having the principle tested with a Continental 0-200 in a NASA-Glenn facility, an aircraft owner named Dr. Forrest Bird, of Cherry's state of Idaho, stepped forward to volunteer his special J-3 (0-200, floats, droop tips, extended wings, 4130 WWII glider fuselage) for use as a guinea pig. Dr. Bird flew it first on 100LL, and then on 92-octane unleaded Mogas. During the transition, there was a period when the two fuels were mixing, as well. Data are preliminary and far from conclusive, but Dr. Bird reports an increase of 200 rpm through the test, and a notable increase in the smoothness of the engine, with "at least as good" performance. Not definitive, but much better than the usual "first effort."
The 0-200 at Glenn has produced equivalent-to-stock horsepower, running Jet-A.
Now, there are a lot of other tests, and test engines, that Cherry has equipped with these plugs; we're just bringing you some highlights. If you're interested, you should look at the website, and notice the myriad applications, from watercraft, to gen sets, to military outboard motors.

How can it work?
Being an old engine guy myself, I was interested in how an engine can be timed using these devices. There are several principles at work. The tiny combustion chamber in the plug (the "pre-combustion chamber") is a replica of the cylinder it's installed in, except that it always has a portion of spent, burned gases in it. As the new charge of fresh air-fuel mix gets pushed into the pre-combustion chamber by the piston's compression stroke, the burnable mix compresses the dead gases above it, in direct proportion to the piston's position in the cylinder. By varying the length of the catalyst rod (and varying the ratio of the catalyst's diameter to the pre-combustion chamber diameter), the point of combustion can be fairly closely set. This "static" timing becomes one important factor in tuning the system. 
The "dynamic" timing, the timing that is actually experienced while the engine is running, needs to change, mostly according to the speed and load of the engine. the SmartPlug has two methods of varying dynamic timing. SmartPlug catalysts can be designed to work without any current's going through them at all, once the engine achieves operating temperature, just like the glow plugs in your model airplane or Caterpillar tractor. The ignition point with these "passive" catalysts will vary, depending on the speed of the engine (as the engine goes faster, more heat is retained in the catalyst, prompting earlier ignition of the charge in the pre-combustion chamber, and vice versa), and, to a smaller extend, the load under which it is operating. Once the engine is running, the plug requires no more power, so the engine is shut off with a mixture (of fuel) control. The other method of varying the timing involves using an "active" catalyst, one which is designed to require a current's flowing through it all the time. The amount of current that is used will allow the catalyst to be either "hot," "very hot," or "really, really hot," and degrees in between, changing the ignition point of the compressed gases forced into the pre-combustion chamber. "Active" catalysts require an engine "mapping," to vary the wattage directed to the  plug.
Each SmartPlug uses anywhere from about six watts on up for warm-up and running, depending on the application; and, of course, in the "passive" mode, it requires no electricity at all when it's running.
In the J-3, both types of plugs are used, with one of each type in each cylinder. The passive plug is set to fire sooner as the load and speed increase; it is too retarded at idle to be considered smooth. The active plug is set to take care of the idle timing, and its power is varied so that, at full power settings, it fires at the same time as the passive plug. The two plug systems in tandem have produced improved power and smoothness, according to Dr. Bird.
If there is a slight difference in ignition timing, it is fixed by an interesting "self-compensating" effect: as the first plug in the cylinder fires, the pressure in the cylinder rises immediately, forcing the charge faster into the other plug's pre-combustion chamber, and leading to quicker ignition. The whole operation -- from first plug's firing to second plug's firing -- happens almost immediately.
Because the temperatures developed at the catalyst are extremely high, special ceramic technology was adapted in partnership with NASA. Without this new technology, it is doubtful that the SmartPlugs could exist.

Benefits
Because the SmartPlug ignites a portion of the air-fuel mix, which then comes blasting out of the pre-combustion chamber with its tail on fire, the ignition in the cylinder's combustion chamber itself is more complete than if the ignition were precipitated by just a spark alone. This has implications for fuel economy and carbon deposit accumulation (hence engine wear) that are appealing. Because the SmartPlug works without complicated timing mechanisms (and can, indeed, work without any electrical hookup at all, once it's running), reliability should increase. Because it doesn't require spark-making equipment, your magnetos or coils, points, etc., can be left on the ground; and because there's no electrical spark, your radio reception should be enhanced. Because your engine will run without electricity, you will be forced to shut off the fuel, and there will never be the possibility of uneducated hands' turning the prop over with an ungrounded mag, just to get their knuckles rapped.
The lure of alternative fuels' being burned is also attractive, although the SmartPlug must be matched to each fuel -- you can't expect to fly to grampaw's on alcohol, refill on diesel, fly down to the gas station, and end up at another airport pumping Jet-A.

Concerns
One of our big concerns had to do with the buildup of carbon and grunge inside the device, around the catalyst and on the walls of the pre-combustion chamber. Tests have been run for 250 hours, so far, with diesel fuel, and the teardown showed about what you'd expect in the head and on the cylinder walls, but "virtually no" buildup inside the SmartPlug. Mark has some theories about that, and he stresses that they're only theories; but they make sense. He thinks the clean results were, "...due perhaps to the high temp of the catalyst, and some superheated steam, shielding the walls [of the pre-combustion chamber]," he told us.
Another concern we had, from a theoretical standpoint, was that the SmartPlug effectively turns the old spark-ignition engine into something approximating a diesel. Not really; but the SmartPlug, because of its shooting a big flame into the combustion chamber, does ignite the mixture faster than a spark plug. We were worried that there would be potentially much-higher post-compression loads and pressures. NASA tested that. "Because combustion is faster, we do reach 2~5% higher pressures, but that's not a severe extra load." Probably not significant, even. Because of cleaner, more-complete burning, there was observed a bit less washdown of the cylinder walls. That's why Mark and his team expect lower cylinder wear.

More tests
NASA is putting the SmartPlug into an airboat for extended testing; the Marines are putting it through tests in extreme cold, as well as in outboard motor configurations, small gasoline engines, and in the "one-fuel-forward" program. SmartPlugs have run successfully in two-stroke and four-stroke and diesel engines, burning Mogas, Avgas, alcohol/water mix, diesel, and Jet-A. Interestingly enough, when the SmartPlugs are used in personal watercraft two-strokes (using a biodegradable vegetable oil for lubrication), the unused fuel is biodegradable, and actually reduces the nitrogen content of the water it's used on, performing one of the same functions that sewerage treatment plants do.
Availability
SmartPlugs are not yet commercially available to the mass market. Each application needs a bit of research. For this reason, the plugs are available only to bonafide manufacturers and others who have the facility to do the requisite testing.
FMI: http://www.smartplugs.com/

Phone: 208.265.2723
Email: info@smartplugs.com
SmartPlug is protected by US and International Patents.