Design News; May 22, 1995 Goto Design News Website

Catalytic Ignition

Replaces Spark Plugs

Design varies timing with constant ignition source, improves combustion, mileage, and emissions

Mark A. Gottsthalk, Western Technical Editor

SMARTPLUG AUTO-TIMED CATALYTIC IGNITION

San Diego, CA-Ever wonder what would happen if your car's catalytic converter was pulled from the tailpipe and placed in the engine'?

Mark Cherry has. The thought, in fact, inspired him to develop and patent what he calls the Smartplug, a device that exploits a technology called Auto-timed Catalytic Ignition, or ACI. A replacement for the ubiquitous spark plug, it potentially offers more thorough combustion. increased mileage, extra-lean burn capability, and improved emissions.
If all goes well, Cherry, president of Automotive Resources, hopes ACI will enable engines to meet 1999 automobile-emissions standards without any exhaust after-treatment.
Externally, SMARTPLUGs look much like conventional spark plugs. They thread into the cylinder head and connect to an ignition system via wires protruding from their tops. But the similarities end there.
Inside each unit lies a ceramic rod coated with a catalyst-typically platinum, but sometimes rhodium, palladium, or ceria. The rod threads into the SMARTPLUG's crown and lies centered within a hollow cylindrical chamber that extends the length of the body. At the tip of the SMARTPLUG, a set of flame nozzles exhaust the chamber to the engine cylinder.
When a user starts the engine. a constant dc power source supplies voltage to each SMARTPLUG, heating the catalyst to operating temperature. It's the heated catalyst-not simply thermal energy-that causes combustion of the fuel/air mixture. Once the engine is running, the voltage may be cut or reduced, because combustive heat usually can sustain catalytic ignition.
A combustion cycle occurs in two distinct steps. First. the catalyst lights the small volume of mixture that collects inside the SMARTPLUG's chamber. This event leads to the second step. during which jets of burning gas shoot from the flame nozzles to the periphery of the cylinder and ignite the main charge. 'Essentially we have a diesel cycle occur ring inside the pre-chamber and an Otto cycle via flame ignition in the cylinder," says Cherry.
The difficulty with such a process involves providing for variable ignition timing. Because combustion occurs spontaneously, Cherry had to develop a way to control the mixture's progress to the catalyst. To do so he designed the SMARTPLUG's chamber to retain combustion gases after firing-it essentially remains unscavenged. "This design shields the ignition source from the fresh mixture until we want ignition to take place," he says.
Static timing depends upon the ratio of chamber length to cylinder length. During the compression stroke, Cherry found that the boundary-layer interface between the un-burned mixture in the cylinder and the spent gases in the chamber moved in lock-step with the piston position. If, for example, the chamber is half the stroke length, the boundary moves at half the piston speed. "We can calculate the precise moment that the mixture will touch the catalyst," he explains. "This function stays constant throughout the load and speed range of the engine." By varying the length of both the chamber and the catalyst, he's varied static timing from 170 degrees to 15 degrees BTDC.
By contrast, dynamic timing depends on the density of the fuel/air charge. As the mixture density (or engine load) increases, timing advances. This phenomenon is exactly the opposite of normal automobile ignition, but perfect for two-stroke boat engines that require a reverse timing curve. It also works well with constant-speed motors such as generators, drag-racers, or lawn mowers.
For automobile applications Cherry developed and patented a third version of the SMARTPLUG in which the mixture cools the catalyst. Thus an increased load (and denser mixture) retards timing. Not limited to small changes, this method allows for timing advances as great as 60 degrees.
Automotive Resources claims that their catalytic ignition's jet-flame improves combustion efficiency and increases mileage because of its ability to burn extra-lean mixtures. "The conventional limit is around 22:1," Cherry claims, "but we've run at 28:1, and our Iloly Grail is A2; twice as much air as fuel to burn."
Employing neither spark plugs nor magnetos, the system emits zero EMI, a potential boon of designers of light aircraft. It also means no electrical energy is wasted on a conventional ignition system.
Emission improvements are tougher to explain. though quite dramatic to demonstrate. Drops in NO, of 90% have been recorded with no loss in performance. Cherry theorizes that conventional ignition ionizes nitrogen whereas catalytic ignition does not. When you keep combustion temperatures low with a lean charge, nitrogen compounds won't form. It's also possible that catalytic ignition induces some of the water/gas shift-phase reaction that occurs in a catalytic converter. Whatever the mechanism. he believes Auto-timed Catalytic Ignition will enable more fuel-efficient. higher-power. cleaner engines with little or no exhaust gas processing.

Other Applications:
* Automobiles
* Outboard motors
* Industrial generators
* Lawn mowers





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