Its basic design dates back 170 years, and it's one of the most reliable, robust, and cost-effective components in a modern vehicle. But can the humble spark plug survive the relentless race for improved fuel consumption and lower emissions?
Not as it is presently designed, according to engineers and researchers at Federal-Mogul. Their Advanced Corona Ignition System (ACIS) could replace the device that helped make Albert Champion, Robert Bosch, and Kenelm Lee Guinness (KLG) famous, while improving fuel consumption by up to 10%.
ACIS, now in development at the company’s technical centers in Europe, the U.S., and Asia, generates an electrical discharge with a much higher degree of in-cylinder coverage than spark-ignition systems, according to Kristapher Mixell, Federal-Mogul’s Director, ACIS Powertrain Energy.
“Corona ignition creates a significantly larger ignition source, of higher intensity, spread throughout the combustion chamber,” he explained.
Mixell told AEI that the ACIS technology is being developed to provide more thorough combustion. It facilitates advanced combustion strategies including lean burn, highly diluted mixtures, and very high rates of EGR (exhaust gas recirculation) to further increase fuel efficiency.
“With proper calibration, ACIS will allow automakers to increase EGR dilution to enhance fuel economy and reduce emissions, while still providing excellent drivability,” he said.
ACIS uses a high-energy, high-frequency electrical field to produce repeatable, controlled ionization, creating multiple streams of ions to ignite the fuel mixture throughout the combustion chamber. By comparison, conventional spark ignition creates only a small arc in the gap between the electrodes of a spark plug.
By eliminating the spark plug and its arc, ACIS also eliminates the source of electrode erosion—the main cause of wear in a conventional spark-ignition system. This prolongs ignition system durability and extends service intervals even further than the 60,000 km (37,000 mi) recommended by Ford of Europe, for example.
By designing it to fit within the space of a spark-ignition system, Federal-Mogul has optimized ACIS for ease of implementation in high-volume applications for both current and future powertrain architectures.
Its “two-piece igniter” architecture is designed to allow engine manufacturers to replace traditional coil and plug systems with no adverse impact on engine design or assembly. Cylinder head layout and spark plug bore configuration can be largely carried over, Mixell claimed.
ACIS uses materials that are already proven in automotive applications to ensure durability throughout the designed service life. “By using currently available materials and processes, ACIS can be brought into a production environment without roadblocks arising from problems with exotic materials or processes,” said Mixell.
The company also states that the technology allows more optimal timing of the start of combustion for more rapid ignition and burning, allowing engines to achieve greater conversion of the fuel energy to mechanical energy. There is added potential for simultaneous reduction in engine cooling requirements.
Corona ignition technology is also claimed by the company to provide higher energy and greater opportunities for ignition than a spark-ignition system, readily accommodating different fuel characteristics.
“The technology enables powertrain engineers to develop more efficient combustion strategies, such as stratified charge, lean burn, and high levels of EGR to reduce fuel consumption and exhaust emissions,” explained Mixell. “We have already recorded fuel consumption improvements of up to 10% on a 1.6-L turbocharged gasoline direct injection engine, and there is potential for further improvement."
ACIS is a game-changing technology, he said, "because it makes so many other combustion improvements possible.”