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The igniting spark
The trends towards high-pressure injection and engine downsizing are also challenging spark plug manufacturers. They rely on new designs and innovative materials to ignite the fuel mixture even cleaner and more efficiently.
The igniting spark
Villach in Carinthia almost marked the end of the electric spark plug. At the non-university research center Carinthian Tech Research, or CTR for short, it was possible to ignite the fuel-air mixture in a test engine with previously unattainable precision and efficiency - using laser light instead of the electrical ignition spark. “The laser pulse only lasts a few nanoseconds, creates a plasma cloud of several hundred thousand degrees, can be precisely adjusted to the ideal crankshaft angle and can ignite all conventional and alternative fuels equally well,” explains Gerhard Kroupa, head of the laser ignition project at CTR. But despite these convincing advantages, the laser spark plug developed together with Graz-based AVL List GmbH has been put on hold by the automobile manufacturers for the time being. “Apparently still too expensive at the moment,” Kroupa briefly comments on the decision and consoles himself with the fact that the high-tech spark plug, which has matured over years of development work, will soon be used in an industry in which not every cent is turned around three times: in space travel.
Innovations required
Although the laser spark plug will only fire rockets for the time being, development in the field of electric spark plugs for automobiles has by no means stood still. While in naturally aspirated engines an ignition voltage of 20,000 to 30,000 volts is sufficient for reliable ignition of the fuel-air mixture, highly charged engines of the latest generation require ignition voltages of up to 40,000 volts. “When it comes to spark plugs, not only the purity of the ceramic but also the overall design has to be right,” explains Tobias Ruf, Vice President Engineering Spark Plugs at Bosch. In his opinion, the big topic in spark plug development is currently miniaturization. “Today we are witnessing the transition from plugs with M14 threads to M12, and from 2020 plugs with M10 threads will play an important role,” says Ruf. Bosch has recently started manufacturing the center electrode of its high-performance spark plugs from the nickel alloy Alloy 602, which is significantly more resistant to high-temperature corrosion than alloys previously used.
New candle design
The Japanese manufacturer NGK, also an original equipment manufacturer for major car and motorcycle manufacturers, sees the future in different types of single-mass precious metal spark plugs. In 2011, NGK introduced an innovative cup design for the spark plug contact, which enables extreme ignition voltages in highly charged engines without the risk of breakdown or flashover. NGK demonstrates how much high-tech there can be in a spark plug with its series spark plug for the 360 hp four-cylinder turbo Mercedes A45 AMG. In addition to the “cup design” mentioned, it is equipped with a long insulator made of new, particularly dielectric-resistant ceramic. The quickly heating insulator base ensures good cold start properties, the slim M12 thread leaves more space for cooling channels. The 0.8 mm fine two-stage iridium center electrode reduces wear, the beveled SPE ground electrode with platinum blocks on the edge improves mixture accessibility and flame propagation.
The Japanese supplier Denso also uses the silvery precious metal, which is similar to platinum, for its “Iridium Power” spark plugs. Denso presents measurement results according to which iridium spark plugs increase engine performance by at least half a horsepower compared to conventional spark plugs. When it comes to design, Denso goes its own way and shapes the tip of the ground electrode in the shape of a fine cone. This reduces the heat absorbed by the electrode and improves ignition performance because the area on the ground electrode that actually comes into contact with the pilot flame is very small. The streamlined cone allows the fuel-air mixture to flow past with less friction, allowing for consistent ignition.
The German supplier BorgWarner Beru Systems has developed an intelligent solution for use at the highest ignition voltages with its plug-in ignition coil “Plug Top Coil”. A special compression spring connection allows the use of spark plugs with an extended insulator neck and a new, bowl-shaped “bowl” connection, which ensures reliable ignition of the fuel-air mixture. Another innovation from Beru is the “Dual Coil Ignition System” with two solenoid coils in one housing. The advantages over conventional ignition coils: Shorter ignition intervals and more precise timing at different speeds and rapid charge changes.
The future of ignition
The US spark plug manufacturer Federal Mogul Motorparts has developed the innovative Corona ignition system specifically for gasoline engines in lean-burn operation and has proven fuel savings of up to ten percent in tests. The ignition unit of a corona candle consists of an induction coil and a control unit that converts the twelve volt input voltage into an alternating voltage with a frequency of around one MHz. From four ignition electrodes, a strong alternating electric field radiates far into the combustion chamber, transforming the air-fuel mixture in the area of the ignition electrodes into a plasma that ignites the charge within a few nanoseconds. Klaus Bolay, technology trainer at Federal Mogul: “The Corona ignition is already being used successfully in stationary industrial engines and has a good chance of being used in passenger car engines in the near future.”