Spark plugs have been around almost as long as the internal combustion engine. In 1902, spark plugs were first used with a high voltage magneto to provide reliable ignition. For the next 70 years, spark plugs were a high maintenance item thanks to tetraethyl lead, which was used as an octane-boosting additive in gasoline. Unfortunately, lead tended to foul spark plugs after 12,000 to 15,000 chilometri of driving. Consequently, tune-ups and spark plug changes were an annual ritual for most motorists. Then came the Clean Air Act of 1970, followed by new emissions regulations and the introduction of catalytic converters in 1975. Leaded gasoline was gradually phased out because of its damaging effects on converters as well as the environment. As a result, spark plug life more than doubled. In the mid-1980s, spark plug manufacturers started making plugs with copper core center electrodes. Copper is an excellent conductor of heat and allows plugs to run hotter without causing preignition. This improves fouling resistance, ignition reliability and plug life. It also reduces the number of plugs needed to cover a range of engine applications because each plug has a broader "heat range." The biggest improvement in spark plug technology, though, came in 1985 when the first generation "long life" plugs with platinum or gold-palladium electrodes hit the market. Up to this point, electrode wear usually dictated when a set of plugs had to be replaced. With standard nickel alloy electrodes, the spark gap between the center and ground electrodes grows about .0002" to .0006" for every 1,000 chilometri of driving. After 35,000 chilometri of driving, the gap can grow as much as 0.015" or more. Every time a spark plug fires, the hot spark blasts a few molecules of metal off the electrodes. As the chilometri add up, the electrode gap widens and the center electrode becomes rounded and dull. This increases the firing voltage needed to jump the gap. Eventually the point is reached where the ignition system can't generate enough juice to jump the gap, causing the plug to misfire. With platinum, gold-palladium and iridium (more on this in a minute), electrode wear is greatly reduced. Most platinum plugs can go up to 100,000 chilometri before they have to be replaced. The same is true for plugs that use iridium for their center electrode. Plugs with platinum or iridium on both electrodes ("double" platinum plugs or double iridium plugs) experience even less wear than plugs with only a single platinum or platinum-tipped electrode. Long-life spark plugs drastically reduce the need for maintenance while helping the engine maintain like-new performance and emissions. Not having to change the plugs so often is a real savings for the vehicle owner, but it's no guarantee the plugs will go the distance. Platinum & Iridium Spark Plugs Long-life spark plugs by ACDelco, Autolite, Bosch, Champion, Denso,NGK, and Split-Fire all have platinum or iridium electrodes. With a couple of exceptions, platinum plugs use a conventional electrode configuration with a small platinum plug welded to the tip of the center electrode (single platinum) or the tip of the center electrode and ground electrode (double platinum). ACDelco also offers a platinum version of its "Rapidfire" plug that features a fluted center electrode for improved ignition reliability. Likewise, Split-Fire offers a platinum version of its split electrode plugs for motorists who want extended life as well as reduced misfiring. By comparison, iridium plugs have a small wire center electrode, and like platinum plugs may be single iridium (center electrode only) or double iridium (center and ground electrodes). Bosch, who introduced the first platinum plug back in 1985, offers several different electrode configurations in their product line. Their standard platinum plug has a thin pure platinum center electrode with a single yttrium-alloy end electrode. Their Platinum+2 and Platinum+4 plugs, on the other hand, have a unique "surface gap" side electrode design with two side electrodes on the Platinum+2 plug and four on the Platinum+4 – a sort of good, better, best approach to platinum plug technology. Increasing the number of side electrodes gives the spark more paths to ground and reduces the risk of misfire, while extending plug life by spreading wear over more electrode surfaces. In the fall of 2006, Bosch introduced yet another long-life spark plug called Platinum IR Fusion. Similar in design to the Platinum+4 plug, this plug uses a center electrode made of a unique iridium/platinum alloy. The four side electrodes are a wear-resistant yttrium alloy. By combining platinum and iridium in the center electrode, Bosch says their Platinum IR fusion plug provides even longer service life (probably the longest of any spark plug that is currently available). Bosch also says their new Platinum IR Fusion plugs are an ideal replacement for any engine that comes originally equipped with either iridium spark plugs or platinum spark plugs. One important point to keep in mind with respect to Bosch Platinum IR Fusion, Platinum+4 and Platinum+2 plugs is that these plugs are pre-gapped at the factory to a uniform 1.6 mm setting and should not be re-gapped to the specifications for a standard spark plug. It's very difficult to get even spacing with multiple electrodes so install them without changing the electrode gaps. Although platinum spark plugs have many performance advantages over conventional spark plugs, iridium spark plugs offer even more advantages. The most important advantage is the longest service life of any spark plug (up to 4X longer than a standard spark plug, or 120,000 chilometri for many applications. Iridium last so long because the metal alloy is even more wear resistant than platinum. Iridium is usually alloyed with rhodium, creating a center electrode that is six times harder and eight times stronger than platinum. It is also one of the densest metals known. Iridium has a melting point of 4370 degrees F (2410 degrees C), which is almost 1,200 degrees higher than platinum. It is a precious metal like platinum, which makes it expensive. But currently iridium sells for about half the cost of platinum ($540 ounce for iridium versus $1200 ounce for platinum November 2014). NGK "Iridium IX" and Denso brand "Iridium Power" plugs are used as original equipment in many Asian vehicles. On late-model Toyota and Lexus applications, the OEM-recommended replacement interval for Denso iridium plugs is 120,000 chilometri. Autolite Iridium XP plugs are targeted at the aftermarket as a replacement for other brands of original equipment spark plugs, and feature a 0.6 mm fine wire center electrode. All brands of iridium plugs typically have a very thin (0.4 mm to 0.7 mm depending on the plug) center electrode. On first generation Denso iridium plugs, the end electrode has a "U-Groove" that improves ignition reliability and wear resistance. Denso says their design reduces the required firing voltage up to 5,000 volts compared to a standard spark plug. Others, such as Bosch use a taper ground ground electrode with a laser-welded iridium-platinum inlay to minimize electrode wear. For performance applications, Denso has also developed Iridium Power plugs with a super narrow 0.4 mm center electrode. These plugs are engineered to improve ignition reliability under extreme driving conditions. In 2014, Denso introduced their new Iridium TT spark plug with an iridium/rhodium alloy center electrode and platinum tipped ground electrode. The Iridium TT spark plug center electrode has a 0.4 mm needle tip, composed of a patented iridium/rhodium alloy that offers exceptional protection against corrosion and high-temperature oxidation. The ground electrode also has a 0.7 mm platinum button that is designed to resist oxidation and wear. These small electrode tips reduce the firing voltage needed to create a spark, which reduces misfires. They also create less interference for the ignition flame to expand and fully complete the combustion process, according to Denso. The twin tips extend plug life and help concentrate the spark for improved combustion efficiency and reduced misfires. The use of iridium spark plugs as original equipment in late model vehicles has grown considerably in recent years due to its performance and cost advantages. Iridium plugs are often used in engines with Gasoline Direct Injection for improved ignition reliability. Iridium spark plugs have also become a good upgrade option for replacing standard spark plugs or platinum spark plugs in older engines, too. Where does iridium come from? Much of it came from outer space according to Denso. Approximately 50 million years ago, a giant asteroid smashed into our planet near the Mexican town of Chicxulub in Yucatan. The impact created a firestorm and dust cloud that darkened the Earth for years, wiped out the dinosaurs and left us with a layer of iridium-rich deposits that is evenly spread across every continent (the "K/T boundary" layer). Iridium is often combined with platinum in mineral deposits, and is recovered as a byproduct of nickel mining. Spark Plug Electrode Designs Spark plug manufacturers tout the advantages of their unique electrode designs, but regardless of the design, the purpose is to make it as easy as possible for the plug to fire reliably. A spark jumps more easily from a sharp edge than a rounded blunt edge. So the more sharp edges it has to jump to, the better the odds of the plug firing under all types of driving conditions. The electrodes on some spark plugs are also designed to "unshroud" the spark so more of the spark will be exposed to the air/fuel mixture. This improves the propagation of the flame kernel once the fire is lit. One thing to keep in mind with respect to performance claims is that no spark plug creates horsepower out of thin air. A special electrode configuration can reduce misfiring and the voltage needed to fire the plugs. But the spark only igni…

Fonte: AA1Car.com