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Performance & Hotrod Business February '14

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HOTROD An illustrative example of how a catalytic converter works. Exhaust emissions containing hydrocarbons, oxides of nitrogen and carbon monoxide leave the engine and enter the converter. As these particulates enter the washcoated substrates inside the converter, NOx is reduced and CO and HC are scrubbed. Exiting the converter is harmless water vapor, carbon dioxide and nitrogen. The washcoat catalysts typically consist of precious metals such as platinum, palladium and rhodium. (Courtesy Eastern Catalytic) A Good Scrub Reviewing catalytic converter functions and available performance options. By Mike Mavrigian A catalytic converter, as the term implies, is a component that uses a catalyst (in the form of certain precious metals) to create a chemical reaction that converts certain exhaust particulates. Catalytic converters are placed in the exhaust stream between the engine's exhaust manifolds (or headers) and the muffler(s), serving as chemical conversion units that "scrub" harmful emissions. The goal is to reduce NOx (oxides of nitrogen) levels and to change HC (hydrocarbons) and CO (carbon monoxide) into harmless emissions. HC and CO are chemically altered to change into water vapor and CO2 (carbon dioxide). The same air that we breathe is drawn into the engine. Ambient air includes a number of different gasses including nitrogen, oxygen and carbon dioxide (plus small percentages of argon, hydrogen, neon, helium, krypton and xenon). Nitrogen content in the air accounts for about 78 percent. Oxygen content is about 21 percent and carbon dioxide accounts for about 0.03 percent. During the combustion process, the three harmless primary gasses in the air (nitrogen, oxygen and carbon dioxide) burn with the fuel mixture, which creates harmful levels of NOx (created as the result of burnt nitrogen), HC and CO that enter the exhaust stream. The catalytic converter's job is to chemically transform these exhaust byproducts back into a harmless state before they enter the atmosphere via the exhaust tips. The catalytic converter features a substrate, made of either ceramic or metal, in a "honeycomb" configuration. The small holes or "cells" allow gasses to pass through. The surfaces of the substrate structure are "washcoated" with various precious metal compounds that react to the unburnt emissions particles. These washcoatings typically involve platinum, rhodium and palladium. 52 n Performance & Hotrod Business PHBFEB_52-77.indd 52 n Rhodium and palladium are effective in reducing NOx, while platinum and rhodium are effective at converting HC and CO. Over the years, three different catalytic converter designs have been used in production vehicles. This includes two-way, three-way and three-way-with-air designs. The terms refer to the number of emissions particles that they are able to treat. Two-way converters, loaded with chemically treated pellets, were designed to treat only carbon monoxide and hydrocarbons. Around 1981, three-way converters were introduced to treat carbon monoxide, hydrocarbons and oxides of nitrogen. These converters featured ceramic substrates with tiny cells, or passages, in a honeycomb construction. The substrates were washcoated in precious metals. Three-way-with-air converters added an air injection tube to the converter that helps to promote emissions conversion efficiency. A three-way-with-air converter features two separate substrates. The first substrate (the February 2014 1/7/14 2:14 PM

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