'Catalytic Converters'

• First widely introduced on series-production automobiles in the US market for the 1975 model year, to comply with tightening EPA regulations on auto exhaust, catalytic converters are still most commonly used in motor vehicle exhaust systems
• Three-way catalytic converters: Since 1981 three-way catalytic converters have been at the heart of vehicle emission control systems in North American roadgoing vehicles, and have been used on "Large Spark Ignition" engines since 2001 in California and from 2004 in the 49 states
• Two-way catalytic converters: This type of catalytic converter is widely used on diesel engines to reduce hydrocarbon and carbon monoxide emissions. They also were used on spark ignition (gasoline) engines in USA market automobiles up until 1981, when they were replaced by three-way converters due to regulatory changes requiring reductions on NOx emissions
• Catalyst poisoning and deactivation: A variety of conditions may cause the catalyst to overheat (heat deactivation) and potentially to melt down. Some factors that can cause this are:
  • Lubricating oil in the exhaust system (caused by engine wear, or by damaged rings or valves)
  • An engine misfire or ignition failure (causing unburnt fuel to enter the exhaust)
  • A cracked exhaust valve (again, causing unburnt fuel in the exhaust)
• Rich Burn Spark Ignition Engines: For spark ignition engines the most commonly used catalytic converter is the three-way converter, which works best used on engines equipped with closed-loop feedback fuel mixture control employing one or more oxygen (lambda) sensor
• Oxygen storage in 3-Way Converters: In order to oxidize CO and HC, the catalytic converter also has the capability of storing the oxygen from the exhaust gas stream, usually when the air fuel ratio goes lean

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