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Emission Control Systems

Emission Control Systems. Vehicle Pollution Sources. 3 areas of a vehicle that can pollute… tailpipe emissions fuel tank vapors (and carburetor vapors) crankcase blow-by gases. Major Engine Pollutants.

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Emission Control Systems

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  1. Emission Control Systems

  2. Vehicle Pollution Sources • 3 areas of a vehicle that can pollute… • tailpipe emissions • fuel tank vapors (and carburetor vapors) • crankcase blow-by gases

  3. Major Engine Pollutants • hydrocarbons: produced when some or all of the fuel does not get burned during combustion, or from raw gasoline vapors • tailpipe emission • fuel tank & carburetor emission • carbon monoxide: produced when there is insufficient oxygen to support combustion • tailpipe emission • oxides of nitrogen: produced when combustion temperatures exceed 1400°C / 2500°F • tailpipe emission

  4. Blow-by Emission Control • crankcase ventilation system handles blow-by gases • hydrocarbon emissions • road-draft tube used until 1962

  5. Blow-by Emission Control • Positive Crankcase Ventilation system (PCV system) in use since 1963

  6. Checking PCV System • replace the Positive Crankcase Ventilation valve and check its hose (inexpensive)… • Tech Tip: • pull the PCV valve out of the engine while it’s running • place your finger under the valve • you should feel and hear suction & the valve should click

  7. Fixed Orifice Tube PCV Systems • a precisely determined hole size acts as the valve • no need for a spring and valve assembly

  8. Evaporative Emission Control System • prevents raw HC’s (from gasoline) from being vented into the atmosphere • (in use since 1971) • charcoal canister absorbs fuel vapors when the engine is off & sends them to the intake manifold so they can be burned when the engine is running

  9. Evaporative Emission Control Systems • on 1996 & newer vehicles, PCM… • purges canister vapors via a purge solenoid • monitors vapor flow • monitors the system for leaks • vehicle may use a separate pump to pressurize system to see if pressure can be maintained • if PCM detects a leak, check engine light will illuminate

  10. Reducing NOx Tailpipe Emissions • Exhaust Gas Recirculation valve (EGR) allows some exhaust gas back into the intake air stream • used on most engines since mid-1970’s but not all • EGR dilutes/displaces fresh, incoming AFM which drops combustion temperature = < NOx

  11. EGR typically operates under light throttle, cruising conditions on a warmed up engine • during warm up, WOT & at idle, it does not operate EGR Valve EGR Pipe

  12. EGR Valve Styles • 1) mechanical EGR operated by engine vacuum • vacuum acts on a diaphragm to open the valve (fig. a) • some EGR valves use a computer controlled solenoid to modulate the vacuum signal to the diaphragm (fig. b) • others use an exhaust pressure sensor to help determine rate of exhaust gas flow (fig. c) fig. c fig. b fig. a

  13. EGR Valve Styles • 2) digital or electronic EGR valve • PCM controls 1 or more solenoids to modulate EGR flow • no vacuum diaphragm is used • each solenoid has an integral pintle position sensor • this sensor “tells” the PCM the position of the pintle valve • the solenoids are pulsed on & off by the PCM many times/second when needed

  14. EGR Service • Inoperative EGR systems can lead to… • excessive NoX emissions (possible failure at AirCare) • detonation (knocking & pinging) • caused by… • defective diaphragm • weak vacuum signal • defective or incorrectly routed vacuum hoses • shorted or open solenoid • exhaust passage blocked with carbon

  15. EGR Service • Excessive EGR operation can lead to… • rough idle • stalling • caused by… • improperly routed vacuum hoses • carbon on pintle valve seat • faulty EGR valve

  16. Reducing Tailpipe Emissions • catalytic converters reduce HC, CO & possibly NOx • used on all vehicles since mid-1970’s • HC & CO in the exhaust is oxidized by the catalyst which can contains platinum, palladium & rhodium • HC + O2 = CO2 & H20 • CO + 02 = CO2 • this is a two-way catalyst • needs ≈ 315°C / 600°F to operate

  17. Three Way Catalysts • reduces HC, CO and NOx levels • NOx is converted to nitrogen & CO2 • front ½ controls NOx & back ½ reduces HC & CO • contains cerium – has the ability to store oxygen • the oxygen is used to oxidize HC & CO • in use in Canada since 1988

  18. Reducing Tailpipe Emissions • air injection systems • used on some engines, but not all • cold engine: air is injected into the exhaust manifold to oxidize HC & CO • warm engine: air is injected into the converter to oxidize HC & CO

  19. Air Injection Systems

  20. Causes of excessive hydrocarbons…

  21. Causes of Excessive Carbon Monoxide… • plugged air filter • high float level • choke not opening • faulty fuel injector • higher than normal fuel pressure • faulty EFI sensor

  22. Causes of Excessive NOx… • carbon deposits • inoperative EGR valve • some valves are vacuum operated • others are electronically activated • higher than normal coolant temperatures

  23. Pollution Sources & What Controls Them – a Recap… • 3 areas of a vehicle that can pollute… • tailpipe emissions • fuel tank vapors (and carburetor vapors) • crankcase blow-by gases

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