Emission Control System Fundamentals Chapter 43 2012 Delmar, Cengage Learning Objectives Describe the different types of air pollution caused by motor vehicles Explain the fundamentals of the major emission control systems Label the parts of emission control systems
Explain the operation of electronically controlled emission systems 2012 Delmar, Cengage Learning Introduction Emission controls Began to be included on cars in the 1960s Complicated specialty area Most states: emission specialists are required to be licensed to perform repairs
2012 Delmar, Cengage Learning Air Pollution Photochemical smog Hydrocarbons and oxides of nitrogen react with sunlight Warm air inversion layer traps smog Pollution laws Administered by the EPA Vehicles manufactured today produce less than 5% of the air pollution of 1960s models
2012 Delmar, Cengage Learning Automotive Emissions Sources of emissions Exhaust pipe, crank-case, and vapors Hydrocarbon sources
Blowby gases Skin effect Raw gas in exhaust Insufficient compression Inadequate ignition spark 2012 Delmar, Cengage Learning Automotive Emissions (cont'd.) Carbon monoxide emissions
Result when gasoline not completely burned Oxides of nitrogen Produced when combustion temperatures are too high Particulates Are airborne microscopic particles Carbon dioxide and oxygen Used to diagnose combustion problems Carbon dioxide is a greenhouse gas
2012 Delmar, Cengage Learning 2012 Delmar, Cengage Learning Pollution Control Early 1960s: California led emission control legislation 1961: crankcase emission system required on all new cars in California 1963: crankcase emission system required on all new cars in U.S.
1966: exhaust emission systems required on new cars in California 1970: U.S. Congress passed Clean Air Act 2012 Delmar, Cengage Learning Automobile Emission Control Systems Lower exhaust emissions Engine design Fuel and ignition system controls Devices designed to control emissions
Reintroduces blowby gases into combustion chambers Benefits of PCV system Prevents emissions of HCs Reduces sludge Reduces oil leakage Closed ventilation system Filtered intake air is supplied through hose from air cleaner 2012 Delmar, Cengage Learning
Air Injection System Feeds hot gases to keep them burning Air is provided by belt-driven air pump, electric motor-driven pump, or non-pump pulse air system Functions Provides low-pressure air supply Provides air to catalytic converter Air injection system uses an air pump, control
valves, and lines to manifolds Some vehicles have electric air pumps 2012 Delmar, Cengage Learning Aspirator Valve or Pulse Air System Momentary low-pressure condition (pulse) occurs at end of exhaust stroke Aspirator valve or pulse air system uses pulses to blow fresh air into exhaust Not efficient at high speeds
One-way check valve (i.e., aspirator valve) allows fresh air from cleaner Flows when vacuum created by exhaust pulse Closes when exhaust pressure builds 2012 Delmar, Cengage Learning 2012 Delmar, Cengage Learning Exhaust Gas Recirculation Lean air-fuel mixtures and higher operating temperatures raise NOX
Exhaust gas recirculation (EGR) system allows exhaust gas into air-fuel mixture Diluting air-fuel mixture with exhaust gas lowers combustion temperature by 300F EGR improves fuel economy Early EGR systems were often disabled to improve fuel economy 2012 Delmar, Cengage Learning EGR System Operation
Simple EGR system has an EGR valve operated by engine vacuum Located on intake manifold Little NOX is formed at idle EGR valve is closed at these times Exhaust backpressure is a good indicator of engine load More EGR flow needed under load Thermal vacuum valve (TVV)
Prevents vacuum operation before engine is warm 2012 Delmar, Cengage Learning 2012 Delmar, Cengage Learning Computer-Controlled EGR Systems Todays cars have computer-controlled EGR systems EGR valve is controlled by input signals of engine temperature and load Vehicle speed signal or PRNDL switch
Position sensors on EGR valves: included in late-model engines Digital EGR valves: EGR flow regulated by computer using a series of solenoids Linear EGR valves: include a stepper motor 2012 Delmar, Cengage Learning Catalytic Converter Catalyst Causes chemical reaction without changing itself Chemical reaction only occurs in presence of
catalyst or occurs faster because of one Catalytic converters Must be hot to operate Monolithic catalyst has thing coating of platinum applied to ceramic coated with alumina Late-model vehicles have pre-catalysis which begin operating earlier 2012 Delmar, Cengage Learning Types of Catalytic Converters Two-way catalyst; changes HC and CO into
CO2 and H2O Three-way catalytic converter: used with oxygen sensor Reduces NOX and oxidizes HC and CO Single or dual bed design Dual bed catalytic converters include air switching valve and diverter Use rhodium as a catalyst Needs heat and regulated air-fuel mixture 2012 Delmar, Cengage Learning
Evaporative Controls Control emission of gasoline vapors from tank Activated charcoal store gasoline vapors until they are drawn into the engine and burned Emission of fuel vapors is controlled by sealing the fuel system Gasoline tanks allow for fuel expansion of 10% Expansion dome and liquid/vapor separator Expansion tank Filler neck design
Gas caps sealed or have pressure vacuum valve 2012 Delmar, Cengage Learning 2012 Delmar, Cengage Learning Other Parts of the Fuel Tank System Include: Liquid vapor separator keeps liquid fuel from being drawn into charcoal canister Charcoal canister stores vapors from fuel tank Thermostatic air cleaner (TAC) maintain
consistent air-fuel mixture Manifold heat control valves were used to reduce exhaust emissions and improve drivability during engine warmup 2012 Delmar, Cengage Learning On-Board Diagnostics 1988: on-board diagnostics regulations became law Require computer to monitor engines O2 sensor, EGR valve, and charcoal canister purge
solenoid Malfunction indicator light was also required Names of emission parts and connections for test equipment were standardized Part of the OBD II regulations 2012 Delmar, Cengage Learning Engine Emission Modifications Common modifications As little as possible exposed surface area on the
combustion chamber and top of piston Engines run with higher cooling system temperatures Advancing ignition timing can increase fuel economy Changing cam design specifications results in different emissions Domestic diesel light trucks and vans are now using urea selective catalyst reduction 2012 Delmar, Cengage Learning
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