Evaluating Vehicle Emissions Inspection and Maintenance Programs (2001) / Chapter Skim
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2 Vehicle Emissions-Control Technologies
2 Vehicle Emissions-Control Technologies
Pages 46-56
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From page 46... ...
: Engine Emission Controls · Engine Adjustments (l 968 to ~974) Primary control consisted of modifications to mixture strength and spark timing.
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From page 47... ...
Material in the detail seals on the carburetor are claimed for reduced permeation and increased purge. · Enhanced Evaporative Emissions Controls (1996 to 2003)
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From page 48... ...
The most recent version of OBD, known as OBDIT, is required on all model-year ~ 996 and newer vehicles. ENGINE CONTROLS The conbo} of engine emissions canbe segregated into crankcase controls, combustion controls, and exhaust ailcer-~eahnent.
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From page 49... ...
Combustion Emissions Controls The combustion emission controls, used on the precatalyst vehicles in 1968 through ~ 974, involved proper engine mechanical operation, lean (excess air) air/fuel combustion ratios, spark modifications, and external exhaust gas recirculation.
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From page 50... ...
In general, emissions-control systems used on the precatalystvehicles in 1968- ~ 974 relied completely on combustion controls and usually compromised the performance ofthe engine, resulting in degraded dnveability and fuel economy, end promoting the practice oftampering wish, or defeating, the emissions-control system. Engine design modifications coupled with exhaust after-treatment devices represent the best method for meeting current and future emissions standards.
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From page 51... ...
The three-way catalytic converter introduced in 1981 and later model years looked very much like the previous oxidizing models but included NOx control. Figure 2-3 illustrates that if a 14.7: ~ (stoichiometnc)
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From page 52... ...
These emissions include fuel and vapor leaks from the tank and plumbing, refrigerant from the air-conditioning system, coolant leaks, tire emissions, and solvents in the vinyls and adhesives ofthe vehicle. Such sources contribute significantly to overall HC emissions.
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emissions have become increasingly important as other sources have been controlled. Figure 2-4 shows model projections for the aggregate exhaust and evaporative emissions for the South Coast Air Basin for an average summer day in 2000 and 20 ~ 0.
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From page 54... ...
A similar flexible connection is made to the engine at the front ofthe vehicle. Many engine fuel systems use an eng~ne-mounted pressure regulator and return excess fuel back to the tank through a duplicate chassis line.
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From page 55... ...
Such a system can communicate its findings to a service technician using diagnostic trouble codes stored in the computer's memory. California regulators recognized the potential ofthe OBD system, expanded the scope, and required it on new vehicles starting with a 1988 mode} year phase-in.
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From page 56... ...
allowed major reductions in CO and HC emissions levels but still relied on engine adjustments and periodic inspections to ensure good performance. An important aspect of the periodic inspection was to ensure that the vehicle still had a functional, nontampered emissionscontro]
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