Chevrolet TrailBlazer, Руководство по обслуживанию

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Emissions Controls System Overview
General Information
The first emissions controls implemented in the mid 1960s consisted of engine
modifications and add on pollution control devices. These pollution control systems
moderately lowered emissions, but they also caused a reduction in engine performance
and increased fuel consumption.
In 1972 the federal government initiated a standardized test procedure for measuring
vehicle compliance with federal emissions standards. This test incorporates a chassis
dynamometer to provide a consistent and accurate way to measure the amount of HC,
NO
x
, CO, and CO
2
that a vehicle produces. This Federal Test Procedure (FTP) applies to
both Light-Duty Vehicles (LDV) and Light-Duty Trucks (LDT). Over the years it has been
tailored to the support the amended federal emissions requirements.
The FTP is designed to simulate typical driving conditions in urban areas. This FTP
certification is a requirement of all pre-production vehicles that are to be sold in the U.S.
Being compliant includes being able to pass the FTP throughout the vehicle's useful life.
Because of this, the FTP is also used on in-use vehicles.
In 1975, catalytic converters were introduced to help lower the emissions of HC and CO.
Catalytic converter efficiency of this era was poor and required cumbersome air
management systems. By cleaning-up the exhaust (post-combustion) instead of reducing
engine emissions (pre-combustion), auto manufacturers were able to address the Federal
Government's concerns regarding pollution contributed by automobiles, however this did
nothing for fuel efficiency.
The Federal Government's emissions standards combined with the price and availability of
fuel at the time created a demand for the auto manufacturers to produce vehicles that
were more fuel efficient and had lower emissions. At the time, the easiest way to reduce
both fuel consumption and vehicle emissions was to lower the engine displacement and
lean the air/fuel ratio out. Though emissions were lowered, the smaller, leaner engines
created additional hurdles including a lack of performance.
One hurdle caused by the smaller engines pulling heavy vehicle weights was compounded
by the leaner air fuel mixtures, which resulted in increased cylinder temperatures. These
increased cylinder temperatures caused a dramatic rise in the production of oxides of
nitrogen (NO
X
).
The air that enters the combustion chamber consists of approximately 20.8 percent
oxygen, 78 percent nitrogen and 1.2 percent mixed gases. As the air/fuel mixture enters
the combustion chamber and ignition occurs, the nitrogen forms various compounds with
the oxygen. These compounds have varying amounts of oxygen and are know as NOX -
oxides of nitrogen.
Oxides of nitrogen are present during all phases of combustion; however, they are
developed in high quantities when combustion chamber temperatures reach 2500° F.