Easy step by step guide on how automotive emissions systems work, though appearances
may vary, the process is the same for most vehicles.
- The vehicle computer is responsible for
the emissions produced by the internal combustion
it controls. By using many
sensors such as an
mass air flow
, which provide feedback data for the computer to analyze and adjust
engine emissions, which are controlled to within manufacturer specifications.
Step 2 - The exhaust system
is designed to sense the amount of oxygen in the exhaust system and send feedback
data to the computer.
Step 3 - An EVAP (evaporative emission) solenoid
is used to purge raw gas vapor from the fuel tank as to not allow these fumes to
enter the atmosphere.
Step 4 - An electronic throttle actuator is designed
to move the throttle plate only when the engine can utilize the fuel being consumed.
This control helps unneeded emissions when a driver over advances the throttle pedal.
EVAP Purge Solenoid
Step 5 - A
Electronic Throttle Actuator
is utilized to expend un-burnt fuel in the exhaust system. The unit
is heated by exhaust gases as thermo reaction heats up to achieve the design goal
of lowering exhaust emissions. By using primary and secondary oxygen sensors the
efficiency of the catalytic
is monitored. An electric air pump is sometimes used to help heat
up the catalytic converters to optimize efficiency.
Step 6 - The
mass air flow sensor
monitors airflow that enters the engine by measuring resistance
across a hot wire that is cooled while various amounts of air pass over it. This
feedback data trims the computers adjustments to further help clean emission output.
Step 7 - The gas cap seals the liquid and fumed
gases from escaping the fuel tank. This cap is designed with an automatic tightening
mechanism to support a minimum tension the cap must be installed at.
Mass Air Flow Sensor
Step 8 - An
(exhaust gas recirculation) is use to allow engine exhaust to enter the intake manifold
of the engine which cools combustion temperatures and lowers emissions.
Emission control systems have been incorporated into automobiles to prevent pollution
by limiting the amount of partially burned and evaporated gases into the atmosphere.
These systems have been efficient in reducing the air pollution caused by automobiles
to a large extent. Increased engine efficiency and lighter vehicle construction
has also contributed to helping reduce emissions. The different aspects of emissions
are tailpipe emissions, life cycle emissions and evaporative fuel emissions.
Unspent fuel vapors are known as the main contributors to air pollution. These
omitted gases consist of carbon monoxide, hydrocarbons, carbon dioxide and nitrogen
Lifecycle emissions are byproducts which are released into the environment during
the manufacturing, maintenance and disposal of the vehicle. These products include
volatile solvents such as auto paint and lubricants, manufacturing plant waste,
petroleum, heavy metals and many more. The name "catalytic converter" was derived
from the operation the device performs. A catalyst material converts partially burned
gases to completely burned gases.
Automobiles were first manufactured with exhaust emissions control systems in
1966. Since then, technology has undergone several advancements that have increased
the efficiency of the internal combustion engine. Older emission control systems
inject air into the exhaust manifold which are known as, air injection reactor (AIR.)
The catalytic converter was developed in the early 1970's when severe air pollution
was widespread and was made mandatory by the US government in 1976. An EGR valve
is used is to lower KNOX (NO2) gases which occur when the combustion chamber when
temperature reaches over 3500°.
Tailpipe emission are measured in parts per million or PPM. The first smog emission
test was conducted in the mid 1980's. Restrictions in smog laws came later which
ushered in the use of a dynamo-meter so vehicles could be tested as if they were
being driven, the number of gases measured also increased.
Article first published 2016-02-04