Friday, May 11, 2012

Automobile Pollution and Emission Control Systems

Growing population, extraordinary rise in the number of vehicles and the crowded traffic intersects the symptoms that characterise the main reason for increase in vehicular pollution. Vehicles emit, exhaust chemicals, such as carbon monoxide, nitrogen dioxide, nitrogen monoxide, sulphur dioxide and suspended particulate matter. Other constituents of vehicular exhaust include benzene, toluene, xylene, aldehyde etc., which have systemic toxicity on human beings.

Motor vehicles are the considerable sources of pollution that can damage the environment and cause public health issues. Everyone has a stake in limiting the motor vehicle emissions. Carbon monoxide, nitrogen oxides, and hydrocarbons are released when fuel is burned in an internal combustion engine and when air/fuel residuals are emitted through the vehicle tailpipe.

The need to control the emissions from automobiles increased the computerization of the automobile. Hydrocarbons, carbon monoxide and oxides of nitrogen are created during the combustion process and are emitted into the atmosphere from the tail pipe. There are also hydrocarbons emitted as a result of vaporization of gasoline and from the crankcase of the automobile.

A comparatively new source of air contamination, and automobile emissions posed different problems than manufacturing discharges such as coal smoke. Before the Industrial Revolution, levels of toxic chemicals in the air were relatively low, but increased due to fossil-fuel production and used dramatically decreased air quality.

Pollutants emitted directly from the vehicles are not the only cause for concern. In warm and sunny days, hydrocarbons react with the oxides of nitrogen to create a secondary pollutant, ozone. Ozone causes coughing, wheezing and shortness of breathe, and can bring permanent lung damage, making it a cause of critical health problems.

When computer systems have progressed, they were able to adjust ignition spark timing as well as operate the other emission controls that were installed on the vehicle. The computer was also capable of monitoring and diagnosing itself. If a fault is seen, then the computer will alert the vehicle operator by illuminating a malfunction indicator lamp. The computer will at the same time record the fault in its memory, so that a technician can later retrieve that fault in the form of a code which will help them to determine the proper repair.

More popular emission control devices installed on the automobile are as follows:

EGR VALVE: The main purpose of the exhaust gas recirculation valve (EGR) valve is to indicate a small amount of exhaust gas into the intake system, this dilutes the air/fuel mixture so as to decrease the combustion chamber temperature. Excessive combustion chamber temperature creates oxides of nitrogen, which is a major pollutant. EGR valve is the most effective method of controlling oxides of nitrogen.

CATALYTIC CONVERTER: The catalytic converter looks like a muffler. It is located in the exhaust system ahead of the muffler. Automotive emissions are mainly controlled in three ways, one is to promote complete combustion so that there are less number of products. The second is to reintroduce excessive hydrocarbons back into the engine for combustion and the third is to provide an additional area for the oxidation or combustion to occur. This additional area is called a catalytic converter.

AIR PUMP: Combustion requires fuel, oxygen and heat. Without any one of the three, combustion cannot occur. This combustion will not produce any power, but it will reduce excessive hydrocarbon emissions. There are times under normal conditions, such as deceleration, when the fuel content is excessive. Under these conditions we would like to shut off the air injection system. The only maintenance that is required is a careful inspection of the air pump drive belt.
PCV VALVE: The purpose of the positive crankcase ventilation (PCV) system, is to take the vapors produced in the crankcase during the normal combustion process, and redirecting them to the air/fuel intake system to be burned during combustion. These vapors dilute the air/fuel mixture so they have to be carefully controlled and metered in order to not affect the performance of the engine.

CHARCOAL CANISTER: A charcoal canister is used to trap the fuel vapors. The fuel vapors adhere to the charcoal, until the engine is started, and engine vacuum can be used to draw the vapors into the engine, so that they can be burned along with the fuel/air mixture. This system requires the use of a sealed gas tank filler cap. This cap is so important to the operation of the system, that a test of the cap is now being integrated into many state emission inspection programs.

Proper maintenance of car and truck emission control systems not only limits harmful emissions, but also can improve fuel efficiency and vehicle performance extending the life of the vehicle. Care in storing and handling gasoline and other solvents also reduces evaporative losses to the atmosphere.

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