The exhaust emission control system, is the last line of defense, against harmful hydrocarbons (air pollution).
So, any shortage of spark or if the spark occurs, at the wrong time; incomplete combustion and higher hydrocarbons will result.
The exhaust emission control, consists of three additional systems. The secondary air injection system, the exhaust gas recirculation (EGR) system and finally the catalytic converter.
Consequently, all parts of the exhaust emission control system; need to work together to provide, a good defense against overall air pollution.
So, by cleaning up the pollutants left over from combustion; they reduce tailpipe emissions of hydrocarbons (HC) and carbon monoxide (CO).
Exhaust Gas Recirculation (EGR)
So, exhaust gas recirculation, reduces the formation of NOX. Consequently, by allowing a small amount of exhaust gas to “leak” into the intake manifold. The amount of gas leaked into the intake manifold is only about 6 to 10% of the total. But, it’s enough to dilute the air/fuel mixture, just enough to have a “cooling effect” on combustion temperatures. This keeps combustion temperatures below 1500 degrees C (2800 degrees F). As a result, reducing the reaction, between nitrogen and oxygen that forms NOx.
Secondary Air Injection System
With spark-ignition engines, the greatest pollution occurs on cold starting. Secondary-air systems have been successfully employed, to reduce such cold starting emissions. The secondary air injection pump is responsible for, pumping fresh air from outside, into the exhaust stream.
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