Exhaust Gas Recirculating (EGR) Systems:

In this day and age governments have made it mandatory to install emission control systems in each and every vehicle and are also constantly upgrading the emission norms. So it's little wonder that engines get more and more restricted as these norms get leaner and meaner by the day. While that may be the negative aspect of emission control, on a positive note it helps extend human life-span, reduces global warming and generally makes earth a better planet to live on.

There are various forms of emission control employed within a vehicle, some of which are the Positive Crankcase Ventilation (PCV) system, heated air intakes, exhaust gas recirculation (EGR), aspirator valves and catalytic convertors. In this edition we take a look at the exhaust gas recirculating system, a pre-combustion control system.

In a nutshell, the EGR reduces NOx (nox) a compound of nitrogen and oxygen by diluting the air fuel mixture with some exhaust gas which does not burn. Since the exhaust gas does not burn it lowers the peak combustion temperature. At a lower combustion temperatures nitrogen cannot form compounds with oxygen and is carried out of the system by the exhaust gas. NOx control requirements vary on various engines and so there are various control systems to provide these functions. The most commonly used in most modern day cars is the vacuum-operated EGR valve. There are also other controls that relate directly to the EGR systems and which complete the same function within the system like the thermal vacuum switch, ported vacuum switch, venturi vacuum amplifier, EGR delay timer control, back pressure transducer etc. The amount of EGR gas flow for each engine has to be calibrated as too much or too little can hamper performance by changing the engine breathing characteristics.

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