Exhaust Gas Recirculation (EGR) is an emission control that lowers the amount of NOx (Oxides of Nitrogen) formed during combustion process in ICE (Internal Combustion Engine). Internal combustion engines releases NOx which is one of the most toxic emission for the living beings and the environment. NOx has a direct connection with the formation of smog in the atmosphere. Currently, NOx gas emission has been strictly constrained by emission law in EU (European Union) and USA (United States of America). ICE releases NOx at elevated temperature inside the engine cylinder. Nitrogen (N2) and Oxygen(O2) molecules are separated into individual atoms of nitrogen and oxygen during the combustion process. These then bonds to form NOx (NO, NO2). When combustion flame front temperature exceeds 2,500oF (1370oC), NOx formation increases dramatically.
EGR works by recirculating a portion of exhaust gas back to the engine cylinders. In EGR technique, when NOx is generated at elevated temperature, some portion (10-15%) of exhaust gas is circulated back to the engine cylinder via intake manifold by activating EGR valve. So that the exhaust gases enter in the cylinder, takes the place of combustible oxygen, and provides inert atmosphere to combustion. As a result of that the amount of fuel burn in the engine reduces, which results in the corresponding reduction in the peak temperature as well as in NOx emission. Engine control unit (ECU) is used to send signals for EGR valve activation in advanced technology vehicle.
Components of EGR
- EGR Valve:It is a diaphragm type vacuum operated which contains a closed chamber having diaphragm connected to middle portion of it. The valve shaft is connected to a spring which contracts when vacuum is applied & expands when vacuum is removed. This valve is the only connection between exhaust & intake manifold.
- Vacuum Modulator: It is the distributor of the vacuum generated by the vacuum pump to the various portion of engines where vacuum is needed i.e. Vacuum booster, EGR valve, Variable geometry turbocharger.
- Vacuum Pump: It is the device which generated vacuum for operating the EGR valve. It is driven by the power coming from the crank shaft. The power is provided through gears.
- EGR centre pipe (EGR Cooler): The exhaust gases after combustion are very hot. If they sent directly to the cylinder, the density of the charge sent to the cylinder can be decreased and the thermal efficiency can be decreased. To prevent this, an EGR cooler is employed between EGR valve and intake manifold in the form of centre pipe which decreases the temperature of the exhaust gases.
- Hose Pipes: These are the pipes which connects the vacuum pump to modulator & the vacuum modulator to EGR valve.
- NOx emission is reduced
- Heat rejection during combustion is reduced
- Make the vehicle more safer as far as environment is considered
- EGR is typically not employed at high loads because it would reduce peak power output
- EGR is also omitted at idle (Low speed, Zero load) because it would cause unstable combustion
Overall we can say that EGR technology is helpful to reduce the NOx emission by ICE vehicle at a cost of small reduction in peak power output. This technology helps in preventing the environment from toxic gases.
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