Write a short note on: Exhaust Gas Recirculation.

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written 8.6 years ago by

teamques10 ★ 69k

Exhaust Gas Recirculation (EGR) technique is used in petrol and diesel engines to reduce nitrogen oxide (NOx ) emissions. NOx is formed in the combustion chamber, where excessively high temperatures cause the oxygen and nitrogen present in the intake air to combine.
EGR works by recirculating a controlled amount of engine’s exhaust back into the intake air using a valve.
This re-introduction of exhaust gas, which is inert in nature, displaces and reduces the proportion of combustible matter in the cylinder. This in turn causes a lower heat release and peak cylinder temperature and reduces formation of NOx
The gas to be recirculated may sometimes be passed through an EGR cooler, which reduces the temperature of the gas, consequently reducing the cylinder charge temperature.
EGR is implemented by:
- Recirculating exhaust gas from exhaust to inlet manifold called External EGR
- Using Variable Geometry Turbocharger for the EGR flow
- Using throttle to initiate EGR flow
Advantages of EGR:
- Reduced NOx
- Potential reduction of throttling losses on spark ignition engines at part load
- Improved engine life and exhaust valve life through reduced cylinder temperatures
Disadvantages of EGR:
- The deliberate reduction of the oxygen available in the cylinder will reduce the peak power available from the engine
- Since EGR reduces the available oxygen in the cylinder, the production of particulates is increased when EGR is applied.

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