Exhaust Gas Recirculation System
EGR system I.e. exhaust gas recirculation system is one of the processes of controlling pollution emitted from automobiles.
What is EGR?
The full form of EGR is an exhaust gas recirculation system. It reduces the formation of NOx gas from the combustion chamber. This is the main purpose of EGR.
The oxides of nitrogen are harmful to our environment so, in order to control it, a system is introduced in bs4 model vehicles.
How does EGR work?
The working of EGR is simple and clear to understand. As the name suggests, exhaust gas recirculation, means exhaust gases are recirculated and sent back to the intake manifold of the engine. Only 6 to 10% of exhaust gases are sent to the combustion chamber via the intake manifold.
Between the intake manifold and exhaust manifold, an EGR valve is fitted. Which allows the exhaust gas to enter the intake manifold. The EGR valve is automatically controlled by ECU (engine control unit). An EGR position sensor gives data to ECU and ECU opens the valve with the help of an actuator. Here a stepper motor is used as an actuator.
At what RPM does EGR start working?
The EGR starts to work When the engine's RPM is between 1050 to 3050.
Process of Reducing NOx
The only suitable method of reducing NOx is to prevent the temperature of the combustion chamber to rise. The higher the temperature, the higher the formation of NOx, so if a few amounts of exhaust gas are mixed with the fresh air and sent into the combustion chamber then it could reduce the temperature inside the cylinder.
Apart from this, it has some pros and cons also which you must need to know.
Advantage Of EGR
- Reduce throttling losses
- Reduce heat rejection
- Reduce chemical dissociation
Disadvantages Of EGR
- Decrease in volumetric efficiency of an engine.
- Reduce engine power and acceleration.
- Reduce fuel efficiency.
As you can notice the pros and cons of using EGR is almost stable. There was no doubt that it was reducing NOx but using this system also reduces engine power and efficiency.
So in order to make the engine more efficient and completely reduce NOx, engineers have added SCR with it. Let's get to know more about SCR.
What is SCR?
SCR in automobiles stands for Selective Catalytic Reduction. It is coupled with EGR in vehicles. EGR was not able to remove the NOx completely. So, SCR is introduced to reduce the NOx generated from the combustion chamber. After using this system 93% of NOx coming out with exhaust gases is reduced.
How does SCR work?
SCR purely works on chemical reactions. It uses a reduction process to change the oxides of nitrogen into nitrogen and water.
There are 4 major components of SCR
- DEF - Diesel Exhaust Fluid (A urea-based solution)
- DEF injector
- Mixing Tube
- Some Catalyst
DEF is injected into the mixing tube. Due to the effect of higher temperature, it breaks into the molecules of ammonia and carbon dioxide. And in the presence of some catalyst ammonia is reacted with oxides of nitrogen and forms water and nitrogen.
Conclusion
EGR system is used to reduce the production of NOx from the engine's combustion chamber and if somehow NOx is generated then SCR is used to reduce it completely into nitrogen and oxygen. Using both processes simultaneously the production of NOx is reduced to almost zero.
Also: Nowadays, Electric cars are also getting launched. Have you checked the new ola car which is battery-operated? And it doesn't have any EGR and does not emit any pollution.
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