What Is An Exhaust Gas Recirculation System? | How does EGR System work?

What is Exhaust Gas Recirculation System?

EGR stands for Exhaust Gas Recirculation. Exhaust gas recirculation (EGR) is an emission control technology used in modern IC engines (gasoline/petrol engines and diesel engines) to reduce NOx emission.

The EGR system is most commonly used in diesel engines because these engines release very high levels of nitrogen oxides which are injurious to the human body and environment.

NOx emission pollutants to the environment and these gases birth different dangerous diseases. Nitrogen oxide (NOx) produces inside the engine cylinder due to the high compression ratio and the high temperature of the engine cylinder.

To reduce and control NOx emission, manufacturers introduce the “EGR (Exhaust Gas Recirculation)” technique in the various vehicles’ engines. It is one of the most important parts of a vehicle engine.

The Exhaust gas recirculation system has the ability to protect the environment and human life from the engines‘ harmful gases.

Exhaust Gas Recirculation system

The EGR system returns the engine exhaust gases back to the engine cylinder. During this process, it reduces the temperature of the exhaust gases and the oxygen level in the cylinder of the engine. Both factors inhibit the formation of NOx.

In this way, the EGR valve controls the emission of exhaust gases. The composition of the exhaust gases has higher specific heat than the mixture in the engine cylinder.

Working of EGR System

The EGR valve uses to control the emission of NOx. Because the exhaust gases are inert, it is also useful for starting a cold engine. The exhaust gas recirculation system works in the following way:

When the product of combustion leaves the cylinder through the exhaust manifold, then some part of the exhaust gases in the engine is recirculated through the intake manifold. Therefore, the unburned fuel in the exhaust gas recirculation system mixes with the fresh raw material (fuel-air mixture) and ignites at the end of the compression stroke.

Therefore, less CH3 (hydrocarbons) are generated in the exhaust stream. These hydrocarbons produce due to unburnt fuel. The disadvantage is that engines with an EGR system have overheating problems due to the heat of the exhaust gases.

To overcome the problem, automakers have come up with an EGR intercooler that cools the exhaust gas and increases the oxygen density in the exhaust gas, which results in better combustion and much less emission, even better than the traditional air injection system.

Function of the Exhaust Gas Recirculation System

The main function of the Exhaust Gas Recirculation (EGR) system is to reduce NOx emissions. NOx produces only at very high cylinder temperature and pressure.

EGR recirculates the exhaust gas in a particular percentage of about 6–10 again into the intake manifold. Due to this, the temperature of the overall mixture goes down and hence prevents the formation of NOx, which generally needs a temperature condition of about ~1500°C.

EGR Valve

A lean mixture is used in a diesel engine, which means that the oxygen is more than the fuel. Due to this, there remains enough oxygen in the combustion chamber, which remains unburnt. So, this oxygen can be chemically reacted into NOx, although that’s not the case in the Petrol engine in which the mixture is in proper stoichiometric ratio.

Apart from the NOx reduction in diesel engines, EGR also helps in petrol engines by reducing the knocking tendency. It reduces the temperature in the chamber and reduces the possibility of self-ignition of the end mixture on the opposite side of the flame travel area. EGR even aids in the vaporization of the liquid fuel in SI engines. 

In simple wording, EGR takes waste gases from the exhaust. These gases are cooled using an EGR cooler to increase effectiveness and fed to the intake manifold.

As the relatively cool carbon dioxide is mixed with the air and is pumped into the cylinder, it absorbs engine temperature and reduces it up to a certain level. This is the main function of the EGR valve.

Another function of the exhaust gas recirculation system is to increase mpg by acquiring some volume of the cylinder. This is done when on low loads, power is not needed.

Types of EGR Valve

EGR valve has different types (older systems use vacuum-actuated valves, and newer automobiles use electronic controls). The EGR valves have the following types:

1) High-Pressure Diesel EGR Valve

These types of valves transfer high flow, high soot exhaust gases before they enter the diesel particulate filter. This soot combines with oil vapors to generate sludge. The gas then flows back to the intake manifold either through the cylinder head pipe or internal drilling.

A secondary valve is also used to produce a vacuum in the intake manifold, as it is not present in the diesel engine.

2) Low-Pressure Diesel EGR Valve

This valve diverts the exhaust gases after passing through the diesel particulate filters. This exhaust gas flow is low, but the soot is almost completely removed. The gas then returns to the intake manifold through the pipe.

3) Gasoline EGR Valves

This valve diverts the exhaust gases, just like a high-pressure diesel valve. The vacuum formed through a cylinder pressure pulls the exhaust gas into the cylinder, and the flow regulates by closing and opening the EGR valve.

4) Vacuum actuated EGR valve

This valve uses a vacuum magnet to change the diaphragm vacuum, thereby opening and closing the EGR system. Some types of valves also contain feedback sensors that tell the valve position ECU.

5) Digital EGR Valve

It features a stepper motor or solenoid motor and mostly a feedback sensor. It receives pulse width modulation signals from the ECU to control the flow of exhaust gases.

How to replace a faulty Exhaust Gas Recirculation System?

  • First of all, remove the casing of the engine.
  • Then loosen the wires of the electricity that are attached to the valve and disconnect the vacuum line and electrical connections.
  • Eliminate the zip-up screws and check the valve for corrosion, damage, or carbon deposits.
  • Thoroughly clean the mounting surface of the EGR valve and install a new valve and gasket. Also, removes all of the loose carbons from the Exhaust Gas Recirculation supply port.
  • Align to this valve with the gaskets and screw holes and reinstall it in the casing.
  • Squeeze all fasteners to the recommended torque setting.
  • After securely seating, recouple the electrical connection or the vacuum line.
  • Finally, use the diagnostic scan device to rearrange the engine management lights and check for other errors. Make sure the fault indicator is off before you take the test drive. In many automobiles, the EGR valve must be reset after the change. This means that the control unit can only learn the stop positions at the start and endpoints. Otherwise, the valve will explode and fall into the diverse.

How does EGR blanking affect the car’s performance?

In theory, Exhaust Gas Recirculation would have a very negative effect on performance. Introducing exhaust gas into the intake rather than fresh air has the effect of reducing volumetric efficiency, which limits the amount of power an engine can produce.

However, EGR does not operate during acceleration or other times when power is demanded. Rather, it operates during a cruise. While cruising down a road, the power required is FAR less than the engine can produce. So, any reduction in output as a result of EGR goes unnoticed.

On the other hand, as you can imagine, the exhaust is pretty dirty stuff. Especially before it goes through the car (which is true of exhaust used for EGR). This exhaust tends to produce lots of soot deposits in the intake manifold. With time, these deposits can effectively reduce the size of intake runners and ports, which reduces airflow capacity. This can reduce power output.

Can an EGR increase the speed of a car?

The only thing EGR speeds up is the contamination of your engine.

EGR is not an object; it’s a system. It means exhaust gas is recirculated into the intake to decrease the combustion chamber’s temperature, reducing emissions, most notably the NOx emission. Exhaust gas brings up the specific heat of the gases in the combustion chamber, predominantly because of the water vapor in it from the previous combustion.

It can quickly and severely contaminate an engine, even more so with diesel engines. The throttle bodies are the most know part to suffer from Exhaust Gas Recirculation.

Does EGR help to reduce knocking in both Diesel and Gasoline Engines?

EGR was designed to satisfy the strict Californian air pollution laws. It reduced the nitrogen oxides produced at idle. It can enable knocking reduction in some circumstances but is more a matter of ignition timing retardation in patrol cars.

Constant EGR helps very small turbocharged engines with high boost turbos. Cooled EGR is useful to reduce the uncontrolled detonation by a small amount inside the smaller engine running at maximum power where exhaust temperatures can reach 1000°C.

It must be cooled EGR, though. Brake-specific fuel consumption improvement of 3.7% is achieved using 10% cooled EGR and an increased boost at full load instead of fuel enrichment to control detonation knock.

Diesel engines do not knock, so there is nothing to reduce. In diesel engines, it is used to reduce the emissions of NOx. In gasoline engines, EGR is used to improve light-load fuel economy (by reducing throttling losses) and reduces knock tendency at high loads to allow higher compression ratios (especially in boosted engines). A higher Compression Ratio improves fuel economy.

Advantages of Exhaust Gas Recirculation 

  • The EGR system reduces the emission of exhaust gases.
  • It reduces the combustion temperature, which helps to reduce the emission of NOx.
  • It improves fuel economy.
  • It is an inexpensive system.
  • It improves vehicle engine performance. 

FAQ Section

What is EGR?

Exhaust gas recirculation (EGR) is an emission control technology allowing significant NOx emission reductions from most types of diesel engines: from light-duty engines through medium- and heavy-duty engine applications right up to low-speed, two-stroke marine engines.

What is the Exhaust gas recirculation system performance?

The EGR has proven to be an efficient and inexpensive system to reduce nitrogen oxide emissions. The lower the temperature of the exhaust gases, the higher the density. By cooling the exhaust gas, before recirculation into the intake manifold, the efficiency of the EGR system is improved.

Does EGR improve engine performance?

One method to decrease the engine knocking is by introducing Exhaust Gas Recirculation (EGR) into the combustion chamber. Exhaust Gas Recirculation also helps improve fuel economy and can reduce NOX emissions. EGR reduces volumetric efficiency, which places challenges on the boosting system.

What is the function of the EGR system?

The main function of the EGR system is to lower the combustion chamber temperature and reduce the emission rate of exhaust gases.

Read More
  1. Different types of Engines
  2. Different types of IC Engines
  3. Working and Function of EGR Valve
  4. Working of Combustion Chamber

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