How does egr work

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All Rights reserved. Therefore, incorporating EGR systems into the design of a car is important with regards to lowering harmful emissions to save the environment and have a positive impact on human health. The majority of modern vehicles incorporate EGR valves into their design to reduce NOx emissions and therefore meet stringent emissions regulations.

EGR systems recycle a portion of the exhaust gas back into the combustion chamber, where it combines with fresh intake air. This lowers the amount of Oxygen and increases the water vapour content to the combustion mixture which reduces the peak combustion temperature. Because more NOx is created as peak combustion temperature rises, the EGR valve effectively reduces the amount of NOx produced by the engine.

The EGR valve begins working once the engine has started, attained the correct operating temperature and the vehicle's speed increases.

Gradually, the EGR valve regulates the flow of exhaust gases. Once the vehicle slows down and the engine stops, the EGR valve will return to its closed position and prevent the flow of exhaust gases. A frequent problem with the EGR valve is sticking due to a build up of carbon deposits. In worst cases, the EGR valve and EGR passages can be completely blocked, preventing the process of recirculating the exhaust gases.

Clogged EGRs are often the cause of black smoke escaping the exhaust, in addition to increased fuel consumption or reduced performance.

Exhaust gas recirculation can reduce nitrogen oxide emissions by around 40 percent. Depending on the application, SCR systems remove up to 90 percent of the nitrogen oxide from exhaust gases.

In the case of particularly stringent emission standards, exhaust gas recirculation and a SCR system must be combined to ensure the limits are met. This applies to mtu Series , and engines.

Series and units meet the targets using exhaust recirculation technology. Nitrogen oxide and hydrocarbon HC emissions combined may not exceed 4. For this reason, mtu is equipping its Series engines for under floor drive systems with an SCR exhaust aftertreatment — with no exhaust gas recirculation. In this case, the nitrogen oxide limits are down 90 percent to 0. To meet these demanding targets, mtu uses both exhaust recirculation technology and an SCR system. As the introduction of Tier 4 final emissions regulations involves no further tightening of NOX values, mtu will retain ist exhaust gas recirculation technology.

This will involve optimization and further development of the injection and combustion systems and of turbocharging technology. The resultant mixture of fresh air and exhaust gas has a lower calorific value in terms of the volume. This lowers combustion chamber temperatures, thus reducing the production of nitrogen oxide NOX. Benefits of exhaust gas recirculation from mtu Generally speaking, systems designed to reduce emissions must be modified to match the drive systems.

It is necessary to modify the radiator, however, in order to cope with the increased cooling capacity of the engine. Compared to engine modifications involving an SCR system, this makes it much easier for customers to convert their units to meet new emissions standards because EGR systems for reducing nitrogen oxides require no additional operating media and thus involve no further expense or work on extra tanks and lines.

The customer benefits in terms of reduced costs for handling and maintenance. Principle of operation In exhaust gas recirculation, some of the exhaust gas is drawn off from the exhaust system, cooled and redirected back into the cylinders see Figure 2. Although the exhaust fills the combustion chamber, it is not involved in the combustion reaction that takes place in the cylinder due to its low oxygen content.

The speed of the combustion process overall is thus reduced, with the result that the peak flame temperature in the combustion chamber is lowered. This dramatically reduces the production of nitrogen oxides. Patented solution from mtu : the donor cylinder concept Exhaust gas recirculation places higher demands on exhaust gas turbocharging, since higher boost pressures have to be achieved with reduced mass flow in the turbocharging system. These high boost pressures are required to direct the increased mass flow resulting from the exhaust gas recirculation rate into the cylinder during the gas cycle.

In addition, the exhaust gas can only be redirected back into the cylinders when there is a pressure drop between the exhaust and the charge air systems. This pressure drop must be established with an appropriately configured turbo charging system, which results in a reduction in turbocharging efficiency.

The pressure drop between the exhaust and the charge air systems leads to gas cycle los - ses. These factors tend to result in lower engine performance or higher fuel consumption. To improve the combined effect of exhaust gas recirculation and turbocharging, mtu has developed what is known as the donor cylinder exhaust gas recirculation system see Figure 3.

An exhaust valve donor valve holds back the exhaust gas flow downstream of the donor cylinders and thus creates the necessary pressure drop between the exhaust and the charge air systems. This means that the turbocharging system can be optimized to a very good efficiency level, with gas cycle losses only affecting the donor cylinders.

Compared with conventional high-pressure exhaust gas recirculation as in the case of the Series engine , the donor cylinder concept Series and achieves lower fuel consumption, since it reduces the gas cycle losses in the engine and permits higher turbocharger efficiency levels. For this purpose, an additional donor cylinder exhaust valve is required in comparison with high-pressure exhaust gas recirculation. Dirt build-up on components and the amount of servicing required over the service life of the application are lower with the donor cylinder concept, as is the case with high-pressure exhaust gas recirculation: unlike the situation with low-pressure exhaust gas recirculation, the exhaust gas is not fed into the intake air until immediately before it enters the cylinder, which means that only clean air flows through the compressor impeller and the intercooler and not exhaust gas containing particles as well.

This requires an additional donor cylinder exhaust valve.