With growing pressures to reduce emissions, the EGR valve will play an increasingly important role moving forward. It's important to know what it does, why it fails and how to replace it when it does. Nearly 80 percent of the air we breathe is nitrogen. To help minimize this, the EGR valve allows a precise quantity of exhaust gas to re-enter the intake the system, effectively changing the chemical makeup of the air entering the engine.
The EGR valve has two primary settings: open and closed, although the position can vary anywhere in between. The EGR valve is closed when the engine is starting up. However as more torque and power is required, for example during full acceleration, the EGR valve closes to ensure as much oxygen enters the cylinder. As well are reducing NOx, EGR valves can be used in downsized GDi engines to reduce pumping losses and improve both combustion efficiency and knock tolerance.
In diesel, it can also help to reduce diesel knock at idle. Although there are several types of EGR valve -- earlier systems use a vacuum-operated valve, while newer vehicles are electronically controlled -- the main types can be broadly summarized as:. Diesel high pressure EGR valves divert the high-flow, high-soot exhaust gas before it enters the diesel particulate filter — the soot can combine with the oil vapor to create sludge. Regulations are becoming increasingly strict to combat the amount of GHG emissions emitted from road transport.
Car manufacturers are having to make adaptations to the designs of their vehicles to meet the stringent limits. One method of reducing exhaust emissions is the use of after-treatment devices. But, what is an EGR? Air from the environment, mostly a combination of Oxygen and Nitrogen, combines with fuel and ignites inside the combustion chamber, temperatures increase and produce NOx emissions. The EGR system works by returning a small portion of exhaust gas to the engine's combustion chambers through the intake manifold, lowering combustion temperatures and therefore reducing the amount of NOx emitted.
It connects the exhaust manifold to the intake manifold and is controlled by either a vacuum or a built-in electric step motor. The function of the EGR valve is to control the flow of exhaust gas being recirculated depending on the engine load. At lower combustion temperatures, nitrogen oxide emissions are low, but the production of soot particulates is high.
To find the right balance, therefore, all the key technologies that affect combustion must be perfectly matched. When combined with fuel injection and turbocharging in particular, the use of exhaust gas recirculation results in a combustion process that produces significantly lower levels of nitrogen oxide.
The second way of reducing nitrogen oxide emissions is to use exhaust gas aftertreatment with an SCR catalytic converter selective catalytic reduction, short: SCR. Very low limits for both nitrogen oxide and diesel particulates can make the use of such an SCR system necessary. 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. Light-Duty Engines. The introduction of EGR technology to diesel passenger cars in the s went almost unnoticed and was not considered a major breakthrough for several reasons.
Typical passenger car engines operate mostly at part load conditions where temperatures are relatively low. Heavy-Duty Engines. The wide scale launch of cooled EGR on heavy-duty engines that attracted a lot of attention to the technology took place in late in the North American market.
High pressure loop cooled EGR was the most expedient in-cylinder NOx reduction technology that could achieve this emission level []. There was a considerable apprehension in the field regarding the performance, fuel economy, and the durability of these new engines. While initial statements from fleet managers appeared to praise the new technology [] , some users have complained of the increase in fuel consumption. For EPA , the 0. Navistar—the only manufacturer to temporarily use EGR without aftertreatment for EPA —was able to do so only by certifying engines to 0.
However, the use of EGR was often minimized and in some cases, restricted to certain low load conditions with no EGR used at higher load operating conditions such as highway cruise. Examples of the later approach are the Volvo D11 and D13 engines launched in that utilized uncooled EGR to control NOx and increase the exhaust temperature for the SCR catalyst at low engine loads.
Since the release of the initial Euro VI product lines, systems with over The advantages of eliminating EGR include weight, cost and complexity reduction.
On the negative side, SCR-only engines have higher urea consumption and require a larger urea tank.
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