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. Nitrogen oxides are emissions produced as a by-product from the process of combustion, Nitrogen and Oxygen gases in the air react during combustion, especially at high temperatures. NOx is a major component of smog and can have detrimental affects on human health as well as well as ecosystems and agricultural crops.
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. Full access requires DieselNet subscription. Please log in to view the complete version of this paper.
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.
While the application of EGR for NOx reduction is the most common reason for applying EGR to modern commercial diesel engines, its potential application extents to other purposes as well. Some of these include: imparting knock resistance and reducing the need for high load fuel enrichment in SI engines, aiding vaporization of liquid fuels in SI engines [] , as an enabler for closed cycle diesel engines [] [] , for improving the ignition quality of difficult-to-ignite fuels in diesel engines [] or for improving the performance of SCR catalysts [] [].
While NOx reductions had been reported with EGR as early as [] , the first engine experiments to investigate the NOx reduction potential of EGR appeared to be carried out in the late s in SI engines []. By the s, EGR was being seriously considered as a NOx control measure for diesel engines [] []. After the early s, some gasoline fueled applications were able to dispense with EGR. Following the early gasoline application, EGR was also introduced to diesel passenger cars and light-duty trucks and then heavy-duty diesel engines.
While there were applications to heavy-duty diesel dating back to the s, it was not until the early s that cooled EGR became very common in heavy-duty diesel engines in North America []. It was this heavy-duty application that attracted the most attention to EGR, due to the more difficult technical challenges compared to the earlier light-duty applications.
After , the application of EGR into spark ignited engines was expanded—not for NOx control but for fuel economy purposes. It was applied not only to light-duty gasoline but heavy-duty gasoline, natural gas and propane fueled engines.
For SI engines, EGR can reduce pumping losses, improve combustion efficiency, improve knock tolerance and lessen the need for fuel enrichment []. A potential non-NOx reducing application EGR for modern diesel engines is to combine it with other engine control measures to increase exhaust gas temperature and facilitate the regeneration of diesel particulate filters [].
The NOx emission benefit of EGR comes at a cost: other measures are usually required to avoid unacceptable increases in fuel consumption, emissions of PM, HC, and CO, engine wear and reductions in engine durability. In order to address these trade-offs in commercial diesel engine applications, engine manufacturers have had to simultaneously adopt a range of other technological changes such as:. More than one technical route exists to meet a given NOx limit, and EGR can sometimes be used as one of several alternative technologies.
Commercial applications of EGR on diesel engines are summarized in the following table. On several occasions, small scale EGR applications occurred earlier than indicated in the table, typically driven by various voluntary incentive programs. As the diesel engine is the biggest offender when it comes to these emissions, their petrol-powered brethren are usually only fitted with an EGR valve.
As emissions targets became stricter across the world, manufacturers had to come up with more efficient EGR operation to further reduce their impact.
This is where the EGR cooler comes into play. The EGR cooler utilises the cooling system of the engine to further cool the exhaust gasses before they enter back into the air intake, thus bringing down combustion temperatures even further, but increasing the workload of the DPF.
If any of these systems become clogged with excess carbon build up, drivability may be compromised and more harmful emissions will be released into the atmosphere. It is possible to try cleaning the EGR valve, and there are dedicated cleaning products available in the aftermarket. Unfortunately, if the cleaning is not successful, replacement may be the only option.
0コメント