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Diesel EGR

Glossary

Every year the EPA and the clean air act tighten emissions requirements for engines, gasoline and diesel alike. All internal combustion engines produce harmful greenhouse gasses like hydrocarbons and carbon dioxide along with ozone depleting gasses like oxides of nitrogen (NOx). Particulate emissions are also a problematic characteristic of diesel engines that contribute heavily to the production of smog. EGR systems are used to lower NOx emissions.

EGR recirculates some of the exhaust gasses back into the engine intake to help reduce peak temperatures in the cylinders where NOx are formed. Cooled exhaust gas recirculation uses back-pressure to force the exhaust into a cooler, lowering its temperature from about 1,100 degrees to 450 which improves the NOX reduction even more. EGR flow is aided by increasing exhaust backpressure through the use of a variable geometry turbocharger or by causing the engine to scavenge exhaust with the aid of an intake throttle plate. In simple terms: EGR absorbs heat, which reduces NOx. Additionally, the cooled air allows more efficient combustion, resulting in increased engine performance.

Cooled EGR systems are now installed on many new diesel engines manufactured today and the International 6.0L Power Stoke Diesel engine is one of them. The two components of this EGR system are a tubular type heat exchanger and the EGR valve itself. One drawback to cooling peak combustion temperatures is an increase in particulate emissions or soot. These particulate emissions can also reduce the performance and effectiveness of an EGR system because of particulate deposition known as fouling. This soot builds up in the EGR cooler reducing the transfer of heat and also causes problems in some EGR valves like sticking and blocked passages. The photograph (right) shows an EGR valve that has failed and stuck in the open position. There are concerns about reintroducing some of the soot and acids back into the intake of an engine from the exhaust that might affect the longevity of the engine. New oils with a CI-4 designation by the American Petroleum Institute (API) have been developed to carry more soot and acids. Sticking to a maintenance schedule is crucial for an EGR diesel engine and will affect the longevity of these engines.

A 6.0L Powerstroke Diesel Engine EGR Cooler.

The EGR cooler shown above is from a 2005 6.0L Powerstroke Diesel Engine. An EGR cooler is a heat exchanger that uses engine coolant to reduce the temperature of the exhaust gasses before entering the intake manifold when the EGR valve is opened. EGR cooler design differs among engine manufacturers, but all use engine coolant to reduce exhaust temperature from around 1,100F to 450F or lower. Corrosion-resistant alloys help protect coolers from acidic exhaust gases and poorly maintained coolant therefore proper cooling system maintenance is equally as important as maintaining the engine oil. On the right is a photo of the EGR Throttle Plate assembly with the intake elbow removed. This is an electric throttle plate that is controlled by the PCM. Closing this valve under certain conditions aids in scavenging exhaust gasses from the EGR valve into the intake manifold. This throttle plate can be used to limit the amount of air charge entering the intake for the purposes of EGR flow making the EGR system more effective.

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