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Cooled-EGR (Exhaust Gas Recirculation) systems have been used since October 2002 by five major engine manufacturers (Cummins, Detroit Diesel, International, Mack and Volvo) to reduce emissions of smog-producing nitrogen oxides (NOx) from diesel truck engines. Depending on engine operating conditions, these systems divert from 5 to 30 percent of an engine's exhaust stream through an air-to-water cooler, then back into the combustion chambers, where the cooled gases reduce peak temperatures and, t
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  Cooled-EGR (Exhaust Gas Recirculation) systems have been used since October 2002 by five major enginemanufacturers (Cummins, Detroit Diesel, International, Mack and Volvo) to reduce emissions of smog-producingnitrogen oxides (NOx) from diesel truck engines. Depending on engine operating conditions, these systems divertfrom 5 to 30 percent of an engine's exhaust stream through an air-to-water cooler, then back into the combustion   chambers, where the cooled gases reduce peak temperatures and, thus, retard NOx formation.Cooled-EGR systems incorporate a number of sensors and actuators that are controlled and monitored by theengine's electronics, and any malfunctions show up as fault codes in the diagnostic log. On a routine basis, however,   cooled-EGR systems are virtually maintenance free. But, that said, the day-to-day health of a cooled EGR system — and that of an engine running with such a system — depends closely on the health of related systems.With the advent of cooled-EGR, turbochargers have become more complex. Most now have moving parts in theturbine section that allow continuous adjustment of exhaust-manifold and boost pressures to keep the combustionprocess efficient and legal. Turbocharger manufacturer Holset handles these adjustments with a variable-geometryturbine (VGT), which uses a sliding nozzle ring to vary the turbine-blade area upon which exhaust gases can act.Garrett, another major supplier, employs a variable-nozzle turbine (VNT), which uses a set of adjustable vanes, ornozzles, to direct flow into the turbocharger's turbine.The moving parts of these turbochargers can be actuated electrically (with stepper motors) or pneumatically, typicallyusing air from the truck's braking system. In either instance, the actuators are controlled by the engine's electronic   control module (ECM). Likewise, the EGR valve, which regulates the volume of exhaust gas diverted to the cooler,may be electrically or pneumatically (or hydraulically) activated, again under the authority of the ECM.For turbochargers and EGR valves using pneumatic-actuation systems, maintenance is twofold. First, if a small in-   line filter is used in the air-actuation circuit, service it as directed by the engine manufacturer. Second, follow thevehicle maker's recommendations to the letter for maintaining the chassis air system. This includes faithfully servicingthe desiccant cartridge in the air-dryer and regularly checking for moisture in the air tanks. More than a tablespoon of   water in the tanks could mean it's time to replace the dryer cartridge.Keep in mind, too, that an air compressor running hot (because of a faulty governor, a faulty air-dryer purge valve orbraking-system leaks) can vaporize compressor oil and may foul pneumatic actuators. More stress on coolant  The cooler in a cooled-EGR system typically is made of a corrosion-resistant alloy, and its job is to reduce exhaust-gas temperature from around 1,100F to 300F. The cooler depends on a well-maintained engine-cooling system to doits job. This means, first of all, keeping the system full of coolant. Big trucks typically require frequent radiator top-offs,and paying attention to the coolant level becomes more critical with cooled-EGR engines. Be more conscientious,too, about checking for leaks in these higher-pressure systems, and be equally vigilant about checking belt tensionand fan-drive operation.   Because the cooling system is working harder in a cooled-EGR engine, you'd be well advised, also, to keep a closewatch on coolant condition. Fully formulated conventional antifreeze is standard factory fill for most big trucks, butlong-life coolants with carboxylate- or bezoic-acid formulations are popular options. Whatever antifreeze you're using,   check it regularly for freeze point, for correct color (has it been mixed with another type of antifreeze?) and for clarity(rusty?). And, remember, conventional antifreeze must be checked regularly for nitrite content to protect the engine'scylinder sleeves.   In a perfect world, antifreeze types would never be mixed in a truck's radiator. But they are, frequently, and twopotential effects are worth noting. Some say that if a carboxylate-inhibited antifreeze (which includes most long-life products) is mixed with fully formulated conventional antifreeze, then the coolant becomes more acidic. This conditionmay cause silicates in the conventional to drop out. Some question if the resultant solids could deposit in the EGRcooler or in the coolant passages of water-cooled turbochargers. Also of potential concern is that mixing antifreezetypes will dilute their respective inhibitor packages, to the point that not enough of either inhibitor technology remainsto afford corrosion protection.   So the advice is easy, but the application difficult: Do your best to keep one type of antifreeze in your truck's coolingsystem. Oil-change intervals     As you may know, concerns about cooled-EGR engines running hotter and potentially dumping more acid and sootinto the engine's lubricating oil prompted the development of a new heavy-duty oil, designated CI-4 by the AmericanPetroleum Institute (API). By all accounts, the new oil is doing a good job, and many truck owners are tempted to use   the same extended drain intervals established for the previous oil, CH-4.  While some in the industry say that's probably okay to do, others advise caution. The best advice is to follow themanufacturer's recommendations until a cautious oil-analysis program, involving both the engine manufacturer and oilsupplier, yields convincing evidence that extended drain intervals are justified. EGR Coolers   An EGR (Exhaust Gas Recirculation) cooler is a heat exchanger that cools the exhaust prior to recirculation back tothe engine in order to reduce NOX (Nitrous Oxide) emissions. NOX is formed at higher temperatures and byrecirculating the exhaust in to the combustion chamber the amount of available oxygen is reduced and the   combustion temperature is lowered. In order to minimise the loss of power the exhausts have to be cooled beforeentered into cylinder.While various heat exchanger technologies are used, tube and shell are the most common types used today. Enginesize and emission legislation are two factors that influence the required size of the heat exchangers.High corrosion resistance and heat resistance are two major requirements of the brazing filler metal for EGR coolerapplications. When brazing the components of an EGR cooler, the melting point of the brazing filler metal should beas low as possible. Brazing at too high temperatures deteriorates the base metal and also produces an adverse effecton corrosion resistance due to precipitation of chromium carbide (Cr 3 C 2 ).Corrosion of the brazing filler metal is caused by exhaust gas condensation as it is circulated in the EGR system. As   condensate contains sulfuric acid, corrosion may be caused to the brazing filler metal and the diffused part as aresult.Höganäs products are able to combine low brazing temperatures with high corrosion- and oxidation resistance. Thismakes them very suitable for applications such as EGR coolers. New EGR Cooler with Bypass Reduces IncompleteCombustion 10 August 2006 Nikkei. Tokyo Radiator Mfg. Co.,an established maker of    cooling systems, has developed a new exhaust gas   recirculation (EGR) cooler with a bypass channel toreduce incomplete combustion and the resulting   emissions of hydrocarbons and soot.NO x forms primarily due to the presence of oxygen andhigh temperatures. By recirculating exhaust gas back into   the cylinders, EGR lowers the heat of combustion andthereby reduces NO x . EGR coolers further lower the temperature of theexhaust gas before recirculation, thereby achieving an even greaterreduction in NO x . A conventional EGR Cooling System.    However, the constant use of cooled exhaust gas results in the engine takinglonger to reach optimal combustion temperatures. Incomplete combustion — and the associated emissions — can result during that period. Tokyo Radiator’s new EGR cooler has a built -in bypass channel to sendexhaust gases directly back to the combustion chambers when the enginetemperature is low. Sensors calculate the engine temperature from thetemperature of the radiator coolant, and a pressure valve opens the bypasschannel whenever the temperature is below a set value. This helps theengine warm faster, reducing the time for incomplete combustion.The company plans to mass-produce the new EGR cooler starting this fall.GM reportedly plans to use the device in passenger cars for Europe next   year.GM and Ricardo have been developing an   advanced diesel engine control (ADEC) systemdesigned to enable consistent achievement of very   low emissions levels through closed loop control of the combustion process. An EGR Cooler with   bypass is part of that development, which thepartners will demonstrate on a 1.9-liter engine.The ADEC coordinator uses a range of sensors tomeasure combustion states and then establishes the optimal balance of fuelquantity and timing and air path control (the latter being where the EGRcooler with bypass system comes in). Schematic of advanced EGR system for the Ricardo-GM ADEC engine. Click to enlarge.  
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