Renaissance of exhaust-gas recirculation: EGR still high-rated at automotive manufacturers / Huber Group develops special method for EGR equal distribution

Accompanied by the realization of Euro-5 emission standard, many experts had assumed the end for exhaust-gas recirculation systems in favor of Selective Catalytic Reduction (SCR) or other technologies. Meanwhile, it has become a fact that even named automotive manu-facturers still appreciate the advantages of EGR: BMW for example has recently presented its new 730d model with integrated EGR sys-tem. Huber Group, R&D service provider and TIER1 supplier for au-tomotive and engine manufacturers has been following this trend and has enhanced its own exhaust-gas recirculation system.

Similar to ordinary EGR systems, Huber Group method is based on withdrawing exhaust-gas out of the exhaust manifold and leading it back into the intake manifold over the EGR valve. This increases the proportion of inert gas within the unburnt gas fill. Consequently, the burning rate gradually gets slowed down and the burning tempera-ture is reduced which in the end leads to a reduction of the tempera-ture-dependent NOx formation. In order to additionally increase the potential of reduction, Huber Group also uses an EGR-cooling with bypass solution. A part of exhaust-gas is withdrawn before it passes the turbine of the turbocharger, gets cooled inside the EGR-cooler and is mixed with the fresh air afterwards. In addition to the EGR-cooling, Huber system also includes an Electronic Control System that is able to distinguish between transient and stationary operating modes. Depending on the degree of engine speed alteration, the sys-tem measures a lower or higher shortage quantity compared to the quantity led back in stationary mode at every single load/ speed point that has been passed through. Whereas usual systems operate with conventional map solutions that more or less successfully cover the dynamic operation mode by a feed forward control, Huber System uses a cube model with „acceleration“ as third dimension.

Moreover, Huber System bears further advantages by means of a special mixing chamber: Exhaust-gas does not only get mixed with fresh air from one side as usually, it is leaded from the EGR valve into a preceding mixing chamber before. By means of an integrated aperture ring being adaptable to the according engine, the floating of exhaust-gas can be selectively influenced. Thus, a homogeneous distribution of EGR quantity over the complete duct cross-section of the fresh air supply can be achieved. The resultant equal distribution of exhaust-gas over all cylinders leads to an increased EGR rate, because as a result the NOX/PM trade-off of all cylinders is nearly the same without the negative effect of an increased soot production at one or more cylinders. Based on several projects with older engine generations, a considerable potential for Nox-reduction could be proved and generally, the engines could be upgraded by one emis-sion level without any design modifications in the field of fuel-mixture generation or combustion chamber design. A feasibility study re-sulted in the fact that even Euro-6 emission level can be achieved by using an EGR system.

„In case of smart use, EGR still offers the possibility to reduce nitro-gen oxides not only in a highly-efficient but especially cost-effective way. Even though we have already offered system solutions in the field of Selective Catalytic Reduction (SCR), we have been con-vinced especially by the inquiries from OEMs that the potential of exhaust-gas recirculation systems has not been tapped by now.“, points out Juergen Pilsl, head of application and testing at Huber Group. 

The development and product range of Huber Group regarding emis-sion reduction systems and components thus comprises also SCR and DPF (Diesel Particulate Filter) system solutions. The decision on using a specific method or an individual combination of systems is made in close co-operation with the according customer. By this, cost advantages can be fully achieved as well as specific customer re-quirements can be realized in an ideal way.

The development of engine and powertrain control systems with the focus on emission reduction for diesel engines also counts to the core competences of Huber Group. The international know-how ranges from exhaust-gas after-treatment for diesel engines, design-ing and application of dynamic exhaust-gas recirculation systems in transient operating mode to R&D projects for complete engine con-trols in the field of gasoline engines and hybrid drive. Functional de-velopment and control systems for exhaust-gas after-treatment (SCR and DPF) complete the business activities of Huber Group.

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