Press Release 081/2011

From Sketch Pad to Patent Application

KIT Students of Mechanical Engineering Developed a System to Reduce Emissions of Combustion Engines
Auf dem Prüfstand erfolgreich getestet: KIT-Studierende entwickeln ein Rückführsystem zur Emissionreduzierung (Foto: Michael Hörig)
Tested successfully: A refeed system for emission reduction developed by KIT students. (Photo: Michael Hörig)

Attempts to reduce CO2 emission and fuel consumption of combustion engines mainly focus on improvements inside the engine. Michael Hörig and Norman Nagel have now developed a process, by means of which emissions can be reduced without larger interventions in the engine. A patent has been applied for by the two students of mechanical engineering.

“If a combustion engine is operated in the overrun mode, i.e. in the mode in which no fuel is supplied and the engine is driven by the vehicle alone, cold air flows into the catalytic converter,“ Michael Hörig describes the problem. „For operation, however, the catalytic converter needs a temperature of about 300°C. Depending on the length of the overrun phase, this temperature is not reached and during subsequent normal operation, exhaust gas cleaning is worse for a certain time or does not take place at all.“ For this reason, Mi-chael Hörig and Norman Nagel have developed a system that collects the cold air upstream of the catalytic converter using a flap and feeds it back into the engine. The result: The operation temperature of the catalytic converter does not drop, it operates continuously, and emissions are reduced. “These overrun phases occur quite frequently during normal driving operation. Hence, our system will work quite often and total emissions will be reduced considerably,” says Norman Nagel.

The students performed measurements at the vehicle test rig of the Institute of Product Engineering (IPEK) and found that the emission reductions achieved even exceed those of similar systems. “Moreo-ver, our invention increases the efficiency of the catalytic converter, as we succeed in keeping the complete air flow away from the cata-lytic converter,” says Michael Hörig. Another big advantage compared to other developments lies in the comparably simple handling: The refeed system can be integrated easily in existing engine systems. Its installation by the automotive manufacturer is associated with low costs and low expenditure.

Both students of mechanical engineering had the idea to reduce emission about one year ago during a lecture. By and by, they de-veloped their idea further on their own initiative: From first principle sketches on a sheet of paper to the assembly of a test vehicle at their garage at home. “When we needed the support of KIT for our measurements, we met with the immediate approval of Professor Ulrich Spicher, Head of the Institut für Kolbenmaschinen (IFKM) and the staff of IPEK,” says Hörig. For several weeks, test series were performed on the KIT Campus for Innovation and Mobility, the area of the former Mackensen barracks. “KIT scientists and representatives of industry were highly interested in our positive measurement re-sults.” The young engineers now plan to enhance this interest. Within the next six months, they will make additional measurements to ex-plore the potential of their invention. Michael Hörig and Norman Nagel will present their ideas at international conferences. They have already established contacts to the big automotive manufacturers and wish to develop their system to maturity.   

The Mobility Systems Center pools KIT activities relating to vehicle technology. Presently, 40 institutes with about 800 em-ployees on KIT Campus North and Campus South are working on methodological and technical fundamentals for tomorrow’s vehicles. It is their objective to develop energy-efficient, low-emission, and safe vehicles and mobility concepts. Research also covers the complex interactions of vehicle, driver, traffic, and society.

Under the heading of “Future Mobility”, KIT will present its sci-entific activities on its new “Campus East – Mobility and Innovation” during an Open Day on July 02. More information can be found at:


Being “The Research University in the Helmholtz Association”, KIT creates and imparts knowledge for the society and the environment. It is the objective to make significant contributions to the global challenges in the fields of energy, mobility, and information. For this, about 9,600 employees cooperate in a broad range of disciplines in natural sciences, engineering sciences, economics, and the humanities and social sciences. KIT prepares its 23,300 students for responsible tasks in society, industry, and science by offering research-based study programs. Innovation efforts at KIT build a bridge between important scientific findings and their application for the benefit of society, economic prosperity, and the preservation of our natural basis of life. KIT is one of the German universities of excellence.

le, 19.05.2011


Monika Landgraf
Head of Corporate Communications, Chief Press Officer
Phone: +49 721 608-41150
Fax: +49 721 608-43658
presseVvi1∂kit edu

Contact for this press release:

Margarete Lehné
Press Officer
Phone: +49 721 608-41157
Fax: +49 721 608-41157
margarete lehneJfl2∂kit edu
The photo in the best quality available to us may be requested by
presseFcn2∂kit edu or phone: +49 721 608-41105.

The press release is available as a PDF file.