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Institute for Powertrains and Automotive Technology
Vienna University of Technology 
Getreidemarkt 9
1060 Vienna, Austria
Phone: +43 1 58801 31500
Mail: info[at]

Office opening hours:
Mo-Fr: 8 am - 4 pm

CNG engine

One key aspect of the research activities of the Institute for Powertrains and Automotive Technology are alternative fuels and therefore adapted combustion processes. In addition to the blends of the liquid fuels diesel and gasoline, gaseous fuels like methane are in focus. Methane is the essential part of CNG (Compressed Natural Gas) and biogas. Due to the higher Hydrogen (H) to Carobon (C) ratio of methane lower CO2 emissions occur at combustion. A further advantage of CNG is the extensive distribution network and the possibility of producing CNG in biogas plants and feeding into the natural gas grid.

The mixture preparation is easier because CNG is already gaseous at the injection. Due to this fact the ability for lean combustion processes of methane is much higher than gasoline. The high knock resistance of methane allows a high downsizing level which is generated by a combination of an increased compression ratio and turbocharging. A very innovative concept is to inject CNG directly into the combustion chamber. Because of the CNG Direct Injection (DI) the charge disadvantage as a result of fresh air expulsion by fuel inside the intake manifold is avoided.

In contrast to port fuel injection of CNG, direct injection can use scavenging strategies. At low engine speed and high load fresh air flushes the combustion chamber by adjusting high valve overlap with a camphaser. Hence an increasing mass flow speeds up the turbocharger, less time is needed to reach a certain boost pressure and the turbo gap is reduced. The injection of CNG occurs after the intake valves are closed and no fuel is flushed into the exhaust manifold. This strategy improves the Low End Torque significantly and high transmission ratios downspeed the engine for low fuel consumtion.

A great potential of DNG DI is the possibility of exhaust gas catalyst heating by injecting CNG close to the exhaust valve opening. The additional very late combustion does not lead to an increasing of the torque but to an significantly higher exhaust gas temperature which accelerates the catalyst heating. This fact is very important for CNG vehicles, because the methan deamands much higher temperatures in the catalyst to be converted. With this technology the very strict exhaust gas regulations can be observed.


Dipl.-Ing. Marko Damböck
Tel.: +43 1 58801 31615
Mail: marko.damboeck[at]

Dipl.-Ing. (FH) Thomas Hofherr MSc.
Tel.: +43 1 58801 31584
Mail: thomas.hofherr[at]