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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

High supercharging level at SI-Engine

Because of the fact, that energy sources are running short and the reduction of the emission of CO2 becomes the main goal, the automotive industry has to offer more and more efficient powertrains. The SI-Engine has a further potential for improve-ment, especially due to the easier exhaust gas aftertreatment considering the devel-opment of the limits. Further advantages are the lower weight of the engine, com-pared to the diesel engine, and the lower manufacturing costs. The lower cost level is based on the lower peak pressure in the cylinder and the lower effort on the ex-haust gas aftertreatment.

Downsizing and downspeeding are the keywords at the improvement of the power-train efficiency. Downsizing means that an existing engine is replaced by one with smaller displacement but the performance has at least to stay equal. To reach this goal supercharging is necessary, so the torque level of the new engine can even be higher. At the same time the fuel consumption can be lowered. Downspeeding be-comes possible because the higher mean effective pressure allow to shift the rated power to lower speed. Lower gear ratios are used and the usual engine speed is shifted to a lower level.

The mentioned measures cause a more frequent operation at low engine speed an high load level. In this area of the engine map the probability for occurence of ab-normal combustion (A.C.) is  higher (picture1). 
Picture 1: Critical area for irregular combustion within the engine map
Picture 1: Critical area for irregular combustion within the engine map
The knocking phenomenon is already well known, it occures also at the natural as-pirated engines. Design features (lower wall temperatures, high flame velocity) are able to minimize it as well as the shift of the ignition timing.

At higher supercharging levels (and therewith higher power density) the tempera-ture level at the end of the compression stroke becomes that high, that the mixture can auto-ignite without the external spark. The very early ignition leads to high pres-sure values, followed by strong knocking. The components are usually designed for pressure values of ca. 100 bar, but at the auto-ignition events it exceeds 200bar. So these events have a high damage potential, already a few of them can cause dam-ages like shown in picture 2.

Picture 2: Piston damage after autoignition events
Picture 2: Piston damage after autoignition events
A great effort is the avoidance of such autoignition phenomena, respectively the shift to higher engine load level. But  alike important is to determine the causes for these phenomena.

At the IFA many research work was done in the past and in the present, in collabora-tion with industrial partners. The focus is on following topics:
  • Fundamental research, assisted by optical methods in order to localize the ignition sources
  • Impact of the fuel
  • Impact of the lubricant
  • Design features, like the layout of the injector spray

For the optical investigation a high speed camera is used, combined with an image intensifier. The optical access to the combustion chamber was developed at the IFA, and the application on the delivered cylinder heads is done at the institute. Further-more the light emission can be detected by an optical spark plug. The digitalizing system is provided by the AVL. It allows to detect the flame propgation by 8 optical channels (picture 3).
Picture 3: Optical access to the combustion chamber; Spark plug with optical fibres[AVL]
Picture 3: Optical access to the combustion chamber;  Spark plug with optical fibres[AVL]

Dipl.-Ing. Nikola Bobicic
Phone: +43 1 58801 31574
Mail: nikola.bobicic[at]