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B. Geringer, P. Hofmann, G. Prochazka, C. Jelitto, J. Willand:
"Comparison of the Phenomena of Autoignition in Highly Charged SI Engines with External and Internal Mixture Formation Regarding Influencing Variables, Mechanisms and Preventive Measures";
Talk: FISITA 2006 World Automotive Congress, Yokohama/Japan (invited); 2006-10-22 - 2006-10-27; in: "FISITA 2006 World Automotive Congress", Society of Automotive Engineers of Japan, Inc., (2006), 11 pages.

The reduction of the fuel consumption is the main target of the development of new propulsion systems. Highly charged engines which provide a high mean pressure level over nearly the entire speed range are a very interesting possible solution. This strategy,known as downsizing, is characterised by a reduction in displacement and the related shift of the operating-point (1). It is already state of the art in diesel engines. The engine-torque characteristic, primarily affected by the charge boost, is important for customer acceptance.
The maximum realisable boost ratio of SI engines is, beside the well known knock limit, also restricted by autoignition. In consequence, the effective mean pressure cannot be increased above a certain level. Thereby, a particularly high compression ratio has a negative effect.
This, however, should be set as high as possible, taking into consideration part load efficiency.
The topic of autoignition was analysed in research projects at the Institute for Internal Combustion Engines and Automotive Engineering of the Vienna University of Technology in highly charged SI engines with external as well as internal mixture formation.
During practical investigations, autoignition occurred and prevented higher boost ratios at low engine speeds. The measured in-cylinder pressure thereby was similar to an HCCIcombustion.
Extremely high peak pressures were reached (2), (3), (4) which caused, in most cases, immediate damage to the engine. It was shown that the causal mechanisms for these autoignitions have to be differentiated.
This lecture describes various influencing variables and mechanisms of the phenomena of autoignition, focusing also on the specific differences of external and internal mixture formation. Finally the different preventive measures are discussed.

Autoignition, Irregular Combustion, External Mixture Formation, Internal Mixture Formation, Optical Measuring Techniques

http://aleph.ub.tuwien.ac.at/F?base=tuw01&func=find-c&ccl_term=AC06587309