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The design and adjustment of modern engines is limited by combustion behavior of the fuels. In the application of present fuels knock is the dominating factor, usually defined as Research -and Motor Octane Numbers (RON and MON). Alternative fuels prove to be different in some cases. So some engines react more sensitive with regard to knock as to be expected from the octane numbers when oxygenated fuels are utilized. In the application of alcohol fuels pre-ignition is an important factor besides knock, mainly in case of methanol. The investigation of pre-ignition and knock effects in high compression alcohol engines answers the question how the adjustment parameters such as air-fuel ratio, ignition timing and the temperatures of intake air and water will have an influence. As pre-ignition is a fuel property, a relation to other fuel properties, for instance octane numbers, is expected. It was found that the knock sensitivity gives a correlation to pre-ignition effects.