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Downsizing is one of the most promising concepts to reduce fuel consumption of gasoline engines. However, it is currently limited by the occurrence of irregular combustion phenomena at high loads. This paper provides an overview of the combustion phenomena to be taken into account. At first, knock, extreme knock, surface ignition, and pre-ignition are briefly introduced by a description of their phenomenology. Since pre-ignition is the newest and least explored of these phenomena, the results of a study about its phenomenology and reasons for its occurrence are presented. Finally, auto-ignition in general is discussed, taking into account its occurrence, its effect, and its avoidance. Thereby, the general remarks about auto-ignition are related to the phenomena observable in real engines.

In this work the formation and oxidation of soot inside a direct injection spark ignition engine at different injection and ignition timing was investigated. In order to get two-dimensional data during the expansion stroke, the RAYLIX-technique was applied in the combustion chamber of an optical accessible single cylinder engine. This technique is based on the quasi-simultaneous detection of Rayleigh-scattering, laser-induced incandescence (LII) and extinction which enables simultaneous measurements of temporally and spatially resolved soot concentrations, mean particle radii and number densities. These investigations show that in our test engine the most important source for soot formation during combustion are pool fires, i.e. liquid fuel burning on the top of the piston. These pool fires were observed under almost all experimental conditions.

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