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This paper describes research and development activities dealing with a technique which allows the measurement of gaseous and particulate concentrations inside the combustion chamber. This so-called fast-timed gas sampling technique was used for both the observation of the development of gaseous pollutants and soot during combustion and expansion and for getting information about the particle size history. The system has been applied to a modern passenger car DI diesel engine (Volkswagen). The investigation covers the early combustion phase beginning with the start of combustion and throughout the expansion phase until exhaust valve opening. Particles with a size of about 10 nm up to 1 μm were found. Slight variations in the smaller size classes could be observed during the combustion and expansion process.

During the lifetime of an internal combustion engine, deposits are formed at various locations. In diesel engines, deposits in the combustion chamber and at the injection nozzles lead to an increase in the emissions, especially the particulate emissions, and the exhaust gas odor. Additionally, durability problems can also arise. Deposits in the combustion chamber of SI engines can increase the octane requirement, deposits at intake valves can reduce engine efficiency and driveability and increase emissions. A detailed theory on the mechanism of deposit formation, considering the physical effects, is presented. This theory contains a deposit transport mechanism, a mechanism of deposit attachment including an induction phase, a deposit growth phase and a deposit removal mechanism. This complex theory is based on fundamental investigations at different locations in and around internal combustion engines.