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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.

Diesel fuels have been tested in both a naturally aspirated and an externally supercharged single cylinder, air cooled KHD DI-diesel engine, to determine the influence of poor fuel quality on combustion and emissions. A thermodynamic analysis of the cylinder pressure was conducted and the emissions were measured both gaseous as well as the particle emission (by means of a dilution tunnel). Additionally, extensive cold start tests were conducted. Under steady state conditions the cetane number seems to be a good parameter which describes the ignition behavior of different fuels. At low load, a change in combustion and a high increase in CO, HC and particle emissions were found with decreasing cetane number. During cold starting and warming up, a clear deterioration of the emission and combustion characteristics was also observed with decreasing cetane number when basic fuels were used.

In the recent years diesel engine developers and manufacturers achieved a great progress in reducing the most important diesel engine pollutants, NOX and particulates. But nevertheless big efforts in diesel engine development are necessary to meet with the more stringent future emission regulations. To improve the knowledge about particle formation and emission an insight in the cylinder is necessary. By using the fast gas sampling technique samples from the cylinder were taken as a function of crank angle and analyzed regarding the soot particle size distribution and the particle mass. The particle size distribution was measured by a conventional SMPS. Under steady state conditions the influence of aromatic and oxygen content in the fuel on in-cylinder particle size distribution and particle mass inside a modern 4V-CR-DI-diesel-engine were determined. After injection and ignition, mainly small soot particles were formed which grow and in the later combustion phase coagulate.