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The sooting propensity of dual-fuel combustion with n-dodecane pilot injection in a lean-premixed methane-air charge has been investigated using an optically accessible Rapid Compression-Expansion Machine (RCEM) to achieve engine-relevant pressure and temperature conditions at the start of pilot injection. A Diesel injector with a 100 μm single-hole coaxial nozzle, mounted at the cylinder periphery, has been employed to admit the pilot fuel. The aim of this study was to enhance the fundamental understanding of soot formation and oxidation processes of n-dodecane in the presence of methane in the air charge by parametric variation of methane equivalence ratio, charge temperature, and pilot fuel injection duration. The influence of methane on ignition delay and flame extent of the pilot fuel jet has been determined by simultaneous excited-state hydroxyl radical (OH*) chemiluminescence and Schlieren imaging.

Fuel spray propagation and its morphology are important aspects for the in-cylinder mixture preparation in Diesel engines. Since there is still a lack of suitable measurements with regard to large 2-stroke marine Diesel engines combustion systems, a comprehensive data set of spray characteristics has been investigated using a test facility reflecting the specific features of such combustion systems. The spray penetration, area and cone angle were analysed for a variation of gas density (including the behaviour at evaporation and non-evaporating conditions), injection pressure and nozzle diameter. Moreover, spray and swirl flow interaction as well as fuel quality influences have been studied. To analyse the impacts and effects of each measured parameter, an empirical correlation for the spray penetration has been derived and discussed for all measurements presented.

In view of the large (and further increasing) range of fuels applied in marine diesel engines, there is a clear need for obtaining a better understanding of the effect of those fuels on the key in-cylinder processes governing the combustion characteristics of these engines. For this purpose, a constant volume chamber representative of the combustion system of large marine diesel engines has been complemented with a device allowing the investigation of small fuel quantities and the resulting setup has been used for studying the combustion behaviour of typical marine diesel fuels at conditions relevant for large marine two-stroke diesel engines. Specifically, two clearly distinct heavy fuel oils have been compared to a light fuel oil. Two optical measurement techniques were used to complement the findings made on the basis of rate of heat release analysis.