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The chemical behaviors of diesel fuel and the effects of aromatic content on combustion characteristics and NOx histories were experimentally investigated using a rapid compression machine and a total-gas sampling device. The aromatic content was changed under constant cetane number. Composition of the individual hydrocarbons, inorganic gases and NOx under various ambient temperatures and fuel injection pressures were analyzed with aromatic-free and aromatic-containing fuels. The results indicate that injected fuel is rapidly decomposed and dehydrogenated during the ignition delay period. The decomposed low boiling-point hydrocarbons consist of mainly unsaturated hydrocarbons such as C2H4, C2H2 and C3H6 at the initial combustion phase. At the diffusion combustion phase, the low boiling-point hydrocarbons consist of mainly CH4.

A single nano-spark back light photography method has been developed to record the image of non-evaporating diesel sprays injected into high pressure nitrogen gas. Relatively clear image of fine droplets and spray was obtained. An image analysis method has been developed to quantify the droplet characteristics which are in focus, such as droplet size and shape. Spatial and temporal distribution of droplets has been clarified. It was observed that the number of droplets around the nozzle tip region decreases by time, however a large number of droplets were observed at X=13∼25 mm from nozzle tip at t=300∼700 μs from injection start. Double-nano spark photography of diesel sprays was carried out and relatively clear double exposure images of droplets were obtained on the same film. Two dimensional size and velocity measurement of droplets were simultaneously carried out based on these photographs.