The direct view into the combustion chamber of a direct injection (DI) Diesel engine allows a fast, comprehensive analysis of the influence of different engine parameters on the combustion process. Therefore and in order to acquire a maximum amount of information from one engine cycle, a combination of four non-intrusive temporally and spatially highly resolving optical measurement techniques were applied simultaneously to a passenger car DI Diesel transparent engine. These measurement techniques include the detection of the flame luminosity in the UV-range as well as the detection of thermally excited soot radiation in the visible range, the visualization of the distribution of the liquid fuel phase by the Mie scattering technique and the laser-induced incandescence (LII) technique for the characterization of the two-dimensional soot distribution inside a selected plane of the combustion chamber.
With these four measurement techniques the influence of the flow value of three different geometries of the nozzle-holes on spray formation, mixing, ignition, combustion and soot formation was examined. Besides significant influence of the flow value, the investigation also revealed the relevance of the combustion bowl wall on mixture formation and combustion. The increasing flow value intensifies the spray wall interaction, which improves the mixture formation and leads to a reduced soot formation for the examined operating points. Additionally for an operating point with pre-injection the swirl in the combustion bowl was increased. The resulting reduction of soot formation indicates that not only fuel propagation is important for the quality of mixture preparation, but also the charge motion.
The acquired results are condensed in a schematic, which illustrates plastically the differences of the engine parameters on mixture formation and combustion.