DIESEL SPRAY VISUALIZATION AND SHOCKWAVES

The paper discusses some fundamental spray properties and new aspects of measuring the spray behavior. The fuel injection measurements were done with marine common rail diesel injection equipment under nonevaporating conditions in a pressurized test rig. The tests were made at room temperature to ensure a constant environment for the sprays and to study the fundamentals of transient fuel jet. Fuel injection was performed with 1400 bar pressure to 35 kg/m3 ambient gas density with different nozzle orifices. Some fundamental phenomena in dense and high-velocity diesel spray can be confirmed by short exposure spray imaging. Imaging was based on planar illumination and digital imaging. The main findings were high-definition shockwave images. Shockwaves can be seen when the supersonic fuel spray exits the nozzle orifice. Shockwave imaging is used to estimate the velocity difference of the fuel and ambient gas. Boundary layer velocity measurements are shown at the vicinity of the nozzle orifice. Velocity measurements can be used to estimate nozzle discharge coefficients. The initial laminar core flow of the liquid and the collapse of this initial region were recorded. This may seem like a rather unlikely phenomenon in diesel injectors and it can well be considered as a special case. Spray-to-spray variation of the spray exit has also been recorded. Some time scales of the transient spray phenomena are also drawn.