Numerical Study of Thermal-Fluid-Interaction in a Diesel Fuel Injector

There is experimental evidence that flow optimised Diesel injectors using ks-nozzles show an increased tendency towards the formation of deposits. These deposits reduce spray quality and have an adverse effect on soot emissions and engine performance. Since deposit formation is known to be caused by locally high temperatures, the thermal behaviour of Diesel injectors using cylindrical and ks-nozzle was investigated. For this reason a coupled fluid-thermal analysis for a Diesel fuel injector was performed using a 3D-CFD-Code for both the solid structures and the fluid domain. As a first focus of this work the thermal conditions at the injector tip have been extracted from a complete in-cylinder-flow-simulation and a subsequent sensitivity study at the injector tip showed the influence of boundary conditions and configuration changes. The second focus of our work was the calculation of the temperature increase of the fuel remaining in the nozzle holes and in the sac hole between two injections. To this end, a coupled simulation over two working cycles has been performed for both cylindrical and ks-nozzles to investigate the heating and vaporisation of fuel within the injector in the time period between injections, which may contribute to the formation on deposits in injector nozzles