Alongside the well-known injector deposits on the nozzle tips and inside the spray holes, the so-called „external diesel injector deposits“ (EDID), deposits within the injector, so-called „internal diesel injector deposits“ (IDID) have been reported worldwide since 2008 [1-8]. At the same time, the developments in diesel engine technology mainly aimed at fast reacting highly sophisticated injectors in conjunction with steadily increasing injection pressures. This combination enables combustion shaping by multiple injections. Each increase in injection pressure is accompanied by ever smaller clearings within the injector. This ongoing trend continues towards higher injection pressures, smaller clearings and more sophisticated injectors. Such highly sophisticated injectors are assumed to be less resistant against IDID compared to “older” ones [3, 4, 8-13]. At the same time, the fuel temperature increases steadily. The return flow from the injectors can reach temperatures of 150 °C [14] or even 190 °C at 250 MPa [15]. An increased fuel temperature on the other hand leads to an increased IDID formation tendency [1, 11-13, 16-17].
