Modern diesel passenger car technology continues to develop rapidly in response
to demanding emissions, performance, refinement, cost and fuel efficiency
requirements. This has included the implementation of high pressure common rail
fuel systems employing high precision injectors with complex injection
strategies, higher hydraulic efficiency injector nozzles and in some cases
<100µm nozzle hole diameters. With the trend towards lower diameter diesel
injector nozzle holes and reduced cleaning through cavitation with higher
hydraulic efficiency nozzles, it is increasingly important to focus on
understanding the mechanism of diesel injector nozzle deposit formation and
growth. In this study such deposits were analysed by cross-sectioning the diesel
injector along the length of the nozzle hole enabling in-depth analysis of
deposit morphology and composition change from the inlet to the outlet, using
state-of-the-art electron microscopy techniques. Deposits produced in the
injector nozzles of the industry standard fouling test (CEC F-98-08 DW10B bench
engine) were compared with those formed in a vehicle driven on a chassis
dynamometer, using a drive cycle more representative of real world vehicle
conditions, to explore the effects of differing drive cycles and engine
technologies. Fouling in all tests was accelerated with the addition of 1ppm
zinc neodecanoate, as specified in the CEC DW10B test. This in-depth
characterisation revealed a complex multi-layered system of deposits inside the
diesel injector nozzle. Through analysing these layers the mechanisms enabling
the initial deposit formation and growth can be postulated.
