A Contribution to the Investigation of Internal Diesel Injector Deposits

Internal Diesel Injector Deposits (IDID) are acknowledged to be an important issue with regards to engine durability, customer satisfaction and emissions regulations. The knowledge about IDID, though, is still limited, despite research being done on a broad basis. Two technical factors generally agreed upon to be of importance in the occurrence of engine failures due to of IDID are increasing temperatures and lower clearings within the injector. Due to current engine development trends with ever increasing injection pressures, these two factors will probably continue to develop into critical areas. The development of test methods to investigate IDID does not proceed as fast as the technological progress in injection technology.
A solution to this situation might be the use of injector test benches, where complete fuel systems of common rail engines are operated outside an engine and without combustion. Since the injector's interior does not come into contact with the combustion directly, this is a suitable method to investigate IDID.
This work contains a discussion on the aspects influencing the occurrence of IDID and their impact on injector function. Both measurements performed with the "ENIAK" injector test bench and published data are used for the analysis of IDID.
The main result of this is the identification of each technical, chemical, and physical aspects being important for the occurrence of injector malfunctions caused by IDID. The technical aspects include the thermal distribution within the injector as a factor in the formation of IDID, and the resilience of the injector as a whole system against malfunctions due to the presence of IDID. It was furthermore shown, that chemical aspects are of key importance as well.