Development and Application of an Engine Test Method to Rate the Internal Injector Deposit Formation of Diesel Fuels and Additives

Design efforts to improve the hydraulic efficiency of high-pressure diesel fuel systems and thus further improve overall engine efficiency have resulted in the utilisation of low-spill control valves and reduced injector component clearances to reduce general leakage losses. Overall, these advances have contributed significantly to the high efficiency diesel engines of today. However, the combination of very high fuel pressures, cavitation and low fuel leakage volumes increases the heating of the remaining fuel, increasing temperature and, in turn, the propensity for deposits to form inside the injector. This deposit phenomenon is commonly known as Internal Diesel Injector Deposits (IDID) and can cause rough engine running and failed engine starts requiring injector cleaning or replacement. Methods studying this phenomenon are under development in the industry. Meanwhile this paper describes the development and application of an in-house engine test method to rate the IDID control performance of deposit control additives (DCA). A 2.0L, 4-cylinder light-duty engine is run with a fuel containing a contaminant to provoke the occurrence of deposit formation within a reasonable test duration. In ‘keep clean’ test mode the performance of the DCA is assessed based on its ability to prevent IDID symptoms that routinely manifest in unadditivated test runs, primarily between-cylinder deviation in exhaust port gas temperature as the operation of individual injectors is impaired by deposits. In ‘clean up’ test mode the DCA is assessed on its ability to reverse IDID symptoms that manifested in a preceding unadditivated test run. In initial tests the methodology has proved capable of differentiating between a novel DCA chemistry that exhibits good IDID control behaviour in keep clean and clean up modes and a conventional DCA chemistry that did not. Temperature deviations were reduced applying the novel DCA at premium dose in keep clean mode. In clean up mode, temperature deviations were reduced from the end of dirty up to the end of clean up, with premium plus dose rate of the novel DCA. In both cases the improvements were statistically significant at the 95% confidence level.