The need for improved emissions and fuel economy are placing increasingly severe performance requirements on compression ignition engines. These are satisfied in part by advanced fuel injection equipment that provide multiple injections and increased injection pressures along with higher operating temperature. Fuel composition is also changing, with increased use of non-traditional feedstocks combined with a range of additive chemistries to restore or enhance fuel quality.
Within this environment, a number of worldwide automotive companies have noted a trend towards increased Internal Injector Deposits (IID). Little quantitative information to understand the root cause is available, largely due to difficulty in reproducing the issue under controlled conditions. The present study details the results of an accelerated test methodology, which is used to evaluate the interrelated effects of fuel composition and operating environment. In general, the results indicate low deposit tendencies with pure hydrocarbons and high quality Fatty Acid Methyl Ester (FAME). The results identify a number of potential deposit precursors that are likely to be responsible for soft metal carboxylate soap deposits and also hard polymeric lacquers.