Effect of trace zinc amounts introduced in various chemical structures in diesel fuel on coke deposits of fuel injectors of a CI engine

Abstract

The goal of the article was to carry out a comparative research on the propensity of a standard-class commercial diesel fuel, consistent with the requirements of the EN-590 standard, with zinc catalysts of various chemical structures introduced, to form deposits on the tips of fuel injectors of a compression ignition engine. Studies on structures of zinc carboxylic salts type dissolved in the fuel and dispersed zinc oxides/hydroxides type were planned. The influence of zinc dialkyldithiophosphates (ZDDP) on the deposit formation was not investigated because of their complex structure and inability to evaluate the additional impact of phosphates(V) on the deposit formation process. Studies of pre-prepared fuel samples without zinc and with various zinc contents of various origins, which may constitute trace impurities of diesel fuel, were carried out using a standardised engine test acc. to the general European CEC F-98-08 procedure, in which the amount of the engine power decrease was adopted as an evaluation criterion for the size of the deposits formed on the tips of fuel injectors. Also, an analysis of elemental composition of the coke deposits formed on the tips of fuel injectors of a Peugeot DW10B engine was carried out by the X-ray fluorescence method. In the results of the studies carried out, it was found that in the case of commercial diesel fuel used for the tests, none of the zinc compounds assumed as deposits precursors had a significant influence on the chemistry of the deposit formation process during combustion of the diesel fuel in the engine. The deposits being formed are characterised by practically the same chemical nature. However, differences were found in the case of amounts of deposits forming on the tips of the fuel injectors and their growth rate during the test.