Abstract
Fuels with uncertain property may result in the deposit formation inside the nozzle holes and it causes injection characteristics to deteriorate. In this research, engine tests with zinc added fuels, deposit analyses, laboratory tests and numerical calculations were carried out to clarify the nozzle coking mechanism. Initially, lower zinc carboxylate formed close to the outlet side of the nozzle holes by the reaction between zinc in the fuel and lower carboxylic acid in the combustion gas. In the growth phase, the amount of deposits at the inlet side gradually increased and the main component changed from lower zinc carboxylate to zinc carbonate by the reaction with H2O and CO2 in the combustion gas. Zinc concentration, combustion gas and the nozzle tip temperature have effects of deposit formation and the cavitation inside the nozzle holes has an effect of removing deposit.
