Impact of Fuel Additives on Diesel Injector Deposits

Continued legislative pressure to reduce diesel emissions has resulted in the development of engines with advanced fuel injection equipment (FIE). These injection systems produce temperatures and pressures at the injector tips that are considerably higher than those seen in previous technologies. This environment is initiating deposit formation at and around the injector tip which is leading to significant power loss and increased smoke generation.

Investigations have been carried out to understand this phenomenon. Cyclic bench engine testing has generated high levels of deposits when minimal amounts of a fuel soluble zinc salt are doped into clear fuels. The deposits are found both in and around the nozzle tips. Analysis of the deposit shows the presence of zinc. These deposits are proving to be more challenging than those previously seen with older FIE technology. Detergents that have historically been effective in resolving injector deposits are proving less effective.

Investigations to understand possible sources of metal contamination focused first on laboratory tests followed by vehicle trials. Laboratory testing carried out on different fuels and different additive types showed that certain lubricity agents promote the uptake of metals into fuel. Alternative, safe lubricity additive options are available to restore appropriate lubricity to diesel fuel without impacting metal uptake and hence the generation of injector deposits. A field trial using several vehicles has reproduced the findings of the laboratory tests. The field testing has confirmed that low, but significant levels of metals are solubilised into fuel from the tank and the FIE in the presence of a specific lubricity additive technology, whilst other lubricity additives are neutral. The level of metal pick up in the field is comparable with that used in the bench engine testing to generate injector deposits.