Diesel Injector Deposit Control Additives: Chemistry and Functions
Part 1: Introduction (3-Minute Read)
Internal Diesel Injector Deposits (IDIDs) accumulate inside the injector body (not on the nozzle tip) and can cause sticking of moving parts, leading to poor fuel metering, power loss, and rough operation.
Modern diesel engines with high-pressure common-rail injection (pressures >1500 bar) and extreme fuel temperatures (~100 °C) are especially prone to IDID. To combat these deposits, 4+ fuel additive packages include a combination of chemical compounds each serving a specific function. These additives can prevent deposit formation (keep-clean) and remove existing deposits (clean-up) in automotive, industrial, and marine diesel engines.
Deposits can form on internal parts such as the needle valve, seat, and control passages
Deposits and Deposit Control Challenges
Internal vs. External Deposits: Unlike conventional “coking” deposits on injector tips or orifices, IDIDs form within the injector (e.g. on the needle, pilot valve, or control valve surfaces. These varnish-like or waxy deposits can slow or seize the precise motion of injector components, upsetting injection timing and fuel delivery. IDIDs can arise from fuel degradation at high pressure/temperature or from interactions between fuel contaminants and additives. Two main types are often observed:
“Soap”/Waxy Deposits: Often light-colored, waxy deposits formed by metal carboxylate “soaps.” For example, sodium or other metals can react with acidic lubricity additives to form insoluble salts lubrizol.com. A known case is sodium from pipeline corrosion inhibitors (e.g. sodium nitrite) reacting with fatty acid lubricity improvers, yielding sodium carboxylate precipitates. These soap deposits tend to cause sticking in North American engines using ultra-low sulfur diesel (ULSD).
Carbonaceous/Lacquer Deposits: Brown to black, varnish-like deposits of organic material. Studies suggest they form via fuel oxidation or by reactions between certain detergent additives and acidic fuel components. For instance, polyisobutylene succinimide (PIBSI) detergent can react with organic acids in fuel, producing a sticky resin. Such lacquer deposits have been more commonly reported in European designed engines
Early IDID incidents highlighted the importance of additive chemistry design. Additives must be effective at deposit control without themselves contributing to deposits (a “no-harm” requirement). Formulators have responded by developing improved detergents and complementary chemistries that address the specific precursors of IDIDs. Notably, researchers found that low-quality or low-molecular-weight detergents were linked to severe IDID and sticking, whereas properly engineered additives did not cause deposits and in fact prevented them. Replacing problematic additives (e.g. using ester-type lubricity agents instead of free acids or adding stabilizers) has been key to solving IDID issues. All additives are not created equally!
In our next chapter we discuss: Chemical Classes and What They Do.