Sodium Contamination of Diesel Fuel, its Interaction with Fuel Additives and the Resultant Effects on Filter Plugging and Injector Fouling

Abstract

Diesel fuel distilled from crude oil should contain no greater than trace amounts of sodium. However, fuel specifications do not include sodium; there is a limit of five parts per million for the amount of sodium plus potassium in fatty acid methyl esters (FAME) used as biodiesel. Sodium compounds are often used as the catalyst for the esterification process for producing FAME and sodium hydroxide is now commonly used in the refining process to produce ultra-low sulphur diesel (ULSD) fuel from crude oil. Good housekeeping should ensure that sodium is not present in the finished fuel. A finished fuel should not only be free of sodium but should also contain a diesel fuel additive package to ensures the fuel meets the quality standards introduced to provide reliable operation, along with the longevity of the fuel supply infrastructure and the diesel engines that ultimately burn this fuel. There has recently been an upsurge in reported field problems due to fouling of the fuel injection system in modern diesel engines. This can take the form of deposits in the fuel filters or within the fuel injectors themselves. Recent work proposed a mechanism whereby sodium contaminated fuel can undergo adverse reactions between the sodium compounds and fuel additives leading to the formation of material that can impede the operation of diesel fuel injectors. This paper presents new work carried out to enhance the understanding of this mechanism and demonstrates that the fate of any sodium contaminant is highly dependent on (i) the fuel additives present in the fuel (ii) the amount of water in the system, (iii) potentially the intensity of fuel/water mixing and (iv) the identity of the sodium salt involved in the reaction. This can lead to sodium accumulating in the water bottoms, forming sodium compounds that go on to plug fuel filters or which may cause injector fouling. The data found may explain the variation in engine test data regarding sodium induced fouling reported in the recent literature.

A study of factors influencing the formation of harmful deposits in the diesel engine injectors

“…Moreover, added to the fuel as 1-litre premixes were mixtures of chemical compounds which according to the available results of tests performed at various laboratories have the greatest impact on the formation of various IDID [1,2,6,9,10,11,12,14,16]. The said pressures, where fuel heated up to 60 ºC returns many times from the injection systems overflows to the fuel tank, heating up the whole fuel system.…”

Internal Injector Deposits From Sodium Sources

“…With a sodium 2-ethylhexanoate source, both the mono-acid lubricity improver and di-acid DDSA caused injector sticking and sodium carboxylate was observed on the injector needle. Testing of sodium chloride with a mono-acid lubricity improver did not result in engine running problems over the 32 hour test although EDAX studies showed very low levels of NaCl within the injector [1]. This would suggest that although NaCl does not react with the acidic species in the fuel it can still transport through the fuel system to the injector.…”

“…Previous testing has shown that different sodium sources will interact differently with acidic species in the fuel, such as mono-acid lubricity improvers or di-acid corrosion inhibitors. Sodium hydroxide has been shown to cause injector sticking with the di-acid DDSA [6] but in the presence of a mono-acid lubricity improver it was found to cause fuel starvation due to a blocked fuel filter [1]. With a sodium 2-ethylhexanoate source, both the mono-acid lubricity improver and di-acid DDSA caused injector sticking and sodium carboxylate was observed on the injector needle.…”

“…In the US there is a CRC committee sub panel on IDID (CRC DIESEL Performance Group -Deposit Panel Bench/Rig/Investigation sub panel) and in Europe the CEN TC19/WG24 Injector Deposit Task Force, and the CEC TDFG-110 panel is developing a standard engine test, using a "fuel soluble" sodium salt and dodecenylsuccinic acid (DDSA). Further, we have recently published [1] data using the diesel engine nozzle coking test [2] that showed sodium hydroxide and mono-acid lubricity improver resulted in filter blocking, and the same mono-acid lubricity improver with a "fuel soluble" sodium salt (sodium 2-ethylhexanote) gave injector sticking. An ester based lubricity improver was found to cause neither problem.…”

Sulfate Salts in Gasoline and Ethanol Fuels -- Historical Perspective and Analysis of Available Data

“…Contamination of diesel fuel with sodium, potentially originating from salt dryers, has been proposed as a factor in recent incidents of diesel filter plugging and injector fouling (Schwab et al 2010, Barker et al 2013. While this does not represent a direct route to contamination of gasoline with NaCl, there are situations where gasoline or denatured fuel ethanol can come into contact with diesel fuel, for example in transport trucks that have not been properly cleaned.…”