By Hank Hogan

It was a technical mystery, a problem with escalating costs as more and more vehicles underwent warranty repair. The issue? Internal deposits that caused sticking injectors in European diesel engines. The source was eventually traced back to fuel—or more precisely an interaction between fuel, additives and injectors. This mystery had a successful resolution, and the good guys saved the day. But, the tale illustrates the potential for problems ahead.

The story began about 10 years ago. That’s when carmakers throughout Europe started to see sticking fuel injectors in light-duty diesel vehicles. By 2011, the problem and the associated warranty repairs had grown serious, raising alarm among vehicle makers and fuel injection equipment suppliers. They faced a rising tide of costs and increasing customer complaints across the Continent.

“The worst affected country was France, although sporadic problems had been reported in Denmark, Germany and Spain,” said Ortwin Costenoble, secretary of technical committee CEN/TC 19. The committee deals with gaseous and liquid fuels, lubricants and related products of petroleum, synthetic and biological origin, for the European Committee for Standardisation (CEN). This technical committee was coordinating efforts to find the source of the problem and its solution. Costenoble is a senior consultant with NEN, a Delft, Netherlands-based organisation that supports the standardisation process.

At meetings, vehicle makers made presentations about the severity of the problem. The charts they used had an unlabeled y-axis for the number of warranty fixes, and so it was impossible for non-carmakers to determine how many vehicles were coming in for repairs. But, the trend line was clearly going up.

An ad-hoc task force began looking into the issue, which was dubbed IDID. The designator came from the first letters of “internal diesel injector deposit,” a description of what was going on. After some detective work, the investigators discovered that the source of the problem was sodium carboxylate soap deposits. As to why the deposits were suddenly causing trouble, there were several contributors. Some came about because of fuel changes made to reduce emissions.

“This problem is probably aggravated by sulphur-free diesel with lower aromatic levels, resulting in reduced natural fuel solvency, [as well as] increased biodiesel blending up to 7%, providing an additional source of sodium and weak acids,” Costenoble said.

Advanced engine hardware introduced to boost fuel efficiency also played a role. Smaller, turbocharged engines and a push for fuel efficiency meant that injector tolerances shrank. On top of that, these smaller engines operate at higher injector pressure and higher fuel temperature. Consequently, deposit build-up that in an earlier generation of injectors might not have been an issue proved to be problematic.

Looking at the fuel in the country most severely impacted, France, gave the investigators a critical clue. Pipeline operators had used a particular sodium-based additive to inhibit corrosion. That provided the final piece of the solution to the mystery.

“The root cause of the internal injector deposit problem that has resulted in vehicle failures in several EU countries is due to different chemical interactions between fuel corrosion inhibitor additives and contaminants present in the diesel fuel from the production process,” Costenoble said in summing up the task force’s findings, which were published in 2014.

With the mystery solved, the question then was how to fix the problem. An option was to set a maximum sodium limit in diesel fuel. However, that was not deemed practical for two reasons. The first was that the proposed limit would have to be very low, 500 parts per billion (ppb). Second, the limit would need to apply at the pump where drivers fill up, which would be operationally difficult.

Another proposal was to remove the chemical causing the problem in France, possible because of little evidence of internal corrosion with modern fuels. That fix was implemented with good results.

“Reports of injector sticking problems have reduced dramatically since the water soluble sodium nitrite pipeline corrosion inhibitor was removed in France,” said Nigel Elliott, chair of the IDID task force.

THE SEQUEL?

If this were a Hollywood movie, it would be time for the words “The End” to appear. Unfortunately, there might be a sequel, perhaps more than one. As fuels and engines change, problems like this could continue to crop up. After all, there could be other sources of sodium or even other chemicals or elements that by interacting with fuel could cause deposits to form.

French pipeline operators are not alone in using corrosion inhibitors. It’s possible that one of these corrosion inhibitors might react to what’s in a given fuel and that could lead to the creation of particulates, soaps and deposits.

Investigators have started looking into other possible trouble spots along the fuel supply chain. The Alpharetta, Ga.-based Coordinating Research Council (CRC) is looking into this issue with regard to historic pipeline inhibitors being used in the U.S.A., according to Elliot.

There is convincing evidence that other corrosion inhibitors, such as alkenyl succinic acids, also react with sodium in diesel fuel to form sodium carboxylate soaps, according to Costenoble. Other additives could also create problems.

“Dimer acids at higher treat rates of more than 30 parts per million by volume have also been shown to cause inline fuel injector pump sticking when the pump is lubricated with engine oil and the fuel and oil come into contact on the fuel pump plunger and react to form a sticky deposit,” Costenoble said.

The fuels industry must, in effect, perform a balancing act with every fuel and additive blend. For instance, a corrosion inhibitor needs to do its part to improve corrosion resistance. At the same time, it cannot react to what is in the fuel and create problems.

To protect against this possibility, the Coordinating European Council (CEC) is developing a standardised engine test to recreate, and thereby detect, the IDID problem. The test can then be used to judge the impact of different mitigation strategies, as well as the effect of fuels and additives.

“The objective is to develop a test that will discriminate between fuels that differ in their ability to produce IDID in direct-injection, common rail diesel engines,” Costenoble said in discussing the goal of this test development.