An Investigation into Coolant-Related Internal Diesel Injector Deposits from Heavy-Duty Vehicles

The formation of internal diesel injector deposits (IDIDs) in heavy-duty engines is a growing problem as engine technology becomes more advanced while fuel blends become more diverse, posing new challenges for mixing and compatibility. IDIDs have a variety of causes that can be challenging to pinpoint due to the number of factors involved, such as engine operation effects, fuel types, fuel additives, and fuel contamination. The aims of this study were to characterize IDIDs formed in an injector from an engine operating on a biofuel blend contaminated with coolant, gain a deeper understanding of the underlying formation mechanisms, and identify potential markers of coolant contamination in failed field injectors. In this study, a failed injector from the field was examined that was known to have fuel contamination from coolant. Laboratory experiments using the thermal deposit test (TDT) were carried out to generate deposits from a test fuel spiked with coolant. The laboratory and field deposits were characterized and compared using scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), Fourier transform infrared attenuated reflectance spectroscopy (FTIR-ATR), and pyrolysis combined with gas chromatography (Py GC-MS). The results indicate that the deposits generated in the TDT were found to be primarily composed of sodium carboxylates originating from the organic acid technology additives in the coolant. The deposits were found to have structures with similarities to grease soaps, oleogels, or paraffin wax, suggesting that similar formation mechanisms may be involved. In contrast, the field injector deposits consisted of three distinct types: a cracked layer composed of sulfate salts and metal carboxylates, a globular cluster layer consisting of metal carboxylates, and particulate deposits that differ from the surroundings. The high proportion of sodium carboxylates in the globular cluster deposits was the key similarity to the laboratory deposits. In addition to the high sodium content, particulate deposits containing silicon and aluminum or aluminum and nitrogen were identified as potential markers of coolant contamination in IDIDs.