Internal Diesel Injector Deposit Chemical Speciation and Quantification Using 3D OrbiSIMS and XPS Depth Profiling

The impact of internal diesel injector deposits (IDIDs) on engine performance, efficiency and emissions remains a major concern in the automotive industry. This has been compounded in recent years by fuel injection equipment developments and changes to diesel fuel towards ultra-low sulfur diesel (ULSD) and biodiesel as well as the introduction of new fuels such as hydrotreated vegetable oil (HVO). Prevention and mitigation of such deposit formation requires an understanding of the formation process, which demands a chemical explanation. The chemistry of these deposits therefore remains a key research interest to the industry using the latest analytical methodologies to inform and build further on previous investigations. In this work, 3D OrbiSIMS analysis using a time of flight-secondary ion mass spectrometer (ToF-SIMS) with hybrid Orbitrap^TM functionality has been employed for chemical speciation and depth profiling of IDIDs in-situ on two injector needle samples from field failures in China and Eastern USA. The instrument’s soft gas cluster ion beam (GCIB) and high mass resolution enables unequivocal identification of chemistries from several classes of compounds. Here, chemistries identified include alkylbenzene sulfonates, zinc oxides, sodium and calcium salts, carboxylic acids, carbonaceous/polyaromatic hydrocarbons and metal substrate related material. With depth profiling, the distributions of these materials are traced throughout the deposit thickness. Given the semi-quantitative nature of SIMS data, X-ray photoelectron spectroscopy (XPS) depth profiling using an argon GCIB has also been employed to provide parallel data of atomic concentration through the deposit thickness. This data is complementary to SIMS as it places the chemical information in a quantitative context, most notably showing that despite the extreme intensities of salt material in the SIMS data, carbon is the main element throughout both IDIDs. Together the techniques show in general the more functionalized chemistries are at the deposit surface, with underlying salt layers and innermost layers of more amorphous organic material. These techniques represent a new method of comprehensive IDID characterization that affords diagnostic chemical information alongside elemental quantification, thus complementing previous studies.