Time resolved growth of (N)-polycyclic aromatic hydrocarbons in engine deposits uncovered with OrbiSIMS depth profiling

Abstract

Insoluble carbonaceous deposits were grown in internal combustion engine components and interrogated by OrbiSIMS depth profiling, and we uncovered the composition and proposed time resolved growth mechanisms of these materials.

Role of Surface Chemistry in Pyrrole Autoxidation

“…Likewise, to calculate the amount of PPy that formed as particles, we performed particle size analysis of the optical microscopy images for each surface as described in the Materials and Methods section. We note that previous work has examined the topography of gum deposits in engine components in some depth, and the morphology of these deposits is similar to our observations here. ,, …”

“…We note that previous work has examined the topography of gum deposits in engine components in some depth, and the morphology of these deposits is similar to our observations here. 14,15,105 Figure 6b shows the material deposited by thin film formation and particle formation of PPy on different surfaces at 40 °C after 8 days of exposure to the model fuel environment. This analysis indicates that the volume of PPy within the micrometer-scale particles on each sample surface is about 2 orders of magnitude higher than the volume of PPy measured in the thin films.…”

“…Autoxidation also causes issues in other fuels, as well as naphtha, domestic heating oil, and other petroleum products. − Autoxidation produces a gum-like product called “red tar” and contributes to fuel degradation and instability over time, leading to changes in fuel composition, viscosity, and performance characteristics . These gum-like deposits can accumulate on fuel injectors, combustion chambers, and other engine components, causing decreased engine performance, increased fuel consumption, and increased emissions. , It is because of these collective issues that automotive fuel is not recommended for use after storage for more than two months. ,, Recent work has especially identified the important role of N-containing heterocyclic compounds in the formation of these deposits. − Considering these challenges, the petroleum industry would benefit from an improved understanding of autoxidation processes to help inform strategies for mitigation.…”

“…26−29 However, despite these indicators that the homogeneous fuel environment influences the rate of autoxidation, studies comparing Py autoxidation rates in fuels of different origins do not reveal clear trends connecting fuel composition with the varying rates of polymer/gum formation or gum composition. 14,19 Another aspect through which the molecular environment is expected to influence the rate of autoxidation is through heterogeneous interactions with surfaces. Indeed, recent studies have found that the same fuel composition exhibits different rates of polymer gum formation when in contact with different surfaces.…”

“…To this end, a range of studies has examined secondary effects of the fuel environment. For example, acidic conditions have been found to accelerate pyrrole (Py) autoxidation and depending on the specific fuel conditions, Py autoxidation has been found to proceed via different pathways, e.g., via peroxide intermediates or pyrrolines. − However, despite these indicators that the homogeneous fuel environment influences the rate of autoxidation, studies comparing Py autoxidation rates in fuels of different origins do not reveal clear trends connecting fuel composition with the varying rates of polymer/gum formation or gum composition. , Another aspect through which the molecular environment is expected to influence the rate of autoxidation is through heterogeneous interactions with surfaces. Indeed, recent studies have found that the same fuel composition exhibits different rates of polymer gum formation when in contact with different surfaces. − These studies suggest that surface chemistry may be a confounding variable in other studies and that understanding the role of heterogeneous surface processes on Py autoxidation may be crucial for developing strategies to mitigate autoxidation.…”