The Effect of Temperature on the Molecular Compositions of External and Internal Gasoline Direct Injection Deposits

The increased severity and prevalence of insoluble deposits formed on fuel injectors in gasoline direct injection (GDI) engines precipitates negative environmental, economic and healthcare impacts. A necessary step in mitigating deposits is to unravel the molecular compositions of these complex layered materials. But very little molecular data has been acquired. Mass spectrometry shows promise but most techniques require the use of solvents, making them unsuited for analyzing insoluble deposits. Here, we apply the high mass-resolving power and in-situ analysis capabilities of 3D Orbitrap^TM secondary ion mass spectrometry (3D OrbiSIMS) to characterize deposits formed on the external tip and internal needle from a GDI injector. This is the first application of the technique to study internal GDI deposits. Polycyclic aromatic hydrocarbons (PAHs) are present up to higher maximum masses in the external deposit. Lubricating oil derived sulfonates are more intense in the internal deposit, however higher mass sulfonates are only present in the external deposit. None of these molecular species have been identified in internal GDI deposits before. 3D OrbiSIMS depth profiles show that the needle deposit has a uniform deposit layer whereas the injector tip has a more complex layered structure. Comparison of 3D OrbiSIMS data suggests that the higher temperature experienced by the external injector tip explains key compositional differences and leads to growth of a thicker, more complex, layered deposit structure. The new insight into the impact that temperature has on deposit composition will aid in their mitigation and will lead to reduced vehicle emissions and cleaner air.