Understanding the Adverse Effects of Inlet Valve Deposits on SI Engine Operation, through a Novel Technique to Create Surrogate Deposits 2018-01-1742

For gasoline spark ignition engines, port fuel injection (PFI) on a global basis remains the most common type of fuel delivery. When operated with lower quality fuels and lubricants, PFI engines are prone to suffering from the build-up of harmful deposits on critical engine parts including the inlet valves. High levels of inlet valve deposits (IVDs) have been associated with drivability issues like engine stumble and hesitation on sudden acceleration. Fuels formulated with the appropriate level of deposit control additive (DCA) can maintain engine cleanliness and even remove deposits from critical components.

This study, involving a single cylinder research bench engine operated in PFI injection mode and heavily augmented with measurement equipment, aimed to gain a deeper understanding of the detrimental impacts of IVDs on engine efficiency and performance. Guided by 3D-scans of carbonaceous IVDs sourced from industry standard tests conducted per ASTM D5500, surrogate metal deposits were generated, utilizing the novel approach of powder-laser-cladding (PLC). The modified inlet valves were evaluated in the research engine across eight different speed load conditions including full-load. Using this approach and building on the results previously obtained on the industry standard Mercedes-Benz M111 bench engine, it was possible to quantify an increase of more than 3 crank angle degrees in combustion duration at a 95% level of statistical confidence, due to the presence of the simulated IVDs. Similarly, IVDs limited the quantity of air entering the cylinder which reduced power output of the engine for a given condition by 1.9% at a 99% level of statistical confidence. These effects were corroborated by supporting secondary metrics such as exhaust temperature increases and peak pressure reductions. Overall, it was shown that the presence of IVDs shifted the center of combustion away from the engine’s optimum point for efficiency as defined by the maximum brake torque (MBT) spark timing.