Port fuel injected (PFI) technology remains the most common fuel delivery type
present in the marketplace for gasoline spark ignition engines and a legacy
vehicle fleet featuring PFI technology will remain in the market for decades to
come. This is especially the case in parts of Asia where PFI technology is still
prominent, although direct injection (DI) technology adoption is starting to
catch up.
PFI engines can, when operated with lower quality fuels and lubricants, build up
performance impairing deposits on a range of critical engine parts including in
the fuel injectors, combustion chamber and on inlet valves. Inlet valve deposits
(IVDs) in more severe cases have been associated with drivability issues such as
engine stumble and engine hesitation on sudden acceleration. Deposit control
additives in gasoline formulations are a well-established route to managing and
even reversing fuel system fouling.
This study, involving an industry standard, Mercedes-Benz M-111 PFI bench engine
heavily augmented with measurement equipment, was able to obtain a deeper
understanding of the negative impacts of IVDs on engine performance and
efficiency. By using a test cycle based on the CEC method F-20-98 but of
increased severity it was established that IVDs lead to an increased combustion
duration as measured based on the delta of the spark point to the center of
combustion (CA50, MFB50%). This sluggish combustion behavior was corroborated by
supporting secondary metrics such as engine out emissions and increases in
exhaust temperatures. Changes in air-flow into the combustion chamber were
investigated using a steady state flow bench as a potential cause for the
observed changes in combustion phasing and resulting sluggish combustion.