Test and Control of Fuel Injector Deposits in Direct Injected Spark Ignition Vehicles

With the wider use of Direct Injection Spark Ignition (DISI) vehicles in the marketplace, a program was conducted to develop a short-duration fuel injector fouling test. Once a specific driving cycle and base fuel combination was found to produce a significant increase in Long Term Fuel Trim (LTFT), several Deposit Control Additive (DCA) technologies were evaluated for their ability to keep the direct gasoline injectors clean. The increase in LTFT is indicative of fuel injector fouling and a corresponding decrease in flow through them. The test vehicles for this program were a 2008 General Motors Pontiac Solstice GXP equipped with a DISI 2.0 liter turbocharged I-4 and a 2008 Audi A4 equipped with a DISI 3.2 liter V-6 engine.

A proprietary base fuel formulated to mimic a U.S. EPA 65^th percentile fuel was tested to assess its deposit forming tendencies. As a zero percent ethanol (E0) base fuel without a Deposit Control Additive (DCA), it is capable of generating 20% shifts in LTFT in vehicles on a Chassis Dynamometer (CD) driving a specific cycle for forty-eight hours. Work was also done in conventional Regular Unleaded (RUL) gasoline and Reformulated Gasoline (RFG) containing 10% ethanol (E10) with various DCAs to determine their effect on DISI fuel injector deposit formation.

When the base fuel was additized with a DCA previously shown to keep earlier design DISI injector deposits to a minimum, a 90% reduction in LTFT shift versus the base fuel was achieved. Other commercial DCAs were also tested in the Solstice operating on the base fuel. Their performance was found to range from very good to poor.