Causes of Carbon Buildup in GDI Engines
Causes of Carbon Buildup in GDI Engines
Here’s what to look for when you come across an engine with these problems.
Motor Age — Google “gasoline direct injection problems,” and it won’t take you long to see that many early adopters of this technology faced issues with severe carbon buildup occurring on the stem and throat of the intake valve. Narrow that search to just issues with carbon deposits, and you’ll notice that some makes seem to be more affected than others. What causes this build up, and what can be done to prevent it in those platforms that seem to be the most susceptible?
How GDI Works
GDI, or gasoline direct injection, is not a new idea. It was first tried in 1925. As its name implies, GDI differs from multiport injection in several substantial ways. First, and most noticeable, is the placement of the fuel injector directly into the combustion chamber.
Clayton Lindgren, product manager and technical specialist for Bosch Engine Systems, tells Motor Age, “The main differences comparing port fuel injection to gasoline direct injection are with respect to system pressure, injector location, injector timing and fuel spray. Port injectors are exclusively coil driven and utilize a system pressure of 300 to 500 kPa (kilopascals, or roughly 40 to 75 psi for us non-engineer types). They are located in the intake runner”.
“In the time domain there is a single injection event. Their spray pattern is conical and always targets the intake valve(s),” Lindgren adds. “On the other hand, GDI injectors may be coil or piezo driven. These injectors have system pressures of 1-20 MPa (Megapascals, approximately 150-3000 psi). The higher pressure increases mass flow and creates a finer fuel mist, both of which contribute to the trend of engine downsizing while retaining power output.”
As for multiport fuel injection (MPFI) systems, they can inject at almost any time during the engine cycle, relying on the intake valve to time the delivery of the fuel/air mixture to the combustion chamber, adds Dave Sant, senior warranty engineer with Delphi’s Powertrain Systems.
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Source: Motor Age
