|Quote, originally posted by greatfox »|
DI engines inject the gasoline very late in the compression stage. There is no way gas is going backwards into the intake.
I guess I assumed some here could figure out how internal EGR works.
Basically during the exhaust stroke, the intake valves are opened early before the exhaust is finished exiting the combustion chamber. This forces dirty exhaust, oil, and unburned gasoline hydrocarbons back up into the intake valves and intake ports.
It has nothing to do with when fuel is injected into the combustion chamber because EGR function occurs later during the end of the exhaust stroke.
*edit* - To clarify your other point, the injection event doesn't take place late on gasoline engines. You might be confusing things with diesels which inject after the intake valves are closed and during compression.
On gasoline direct injection engines, you are spraying while the valves are open which means some spray ends up on the valves. Watch the video.
Modified by Shomegrown at 1:49 AM 5-20-2009