|
Not just low rpm though; low load. At least that's so with fuel introduced into the inlet manifold. There are also exceptions at constant light loads, such as used while highway cruising. I understand that the most knock resistance is required at medium type loads, where enrichment can't be used, yet the load is high enough to cause knock.
Engine speed may have some effect because the cylinder pressure will reduce faster as the piston moves away faster, while flame speed remains more constant. If there is a difference in power output between EtOH and gasoline then that may be a part of why.
Direct injection may be run globally lean because the mixture can be kept locally stoichiometric (within the cylinder). That's why there is a fuel economy benefit with DI.
|