Discussion and questions related to the course Understand AFR
In the course, I picked up on Andre suggesting that the lambda figures between pump gas and E85 are comparable as a starting point. Then I saw this;
Also attached, in case the link above moves.
What interested me was the significantly larger max power range for E85 is ~1.5 lambda, or ~1.47 ratio points vs ~0.5 lambda and 0.7 ratio points. This suggested to me that if you're targeting the max power stoich for E85, rather than targeting 0.85 lambda, you'd be better off targeting 0.71 to get some extra charge cooling and that 0.85 would be nearer the leaner end of the power spectrum (but obviously still rich). Is that correct, or am I missing something?
I think I can answer my own question, as it's come up on other forums.
It seems knock can be more prevalent on E85 when lambda drops much below 0.8 on E85 with little, if any material ignition gains to be found that can't also be realized at 0.8 with the benefit of higher EGTs on FI engines. Individual results may vary.
In my experience you definitely won't see an engine running well or making good power at 0.71 lambda. Running this rich will have the power drop off and you may also have trouble igniting the mixture, resulting in a rich misfire.
A rich mixture on E85 is not more likely to cause detonation or knock, however it can make the engine more likely to suffer from pre ignition. Knock and pre ignition are often confused but there is an important difference.