FastFourierTransportation wrote:...Ergo, while alcohol burns faster, once the flame wave forms, the flame kernel takes longer to develop (and varies highly, based on CR, squish, A/F ratio, etc) ...
... leading to discrepancies which can't be solved with a simple conversion calculator.
So very true.
More fuel for the fire:
I have only tested E98 ethanol due to an inability to purchase non-denatured ethanol (the law thing), E85 pump fuels, and 85%-95% ethanol mixes with different gasoline compositions. And my most recent testing is in smaller 600cc-1500cc inline performance engines. As a result my information may be corrupted, but I am able to control fuel and timing well at all throttle positions and loads, and I test at reduced throttle and loads regularly.
For best output, I have seen E98 require slightly more timing throughout the powerband compared to pump gas, but about the same as non-oxygenated race fuels. However, as compression is increased from 10.5:1 to 13.5:1, less timing is required for E98 compared to gas fuels. And my thought is that considerably more compression is required for ethanol than gasoline (even 112 octane race gas) in order to make fair comparisons.
When converted to a high output CDI, I normally see a nice gain up to peak torque rpm, and a slight gain beyond this on gasoline fuels, but generally require 3 degrees less advance than with a good inductive system for best output . With E98 and higher gasoline mixes in ethanol, the differences with CDI are even greater compared to gasoline fuels, with less advance needed for best output at WOT. Lower engine loads and speeds tend to require less advance as well.
Total cylinder capacity also seems to play a part. With smaller capacity engines showing slightly different requirements than engines twice their size, but similar design. But these same engines (67mm bore 600cc I4) tend to have total hydrocarbon exhaust counts that are 200%-250% larger than their larger cousins (75mm bore 1000cc I4), running the same fuel.
In my testing with engines limited to under 13.5:1 compression ratios, I have found that E98 does not make as much power as 85-90% mixes with the correct gasoline mixture. Getting the right characteristics for the gasoline making up the mixture definitely has its benefits.
There seem to be way to many variables to give a direct comparison to ignition advance requirements between gasoline and ethanol fuels, and methanol is a different beastie all together, IMHO.
Merry Christmas!
