zlacker

Figures 8 and 9 show that both volumetric and thermal efficiency can be improved with nonzero ethanol in the right circumstances. Increasing efficiency metrics, while combining figure 7's showing that you get more power with ethanol, means that you're getting more power and doing so with greater efficiency.

You mention fuel efficiency. Figure 6 shows that in some cases, looks like the threshold is between 60 and 80% load, the story flips such that adding ethanol to the mixture reduces sfc. In other words, less fuel is needed for the same amount of power. Meaning, if it takes X hp or kw to sustain whatever test speed you're measuring efficiency at, the amount of fuel you use is lowered. I think this is very important to understand. Figure 6 shows that if your engine is sufficiently loaded, nonzero ethanol can improve the amount of energy you get out of the same mass of fuel relative to pure gasoline, which I believe would be directly proportional to better fuel efficiency.

Now very notably, if less heavily loaded, it seems better to use 0 ethanol. The ability to choose lets it get the best of both worlds.