I think what you mean is that there's less thermal energy stored in ethanol per unit volume, as compared to gasoline or heavier petroleum-sourced fuels. That is true.
However, ethanol's lack of BTUs in the juice is at least partly offset by its behavior in an internal combustion engine, in which it acts like a high-octane gasoline. This enables engine designers to build engines with higher compression ratios and increased spark advance, and so scavenge more energy from the fuel.
There's more than one "law of physics" at work in the Otto Cycle engine, after all.
No, sorry, you obviously are conflating efficiency with lower heat content in the fuel.
The heat content of the fuel does not necessarily impact the thermal efficiency of the engine. In existing engines, the amount of ethanol in the fuel does not lower the efficiency of the engine. The lower heat content of the fuel does reduce the amount of work the engine can deliver per volumetric unit of fuel, but it doesn’t change the efficiency, if we hold all parameters of the engine constant between the two fuels.
It would be entirely possible to engineer an engine that uses a gasoline/ethanol blend that delivers more MPG than the current engines. All that is needed is to make effective use of the higher octane that ethanol delivers to the fuel to increase the compression ratio and increase the thermal efficiency of the engine. But Detroit won’t do that.
Consider this: there are more efficient gasoline engine designs out there. Consider the Miller Cycle engine as a starting point.
Who is putting Miller Cycle engines onto the market right now? There are at least two cars using Miller Cycle engines.
Neither one of them is built by a US car company.
Consider that the European auto companies are delivering very high MPG diesel autos to the consumer, and the US companies cannot seem to get their heads out of their rectums on the subject of diesels in cars. Pickups, where they are doing one-up contests with HP and torque, sure, they’re happy to do diesels. But four-place sedans and small cars? Nah. They cannot seem to get their heads out of their plump posteriors and realize that they could deliver on 35 MPG right now, with existing technology. They could deliver a gasoline-powered car with 35 MPG with existing technology.
But they won’t.
And pundits like Flint will give them cover for it — by claiming to know the “laws of physics” but in fact, not knowing anything about them at all.
Alcohol burns hotter than gasoline.
Alcohol has lower BTU content than gasoline, but alcohol+oxygen=hotter flame than gasoline+oxygen.