Turning carbon dioxide into liquid fuel. Scientists have discovered a new electrocatalyst that converts carbon dioxide (CO2) and water into ethanol with very high energy efficiency, high selectivity for the desired final product and low cost.

[u/Wagamaga]

https://www.anl.gov/article/turning-carbon-dioxide-into-liquid-fuel

[u/vAltyR47]

It has to do with the specific energy of ethanol. In layman's terms, because ethanol is a much smaller molecule than gasoline, there is less energy gained from burning it.

The other side of it is that ethanol is much more compressable than gasoline. Commission engines do work by compressibh an air-fuel mix and then igniting it. Basic chemistry tells us that when you compress a gas, the temperature goes up, so there are limits to how much we can compress the air-fuel mix. This is actually what the octane rating of fuel tells us; how much it can be compressed safely, the higher the number, the more compressable the fuel.

Running a higher compression means we can extract more work (and more power) out if a given amount of fuel. So while ethanol has less specific energy than gasoline, we can make back some of that loss by using a higher compression ratio.

Or, we can use butanol, which has roughly the same energy as gasoline, and a similar octane rating too.

I think where we will end up is that instead of having the octane ratings, we'll just have different fuel alcohols depending on whether you want the extra power from ethanol or better range from butanol.

[u/truthovertribe → u/vAltyR47]

Thanks for the info