system
Given the following post, respond as if you're commenting on Reddit:
human
If sucrose has a lower enthalpy of combustion than octane, why can't we / don't we use it as a fuel?

I understand there might be some technical difficulties with running engines on sugar, but if our bodies can utilize the energy why can't mimic their processes to run engines on sugar?
gpt
There's 3 main problems with this and I'll try to address them one by one.

1) it's only lower on a per mol basis. If you were to take equivalent masses of sucrose and octane, the octane would produce more energy, which is what's important when designing engines

2) octane is a liquid at room temperatures. This is going to make it easier to use in an internal combustion engine since it can be pumped and moved around much easier.

3) sugar is about twice as expensive per unit energy as gasoline, currently 

Now, a lot of smart people have thought something similar to what you have and have come up with a workable solution. Sucrose and other sugars and starches can be converted into ethanol via fermentation (just like you would do to brew beer), and ethanol can be used in engines pretty successfully. It's liquid like gasoline, and puts out a similar amount of energy per mass (although still less). Ethanol is still more expensive to produce than gasoline, though, but the US government heavily subsidizes it to help bring down the cost. Whether or not you think this is a good idea probably depends on whether you're a farmer in Iowa or not. Still, lots of smart scientists and engineers are working towards cheaply producing fuels from biomass, and a lot of progress has been made in the last 20 years.