There was a post on r/theydidthemath that asked how far a fuel tanker could go if is tank was connected to it’s fuel line, the op also said to keep in mind fuel efficiency increases as the fuel level gets lower, how does that work?
In: Chemistry
The tanker will weigh less as fuel is used so there will be less weight to move. And less weight equals more efficency.
Simply that your fuel is extra weight that your vehicle is carrying. Effectively as you consume fuel, your vehicle becomes lighter and therefore more efficient. This is the basis of the rocket equation .
https://en.m.wikipedia.org/wiki/Tsiolkovsky_rocket_equation
It’s not a direct correlation. The effect that they are referencing is the fact that weight plays a critical role in fuel efficiency, the less weight the farther you can go with a given amount of fuel/energy.
As fuel tanks empty, the vehicle becomes lighter and therefore is able to travel farther with the same amount of fuel input.
Note that if the truck is just driving along a relatively level road without needing to stop and start then fuel efficiency will hardly change at all. Once it’s up to speed, weight doesn’t affect fuel consumption unless it’s running up or down a slope, except for very minor effects.
The more mass you move the lower the fuel efficiency. For most vehicles this is pretty minimal because you have maybe a 20 gallon tank on the high end. But in the case of a fuel tanker, you’re looking at closer to 3,000 gallons. Going from 3000 down to say 500 is going to be a very massive shift in overall weight, making your gas usage more efficient.
There would be a small gain in efficiency as you burn the fuel, since fuel has a weight and as it goes down the total weight of the car would also go down. Since lighter things have less inertia, it takes less energy to move them.
But, I’m not sure if that is what they meant.
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