Supposedly going faster uses more fuel. But your getting to the place quicker. Shouldn’t you just be using the same amount of fuel as if you were driving slower and getting there later?
In: Chemistry
Since is ELI5 not ELI-15:
Fuel is energy. The faster you go, the faster you use energy. But it also takes energy to get faster. It takes even more energy to stay fast because you’re fighting the wind.
So you’re using so much extra energy to go faster and stay faster than just staying at a slower speed.
Your assumption would be true if vehicles were really efficient, but in reality a lot of your fuel gets used doing things other than moving the car forward, nor is the engine equally efficient at all speeds.
The most fuel economical: drive in the highest gear at the lowest RPM your car engine likes.
You’re burning fuel every time the engine turns over, and the highest gear means that you get the best ratio of engine turns to wheel turns.
The lowest speed your engine can handle in the highest gear both reduces RPM and drag, saving fuel.
Your car is wasting a lot of energy at those lower speeds. Most commercial vehicles actually have an ideal speed to mileage at about 55mph. After that, wind resistance starts to diminish your mileage.
The fuel consumption measure used is mpg (miles per gallon) or l/100km (litres per 100km). As that is always in relation to distance and not time, the arriving sooner or later doesn’t play a part in that equation.
No, because you have higher drag which means you need more power to go through the air which means you have to burn more fuel to get that power
Going faster does not alway mean using more fuel. There is an optimal speed at which a vehicle will have the most efficient fuel consumption.
Going super slow can be less efficient because the vehicle is always trying to overcome friction and other forces that keep the object stationary therefore requiring more energy…fuel.
Going too fast can be less efficient because forces like drag can start to cause more friction leading to increased energy consumption.
Finally, this part I am not 100% certain on so I will leave it up to the community, but I believe vehicle engine/transmission can be altered to change fuel efficiency based off speed.
So the best way to explain this is to use a real example. Lets use the most obvious one and picture a journey in a car. Your fuel consumption is going to be based primarily on 4 things.
1. Distance – This is major factor in this. If you go further, you need more fuel. A shorter trip means less fuel.
2)The effectiveness of the engine consuming fuel. Different cars have different engines and not all are as good at turning the fuel into power as the others.
3) The weight of the car (including all the passengers and the fuel). The more weight you have the more energy you need to put in to get the vehicle moving. This in turn uses more fuel.
4) Drag. This is more specifically what you were asking about, as this is what causes extra fuel consumption at higher speeds. It may look like theirs nothing in the way ahead of a car, but it does actually have to move the air in its path out of the way. The faster you are going the more air you are displacing every second. As the car “pushes” the air out of the way , the air also pushes back against the car, effectively slowing it down. So you have to apply more force to counter the air moved. This again costs energy to do. and increases fuel consumption.
and just to add more to this in the case of driving. Driver behaviour changes fuel consumption. It is much much much less efficient to keep accelerating and slowing down than it is to just keep a constant speed (assuming they average to the same speed). So people who drive really fast and then keep stopping at reds are just wasting fuel. And to go even further…. most car manufacturers have and make available information about the most economic/efficient speed for their cars. Meaning they have worked out the best constant speed to keep to, to minimise fuel consumption.
It depends on how proportionaly faster you will be to fuel consumption. If for example you are spending 20 litres of fuel to travel at 100 kilometers per hour, and you need to travel 200 kilometers, It will take you 2 hours and 40 litres. You spending twice as much to travel twice as fast, it will take you 1 hour and 40 litres, which is faster and takes same amount of fuel. But if you are spending twice as much to travel 1,5 times as fast, it will take you 1,3 hour and will take 52 litres fuel, which is still faster but takes more fuel.
Your statement is true if speed and consumption scales by SAME amount. But in real world they usually not.
If you kept constant speed, yes.
In reality, you will likely have to brake or slow down for turns, pedestrians crossing (if in towns) red lights etc, thus it’s the fact that accelerating faster (in the “going faster” case) makes you use more fuel compared to the other case. Hope I made it understandable enough.
Not only does going faster use more fuel, it uses that fuel less efficiently. Wind resistance increases with the square of speed, if you go twice as fast, all things being equal, you have to burn more than twice as much fuel.
Also, engines have a sweet spot, and rpm range where they work most efficiently. If you car isn’t geared to go 100 mph, then your engine will be operating outside of that sweet spot, wasting additional fuel.
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