On the highway: Driving fast or not?

[Save the World]

two drivers
1er: Roule 140 km / h arrives there quicker, consumes LESS time.

2ième: Roule 90 km / h, slower to happen, consume MORE time.

If both drivers the same distance course, which will have consumed most happened to? Why?

[highfly-addict]

No. 2 consumes less because in these speed ranges, it is the air resistance that consumes the most engine power; or the air resistance increases with the square of the speed. QED.

[Obamot]

Consumption is calculated in "X" liter (s) for 100 km traveled ... regardless of the speed in fact.

As highflyaddict: Knowing that it is between 80 and 90 km / h that the engines consume the least for a vehicle at cruising speed, I would also say the answer "2".

(Note that if the one traveling at 140 km / h were stopped for speeding, he would arrive after vehicle "2" )

[dragonlaoshi]

I would say it depends on the weight of the vehicle with the couple and the gearbox.

[Cuicui]

Consumption is calculated in "X" liter (s) for 100 km traveled ... regardless of the speed in fact

The higher the speed, the greater the consumption (in liters 100 km) increases, despite the fact that travel time is shorter. Perhaps an exception for water that consumes less diesel doped under high load.

[Other]

Hello

I would say it depends on the weight of the vehicle with the couple and the gearbox.

+1

Proportione a good running engine has a maximum torque box report suitable speed a car aerodynamics
there is an economic rate and an economic return on each engine.
So it's a case by case

the best engine performance is when we review the best power / consomation
On self is the aerodynamic drag or speed becomes important

On airplanes we have the same problem it is even easier found
Just a little Cessan 150 with 100CV engine touched by a 150 hp Ganges is not even 18% on speed
or changes propeller a step taller and it becomes barely more economical on a trip.
There is a cruising speed, an engine speed and engine load to be balanced for greater autonomy ..

Andre

[dragonlaoshi]

Thank you Andrew. It's good, I just proposed to establish a new power to weight ratio to the extent reasonable to existing vehicles. This is my concept Performance Automobile. Adjusted for small defects or manufacturers will get more involved and other small misery experienced by some owner, unpretentious but just the engine tuning.

[Did67]

I confirm.

board computers provide consumption l / 100 km.

On my car (a converted gasoline C5 2.0 LPG), there is no picture: consumption increases about the 1 / 100 km when going from 90 km / h in 110 km / h and about as much when going from 110 130 to.

The 90 is often the speed giving approximately the lowest consumption. The manufacturers try to caller the torques and transmission ratio so as to optimize around 90 km / h (more generally from 70 to 90 km / h), because these speeds are the bases of the cycles "extra-urban". They therefore try to display the lowest possible conventional consumption.

So there is no advantage to drive more slowly because after consumption increases because either we move to a lower gear or one is serious under-regime ...

Last point: I was surprised how "efficient" it is for fuel consumption to drive my 2 liter petrol at low speed (a bit like a Diesel!). Maybe the effect of LPG (more "cold" combustion).

[dirk pitt]

The 90 is often the speed giving almost the lowest consumption. .

trying to ride a 60 or 65 stabilized, you'll see if this is the lowest 90 conso !!!

[Remundo]

Ah, an interesting question!

In fact, it is the superposition of 2 problems.

The first is relatively simple, it is the job of the assumed constant frictional force on an assumed fixed distance d.

W = F xd

Here or there's a major physical effect is that, basically, the aero force is proportional to the square of the speed, as rightly says Highflyaddict.

So spend 90 140 to multiply the mechanical energy required by 2,4 = (140 / 90) ² WHATEVER TRAVEL TIME.

Where the problem thickens (2ème problem) and André Dragonlaoshi and put my finger on it, is that the vehicle has an optimum specific fuel consumption at full load and midrange to provide mechanical energy(Energy Progress mech) ...

and this is where engineering must carefully calculate the related transmission with the characteristic torque / speed) or overdrive or under-multiplied on the usual cruising speeds 50 / 90 / 130 in France. .. Basically the 3ème, 4ème and 5ème. The 1ère is there only to start the vehicle stationary. The 2è is useful to draw a slope supported, but few people are in this case (the caravan or the people in the mountains of sand trailer like me ).

Nevertheless, the pb2 (optimization of CSP: specific conso) has a lower effect than 1 bp, ie it is above all the speed that dictates consumption, even if the vehicle engineering can qualify things a bit.