Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Why does it use more gas to accelerate more rapidly?

Maury Markowitz · 08-21-2012, 01:54 PM

I think I'm missing something obvious here, but let's see...

Steady state gas milage is roughly due to two factors, the air resistance which goes with the square of speed, and rolling resistance which goes with the speed. So, roughly, milage is the fuel use at idle dividend by the cube of speed. Roughly. Then you add in things like hills and such.

The part I don't understand is acceleration. It would *appear* that the amount of energy needed to accelerate to a given speed is a fixed, it's simply 1/2*m*v^2. There's no "t" term in there for the time you take, nor an "a" for the acceleration. It's just initial vs. final velocity.

But that certainly isn't the case in practice. "gunning it" up to speed appears, according to my milage readout, take considerably more gas than doing so leisurely. And every reference on gas milage says the same thing.

I know that gas engines have performance curves, and this might be the cause of the problem. Yet most curves I have seen peak at numbers far higher than what I use in my car to get the best milage (54.2 US mpg right now BTW).

So can anyone out there offer an authoritative answer to this?

08-21-2012, 01:54 PM	#1 (permalink)
Maury Markowitz EcoModding Lurker Join Date: Aug 2012 Location: Canada Posts: 6 White Whale - '06 Honda Civic Hybrid DX Thanks: 0 Thanked 0 Times in 0 Posts	Why does it use more gas to accelerate more rapidly? I think I'm missing something obvious here, but let's see... Steady state gas milage is roughly due to two factors, the air resistance which goes with the square of speed, and rolling resistance which goes with the speed. So, roughly, milage is the fuel use at idle dividend by the cube of speed. Roughly. Then you add in things like hills and such. The part I don't understand is acceleration. It would appear that the amount of energy needed to accelerate to a given speed is a fixed, it's simply 1/2mv^2. There's no "t" term in there for the time you take, nor an "a" for the acceleration. It's just initial vs. final velocity. But that certainly isn't the case in practice. "gunning it" up to speed appears, according to my milage readout, take considerably more gas than doing so leisurely. And every reference on gas milage says the same thing. I know that gas engines have performance curves, and this might be the cause of the problem. Yet most curves I have seen peak at numbers far higher than what I use in my car to get the best milage (54.2 US mpg right now BTW). So can anyone out there offer an authoritative answer to this?