Why does it use more gas to accelerate more rapidly?

[gone-ot]

IMHO, this chart:



and this chart:




summarize "...the tale..." quite well.

• The first illustration shows that moderate (1/2) throttle is better than either light (1/4) or full (100%) throttle.

• The second illustration shows how the most economical engine speed lies between 1,000-2,000 rpm.

[ecomodded]

Originally Posted by serialk11r

35hp average is a pretty low number for a 3200lb car. Typical cars are geared so that cruising on the highway is less efficient than wide open throttle 100% load acceleration, at very high rpms they're about even.

You have it backwards, 35 hp is high for a 3200 lbs car.
Wide open throttle High RPM 100% load will consume fuel at the fastest rate possible and cover the least distance possible.
Guaranteed that all North American passenger cars will consume the most fuel and travel the least distance at full throttle.
Highway cruising is the most efficient, 55 down to 40 mph will give you the best mileage.

Very high RPM consumes very much fuel, the two are joined at the hip.

[shovel]

Originally Posted by ecomodded

You have it backwards, 35 hp is high for a 3200 lbs car.
Wide open throttle High RPM 100% load will consume fuel at the fastest rate possible and cover the least distance possible.
Guaranteed that all North American passenger cars will consume the most fuel and travel the least distance at full throttle.
Highway cruising is the most efficient, 55 down to 40 mph will give you the best mileage.

Very high RPM consumes very much fuel, the two are joined at the hip.

If you have a fixed maximum speed (the speed limit) and you spend very little time in the high consumption mode of heavy throttle, then settle into the low consumption-per-distance full cruising speed for the longest duration per interval (between stops), that should use less fuel overall than accelerating for a very long period of time and cruising for a shorter time.

[ecomodded]

Originally Posted by shovel

If you have a fixed maximum speed (the speed limit) and you spend very little time in the high consumption mode of heavy throttle, then settle into the low consumption-per-distance full cruising speed for the longest duration per interval (between stops), that should use less fuel overall than accelerating for a very long period of time and cruising for a shorter time.

Exactly.
I like to accelerate at a reasonable pace, slower than molasses is not required, either is jack rabbiting.
I use very little throttle in my driving, short shift at 1500 rpm when accelerating and still get up to speed fast while maintaining low rpm.
Its the RPM's or even driving it in too low of gear that sucks back the gas.
My driving motto is if it doesn't stumble its going into 5th.
From 30 mph on my car is in 5th gear.

[freebeard]

I found a great quote from Katy Levinson, the drunken roboticist, speaking at Defcon 20

The difference between theory and reality is much smaller in theory than it is in reality

Personally, when the light changes, I clear the intersection as quickly as possible (as a courtesy to other drivers ) and then think about that last 1% of gas mileage. And I'll burn a little extra gas to not have to sit at that long light in Thurston. It's all about position in traffic.

I drive faster in traffic and slower when the road is clear. If everyone did that traffic wouldn't bunch up.

[roosterk0031]

Thinking is just physics, accellerating a given mass from 0 to 55 is the same amount of work in terms of kinetic energy. But doing it slowly you had to go a longer distance so more work is done. So more fuel is used accelerating slowly but more work has also been done.

Proper accelerating is better though, open throttle, but low rpms and short shift. Almost never beat out of a light with my auto's, shifting at 2k the cobalts not so quick.

[kennybobby]

Originally Posted by roosterk0031

...
But doing it slowly you had to go a longer distance so more work is done. So more fuel is used accelerating slowly but more work has also been done.

No, No, No...
Are you another one of them physickists or mathemagicians that don't know the difference between energy and power?

The Work done is exactly equal to the Kinetic energy.

Kinetic energy = 0.5mv^2 = Work = F x distance = m x accel x distance

Power = Work / time

You go a longer distance but the acceleration is lesser, and the Work is the same.

No need for erroneous clutter--do you want to delete your post, then i'll delete mine...

[BigWu]

Originally Posted by Maury Markowitz

Sorry, this is not correct. There is no relation between force and fuel use.

Perhaps I should have mentioned I'm a physicist. Because I am :-)

Clarification: The amount of energy expended at the wheels to accelerate to a given speed is identical (assuming you're not burning rubber on the launch). However, in an internal combustion powered car, the efficiency of the engine in converting fuel to usable wheel power varies. Optimal MPG therefore depends on accelerating at the rate of maximum engine and transmission efficiency.

For an electric car it's simple. The energy expended has zero relation to the rate of acceleration.

Ex: If you drive a distance of one mile with a maximum speed of 40 MPH, the total energy consumed will be ~300 watt hours regardless of if you accelerate to 40 MPH in glacial 30 seconds or in just 3. Note that I have confirmed this countless times in my Tesla S.

[justme1969]

lets dumb this down to under grad level LOL!
Your question is, "Why does it use more gas to accelerate more rapidly?"
The simplistic answers may be insulting so I wont go there, But I think you ask about reworded why Does it absorb more energy to accellerate fast v/s slow.
It does not., the big difference is that engine tuning is designed for what?
Thats the kicker see?', All engines are purpose designed and sacrifices must be made to conform to its intended application, to epa to carb etc etc etc.
My dodge R/T actually does more economy to accelerate quick then glide.
This is pulse and glide basis and It has big effect with cars designed for acceleration foremost .
others it doesnt do so good for because it switches ECM into WOT mode and just dumps fuel unceremoniously.
Unless You have fancy car that has special programs and optimizes itelf better than the standard cars up till about 2005?

Ok its deep its open and its simple I cant break it apart much better without becoming specific.

[SentraSE-R]

Here are the results of 70%, 82%, and 90% engine load P&G cycles with my xB. The 90% engine load gave the best results.


Here are the rest of the testing results, and the discussion.