Increasing fuel savings
- Thread starter epicstruggle
- Start date
I wonder why they didn't separate fast acceleartions from hard braking in the aggressive vs. moderate test, though?
I mean, hard braking is obviously going to dramatically reduce your fuel economy, just because every time you brake, you disippate energy that was originally put into the car through fuel, so if you can minimize the amount of braking you do, it's clear that you will save fuel.
But accelerations? I don't know. This has more to do with the efficiency of the engine at different amounts of power. I'm sure that if you are always flooring the gas pedal when starting from a stop, particularly in a car without a turbocharger, then you're not doing complete combustion. But it seems to me that as long as you're running high enough RPM's to handle the gas input for the power you want, somewhat quick accelerations shouldn't be that bad on fuel economy.
I mean, hard braking is obviously going to dramatically reduce your fuel economy, just because every time you brake, you disippate energy that was originally put into the car through fuel, so if you can minimize the amount of braking you do, it's clear that you will save fuel.
But accelerations? I don't know. This has more to do with the efficiency of the engine at different amounts of power. I'm sure that if you are always flooring the gas pedal when starting from a stop, particularly in a car without a turbocharger, then you're not doing complete combustion. But it seems to me that as long as you're running high enough RPM's to handle the gas input for the power you want, somewhat quick accelerations shouldn't be that bad on fuel economy.
Chalnoth said:
Chanloth hard braking means nothing actually.
If you wait till you get closer to a stop sign to press the brakes but have the clutch in earlier coasting it will not change your fuel economy in any way whatsoever. The only way you would save by braking less is if you went slower in the first place and did not accelerate to as high of a speed as soon. So yes coasting through stop signs would inceras fuel economy, but pressing your brakes softly would not do anything at all.
On my car with a turbocharger if you press the gas pedal down gas consumption skyrockets b/c the injectors put a far greater amount of fuel in.
To compensate for the increase in air. Most cars have mass flow equipment and the electronic injectors determine how much fuel to put in. It is not like with a carbeurator anymore.
As you well know force=m*a thus the more you want to accelerate the greater the force and the more fuel to accomplish it.
On the other hand when stopping quickly that force is creted by friciton and just creates more heat.
Edit:
In my car as an example if I drive the way I do which is quick acceleration I get <200 miles on my tank in town
When I drove from Tenesse to Washington DC and used the cruise at 70mph I got 380 miles on the tank and was not even empty all the way.
Acceleration is quite important in my car. Perhaps others are different.
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Actually, I've found that coasting with the car out of gear improves my gas mileage (ever so slightly). When the transmission isn't engaged, the friction of the engine isn't 'slowing' the car down. Soooo...when I've got a big hill to go down, I take it out of gear and coast.
On my normal commute, it adds about 1mpg for the tank.
On my normal commute, it adds about 1mpg for the tank.
Er, that's not what I meant by hard vs. soft braking. Another way to think about it is avoiding putting more gas in when all you're going to do is stop anyway, i.e. starting to coast long before the stopsign instead of keeping your pedal on the gas to maintain speed until the last second.Sxotty said:
Sure. But if the combustion efficiency doesn't change much, a lot of force for a small time vs. a small amount of force for a long time doesn't make any difference.
I ask the question because I don't notice much fuel economy difference between highway and city driving, though I typically do accelerate much faster than other people on the road. I just make sure that I never put the gas on much until I get to higher rpm's, since I don't have a turbocharger and know that the fuel/air mixture isn't going to be very good without compression at low rpm's.
I've always wondered if that was actually true. If it's out of gear, the engine has to spend gas to keep at its idle speed. If it's in gear, is the same fuel still being fed to the engine? Or is it just depending upon the axle to keep the engine running, until the rpm's drop below some threshold value?RussSchultz said:
I typically leave it in gear so that I can make as much use out of engine braking on the way down long downgrades. I've smelled what can happen to people who ride the brakes the whole way....
RussSchultz said:
I've actually wondered about this but didn't know if shifting an automatic transmission into neutral (while the car is in motion) would be bad. I know that the gearing of my car is eating away at the potential energy we accumulated before by going up the hill.
I don't think that's true at all. Higher rpm's mean more friction, but is there any gas being put into the engine with the foot off the petal if it's running at higher rpm's than idle?NANOTEC said:
After all, with higher rpm's, you can potentially get a better fuel/air mixture, which could potentially lead to higher gas mileage. So I don't think running at high rpm's will necessarily result in worse fuel economy.
Right. I would imagine that there's an optimal revolution rate for each engine, dependent upon things like air pressure and fuel quality._xxx_ said:
I have noticed, for instance, that in situations where I need a significant amount of power, like driving uphill for a fair distance, downshifting results in more power with my gas pedal pressed in the same amount. But I've also wondered whether this just means that the gas pedal is only gauging how much gas per stroke is injected, instead of gas per time.
This is an interesting thread, I've been looking around for various resources on how to change my driving style to save a bit of fuel. Thing is I'm currently in the process of changing from an old car (15-years old) to a new one, which seems to be something of a sea-change in optimum driving style (I'm constantly surprised when I drive new cars for instance how the power-band is shifted to much lower revs than my older car for instance).
Gas pedal curve within the ECU is being shifted depending on operation mode and loads of other params, like for intance up-/downhill, vehicle speed/angle, current engine load, gear,...
There surely is the "optimum point" of operation, but as mentioned it's an unrealistic static state which can only be constantly driven on a test bed. The ECU logically always tries to reach the point of optimal balance between power and consumption within exhaust limits.
There surely is the "optimum point" of operation, but as mentioned it's an unrealistic static state which can only be constantly driven on a test bed. The ECU logically always tries to reach the point of optimal balance between power and consumption within exhaust limits.
Well, the one thing that I've done that has produced a really noticeable impact on fuel efficiency has been speed. Driving 70mph vs. 80mph helped my fuel economy by ~15%-20%. Another thing that can help when driving on a freeway is driving behind a big car, preferably a semi 
Some semi drivers don't like this, of course, but seriously, what's the problem? They can't stop as quickly as a small car can anyway. What can the semi truck driver possibly do that a following car couldn't deal with?
Some semi drivers don't like this, of course, but seriously, what's the problem? They can't stop as quickly as a small car can anyway. What can the semi truck driver possibly do that a following car couldn't deal with?
Chalnoth said:Well, the one thing that I've done that has produced a really noticeable impact on fuel efficiency has been speed. Driving 70mph vs. 80mph helped my fuel economy by ~15%-20%. Another thing that can help when driving on a freeway is driving behind a big car, preferably a semi
Some semi drivers don't like this, of course, but seriously, what's the problem? They can't stop as quickly as a small car can anyway. What can the semi truck driver possibly do that a following car couldn't deal with?
The problem? Well if you have a sh*ty car there there's likely no problem. If you have a nice car then the problem is flying rocks/debris which will give you car's paint a nice beating. I also believe semis tend to lift various objects from the road better than smaller cars meaning it more dangerous to follow them eg large flying debris.
Chalnoth said:
Just a part of it is calculated on the fly, most curves/states are being determined through trial on the test bed and get some adaptations in the car during the test phase. So most situations are covered by default, with ambient temperature, air pressure, speed, angle etc. being used to adjust some stuff. Basically, there's loads of tables in there and loads of pointers to get the values. Where the calculation kicks in is the pointers, the tables are firmly defined. Then there's the "adaptation data", where all the "learning" algorithms save their values (for example, the transmission changes over time through mechanical abrasion and thus some parameters change over the lifetime). That's how most ECU's work, not much deeper science to it.