Well that is completely true. Accelerate hard until you hit the speed you need and then just lift off and let the car roll (with highest possible gear engaged to limit the engine resistance). That is way more efficient than driving at a constant speed. You can even try it for yourself when your car has a average fuel consumption display. Of course you have to drive at the same average speed to spend the same time on the straight.Andres125sx wrote: ↑Tue Oct 10, 2017 5:06 pmHi all,
Some time ago my brother told me he read an article where it was stated for best fuel efficiency it is better to accelerate strongly... but only to the point you get enough momentum to reach next corner, stop, etc., contrary to the general idea that it´s better to not accelerate (hit the throttle) too much.
He told me the article said once a petrol engine is consuming fuel, the difference is not that dramatic between hitting the throtle a 10% or 100%, so it´s better to take advantage of the available power to build some speed quickly and then release the throttle and use the big inertia of our heavy cars. Basically the idea is it´s more efficient to accelerate at 100% for 10% of the time/space than accelerating a 10% for 100% of the time/space. Obviously when I say accelerating at 100% I mean using all the power our engine can provide revving it up, not hitting the throttle to the end but doing an upshift at 3000rpm
It made sense to me, but I´d like to read a bit about that. He can´t remind where did he read it, anyone?
Does anyone know some graph for production cars wich shows fuel efficiency at different rpm? I guess that must be the key factor. When it´s said petrol engines efficiency is below 30% or even 20% I guess that´s reffering to its best regime, but it must be even lower at lower revs so if we want to be fuel efficient, we must use all the available power for as little time as possible
As you can see I´m saying all this from memory, and my memory sucks, so fell free to correct, add or laugh about this
One has to consider extra fuel needed to restart the engine, tho. And if you wanna go even further, cost of battery and starter motor wearing quicker. But yea that would probably be the most economical way of driving, purely based on fuel consumption.Greg Locock wrote: ↑Tue Oct 10, 2017 7:48 pmIn English that is called a brake specific fuel consumption (BSFC) map. Burn and coast is usually the most efficient, that is accelerate hard along the minimalen line in that map, then knock it into neutral and switch the engine off (if you are serious). The choice of gear(s) and the two end point speeds are not entirely straightforward.
As you can see the minimalen line more or less tracks full throttle (Vollastkurve).
Unless you have regen then braking is very bad, whether using the brakes or the engine.
If you look at how a Prius operates it sits on that minimalen curve.
Travel a certain distance within a certain amount of time
and use as little energy as possible, doing so.
I have always wondered what this means: if you can't press the accelerator pedal more than 50% or if you have to apply it slowly?Jolle wrote: ↑Tue Oct 10, 2017 5:25 pmWell, first of all, (hard) acceleration is one of the biggest fuel guzzlers, so driving with an egg under your foot is key. So is braking, because... after braking you have to accelerate again. High corner speed is very very green!
There is no simple graph for fuel consumption because there are to many factors, but generally, the lower (within reason) revs, the lower the fuel consumption because of less friction. Where most people get confused by is efficiency of a petrol engine, which is generally around 70% load. This is why small engines in the same car are more fuel efficient then big engines. To perform the same task (or output) they are more likely to be closer to their max efficiency. A big engine in 6th gear that has 3000 rmp has for instance a load of 30% while, with the extra friction and revs, in 5th gear at 4000 rpm it could be 35%, but with a slightly better efficiency but not enough to counterbalance the extra load.
to safe fuel: take your time to get up to speed and then don't loose that speed again.