Is it true

[jetex]

Once again, if an engine doesn't have air or fuel it will stall.[/quote]


Not if the engine is being rotated via the gearbox and the driven wheels. If the clutch is depressed, the engine revs drop, and the E.C.U switches the injectors back on. I've seen this simulated on a test bed.

 

[Burnerman]

Thats bang on.....coast downhill in neutral or clutch in, and the engine will revert to tickover.
John

 

[Mickymoody]

Once again, if an engine doesn't have air or fuel it will stall.

Not if the engine is being rotated via the gearbox and the driven wheels. If the clutch is depressed, the engine revs drop, and the E.C.U switches the injectors back on. I've seen this simulated on a test bed.[/quote]

What this means is that the engine is being bump started, as the engine will be OFF. The Wiki refers to a Hybrid car.

If the clutch is depressed, then the engine revs RISE, not fall, as the engine has less kinetic energy to drag around.

You run out of petrol on a hill, the car doesn't magically run on, it stops, due to the engine braking. If out of gear it will roll.

 

[Biguns]

Once again, if an engine doesn't have air or fuel it will stall.

Not if the engine is being rotated via the gearbox and the driven wheels. If the clutch is depressed, the engine revs drop, and the E.C.U switches the injectors back on. I've seen this simulated on a test bed.

The Wiki refers to a Hybrid car.
___________________________________________________________
No it does not. The wiki clearly states "most cars" ie cars less than 8 to 10 years old. The vast majority of which have a fuel saving feature, which shuts off the fuel injectors when the vehicle is on the overrun ie going downhill, feet off the accelerator and clutch, and the weight and momentum of the vehicle is turning the engine.
Read this
http://www.thegreencarwebsite.co.uk...rd-explorer-engine-to-slash-fuel-consumption/

Read this especialy the part "Coasting- does it help save fuel"
http://www.theaa.com/motoring_advice/fuels-and-environment/drive-smart.html


I realy thought I'd given up hard work a few years ago

 

[Mickymoody]

Got to agree to disagree on this one I'm afraid. I understand where you are coming from, and what you are saying, but my basic instincts keep saying to have a fire you need two things; fuel and air.

 

[Biguns]

Got to agree to disagree on this one I'm afraid. I understand where you are coming from, and what you are saying, but my basic instincts keep saying to have a fire you need two things; fuel and air.

I give up.

 

[wotan]

Got to agree to disagree on this one I'm afraid. I understand where you are coming from, and what you are saying, but my basic instincts keep saying to have a fire you need two things; fuel and air.

I give up.

Combustion will not sustain with just fuel and air, it also needs heat, remove any one of these three, combustion ceases.

Wotan

 

[Munroast]

Read this especialy the part "Coasting- does it help save fuel"
http://www.theaa.com/motoring_advice/fuels-and-environment/drive-smart.html

coasting - rolling downhill or approaching a junction with the car out of gear - is inadvisable because the driver doesn't have full control of the vehicle, though it used to be quite a common practice to save fuel.

You lose the ability to suddenly accelerate out of tricky situations.
You lose engine braking which takes some of the load off the brakes on down hill stretches and helps to avoid brake fade - overheated brakes require harder pedal pressures to stop the vehicle.
These days, coasting is still inadvisable and changes in vehicle fuel systems mean it won't save you fuel either.

I experimented with this some time ago, I don't do it now as it is not advisable and against the highway code!. However i found I could increase my mpg by about 33% ... a massive saving!

The savings come from the momentum of the car not been compromised by having to spin the engine, diesel engines are particularly very heavy to turn over and will greatly slow the car down, thus wasting a lot of fuel.

I don't entirely agree with the above on the safety issues as if you are driving to save fuel you will be travelling relatively slowly and your concentration levels will be much higher as you will be trying to anticipate the road ahead better so as to limit the use of the brakes. Of course there is one massive safety implication of freewheeling, if your engine cuts out you could very well loose steering and brakes!

I anticipate that the next breakthrough in fuel economy will see the introduction of a type of freewheel drive system, similar to what is on a bicycle. The waste of spinning an engine unnecessarily cannot be ignored. Ever rode a bike with a fixed hub? I guess issues over servo assisted brakes and power steering pumps could be driven directly from the wheels

 

[Biguns]

Read this especialy the part "Coasting- does it help save fuel"
http://www.theaa.com/motoring_advice/fuels-and-environment/drive-smart.html

coasting - rolling downhill or approaching a junction with the car out of gear - is inadvisable because the driver doesn't have full control of the vehicle, though it used to be quite a common practice to save fuel.

You lose the ability to suddenly accelerate out of tricky situations.
You lose engine braking which takes some of the load off the brakes on down hill stretches and helps to avoid brake fade - overheated brakes require harder pedal pressures to stop the vehicle.
These days, coasting is still inadvisable and changes in vehicle fuel systems mean it won't save you fuel either.

I anticipate that the next breakthrough in fuel economy will see the introduction of a type of freewheel drive system, similar to what is on a bicycle. The waste of spinning an engine unnecessarily cannot be ignored. Ever rode a bike with a fixed hub? I guess issues over servo assisted brakes and power steering pumps could be driven directly from the wheels

Saab produced cars with a freewheel facility 40+ years ago
http://www.saabenthusiasts.co.uk/articles/V4-Page1.htm
http://www.saabnet.com/tsn/bb/9x/index.html?bID=10549

 

[looneyfitter]

Most efi engines will will use less fuel when down hill coasting with load/no throttle. he pump will still be running but the injectors will be pulsing less per m/s. That way you are saving fuel. If this was not done, then car would run rich.

Coasting no load (not in gear) could essentially use more fuel.... ie if the tickover rpm was more than the load rpm then you have more fuel. Also fuel req at tick over could/can also be more than load fuel as the engines MAF sensor calculates how much air is entering the engine via the throttle body (contolled by the pedal) and ultimately adds fuel (Helped by the lambda sensor)

 

[0000]

yes coasting can actually waste fuel.

it is simple really. Load breaks, but load also helps turn the engine over through momentum. It is question of how those balance out.

 

[0000]

What is on a bicycle is called an overrun clutch, which facilitates pedal bursts, that is somewhat different from a car, the forces are a lot greater.

 

[looneyfitter]

do a search for mega squirt, loads of tuning info on there. EFI forums etc. I have a kit car which i had to tune. Very interesting tbh

 

[Mickymoody]

Most efi engines will will use less fuel when down hill coasting with load/no throttle. he pump will still be running but the injectors will be pulsing less per m/s. That way you are saving fuel. If this was not done, then car would run rich.

Coasting no load (not in gear) could essentially use more fuel.... ie if the tickover rpm was more than the load rpm then you have more fuel. Also fuel req at tick over could/can also be more than load fuel as the engines MAF sensor calculates how much air is entering the engine via the throttle body (contolled by the pedal) and ultimately adds fuel (Helped by the lambda sensor)

That's what I've said all along, I don't understand this concept of a 'freewheel' being fitted? Is that like SARS on a f1 car?

 

[looneyfitter]

What do you mean by free wheel mate?