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Old 13th September 2015, 15:07   #256
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Lightbulb Re: Does coasting save fuel?

Quote:
Originally Posted by a4anurag View Post

In this I have attached three consecutive shots to show the deceleration (Notice the RPM dropping) but the fuel flow is '0'). Engine load too is 0.
Really appreciate your effort in getting these results

The point proved here is that fuel is not consumed during the period of coasting in gear.

But many people seem to be confused.

They are thinking that coasting in gear saves more fuel than coasting in neutral. If this point needs to be verified, the distance traveled by the vehicle also needs to be taken into consideration:

Does coasting save fuel?-untitled.jpg

Because engine braking will destroy the useful momentum gained by burning fuel, -> which will decrease the distance traveled by the vehicle during coasting in gear, -> which in turn would need additional fuel to be burnt to regain the same distance traveled by coasting in neutral.
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Old 13th September 2015, 16:25   #257
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Default Re: Does coasting save fuel?

nice work to gather the data. but one more metric would be required to make this an aplles to aplles comparison. that is the acceleration figures. or rather the deceleration.

we have established that the fuelling is indeed zero or negligible when coasting. but what about the distance travelled? wouldnt the engine be braking the car while coasting in gear?and you have to accelerate again to regain lost momentum. but in case of coasting in neutral it travels much more distance as there is no engine braking. so coasting in neutral does save fuel if you consider a trip per se..

especially highways (level or small inclines)..accelerate to 100..coast to 85 in neutral. then again. accelerate..to 100 (this ia what many of you have seen drivers do).
If you accelerate tho 100 then coast in gear to 85 then accelerate back to 100 u will have to spend lot more time accelerating than in previous case because engine is braking when you lift off.

if you want to coast to a stop and want engine braking in an mpfi car then costing in gear gives better FE

so there are scenarios where coasting in gear does save fuel and some where you dont.

a note of caution: coasting in neutral reduces drastically the drivers ability to control the vehicle in an emergency. so if you are not an expert driver you may not be able to judge if it is safe to do it or not. experience after all is the best teacher!
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Old 16th October 2015, 21:03   #258
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Question Re: Does coasting save fuel?

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Originally Posted by sgiitk View Post
Try this in the UK and if you are giving a driving test you FAIL.
Volkswagen CC uses the concept of coasting. So if the driving test is done with a Volkswagen CC, will using this car give the test a fail? What do you think?

Please check:

http://www.autocar.co.uk/blogs/green...t-through-life

http://en.volkswagen.com/en/innovati...ffunktion.html
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Old 16th October 2015, 22:43   #259
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Default Re: Does coasting save fuel?

Quote:
Originally Posted by AjayJoshuaN View Post
Volkswagen CC uses the concept of coasting. So if the driving test is done with a Volkswagen CC, will using this car give the test a fail? What do you think?

Please check:

http://www.autocar.co.uk/blogs/green...t-through-life

http://en.volkswagen.com/en/innovati...ffunktion.html
I guess they will ask you to disable the coast feature. I wrote this to highlight the basic - never coast in neutral. Coasting with the gear connected is fine.
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