Author Topic: When Eco mode isn't Eco mode....  (Read 1945 times)

Offline nigeldodd

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Re: When Eco mode isn't Eco mode....
« Reply #20 on: 09 March 2019, 18:44 »
The main reason, or really the only reason for me, is the disengagement of the engine when the car is coasting. It really does improve fuel economy. But for any junction or roundabout I will change to sport mode by pulling the lever back. The combination of the two works well for me.

Offline Watts

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Re: When Eco mode isn't Eco mode....
« Reply #21 on: 09 March 2019, 19:03 »
The main reason, or really the only reason for me, is the disengagement of the engine when the car is coasting. It really does improve fuel economy. But for any junction or roundabout I will change to sport mode by pulling the lever back. The combination of the two works well for me.

I thought engines didn't use fuel at all when you aren't on the accelerator, so long as it is in gear which is regardless of engine mode. If the engine is disengaged then surely it must be using some fuel to keep it running so that must be less economical?
2015 Tornado Red 3dr GTI PP, manual, Santiagos, Audi short shifter.


Offline Finglonga

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Re: When Eco mode isn't Eco mode....
« Reply #22 on: 10 March 2019, 17:27 »


I thought engines didn't use fuel at all when you aren't on the accelerator, so long as it is in gear which is regardless of engine mode. If the engine is disengaged then surely it must be using some fuel to keep it running so that must be less economical?

Exactly, can never understand it as more fuel is used keeping the engine running. Always been more economical to me on Normal than Eco.

Offline nigeldodd

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Re: When Eco mode isn't Eco mode....
« Reply #23 on: 10 March 2019, 19:13 »
When the engine is connected to the wheels through the gearbox there is no fuel consumed on overrun, as you correctly say. The kinetic energy of the car is, however, reduced by compressing air in the cylinders of the engine and turning it into heat. Think how difficult it is to turn an engine over by hand.

When the engine is disconnected from the wheels it is true that a small amount of fuel is needed to keep the engine idling. However the power (energy times time) taken from the fuel is considerably less than the power (kinetic energy times time) taken from the car if it were connected to the wheels. This is simply provable by the increased speed of the engine which runs above idle when the engine is connected.

When I discovered Eco mode last week I was surprised and impressed by how far the car travels in E without the engine connected.

Offline Watts

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Re: When Eco mode isn't Eco mode....
« Reply #24 on: 10 March 2019, 19:18 »
When the engine is connected to the wheels through the gearbox there is no fuel consumed on overrun, as you correctly say. The kinetic energy of the car is, however, reduced by compressing air in the cylinders of the engine and turning it into heat. Think how difficult it is to turn an engine over by hand.

When the engine is disconnected from the wheels it is true that a small amount of fuel is needed to keep the engine idling. However the power (energy times time) taken from the fuel is considerably less than the power (kinetic energy times time) taken from the car if it were connected to the wheels. This is simply provable by the increased speed of the engine which runs above idle when the engine is connected.

When I discovered Eco mode last week I was surprised and impressed by how far the car travels in E without the engine connected.

Thanks for the detailed explanation :smiley:
2015 Tornado Red 3dr GTI PP, manual, Santiagos, Audi short shifter.


Offline nigeldodd

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Re: When Eco mode isn't Eco mode....
« Reply #25 on: 10 March 2019, 19:23 »
Before anybody corrects me I must correct myself. Power is the rate of energy production or consumption. Power is energy per unit time, not as I said energy times time.