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Re: Fuel consumption
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Posted by roberto [Email] (more from roberto) on Mon, 13 May 2002 16:43:24 Share Post by Email
In Reply to: Re: Fuel consumption, Caspar, Mon, 13 May 2002 12:24:38
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Caspar,

I do not know from where the idea that,

"Running at full boost is very uneconomical - also compared to a larger normally aspirated engine with similar power."

comes from but I believe it is wrong.

Friction losses (tyres, transmission, engine) are linear with the speed
and they are probably smaller for a small 4 cilinder engine compared
with a larger 6 cilinder.

Aerodynamical losses are cuadratic with speed and therefore dominate
at high velocities.

The thermal efficiency of an internal combustion engine increases
with the effective compression (that's why diesel's are more efficient
than petrol engines). This implies that in fact running at full throttle
i.e. with maximum filling of the cilinders and therefore maximum effective compression is in fact more efficient than at partial throttle.

The unfortunate fact is that you spend this higher efficiency desplacing air.

If you like to be efficient and save petrol what you need is a SMALL
engine that at full trottle will move the car at a slow speed
so the aerodynamic losses are at most, similar to the friction losses.

Roberto


posted by 192.100.17...

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