[Diy_efi] Dyno. cooling

[Bernd Felsche]

On Tue, Dec 17, 2002 at 05:26:37PM -0800, Adam Wade wrote:
> --- Erik Jacobs <emj14 at columbia.edu> wrote:
> 
> > An ingenious person might even be able to build a
> > fan, or modify an existing one, to provide the
> > appropriate speed of airflow based on the vehicle's
> > estimated speed from the drive wheels, but that's
> > fancy schmancy now, isn't it? :)

> And unnecessary.  ;)  As long as the fans provide at
> LEAST enough airflow to remove heat from the system,
> the thermostat will keep the coolant temperature in
> the engine fairly constant.  It's only when there is

You're not considering the car as a whole... an engine's output
power is determined by ambient conditions. Unrepresentative airflow
through the engine compartment probably means that components aren't
operating at representative temperatures.

Somebody else already mentioned that drawing air from underneath the
car would be a closer approximation to the real road.

Even a wind-tunnel doesn't provide "true" airflow; the boundary
layer at ground level on the road has a different shape (velocity
profile) to that in a wind tunnel; which no doubt peeves some
engineers who've spent hundreds of millions on "the world's best"
wind-tunnel.

In essence what they need is the vehicle/prototype/model moving
relative to the ground with the air "attached" to the ground; but
they're only moving air relative to the ground and the vehicle.

I know that's somewhat esoteric; but keep it in mind when you think
about how representative of road conditions the dynamometer really
is...

> not enough fan capacity, and the coolant temperature
> keeps going up once the thermostat is open, that there
> should be a problem.

> That's the whole purpose of a thermostat; to prevent overcooling.

-- 
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