Driving Without A Thermostat

TE Cheah wrote:

> | Higher power does not equal higher efficiency.
> True only if fuel consumption rises.
>
> | An internal combustion
> | engine IS more efficient the hotter it gets
> Then why do racers use oil-coolers / aluminium radiators ?
> How will intake air & fuel stay cool after entering combustion chamber ?
>
> | Just because a cooler engine churns
> | out a few more peak horses doesn't mean it is running efficiently.
> An engine*'s usual purpose is to produce torque : if * can produce more
> torque ( output ) using the same amount of fuel ( input ), regardless of the
> extra capital cost required, then its efficiency ( ratio of output to input )
> must have risen.

No, because in the case of a "cooler" engine, MORE fuel/air mix is being
drawn in because the intake mixture is denser. Efficiency is a measure
of fuel consumed to power out, not just a measure of power out.

Steve wrote:
> TE Cheah wrote:
>
> > | Higher power does not equal higher efficiency.
> > True only if fuel consumption rises.
> >
> > | An internal combustion
> > | engine IS more efficient the hotter it gets
> > Then why do racers use oil-coolers / aluminium radiators ?
> > How will intake air & fuel stay cool after entering combustion
chamber ?
> >
> > | Just because a cooler engine churns
> > | out a few more peak horses doesn't mean it is running
efficiently.
> > An engine*'s usual purpose is to produce torque : if * can produce
more
> > torque ( output ) using the same amount of fuel ( input ),
regardless of the
> > extra capital cost required, then its efficiency ( ratio of output
to input )
> > must have risen.
>
> No, because in the case of a "cooler" engine, MORE fuel/air mix is
being
> drawn in because the intake mixture is denser. Efficiency is a
measure
> of fuel consumed to power out, not just a measure of power out.


You're confusing intake air temperature with engine temperature. You
want intake air temperature as low as possible, yes, but the engine to
be running as hot as it can. The idea is to have the intake air cool
to pack in as much fuel/air mix as possible, but then get it as hot as
possible after combustion to maximise the power delivered - then
exhaust it to the cool atmosphere again as expediently as possible to
minimise pumping losses. Now there are valid reasons to keep the peak
temperature artificially low - NOx emissions, engine integrity, and
detonation being the obvious three, but if those could be worked
around, efficiency would go up.

nate

N8N wrote:

> Steve wrote:
>
>>TE Cheah wrote:
>>
>>
>>>| Higher power does not equal higher efficiency.
>>>True only if fuel consumption rises.
>>>
>>>| An internal combustion
>>>| engine IS more efficient the hotter it gets
>>>Then why do racers use oil-coolers / aluminium radiators ?
>>>How will intake air & fuel stay cool after entering combustion
>
> chamber ?
>
>>>| Just because a cooler engine churns
>>>| out a few more peak horses doesn't mean it is running
>
> efficiently.
>
>>>An engine*'s usual purpose is to produce torque : if * can produce
>
> more
>
>>>torque ( output ) using the same amount of fuel ( input ),
>
> regardless of the
>
>>>extra capital cost required, then its efficiency ( ratio of output
>
> to input )
>
>>>must have risen.
>>
>>No, because in the case of a "cooler" engine, MORE fuel/air mix is
>
> being
>
>>drawn in because the intake mixture is denser. Efficiency is a
>
> measure
>
>>of fuel consumed to power out, not just a measure of power out.
>
>
>
> You're confusing intake air temperature with engine temperature. You
> want intake air temperature as low as possible, yes, but the engine to
> be running as hot as it can. The idea is to have the intake air cool
> to pack in as much fuel/air mix as possible, but then get it as hot as
> possible after combustion to maximise the power delivered - then
> exhaust it to the cool atmosphere again as expediently as possible to
> minimise pumping losses. Now there are valid reasons to keep the peak
> temperature artificially low - NOx emissions, engine integrity, and
> detonation being the obvious three, but if those could be worked
> around, efficiency would go up.
>
> nate
>

Strictly speaking, yes. But the "happy" operating temperature range for
an engine (minimum wear) is fairly wide- about 180 to 250 degrees F. In
a lot of engine designs (wet intake manifold, for example) keeping the
engine temp in the lower end of that range helps keep the intake charge
temperature down as well. Any colder than that, and you increase engine
wear and decrease thermal efficiency. Its actually pretty clear that
increasing operating temperature by 10-20 degrees does produce a
noticeable increase in thermal efficiency, even if the net power ouput
drops a bit because the intake air temp goes up too. Furthermore, if you
can raise the temperature and back off the timing advance, efficency may
also go up (within limits). The higher temperature can offset the spark
advance, and running less advance means less time that the flame front
is "working against" the engine.