Dave, and group
If you re-read my post, you'll see that I mention the cooler
fuel/air mixture as plus for power, so we are in violent agreement ;-)
I was stating that there is a rationale for a hotter engine, but also a
rationale for keeping the engine compartment cool. Also, engine temp.
and under-hood temp (which will effect the fuel temp more than the
engine temp alone will) are two entirely different things. There are
all kinds of tricks to minimize heat-soak into fuel, such as shields,
insulators, and fuel-coils packed in dry ice, which is great for the
track, but not for our daily drivers.
As far as the absolute engine temperature is concerned, it's a basic
thermodynamics principal that the hotter the combustion temperature, the
more efficient the combustion process is (delta-T for all you other
thermo-geeks). The problems are that in the real world, you can only
get so hot before gasoline explodes, valves burn, and heads crack. In a
nutshell, if the block temp is closer to the combustion temp, there is
less of a temperature gradient and less heat will conduct out of the
combustion chamber. More heat IN the chamber means more hot, expanding
gas, which means more torque. Some people have piston domes and heads
and valves ceramic coated to keep more heat in the chamber, but the
problem is that too much heat leads to detonation, as opposed to
combustion { review--- Combustion: Good :-) Detonation: Bad :-( }
You can avoid this with super-high octane gas, like racers do. With
the Rovers, we have the advantage of aluminum blocks and heads, which
conduct more heat away than iron, thus reducing the odds of detonation
and allowing us to use higher compression ratios with pump gas.
So, as all engineers do, we compromise, and trade this-for-that.
Ultimately we look for a balance: What is the hottest I can run my
engine without boiling my coolant, deep-frying my valve train, or
setting off several thousand tiny little explosions per minute (as
opposed to the far more desirable several thousand rapid little fires)?
I should mention that hotter temps mean higher emissions, too.
What's so amazing is that most of the work has been done for us:
Chemists and chemical engineers produce a product readily available to
all of us at the corner pump that will work perfectly with an engine
made of common materials (iron, aluminum), and a coolant basically made
from water. As long as you keep your compression ratio between 8 and
11, all the hard work has been done for us.
As far as Jim B's oil question, I believe that synthetic oils
maintain their viscosity regardless of temperature (at least the kind of
temps we see in engines). Natural lubricants are pushed to their limits
in cars, but hold their own as long as we don't do anything stupid.
(Unfortunately for me, I do allot of stupid things, like trying to dry
my sink-cleaned underwear in a hotel microwave-oven while on travel. I
never knew elastic could produce so much black smoke.)
Clear as mud? Sorry about my spelling, I know it's awful.
James J.
David Kernberger wrote:
>3/8/03
>
>James,
>
> If this theory is true it certainly goes directly against my
>understanding. The hotter the coolant is, the hotter every other part of
>the engine is also, I would think. This means the entire intake system
>would also be hotter. My thought is that this higher temperature would
>warm up the incoming charge of fuel/air mixture more, thus causing it to
>expand and lose density more than it would in a cooler condition. Then
>there would be less actual mixture (mass) in the cylinder, so less power
>would be produced. This lower density charge however, combined with
>quicker vaporization of the fuel, ought to improve fuel economy slightly--a
>trade off for the power loss.
> Just my -2 BHP.
>
>Cheers,
>Dave Kernberger
>
>----------------------------------------------------
>
>
>
>>In theory, the hotter the enigne is (relative to ambient), the more
>>power it will produce, but I don't know that 20 deg. will make a bit of
>>difference. On the other side, a cooler engine bay will mean a cooler
>>fuel/air charge and less chance of vapor lock, so I'd run it as hot as I
>>could until I had fuel problems or overheating at idle.
>>Just my 2 BHP worth.
>>James J.
>>
>>
>>james wrote:
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