[Vwdiesel] Engine braking --- ( the physics of beer )
h_hagar at prcn.org
Wed Jan 7 17:07:38 EST 2004
WOW --- I can't remember who started this thread ---but it sure
fired up the " BRAINS". As to beer ? when a beer foams like crazy
and you tilt the bottle sideways , the foaming stops ----WHY ?. I read all the
threads on this braking issue. And if some of you were wrong it still gave lots
of food for thought.
The reason I suggested the test was to give the total beginners an easy
way to tell if the over-fueling was the bugger.
If it did brake allot, then fuel economy would be less. ????
The compression ratio differential on a diesel is not much of a
factor . ???? sorry to bring this up again, ( fine with me)
I read Erik Lanes thread , and it looks like he has most of it pretty close.
So why do you think they put those expensive Jake brakes on diesel
trucks? ( from Harmon)
You forgot one thing to do in this test. you have to run a test where you shut off the intake manifold . ( No I did not forget ) but good point I shall do.
The reason I did not do it so far was my lack of confidence
in the plastic to handle the vacuum.. I now have a piece of plywood.
I totally agree with ROGER ---we are dealing with a thermodynamic
issue. Not drag on alternators and what not.
Therefore the higher compression wins, gas or diesel. So looking at it
solely as forces acting on the pistons (pressure or vacuum) .
It totals up like this --- Piston goes down (intake) little drag. Piston goes
up (compression) lots of drag .Piston goes down (power stroke) no drag.
air expands but the momentum is less. since the compressed air (hot) lost a lot of heat the net outcome is drag.
Why the Jake on big trucks -- ??? because it makes sense. I do not think it has to do with
gas versus diesel issue. Remember other types of retarders are used on equipment
some eddy current ones (the best) some works like a transmission turbo.
I look at the Jake as a cheapskate brake.
Physics of liquids again : Yes a supercooled beer will solidify right in your hand .
Water does not always boil at 100C and does not always freeze at 0 C.
the reason water is so easy to superheat is the fact that it is a good insulator.
Put a cup of distilled water in a micro and let it sit still.Then heat to say 110C
watch out if you heat it to max it may explode into instant steam.
Freeze water to say minus 5C then hit the glass with a spoon---bang instant ice.
PS : Up to my ass in ice and snow ---and blockheater quit . As much as I love
physics , I have to admit I have problems grasping some phenomena.
More information about the Vwdiesel