<VV>Cheap Gaz

[Padgett]

>One little comment ... engines are ( theoretically )  more efficient the
>hotter they run .. because energy in the combusted chamber can go more to
>pushing down on the piston than escaping thru a cool cylinder wall ....

Well sorta. You have to look at the combustion model but in simplest terms 
power is a function of the pressure rise in a cylinder during combustion. 
Since pressure and temperature are linked, you burn the fuel to achieve the 
rise. Now if you consider that there is a peak temperature the gas reaches 
in this process then the lower you begin, the greater the pressure rise.

>the crossover point obviously is when the engine melts,

Actually for a gasoline engine the crossover point is when detonation 
occurs - some point in the engine gets hot enough to ignite the fuel/air 
mixture, a second flame front is generated, and combustion goes wonkey with 
front collisions and an unpredictable pressure rise in the cylinder, often 
peaking before TDC is reached. This is not good. One problem the Corvair in 
particular has is that the hottest part of the chamber (near the exhaust 
manifold on the bottom) is about as far from the spark plug on the top as 
you can get. If you look at the SAE papers you will see that the spark plug 
is in an area that is 100F cooler than the bottom of the  head. This means 
that if detonation does occur it will be most likely start in the worst 
possible place.

Now part of the purpose of a squish chamber is to move the fuel-air mixture 
away from that hottest part of the head. If compression is lowered through 
extra head gaskets rather than opening up the squish chamber then 
detonation becomes more likely, not less.

>Which is what all the interest in ceramic engines is about ... ceramics work
>just fine at 2000 degrees F or so.
But not for gasoline (SI) engines unless you want to build a really light 
one or the elves need an alternative to Cold Iron.

>**********
>Oh, purely from efficiency compression is also a very big deal regarding
>wasting energy ... a goal could be the 22 to 1 of diesels ... ( why aren't
>we all running diesels.

Because the entire engine must be much more robustly constructed since a 
Compression Ignition (CI) engine is operating at detonation constantly. 
They also often have no throttle plate & run at WOT constantly, control is 
by the amount of fuel injected which incidentally is usually injected into 
the chamber not the port so the injectors must be much more robust. Also 
since diesel is so hard to burn compared to gasoline (why they can run very 
high compression, they must) special procedures are necessary for cold starts.

If anyone remembers the problems GM had with trying to convert the Olds 350 
(which was one of the best 350s ever built) to diesel in the late 70's and 
early '80s with cranks failing all over the place, that is a good example.

Now the Europeans, fueled by gasoline prices double and triple what we see 
here are being successful in developing some very small diesel engines 
because even with all of their idiosynchrocies, expense to build, 
interesting odors and smoke clouds (usually when the injectors need to be 
cleaned) , lack of vaccuum assists, and difficult maintenance (filthiest 
engine to work on I ever saw was a Mecedies diesel). They can be more 
efficient than spark ignition though "more efficient" is a relative term 
and CI is generally best suited for torque not horsepower. The Smart Car is 
sold in Canada with a 700 cc diesel engine. The gasoline versions are 
governed to 84 mph. I do not believe the diesel needs a governor.

Given all of that, there is No Way a Corvair engine could be converted to 
diesel even with ceramic cylinders, the crank would never take it. If one 
were built it would need to weigh a Lot More.

So it can be done but keep in mind that the reciprocating engine, 
particularly at high speeds, is inherently inefficient and internal 
combustion itself is crude and best suited to constant speed operation. But 
what a wonderful kludge.

Padgett

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