OT: Energy=Horsepower-Hours ???

[John Popelish]

Absence of pre-ignition allows a higher compression ratio which in turn boosts
efficiency ( Carnot Cycle IIRC ).

Exactly. If your engine does not have a high enough
compression ratio to make use of pre-ignition resistant
potential of the fuel, that potential is wasted. And the
additives that are put into low octane rated fuel to raise
its octane rating makes the fuel more polluting both to the
outside environment and to your engine's internals. That
premium gasoline is not better, in general, but better only
in one respect and worse in almost every other respect, is a
BIG secret that is never brought out in gasoline
advertising. They always imply that if you love your car,
you will treat it to premium. What a profit center. Add a
couple cents worth of anti-knock additive and add 20 cents a
gallon to the price.

 

[Joerg]

(snip)

The octane rating is not meant to measure the energy content of fuel.
It is a measure of the knock (pre-ignition) resistance of the fuel. If
you don't have a pre-ignition problem to solve, higher octane fuel is
all cost (including higher exhaust pollution and worse engine grime) and
no benefit for you.

Not necessarily so. Some cars adjust the ignition timing, mixture and
other things to keep the process efficient but just shy of
knocking/pinging. That can yield a few percent on higher octane fuels.
But probably not more than the cost difference.

 

[Eeyore]

Anyone have effective energy numbers for gasoline and ethanol in units
of horsepower-hours?

You can evaluate their relative thermal energy easily enough but the
*horsepower* you get from them varies considerably according to engine design.

Saab seems currently to have the most efficient design for running on any
combination of E85 > standard gasoline but I don't think it's available in the
USA yet.


Graham

 

[Eeyore]

My bet is, when normalized to unit energy, they're equivalent
greenhouse gas polluters.

I believe not actually. C2H5OH has a higher percentane of hydrogen in its
molecule compared to some of the components of gasoline. Compare for example
with benzene C6H6

Graham

 

[John Popelish]

It has always puzzled me why variable compression was never done any
more elegant than by moving the ignition timing. Do you guys have a web
site?

(snip)

Variable compression ratio is not so hard.
http://www.fs.isy.liu.se/Lab/SVC/
But having both variable displacement (over a big range from
fractional horsepower to a hundred or so horsepower) with
constant (over that displacement range) compression ratio,
is hard.

 

[Eeyore]

If you add in all the fuel used plant, fertilize, harvest
and process the grain used to make ethanol, it is clearly
more energy wasteful and carbon emissive to use ethanol as
fuel than it is to just use the fossil fuel, directly.

Another popular myth based only on the use of corn of course and ignoring IIRC
the additional value of the ethanol byproducts such as animal feed..

Even so, the use of corn to make ethanol is a very poor choice from such a
standpoint. Other feedstocks have far better returns.

Graham

 

[Eeyore]

The Swedes allegedly have that working on some scale already. They produce lots
of wood waste and would like to use it for this purpose.

Everyone kids "W" about his references to prairie grass, but I think
that's where it'll be.

In principle any cellulose can be turned to ethanol.

Graham

 

[Eeyore]

Of course that doesn't take into account other nasties such as fertilizer usage.

That's one very good reason against the use of corn.

It's like our wood stove versus other people's gas heaters. Wood burning
is CO2 neutral while gas isn't.

I'm forever amazed that wood burning in modern high efficiency stoves hasn't
become more mainstream yet.

Graham

 

[Eeyore]

How many gallons of fossil fuel does it take to grow and
process that slightly more than 1 gallon of ethanol (that
contains the same energy as a gallon of fossil fuel)?

Right now, it is considerably more than 1.

Not even true.

Graham

 

[Eeyore]

Yep, sounds like hydrogen which, at the present stage of how to go about
it, is IMHO not the solution to our oil dependence.

Making hydrogen is an utterly fatuous waste of energy.

The handling problems are fairly huge too.

Graham

 

[Eeyore]

There is an Octane rating but that does not really equate to the energy
content in a
gallon of fuel.

High octane rating = lower energy content.

Ethanol's octane rating is very high. Engines that can make full use of that
perform a lot more efficiently on E85 than run-of-the-mill ones that have just
had their ECUs 'adapted'.

Graham

 

[Eeyore]

The octane rating is not meant to measure the energy content
of fuel. It is a measure of the knock (pre-ignition)
resistance of the fuel. If you don't have a pre-ignition
problem to solve, higher octane fuel is all cost (including
higher exhaust pollution and worse engine grime) and no
benefit for you.

Absence of pre-ignition allows a higher compression ratio which in turn boosts
efficiency ( Carnot Cycle IIRC ).

Graham

 

[Eeyore]

Anyone have effective energy numbers for gasoline and ethanol in units
of horsepower-hours?

http://en.wikipedia.org/wiki/Gasoline#Energy_content

 

[John Popelish]

I fantasize about adapting one of these:
http://auto.howstuffworks.com/supercharger3.htm
to run backwards - i.e., some high-pressure (like steam, or
maybe freon vapor) working fluid goes into the "discharge
side" and does its work by turning the vanes, and cool(er)
exhaust just wafts out the "intake" side.

Then, of course, while thinking steam boiler and all that
concomitant crapola, I thought, "hell, why not a little
fuel/air injector, and make the high-pressure side a sort
of variable combustion chamber in its own right?

i.e., (assuming you're still looking at the sexy diagram at
http://auto.howstuffworks.com/supercharger3.htm ), you'd
feed a slightly pressurized fuel-air mixture from the
bottom, upstream on the "discharge side" arrow, and there'd
be a spark plug of some kind, hidden behind the rotors in
the illustration. The fuel burns, expands, turns the rotors,
and exhaust comes out of the top.

I have this gnawing feeling that by making the rotor assembly
very "greedy" - i.e., just by the design, it wants to extract
all of the energy it can - in expanding through the rotors,
the exhaust gas would cool, somewhat, and work would be done.

I wonder what it would cost to lash up an experiment? ;-)

I have a similar fantasy for a valveless engine based on a
pair of scroll compressors, one to compress the air (with
fuel continuously injected at its output) and one operating
in reverse to extract mechanical energy from the
decompression of the hot exhaust.

The scroll is easier to build to efficiently compress a
variable volume (compressible gas).

 

[John Popelish]

John Popelish wrote: (snip)

The throttle does indeed put a drag load on the engine.

It is a lot worse than drag. It decompresses the mixture
just before the piston attempts to compress it.

But without variable displacement, it is the only practical
way to vary the total amount of mixture that gets burnt when
the spark goes off. And the very low actual compression
ratio for anything but a wide open throttle body means
crappy efficiency almost all the time.

 

[Joerg]

Joerg wrote:




Making hydrogen is an utterly fatuous waste of energy.

The handling problems are fairly huge too.

And when it gets into the wrong hands you can make that "huge^2".

 

[Joerg]

Joerg wrote:




That's one very good reason against the use of corn.





I'm forever amazed that wood burning in modern high efficiency stoves hasn't
become more mainstream yet.

It has, in many parts of the US. Most certainly in our household

But it's a lot of work. Older people often give up because they can't
schlepp the stuff anymore.

 

[Winfield]

I don't accept it's greenie bullshit, seems more like the
powerful farmer's lobby to me. As for me, I'm for nuclear
and electric or hybrid off-line-chargeable cars. I wish my
new Prius had an electric-outlet jack. Time for a retrofit.

Ethanol is C2H6O - two carbon, six hydrogen and one oxygen.
That single oxygen molecule means that it isn't a hydrocarbon,
but an alcohol.


As has been pointed out by Joerg, ethanol is produced from
green plants, which absorb their carbon from atmospheric CO2,
making ethanol carbon-neutral.

Furthermore, it contains a lttle more hydrogen than regular
hydrocarbons fuels - octane is C8H18 - so a bit more of the
energy you get from burning ethanol comes from turning hydrogen
into water, which isn't a greenhouse gas.

OK, Bill, thanks for the chemist's perspective. What about
the hydrocarbons burned in making the fertilizer and planting,
maintaining, harvesting and processing the corn crops into
ethanol? How does that sum play out?

 

[Joerg]

The internal combustion I am looking forward to operating is a variable
displacement, variable compression ratio design that has no carburetors
or throttle body, but just intake ports with fuel injectors. It adjusts
its displacement and stroke to compress the fuel air mixture to just
below that which causes pre-ignition while producing only the horse
power required, from idle to full, high speed acceleration. It can also
adjust to run on any vaporizable fuel of any octane rating, from
hydrogen to ethanol to 98 octane jet fuel, obtaining the maximum
practical mechanical energy from it.

Experimental (and impractically heavy) hydraulically adjusted versions
are being tested in dynamometer, and the test results, so far, indicate
that a typical vehicle with a given peak horsepower capability would use
about half the fuel, on average, compared to a fixed displacement and
compression ratio engine in use, today.

It has always puzzled me why variable compression was never done any
more elegant than by moving the ignition timing. Do you guys have a web
site?

How would you like to have a vehicle that goes something like 50 miles
on a gallon of low grade gasoline with 200 HP available, or 55 on
premium with 220 HP available?

I owned a 50 mpg vehicle when I was young:
http://en.wikipedia.org/wiki/Image:Citroen_2cv_1949_060117.jpg
Of course, it had only 16 horses but that was good enough and all it
needed was regular gas. Mine could even take unleaded.

 

[John Popelish]

Why is it you think varying ignition timing is inelegant? Timing is
run advanced, just shy of pinging. What do you think the ping
detector is for?

Ignition timing does nothing to reduce the inefficiency of
decompressing the air with a throttle body before the piston
recompresses it back to about atmospheric pressure at low
horsepower output, where the engine operates the vast
majority of the time.