murdoch wrote:
> One additional thing that occurred while I was reading: with gasoline
> muscle cars and such, you often see folks go to lengths to get even
> more good air to their engines and fuels.
That's because an engine is basically an air pump. Filling the
cylinder with an appropriate mix of air and fuel can be a great deal
more complex than it might seem initially. For those of us who are
really into this, removing intake and exhaust restrictions becomes a
kind of obsession. (We spend hours in the cylinder head pockets with
grinders, pay big bucks for three angle valve jobs, tuned headers and
less restrictive exhaust systems. . .) I long for the day of rotary
valves, variable compression pressure and direct fuel injection. . .
> Ok, but maybe this will
> cost a bit either in reduced aerodynamic efficiency (since you're
> scooping a bit more air out of the flow) and-or using a bit of the
> engine? since some of these air-increase schemes may involve using
> engine power, say to power a super-charger?
The aerodymanic drag under a modern vehicle is normally its weakest
link. My truck IS supercharged, and I take air from the grill without
any aerodynamic add on device. The really nice thing about alcohols,
propane, natural gas and hydrogen, is that we can squeeze those fuels
harder to get more work out of them.
Here's an example:
I built a 5.7 liter small block Chevrolet for my last engine
building project. It replaced a 5 liter, bone stock engine in a full
sized Pontiac. The stock engine had an 8:1 compression ratio,
consistently yielded 5 kilometers per liter of propane, ran smoothly and
was quite reliable. The engine I built for that car had an 11:1 static
ratio, with a compression building camshaft. Compression pressure went
from 110 psi to well over 200 psi, so it sounded like a diesel, but it
had a LOT more power and the fuel economy went from 5 km / l to 6 km / l
in a bigger engine. That's a practical example of why the discussion of
energy per liter for a given fuel can be misleading.
The real problems with renewable fuels for internal combusion
engines relates directly to the degree of engine modifications necessary
to run them efficiently. Any need for gasoline as a back up fuel
immediately puts us into the realm of compromise, which limits both
range and efficiency. An engine I would build for maximum efficiency
running ethanol would differ sufficiently from one I would build for
gasoline that using the latter fuel would likely damage the internal
parts.
> Getting back to the aero, here we have what on the face of it is an
> advantage for EVs (since they can do away with an air intake, except
> if you need air for cooling the batteries or for interior air issues).
I know of a EV Ranger owner whose truck compares nicely to mine.
His vehicle is FIVE TIMES more efficient at getting him down the road
than is my gasoline powered truck, and it's heavier too! EVs are by far
the most efficient solution for automobile transportation.
> I was thinking all this, and then came to the passage where it
> mentioned favoring methanol for racing. I had been thinking that
> whatever minor loss of aero there is for a hood scoop or
> engine-air-intake, and whatever minor increase in complexity there
> might be for a supercharger or turbocharger, there are probably
> offsetting considerations.
Indeed! Any increase in compression pressure will result in higher
efficiency, especially at part throttle, where most of us do our
driving.
> But here we have (some) real racers voluntarily going for Methanol
> because in their view it's the best fuel for the job they have. I'm
> pretty sure Indy racing has been using Methanol, but I don't think
> NASCAR and I don't know about F1.
Methanol is the racer's fuel of choice in most venues. NASCAR
started out because the moonshiners in the southern U.S. were always
boasting about the vehicles they'd modified for running their illicit
product, and enough of them were interested in proving whose car was the
fastest than they began racing one another. Many of those people were
using ethanol as a fuel for the reasons we've been discussing.
> The reason you provide for the use
> of methanol does sort of seem to be related to the way I'm looking at
> it, though not directly. I guess it looks to me like they're "having
> to do less work" to get the necessary air to the fuel for optimal
> burning.
I think you have this backwards! Most of those engines are running
BIG boost from their turbos! Building an engine with slightly dished
pistons and heavy boost yields a more effective burn than flat topped or
domed pistons for the same compression pressures.
> I wonder how this works out with H2 in an ICE engine.
>
H2 has some really interesting properties in an internal combustion
engine. Its wide flammability limits mean that hydrogen can be run VERY
LEAN and still keep the engine turning. Direct injection allows for
variable compression pressure, and such a set up would eliminate pumping
losses from high vacuum conditions and low static compression ratios.
Controlling this is well within the capability of modern, sequential
injection computer systems. Thus, a spark ignited engine running
hydrogen could become as efficient as a diesel.
Unlike ethanol and methanol, however, hydrogen doesn't serve to
keep the intake charge cool and its low ignition energy makes it prone
to preignition. (Hence, water injection becomes a necessity.) The
generation and storage problems are also vexing!
robert luis rabello
"The Edge of Justice"
Adventure for Your Mind
http://www.1stbooks.com/bookview/9782
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