Use of 150 octane fuel in the Merlin (Xylidine additive etc etc)

"Tarver Engineering" wrote in message ...
"Gord Beaman" wrote in message
...
(Hildegrin) wrote:

Higher octane allows you to use higher boost pressures. It doesn't
create more boost, it just allows you to "overboost" the engine at
lower alts. Thus at rated alt and above, increased octane had no real
effect (it may have reduced power by a tiny amount, because the fuel
has a lower calorifc value, I think).


Yes, this is exactly right...some think that the higher the
Octane Rating the more "powerful" the fuel when actually high
Octane fuel is less 'powerful' that low Octane fuel. You get the
extra power because you can increase the Manifold Air Pressure
(boost) without causing DETONATION. This is the whole reason
behind high octane useage. Heavy detonation will trash an engine
in short order so you must prevent it.

Lead tetra ethyl is not short of energy, Gord.

The amount of TEL added makes little difference to the energy content
of a fuel becuase it is so small an amount. I don't even know how
much energy it releases upon combustion if it does so at all.

Ricardo, the great British engineer, developed the idea of using Tetra
Ehyle Lead (TEL) because he reasoned that the milky color of gasoline
was causing it to ignite due to to the transmision and absorbtion of
infra red radiation rather than burn smoothly. TEL acted as a
clarifying agent and this is how it increase the RON in a variable
displacement test engine. That was the theory at least.

Higher RON number do two things: First they eliminate pre-ignition due
to hot surfaces or the high temperatures caused by compression.
Second they prevent explosive combustion. Combustion should be a
controlled burn at subsonic velocities along a wavefront caused by
thermal conduction explosive combustion (not the technical term) means
that the combustion becomes supersonic and is propagated by infra red
radiation simultaneously in the mixture rather than smoothly along a
wavefront.



Water injection also results in higher engine power in a slightly
different manner.

No. Water injection only prevents the connecting rod bearings from being
destroyed by detonation. Much the same as an EGR valve on automobile
engines injecting exast gas into the manifold.

Water injection does two things:

1 It lowers the temperature of the charge thus preventing preignition.
2 It increase the density of the air and thus allows more air into the
combustion chambers and allows the supercharger to compress the same
amount of air for less work.

When engines are run rich the oversupply of fuel also cools the air in
the same way. Side effect is loss of efficiency and flames and smoke
from exhaust which your enemy can use to guage your intentions.

In article ,
(Gregory W Shaw) writes:
Peter Stickney wrote:

Great work Greg, and mighty close. (You forgot to factor in the
increased temperature at the lower altitude, which will reduce power
somewhat. It's one of those things where the 90/90 rule comes in -
teh first 90% of the accuracy in the analysis takes up teh first 90%
of the effort, and the last 10% takes up the other 90%!


Thanks Peter,

I did take temp into account, that dropped power from 2070 to 2030 hp @
500 ft. Although I did fubar it a little, I used 5800 ft for the base
temp rather than 5750 ft, that would change power to 2033 hp instead of
2032 hp.

(sqrt (276.86 / 287.36)) * 2071 = 2032 hp @ 500 ft.

The change from 500 ft to SL drops power down to about 2026 hp. It looks
like I'm about 1% over published figures. Given the amount of slop
involved all around I'll take that. Particularly for something I can do
with a standard atmosphere chart and a $2.00 calculator in about 1
minute.

It's certainly within the difference that you're going to find
between individual engines. ANd therefore, more than accurate enough.

The temperature factor that I was considering, though, was within the
supercharger, and, to split it a bit more, the temperature addition
contributed by the individual stages, with teh intercooling between
the Aux and Mainstage factored in. (Then there's the difference in
impeller efficiency that occurs as the conditions change - If you're
not careful, it can drive you sane! It's that old 90-90 rule again. )
It wasn't the HP value that I was getting different, but the altitude.
Even that was well within tolerance, so I'd say our models agree.

Not Criticism at all, but Congratulation.

I have seen two different methods of calculating temp affects. I am
using (sqrt (old abs temp/ new abs temp)) * hp

Which is the closest one, although there are aberrations. The
published data for teh V1650-7 (The engine used on later P-51Bs and
the P-51D, don't match up. Even the Specific Engine Characteristics
table in the Pilot's Operating Handbook doesn't seem quite right.

I have also seen simpler version of old abs temp / new abs temp * hp

Using that method I come up with 1996 hp @ 500 ft and 1989 hp @ SL. It
could be that simple, a difference in calculation methods.

The Standard Atmosphere of that time was a bit different, as well,
which could also account for it. THe thing with trying to nail down
these numbers is that they aren't that exact in reality. Every
engine's different, every engine wears differently, and every day is
different. They're never that close.

My spreadsheet is a bit more complicated, it takes blower power into
account as well. And being able to see hp/MAP at multiple altitudes
simultaneously allows me to do some curve fitting that makes for a bit
better accuracy.

Good show. I've some similar tools, myself. (Of course). It's turned
out to be a necessity in sorting out the Variable Speed blowers that
the Germans, and later, Pratt & Whitney used. The normal way to
presenting the performance numbers for tham is just too abstract, and
so it requires a lot of backfitting to sort them out.

I have used it for a number of engines successfully. Given two data
points, generally military power and WEP, I can typically get it to
match within .5 in Hg and 1-2 hp at all altitudes I have published data
for. Given the accuracy of the starting data and all the other slop that
is probably about as accurate as possible.

That's excellent. We'll have to compare notes sometime.

Thanks for the additional Merlin & Griffon data, I'll add it to my
stash.

Plenty more if you need it, Greg, just send me a list, and I'll se
what I can do.

--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster

On Mon, 2 Feb 2004 23:39:25 +0100, "Emmanuel Gustin"
wrote:

"Dave Eadsforth" wrote in message

by a Ar 234 based in Stavanger, Norway, on 10 August 1945.


What was a luftwaffe unit doing in Stavanger on the 10 Aug 45 ?



greg
--
You do a lot less thundering in the pulpit against the Harlot
after she marches right down the aisle and kicks you in the nuts.

"Emmanuel Gustin" wrote in message
...
"Greg Hennessy" wrote in message
...

What was a luftwaffe unit doing in Stavanger on the 10 Aug 45 ?

Sounds absurd, but considerable German forces were still
holding far-out regions in late 1945, when the Reich was
crumbling...

As for the presence of aircraft in Stavanger, this was a good
location for recconnaissance (if you did not want to fly through
Allied-controlled airspace on the Western front). The Luftwaffe
still provided some support for the remaining U-boats, and there
was even a plan to attack Scapa Flow with 'Mistel' composites...


However the explanation is probably rather more prosaic

In the book "Wings of the Luftwaffe", written by Eric 'Winkle' Brown
he notes that several Arado aircraft were ferried from Stavanger
to the RAE in the UK. As there was a shortage of qualified
allied pilots a number of these ferry flights were made by
German pilots.The last of these flights was made in October 1945.

Keith

On Tue, 3 Feb 2004 13:32:54 +0100, "Emmanuel Gustin"
wrote:

"Greg Hennessy" wrote in message
.. .

What was a luftwaffe unit doing in Stavanger on the 10 Aug 45 ?

Sounds absurd, but considerable German forces were still
holding far-out regions in late 1945, when the Reich was
crumbling...


I had heard of weather units holding out, However I am suprised that the
norwegians hadnt ejected them considering it was 4 months after the end of
hostilities.

As for the presence of aircraft in Stavanger, this was a good
location for recconnaissance (if you did not want to fly through
Allied-controlled airspace on the Western front).

That I can understand.


greg

--
You do a lot less thundering in the pulpit against the Harlot
after she marches right down the aisle and kicks you in the nuts.

"Eunometic" wrote in message
om...
"Tarver Engineering" wrote in message
...
"Gord Beaman" wrote in message
...
(Hildegrin) wrote:

Higher octane allows you to use higher boost pressures. It doesn't
create more boost, it just allows you to "overboost" the engine at
lower alts. Thus at rated alt and above, increased octane had no real
effect (it may have reduced power by a tiny amount, because the fuel
has a lower calorifc value, I think).


Yes, this is exactly right...some think that the higher the
Octane Rating the more "powerful" the fuel when actually high
Octane fuel is less 'powerful' that low Octane fuel. You get the
extra power because you can increase the Manifold Air Pressure
(boost) without causing DETONATION. This is the whole reason
behind high octane useage. Heavy detonation will trash an engine
in short order so you must prevent it.

Lead tetra ethyl is not short of energy, Gord.

The amount of TEL added makes little difference to the energy content
of a fuel becuase it is so small an amount. I don't even know how
much energy it releases upon combustion if it does so at all.

Thus cancelling your other post, Eunometic.

Ricardo, the great British engineer, developed the idea of using Tetra
Ehyle Lead (TEL) because he reasoned that the milky color of gasoline
was causing it to ignite due to to the transmision and absorbtion of
infra red radiation rather than burn smoothly. TEL acted as a
clarifying agent and this is how it increase the RON in a variable
displacement test engine. That was the theory at least.

In reality, TEL slows the burn rate of gasoline, thus allowing for more
spark advance and the elimiation of detonation.

snip of further cut and paste