"Peter Stickney" wrote in message
...
In article ,
(The Enlightenment) writes:
(Peter Stickney) wrote in message
...
In article ,
Dave Eadsforth writes:

A few points here.

In order to improve altitude performance, you've got to increase
the
compression ratio of the induction system, or add an axidizer to
the
fuel-air mix to help it burn. This can be done by adding
supercharger
stages (Basically one supercharger feeding another, like, say, a
Merlin 60 series engine, or the turbosupercharger/engine driven
blower
setups on the P-47 and P-38, or piping something like Nitrous
Oxide
into the induction system, as the Germans did.

Nitrous oxide was more a technique the Germans were forced into to
help overcome a German disadvantage in high octane or high test
aviation fuels rather than a paucity in thingking.

No. Nitrous Oxide injection (GM1, in the German nomenclature) as
used
by the Germans, did not increase engine power below the critical
altitude of the supercharger. It was used to increase the critical
altitude of the engine, by increasing the partial pressure of oxygen
in the fuel-air mixture.
One of the drivers of the need for this system was the supercharger
layout chosed for their large inline engines, the Daimler-Benz 60x
series, and the Junkers Jumo 211 and 213. Instead of having a
centrifugal blower mounted on the back of the engine, with air fed
from directly behind, thus allowing for easy installation of a
second
supercharger stage, and the intercoolers that it requires to keep
the
charge temperature down, the Germans went for a transverse
supercharger mounted transversely (cross-wise, if you will, with the
supercharger impeller's axis at right abgles to the engine's
crankshaft) fed from the side. This precluded a second supercharger
stage without a lot of drag-prodicing external ducting.

I though one reason the Germans didn't have two stage superchargers
was because the lower levels of boost possible with their lower octane
fuels and larger swept volumes simply made duel stage superchargers
unnecessry or pointless. I also note that the Jumo 213E of the Ta
152H did have a two stage supercharger and an induction cooler so it
must have been possible, possibly with coaxial shafts? The Jumo 213E
also had an induction cooler which is presumably a cooling stage
before the induction manifold unlike the two stage merlin which had
the cooler between stages. I suspect that the intercooler of the
merlin is more efficient while the induction cooler method produces a
cooler charge.




THe Daimlers
also used a hydraylic variable speed coupling to drive the
superchargers on the DB601, DB603, and DB605. This is a very neat
idea. Ideally, it allows the supercharger to only draw off enough
power to produce the desired manifold pressure, so that there is
more
power available at the propeller at altitude below the critical
altitude of the engine. There are drawbacks to this - Becasue it
had
to operate ofer a wider speed range than gear-driven superchargers,
the efficiency of the DVL superchargers on the Merceded engines was
about 10-15% lower than those on, say, a Merlin or an Allison.

I think that some specialist Me 109G, those with the DB605AS engine,
were high altitude specialists. This was the superchager of the DB603
grafted onto to 603.

The supercharger drive also isn't as efficient, with losses in the
hydraulic system eating up about 3-4% of teh power needed to drive
the
supercharger - It's like the lesser efficiency of a car with an
automatic transmission compared with th esame car with a manual
transmission.

This Mercedes system was apparently developed from an mercedes
automatic transmision system for cars.



The Germans _did_ use Anti-Detonant Injection (ADI, or MW50 in their
nomenclature) to allow increased manifold pressures (And thus
increased Horsepower) at lower altitudes. This was a 50/50 mix of
Mathanol and Water, injected into the eye of teh supercharger
impeller. It was used in some instances to make up the difference
between the German Low-Octane Avgas (87 Octane), and their High
Octane
Avgas (96 Octane, not really high octane) in some engines, or to
boost
the power of the high octane-rated engines at low altitudes.


The Germans did have techniques for manufacturing octane and even
higher knock hydrocarbons their technology was however more
cumberson
than the US technology and this limited their production rate.
Why
this was I don't know. It may have had something to do with the
fact
that they had access to only snythetic oils from fischer tropsch
and
hydrogenation plants or their own small crude oil industry or
Romania's all of which are regarded as poor quality crudes.
(California crude was rather highly regarded). It may have just
been
that they were unaware of the US techniques.

U.S. techniques were fairly widely known. Ethyl Gasoline had been
available since the mid 1930s. Most of the high octane avgas
impetus
had come from Jimmy Doolittle at Shell. One would think that when
teh
Germans took Rotterdame and Copenhagen that they'd have turned up
that
information. Shell is a Dutch company, and their headquarters were
in
Rotterdam. (In fact, the Shell Building was used as a Headquarters
building by the Germans.)

The Germans had good chemistry and good chemists. The biggest
industry in the world even today. As early as 1939-40 Goering was
calling for the production of large quanties of high test avialtion
fuels what came of this demand I don't know.

I suspect that the effort of producing octane was such that they
simply did not build their force around it. Synthetic fuel already
cost 4 times the same as mineral oils.





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