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

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. 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.
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.

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.)


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