FIRST STEPS TOWARD SPACE - Smithsonian Institution Libraries

NUMBER 10 235
While the new nozzle was being built, Sanger
worked again on the fuel problem. On 18 June, he
recognized that even with Laval nozzles only a
fraction of the theoretical exhaust velocity could
be attained; for diesel fuel and oxygen burning at
100 atm the exhaust velocity would not be much
higher than 3000 m/sec because of limited chamber
pressures and losses caused by dissociation and friction.
Thus, even before completion of SR-7, he
conducted several preliminary tests on 22 July
1934, with light metal powder suspended in diesel
fuel.
On 23 June 1934, the first test with a closed fuelcoolant
loop was run. With pumps built by the
Bosch Company, diesel fuel was forced at a pressure
of 60 atm through the cooling channels of the
rocket engine being fired; the diesel fuel was watercooled
and returned to the storage tank. During 15
tests, operating times up to 9 minutes and thrust
levels up to 12 kg were demonstrated.
The following test models, SR-8 and SR-9, did
not differ from SR-7 except for nozzle length, nozzle
half-angle, and area ratio. On 24 July 1934, SR-8
produced a thrust of more than 27 kg, and on 31
July 1934, SR-8 delivered a thrust of 30 kg. However,
on 1 August 1934, Sanger wrote:
It seems that the allowable combustion chamber reaction rate
is being exceeded, as combustion partly occurs in the open.
During the last test series, increases in thrust reduced the
temperatures of the fuel coolant, thus indicating that a larger
and larger part of the nozzle was used for mixing instead of
burning. This is in agreement with observations made on
very short nozzles on 26 July 1934 (SR-8). Apparently, propellant,
mixing was not completed entirely within, but partly
outside the nozzle.
Therefore, the configuration of SR-10, SR-11, and
SR-12 was again based on Sanger's design published
in the October 1933 issue of the magazine Radio-
Welt (Radio World); but it included forced coolant
flow as proposed on 15 May 1934, and utilized
previous test experience on allowable combustion
chamber reaction rates. Model SR-11 delivered
again an exhaust velocity of over 2700 m/sec. The
coolant tubing could be separated at midlength for
easier disassembly of a defective thrust chamber
portion. Furthermore, for the first time, the fuel
coolant of SR-12 could be chilled twice, as it was
found that the fuel exiting from the cooling passages
was critically close to its upper temperature
limit.
Along with these tests for the development of a
regenerative cooling system with forced fuel flow
as coolant, the investigations on burning and cooling
effects of liquid oxygen progressed in spite of
temporary disappointments. Sanger, unable to obtain
a suitable oxygen pump, decided on 4 July
1934, to run his ground tests, for the time being,
with pressure-fed liquid oxygen, and he designed
a special set-up for it. The simple testing equipment
consisted of the following components:
1. High-pressure gas supply system consisting of a 40-liter
bottle under an initial pressure of 150 atm and suspended
on a scale.
2. Liquid oxygen tank—a 6-liter bottle enclosed in a vacuumtight
jacket filled with about 100 kg of mineral wool; the
bottle had a thin riser line connected with the supply
line, also a port with a burst-diaphragm and a filler line
branching off to the high-pressure gas tank.
3. Measuring system for consumables—a spring scale holding
the high-pressure gas bottle and lox tank (together weighing
about 200 kg) and clearly indicating weight changes
of about 0.1 kg.
4. System of supply lines—lox supply lines of 5-mm-id copper
tubing, thermally insulated with asbestos cardboard;
a conventional oxygen bottle shut-off valve with hardrubber
gaskets replaced by copper gaskets; valve could be
operated from the blockhouse.
This set-up allowed, over a limited but sufficient
time, lox to be injected under high and constant
pressure through an injector element mounted at
the end of a 10-m-long copper line into the combustion
chamber or into the open, and the oxygen
to be measured consumption during this time. On
20 July 1934, the facility was ready for operation.
Oringinally, tests were to be run with the SR-8
model burning lox and diesel fuel. But it turned
out that the close spacing of lox and fuel injection
elements, unavoidable in Sanger's model combustion
chambers, caused the exiting lox to freeze up
the fuel passages even when they were under full
flow at a pressure of 200 atm. Therefore, testing
was limited to firing in the open; fuel and lox impinged
on each other and were ignited by a gas
flame. The tests were run up to 20 minutes; lox
and fuel injection pressures and impingement angles
were varied. On 24 August 1934, Sanger concluded:
In summary, the open firings with lox have shown:
1. Under continuous ignition, a mixture of atomized lox and
atomized diesel fuel burns very much like gaseous oxygen.
The oxygen mist seems to ignite only after complete
evaporation.
2. A mixture of lox and frozen fuel droplets does not detonate,
but burns stably and quite rapidly.