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Enhanced Reliability Features of the RL10E 1.pdf


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200

48th IAF
greatly simplified compared to the mechanical fMback
system of the RL 1OA4 I thrust control valve.
An improved, dual spark plug, continuous burning
torch ignition system (Figure 4) with a redundant,
modem electronics exciter box permits elimination d
the igniter oxidizer supply valve (recall Figure 2). The
exciter provides 0.2 joules to each spark plug at a rate
of 40- 100 sparks per second. The torch igniter includes
a single shear coaxial oxygen-hydrogen element
injector. The torch combustion chamber is cooled by
hydrogen.

MainCombustmn
Chamber

Figure 4: Torch igniter.

The RL IOE-I control system enables ambient
temperature litlofT and boost phase cooldown. This
eliminates the need for the launch site ground chill
system and the engine prelaunch cooldown valve, either
of which potentially can contaminate the engine. Boost
phase cooldown increases reliability and also conserves
oxidizer compared to current RLIOA4I methods.

For flight operation, the engine lifts otTwith pump
near 450”R. Oxygen side chilldown is
initiated shonly after liftoff by opening the OIV to allow
liquid oxygen to fill the pump to the DCV under
pressure and gravity forces. This cooling phase is
termed percolation chilldown, since oxygen vapor
bubbles evolve from the engine and rise up through the
oxygen feedline to the tank where the gas is vented.
Percolation chilldown lasts about 280 set during the
ascent phase. Fuel side chilldown is initiated after the
vehicle reaches an altitude of 150.000 ft. The FIV is
fully opened and theCDV is opened to 1.15 sq. in. to
allow hydrogen to enter the engine, flow through the
CDV, and then be expelled out an overboard vent
system. Hydrogen Row is stopped temporarily I5
seconds prior to A/C separation to prevent the presence
teIIIpCIaNRS

Congress
of hydrogen gas during the pyrotechnic sepamtion
event. Shortly after separation, the OCV is opened to
0.35 sq. in., the FIV is fully reopened, and the CDV is
reopened to 1.15 sq. in. This 8 second prestart process
flushes any saturated propellant out of the feedlines in
preparation for the first main-engine-start (MES I).
Second burn chilldown is accomplished by frrst
using a CDV flow area of 0.24 sq. in. and an OCV area
of 0.035 sq. in. to provide low oxygen and tire1 flow
rates. This chilldown process is termed trickle
chilldown. Then just prior to start, the valves a~
opened to their prestart positions to again flush any
saturated propellants Out Of the feedlimes. The
significant reduction in propellant consumption required
fbr both fvst and second start chilldown more than
of&s the higher RLlOE-I engine weight, while
eliminating potential fkhure modes associated with air
ingestion and moisture contamination during ascent.
Engine startup is accomplished in a manner similar
to the RLIOA41 startup process, but with the
following differences. At the engine start command the
DCV closes to the ignition area. Shortly themafter, the
FSV onens and the CDV closes to a bleed area. This
sequence with the OCV lead minimizes the ignition
pressure rise and improves torch igniter operation as
described later. The torch igniter is lit by redundant
spark plugs and lights the main chamber. Two pressure
sensors, each electronically redundant, are used by the
DEREC to trigger the valve positions during the start
transient. One sensor measures oxygen pump d&charge
pressure and higgen the opening of the DCV to its
steady state flow area after ignition. The other sensor
measures fuel venturi upstream pressure and triggers the
CDV closed (to control pump stall) and the TCV open
(to control acceleration).
At?er ignition, the engine accelerates open loop to
the 55% thrust level and briefly pauses at that point.
Then the control loop is closed, with the control
parameter being the FSV upstream pressure (FSVUP),
and the engine is ramped up to full power by reducing
the TCV flow area (i.e., reducing the turbine bypass
flow). Mixture ratio is maintained during the ramp by
scheduling the DCV position relative to an FSVUP
control pressure request. The schedule for each engine is
based on development test data and/or acceptance test
data. Once the steady state operating level is achieved,
the closed loop cotmol system maintains a constant
FSVUP using integral and proportional control. Since
FSVUP is exposed only to hydrogen gas, it was
selected as the control parameter to eliminate any
possibility of control sensor moisture contamination
!?om the main chamber combustion products (i.e.,
steam). The RL I OA4- I usesconstantchamber pressure
control. The impact of controlling FSVUP. instead d