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operation principle of liquid propellant propulsion <ul><li>oxidizer and
fuel are stored in liquid phase in the tanks&nbsp;</li><li>propellants
are fed to the combustion chamber&nbsp;</li><li>propellants eventually
used to cool hot combustion chamber wall
structures&nbsp;</li><li>propellants mix and burn in the
combustor&nbsp;</li><li>hot gases expand in the nozzle and exit with high
velocity&nbsp;</li><li>conservation of momentum results in acceleration
of the rocket&nbsp;</li><li>liquid propellant engines can be shut-down
and re-ignited&nbsp;</li><li>long duration operation possible (&gt; 1
hour)</li></ul>
pressure fed engine
<ul><li>high pressure tanks for the pressurizing
gas&nbsp;</li><li>pressure control to control mass flow&nbsp;</li><li>low
combustion chamber pressure&nbsp;</li><li>simple supply
system&nbsp;</li><li>high reliability&nbsp;</li></ul><br>applications
:<br><ul><li>low thrust engines&nbsp;</li><li>position
control&nbsp;</li><li>upper stages</li></ul>
pump fed engines <ul><li>propellants are fed by pumps&nbsp;</li><li>pumps
are powered by turbines&nbsp;</li><li>turbines are driven by the
expansion of hot gases&nbsp;</li><li>high combustion chamber
pressure&nbsp;</li><li>fluid supply systems for two propellants
required&nbsp;</li></ul>applications:<br><ul><li>high thrust
engines&nbsp;</li><li>long duration propulsion&nbsp;</li><li>booster and
main stage engines of launchers</li></ul>
performance characterization "flow in the combustor:<br><ul><li>chemical
energy of the reactants is
converted in elevated pressure and
temperature of the combustion products&nbsp;</li><li>energy is given by a
major part
by pressure and temperature of the hot gases&nbsp;</li><li>convective
velocity contributes to a small amount to the total
energy&nbsp;</li></ul>flow in the nozzle:<br><ul><li>hot gases expand and
cool down&nbsp;</li><li>energy of the hot gases is transferred into
convective velocity</li></ul>exhaust velocity:<br><ul><li>supersonic
expansion:
decrease of the thermal energy of the
exhaust gas<br></li><li>maximizing the exhaust velocity: increasing the
temperature, decreasing the mean molar weight, maximizing the pressure
ratio<br></li></ul>specific impulse = thrust / propellant
massflow<br><br>characteristic velocity<br><ul><li>can be determined with
experimentally easily accessible measurements</li><li>as a measure of
combustion efficiency is easy to determine,
but some necessary correction are difficult to quantify: boundary layer
in the nozzle, losses to the cooling circuit, total pressure</li></ul>"
liquid propellants - advantages
<ul><li>higher specific impulse as
compared to solid propellants&nbsp;</li><li>higher density, smaller tank
mass as compared to gases&nbsp;</li><li>mass flow control enables
throttle ability&nbsp;</li><li>liquid propellants can be used for cooling
of structures&nbsp;</li><li>liquid propellant engines can be tested
before start&nbsp;</li><li>liquid propellant engines can be reused</li></ul>
liquid propellants - disadvatages "<ul><li>huge temperature range, huge
range of thermodynamic states,
sound experience and scientific expertise required for motor
design&nbsp;</li><li>liquid propellants can move in the
tanks&nbsp;</li><li>risk of leackage, especially for
LH2&nbsp;</li><li>turbopump technology is
challenging&nbsp;</li><li>freezing of humidity and condensation of oxygen
on
structures cooled by the cryogenic propellants&nbsp;</li><li>laborious
start preparation procedures</li></ul>"
liquid propellants - selection criteria performance
characteristics:<br><ul><li>high specific impulse (small propellant mass
ratio)&nbsp;</li><li>high density or large impulse/volume-ratio (small
tanks)&nbsp;</li><li>simple ignition&nbsp;</li><li>stable
combustion&nbsp;</li><li>cooling capability&nbsp;</li></ul>economic
aspects:<br><ul><li>availability,
costs</li></ul>handling:<br><ul><li>liquid at ambient conditions, low
vapor pressure&nbsp;</li><li>non toxic&nbsp;</li><li>non
corrosive&nbsp;</li><li>chemically stable</li></ul>
mono-propellants / monergols energy release due to propellant
decomposition:<br><ul><li>propellant stable at ambient conditions
</li><li>ignition: thermal /
catalytic&nbsp;</li></ul>advantage:<br><ul><li>simple tanking
procedures&nbsp;</li><li>simple supply system&nbsp;</li><li>simple
propellant injection system</li></ul>
bi-propellants / diergols
"energy release due to chemical reaction of
two reactants:<br><ul><li>storage in separate tanks, mixing in the
combustor&nbsp;</li><li>ignition: – pyrotechnic igniter
– electric spark
– auxillary combustors producing hot gas
– laser ignition&nbsp;</li></ul>modern liquid propellant engines use bipropellants
due to performance and handling safety<br>"
cryogenic propellants <ul><li>gaseous at ambient
conditions&nbsp;</li><li>liquid at low temperatures: - tanks need thermal
insulation - evaporation losses during storage - storage- and supply
systems sensitive to humidity&nbsp;</li><li>high thrust engines</li></ul>
hypergolic propellants "<ul><li>spontaneous ignition at contact of
propellant components&nbsp;</li><li>no ignition system
required</li><li>MMH, UDMH and NTO are toxic&nbsp;</li><li>specifically
trained team required for tank procedures on ground&nbsp;</li><li>exhaust
gas neutralization required at test benches&nbsp;</li><li>in case of an
anomaly during the start phase risk of contamination of
the launch site<br></li></ul>"
storable propellants
<ul><li>storable for more several
years&nbsp;</li><li>immediate usability of engines&nbsp;</li><li>upper
stages and military applications</li></ul>
subsystems (liquid propellant)
motor (GG-cycle):<br><ul><li>gas
generator&nbsp;</li><li>turbopumps&nbsp;</li><li>combustor&nbsp;</li><li>
nozzle&nbsp;</li><li>nozzle extension</li></ul>propellant
supply:<br><ul><li>tanks</li><li>lines</li><li>sensors</li><li>valves</li
></ul>
subsystems - tanks
<ul><li>propellants&nbsp;</li><li>pneumatic
gases&nbsp;</li><li>purge gases&nbsp;</li><li>pressurization
gases</li></ul>design
parameters:<br><ul><li>mass&nbsp;</li><li>material&nbsp;</li><li>heat
transfer&nbsp;</li><li>center of gravity<br></li></ul>
subsystems - valves
<ul><li>pyrotechnic&nbsp;</li><li>pneumatic&nbsp;</li><li>electric<
/li></ul>
subsystems - combustion chambers <ul><li>residence time has to guarantee
complete evaporation, mixing, and reaction of
propellants</li><li>combustor volume depends on propellants and
conditions of combustion&nbsp;</li><li>minimizing
mass&nbsp;</li><li>lifetime</li><li>cost<br></li></ul>
subsystems - nozzles
<ul><li>expansion of hot
gases&nbsp;</li><li>transformation of thermal into kinetic
energy&nbsp;</li><li>minimizing mass&nbsp;</li><li>minimizing
size&nbsp;</li><li>optimizing contour&nbsp;</li><li>manufacturing
costs</li></ul>
subsystems - injectors&nbsp; <ul><li>feeding fuel and oxidizer into the
combustor&nbsp;</li><li>propellant atomization and
mixing&nbsp;</li><li>acoustic decoupling of combustor and feed
system&nbsp;</li><li>combustion efficiency&nbsp;</li><li>combustion
stability&nbsp;</li><li>loads to the combustor
wall&nbsp;</li><li>manufacturing costs</li></ul>
subsystems - gas generators and preburners
"<ul><li>generation of hot
gas at high pressure&nbsp;</li><li>design parameter similar to main
combustion chambers&nbsp;</li><li>hot gas temperature significantly below
temperatures in main
combustion chambers (mixture ratio significantly different from
stoichiometry, usually fuel rich)</li></ul>"
subsystems - ignition systems
"<ul><li>provide energy to initiate
chemical reaction
of the propellants&nbsp;</li><li>igniter power has to be sufficient to
evaporate liquid propellants and to heat
them up to the ignition temperature</li></ul>"
subsystems - turbopumps
design requirements depend
on:<br><ul><li>engine cycle&nbsp;</li><li>vapor pressure of
propellants&nbsp;</li><li>combustion chamber
pressure&nbsp;</li><li>throttle ability</li></ul>
gas generator cycle
"<ul><li>open cycle&nbsp;</li><li>energy source to
drive the turbine is hot gas from the gas
generator&nbsp;</li><li>small amount of total propellant mass flow (3-7%)
fed to the
gas generator&nbsp;</li><li>turbine working fluid not fed into main
combustion chamber: - separately released and expanded (Vulcain, HM7) used to cool nozzle structures (film cooling of Vulcain 2
nozzle)</li><li>small contribution of turbine exhaust gases to
thrust&nbsp;</li><li>with increasing pc
increased fraction of
propellants required for gas generator&nbsp;</li><li>SC-cycle (closed
cycle) higher specific
impulse than GG-cycle (open cycle) for high
chamber pressures<br></li></ul><img src=""paste27ff8092d049ef967cf14ff0fc2ba5045b888d6b.jpg""><br>"
expander cycle
"<ul><li>closed cycle&nbsp;</li><li>total fuel mass flow
is used for regenerative cooling and then fed to
the turbines.&nbsp;</li><li>turbine exhaust gases (fuel-rich hot gas) are
fed into the combustion
chamber&nbsp;</li><li>no gas generator or preburner necessary: - lower
combustion chamber pressures - long combustion chambers</li></ul>"
expander-bleed cycle
"<ul><li>hybrid of expander cycle and open
cycle&nbsp;</li><li>only part of the total fuel mass flow used for
regenerative cooling
and expanded in the turbines: - smaller cooling fluid mass flow as
compared to expander cycle,
therefore high ΔT&nbsp;</li><li>turbine gases as in the gas generator
expanded, either into the
environment or into main nozzle&nbsp;</li><li>no gas generator or
preburner required: - low chamber pressures (~ 5 MPa) - small Isplosses</li></ul>"
tap-off cycle
"<ul><li>open cycle&nbsp;</li><li>hot gases are removed
from the combustion chamber, mixed
with a small proportion of the fuel from the regenerative cycle and
expanded via the turbines.</li><li>no gas generator or
preburner&nbsp;</li><li>hot gases taken from the combustion chamber are
the energy
source to drive the turbines&nbsp;</li><li>expansion to the environment:
only small mass flow required for
turbines&nbsp;</li><li>small Isp-losses</li></ul>"
staged-combustion cycle
"<ul><li>closed cycle&nbsp;</li><li>energy
source to drive the turbines is a / are several
preburner(s)&nbsp;</li><li>either complete fuel (or oxidizer) mass flow
is fed into the preburner
and burned at a fuel-rich (or oxidizer) mixture
ratio&nbsp;</li><li>mixture ratio ROF chosen in such a way that the
maximum
permissible turbine inlet temperature is not
exceeded.&nbsp;</li><li>turbine exhaust gases fed into the main
combustion chamber</li></ul><div>variants
affect:</div><div><ul><li>pressure losses and therefore power
requirements for the turbopumps&nbsp;</li><li>engine
control&nbsp;</li><li>start-transients</li></ul></div><div>cooling
circuit:</div><div>paralell:</div><div><ul><li>less mass flow for chamber
cooling
available&nbsp;</li><li>less TP-power required</li></ul><img src=""pasted265a343871ce0a301b633adc487520e94cb034f.jpg""><br></div><div>serial:</di
v><div><ul><li>pressure increase of the H2
-pump
has to consider pressure losses of
the cooping channels and turbines&nbsp;</li><li>higher TP-power
required<br></li></ul><img src=""paste080bc8e73b0cbadf0f8ec1df5364373432c8a7db.jpg""><br></div><div>turbines:&n
bsp;</div><div>parallel:</div><div><ul><li>higher pressure loss over the
turbines&nbsp;</li><li>smaller mass flow</li></ul><img src=""paste15c26ba70d8dac8aa1395543a1d652a11ee3a8d2.jpg""><br></div><div>serial:&nbs
p;</div><div><ul><li>low pressure loss over the
turbines&nbsp;</li><li>higher mass flow</li></ul><img src=""pastea54fb128985dcd46274216083c38a263b4ce880e.jpg""><br></div>"