CRYOGENIC ROCKET ENGINE
Presented By: Sushil Lamba
Part IV,Sem VII
HISTORY OF CRYOGENIC TECHNOLOGY
ROCKET ENGINE POWER CYCLES
COMBUSTION IN THRUST CHAMBER
Cryogenics originated from two Greek words “kyros” which means cold
or freezing and “genes” which means born or produced.
Cryogenics is the study of very low temperatures or the production of
the same. Liquefied gases like liquid nitrogen and liquid oxygen are
used in many cryogenic applications.
A cryogenic rocket engine is a rocket engine that uses a cryogenic fuel
or oxidizer, that is, its fuel or oxidizer(or both) are gases liquefied and
stored at very low temperatures.
Oxygen remains a liquid only at temperatures below minus 183 ° Celsius
and hydrogen at below minus 253 ° Celsius.
Notably, these engines were one of the main factors of the ultimate
success in reaching the Moon by the Saturn V rocket.
History of Cryogenic Technology
The United States was the first
country to develop cryogenic
rocket engines with RL-10
engines, registered its first
successful flight in 1963 and is
still used on the Atlas V rocket.
Then The Japanese LE-5
engine flew in 1977 ,French
HM-7 in 1979 , Chinese YF-73 in
The Soviet Union, first country
to put a satellite and later a
human in space, successfully
launched a rocket with a
cryogenic engine only in 1987.
The major components of a cryogenic rocket engine are
the combustion chamber (thrust chamber), pyrotechnic
igniter, fuel injector, fuel cryopumps, oxidizer cryopumps,
gas turbine, cryovalves, regulators, the fuel tanks, and
rocket engine nozzle.
In terms of feeding propellants to combustion chamber,
cryogenic rocket engines (or, generally, all liquidpropellant engines) work in either an expander cycle, a
gas-generator cycle, a staged combustion cycle, or the
simplest pressure-fed cycle.
The cryopumps are always turbo-pumps powered by a
flow of fuel through gas turbines . Looking at this aspect ,
engines can be differentiated into a main flow or a
bypass flow configuration.
In the main flow design, all the pumped fuel is fed
through the gas turbines, and in the end injected to the
combustion chamber. In the bypass configuration, the
fuel flow is split; the main part goes directly to the
combustion chamber to generate thrust, while only a
small amount of the fuel goes to the turbine.
ROCKET ENGINE POWER CYCLES
Gas pressure feed system:-
A pressurized feed system consists of a highpressure gas tank, a gas starting valve, a
pressure regulator, propellant tanks, propellant
valves, and feed lines.
Additional components, such as filling and
draining provisions, check valves, filters, flexible
elastic bladders for separating the liquid from
the pressurizing gas, and pressure sensors or
gauges, are also often incorporated.
After all tanks are filled, the high-pressure gas
valve is remotely actuated and admits gas
through the pressure regulator at a constant
pressure to the propellant tanks.
The check valves prevent mixing of the oxidizer
with the fuel when the unit is not in an right
The propellants are fed to the thrust chamber by
When the propellants are completely consumed , the
pressurizing gas can also scavenge and clean lines
and valves of much of the liquid propellant residue.
The variations in this system ,such as the combination
of several valves into one or the elimination and
addition of certain ,depend to a large extent on the
If a unit is to be used over and over, such as spacemaneuver rocket,it will include several additional
features such as,possibly, a thrust-regulating device
and a tank level gauge.
The gas-generator cycle taps off a small of fuel
and oxidizer from the main flow to feed a burner
called a gas generator.
The hot gas from this generator passes through a
turbine to generate power for the pumps that
send propellants to the combustion chamber.
The hot gas is then either dumped overboard or
sent into the main nozzle downstream.
Increasing the flow of propellants into the gas
generator increases the speed of the
turbine, which increases the flow of propellants
into the main combustion chamber (and
hence, the amount of thrust produced).
The gas generator must burn propellants at a lessthan-optimal mixture ratio to keep the
temperature low for the turbine blades.
Thus, the cycle is appropriate for moderate
power requirements but not high-power
systems, which would have to divert a large
portion of the main flow to the less efficient gasgenerator flow.
COMBUSTION IN THRUST CHAMBER
The thrust chamber is the key subassembly of a rocket
engine. Here the liquid propellants are
metered, injected, atomized, vaporized, mixed, and
burned to form hot reaction gas products, which in
turn are accelerated and ejected at high velocity.
A rocket thrust chamber assembly has an injector, a
combustion chamber, a supersonic nozzle, and
All have to withstand the extreme heat of combustion
and the various forces, including the transmission of
the thrust force to the vehicle. There is an ignition
system if non-spontaneously ignitable propellants are
The four phases of combustion
in the thrust chamber are Primary
Begins at the time of deposition of the
energy into the shear layer and ends
when the flame front has reached the
outer limit of the shear layer.
Starts interaction with the recirculation
Phase typically lasts about half a
It is characterized by a slight but
distinct downstream movement of the
The flame velocity more or less
depends on the pre-mixedness of the
shear layer only.
This phase corresponds to the time span for the
flame reaching the edge of the shear
layer, expands into in the recirculation zone and
propagates until it has consumed all the
This period lasts between 0.1 and 2 ms.
It is characterized by an upstream movement of
the upstream flame front until it reaches a
minimum distance from the injector face plate.
It is accompanied by a strong rise of the flame
intensity and by a peak in the combustion
Flame Lift Off
Phase starts when the upstream flame front
begins to move downstream away from the
injector because all premixed propellants in
the recirculation zone have been consumed
until it reaches a maximum distance.
This period lasts between 1 and 5ms.
The emission of the flame is less intense
showing that the chemical activity has
The position where the movement of the
upstream flame front comes to an end, the
characteristic times of convection and flame
propagation are balanced.
This period lasts from 20ms to more than
50ms , depending on the injection condition.
It begins when the flame starts to move a
second time upstream to injector face plate
and ends when the flame has reached
During this phase the flame propagates
upstream only in the shear layer.
Same as flame lift-off phase the vaporization
is enhanced by the hot products which are
entrained into the shear layer through the
High Energy per unit mass:
Propellants like oxygen and hydrogen in liquid form give very high amounts of
energy per unit mass due to which the amount of fuel to be carried aboard
the rockets decreases.
Hydrogen and oxygen are extremely clean fuels. When they combine, they
give out only water. This water is thrown out of the nozzle in form of very hot
vapour. Thus the rocket is nothing but a high burning steam engine
Use of oxygen and hydrogen as fuels is very economical, as liquid oxygen
costs less than gasoline.
The next generation of the Rocket
All rocket engines burn their fuel to generate thrust . If any other
engine can generate enough thrust, that can also be used as a
There are a lot of plans for new engines that the NASA scientists are
still working with. One of them is the “ Xenon ion Engine”. This engine
accelerate ions or atomic particles to extremely high speeds to
create thrust more efficiently. NASA's Deep Space-1 spacecraft will
be the first to use ion engines for propulsion.
There are some alternative solutions like Nuclear thermal rocket
engines, Solar thermal rockets, the electric rocket etc.