Cryogenic Engine
1.INTRODUCTION
Cryogenic originated from two Greek word “Kyros” which means cold or freezing “gene” which means burn or produced. Cryogenic is the study of production of very low temperature nearly about ‘123 k’ in which the material behavior and properties are studied at that temperature. Cryogenic engine is a type of rocket engine designed to use the fuel or oxidizer which must be refrigerated to remain in liquid state . Liquid propellant Rocket engine(LPRE) are commonly used in space technology. Thrust chamber is one of the most important subsystem of a rocket engine. The liquid propellant (i.e.…liquid hydrogen and liquid oxygen) are metered, injected, atomized, vaporized, mixed and burned to form hot reaction gas product, which in turned are accelerated and ejected at supersonic velocity.Payload capacity of the space vehicle can be increased with the propulsion system having higher specific impulse, in general liquid propellant engines result in longer burning time than conventional solid rocket engine which result in higher specific impulse.
These highly efficient engines were first flown on the US Atlas Centaur and were one of the main factors of NASA‘s success in reaching the Moon by the Saturn V rocket.Rocket engines burning cryogenic propellants remain in use today on high performance upper stages and boosters. Upper stages are numerous. Boosters include ESA’s Ariane 5, JAXA‘s H-II, and the United States Delta IV and Space Launch System.
The use of liquid fuel for rocket engines was considered as early as the beginning of 20th century. The Russian K.E.Ziolkowsky, the American H.Goddard and the German-Romanian H.Oberth worked independently on the problems of spaceflight and soon discovered that in order to succeed, rockets with high mass-flow were mandatory. Already then the combustion of liquid fuels seemed the most promising method of generating thrust.
However it was not later until these pioneers made their attempts, the first big liquid powered rocket the German A-4 became reality in the mid-forties. This rocket became successful as the V-2 weapon. Liquid oxygen was used as the oxidizer and ethyl alcohol as the fuel which gave the rocket more than 300KN of thrust. It`s range was 300km.
As the development of rocket engines continued, higher thrust levels were achieved when liquid oxygen and liquid hydrocarbon were used as fuel. This allowed the construction of the first intercontinental rocket with a range of more than 10,000km.
Under normal atmospheric conditions, at temperature 300k and pressure 1 bar, these substances are in gaseous state. One cannot remedy the low density by increasing the pressure because the required tank structures would end being too heavy. The answer is to liquefy the fuels by cooling them down. This is why the fuels are also called cryogenic fuels.
In the sixties, the steadily increasing payload weights and the corresponding demand for more thrust of the launcher lead to the use of liquid hydrogen for the Centaur upper stage. At the peak of this development was the US Space Shuttle Main Engine (SSME).
2. HISTORY OF TECHNOLOGY
This Rocket Technology has a great History involving many giant nations including USA, Russia, Japan, France etc. A close competition was lead in later half of 20th Century for this technology since it’s invention by USA. When USA successfully launched its 1st Atlas V rocket in 1963 boosted up the cold war between Russia & USA which played a significant role in rapid advancement in this technology in such a short period of time. After USA Russia started its tests of launch vehicles. Firstly, Russia carried a dog named ‘Linus’ in space in 1983. Russia was first to take human in space using sputnik. During this period lot of European countries were trying their rockets with same technologies &succeeded later, But no human being till 1985.
Other countries are like: Japan used LE5 in 1997, France used HM7 in 1979 used the respective rocket engines. Here the mixture of liquid N2, H2 and O2 are used as fuels. In 1987, first CRE was launched with human in space.
Fig:- RL10 Engine
2.1 India
Indian Space Research Organization was also trying its hand on this technology in 20thCentury. ISRO’s then Chairman U.R.Rao in 1993 announced that its Cryogenic engine will have a launch in just 4 years. But it took more than 20 years to Ignite Its Cryogenic Engine so we joined the competition much late in 21st Century due to its frequent failure & no technological support from other developed Countries. But now ISRO is working good with successful launch of Mangalyaan in its first attempt, being the first country of this kind.
Fig:- ATLAS-V Rocket
3. CRYOGENIC FUELS/PROPELLANT
Latent heat of vaporization is the most important characteristic of any cryogen (cryogenic fluid) because of its very easy way to cool equipment. Therefore, the useful temperature range of cryogenic fluids is that in which there exists latent heat of vaporization, i.e., between the triple point and the critical point, with a particular interest in the normal boiling point, i.e., the saturation temperature at atmospheric pressure. This data is giveni In the following, we shall concentrate on two cryogens: helium which is the only liquid at very low temperature, and nitrogen for its wide availability and ease of use for precooling equipment and for thermal shielding.
Table-1 Characteristic temperature of cryogenic fluids
Liquid Neon is a clear, colorless liquid with boiling point at 27.1 K and commonly used in neon advertising boards. It‟s also used as cryogenic refrigerant and this cryogen is compact, inert and less expensive as compared to liquid Helium.
Liquid Nitrogen boils at 77.3 K and freezes at 63.2 K. It exists in two stable isotopes N14 & N15 in ratio of 10000:38. Heat of vaporization of this fluid is 199.3 KJ and it is produced by distillation of liquid air. Nitrogen is primarily used toprovide an inert atmosphere in chemical and metallurgical industries. It is also used as a liquid to provide refrigeration. For food preservation, blood, cells preservation liquid Nitrogen is used and it is has property of high temperature superconductivity. Liquid oxygen (LOX) is in blue color due to long chains of O4. Density of LOX is 1141 kg/m3. O2 is slightly magnetic and exists in 3 stable isotopes- O16, O17, and O18 in ratio of 10000:4:20. Because of the unique properties of oxygen, there is no substitute for oxygen in any of its uses- widely used in industries and for medical purpose. It is largely used in iron and steel manufacturing industry. It applies in Oxidizer propellant for spacecraft rocket.
Table-2 Properties of Cryogen
Rocket engines need high mass flow rates of both oxidizer and fuel to generate useful thrust. Oxygen, the simplest and most common oxidizer, is in the gas phase at standard temperature and pressure, as is the simplest fuel hydrogen. While it is possible to store propellants as pressurized gases, this would require large, heavy tanks that would make achieving orbital spaceflight difficult if not impossible. On the other hand, if the propellants are cooled sufficiently, they exist in the liquid phase at higher density and lower pressure, simplifying tankage. These cryogenic temperatures vary depending on the propellant, with liquid oxygen existing below −183 °C [90 K] and liquid hydrogen below −253 °C [20 K]. Since one of more of the propellants is in the liquid phase, all cryogenic rocket engines are by definition either liquid-propellant rocket engines or hybrid rocket engines.[2]
Various cryogenic fuel-oxidizer combinations have been tried, but the combination of liquid hydrogen (LH2) fuel and the liquid oxygen (LOX) oxidizer is one of the most widely used.[1][3] Both components are easily and cheaply available, and when burned have one of the highest enthalpy releases in combustion,[4] producing a specific impulse of up to 450 s at an effective exhaust velocity of 4.4 km/s.
4.PRINCIPLE :
The principle of rocket propulsion depends on the following two laws: –
(i) Newton ‘s third law of motion
(ii) Law of conservation of momentum
We have already read about these laws, and now we will see how they can be applied for propelling the rocket.
The motion of a rocket is an interesting application of Newton’s third law of motion & momentum principle. The rocket expels a jet of hot gases from its tail. This is say, an action force. The jet of hot gases exerts a force on the rocket, propelling it forward; this is the reaction force.
From the momentum point of view, the hot gases acquire momentum in the backward direction & the rocket acquires an equal amount of momentum in the forward direction.
The simplest example to understand the propulsion of rockets is that of a balloon.
A balloon shooting forward (when the mouth of the balloon filled with air is released) and a rocket hurtling into space are propelled by similar forces. The air in a closed balloon exerts a uniform outward force. But when air rushes out of its neck (similar to exhaust gases leaving rockets) disturbs this equilibrium. Thus an equal and opposite force is exerted on the surface opposite to the neck. This drives the balloon forward.
As we have seen in the previous section propellants are used to provide thrust to the rockets. These propellants on burning produces large amount of gas, which are allowed to pass through nozzle. On passing through the nozzle, high pressure is generated i.e. gas comes out with high pressure.
Now to increase the thrust, one basic property is used while designing the nozzle. The neck of the nozzle is kept very small as compared to the body of the rocket. So the pressure of the gas increases and so does the velocity. Thus high thrust is achieve
5. CONSTRUCTION OF CRYOGENIC ENGINE
What is Cryogenic rocket engine?
- A cryogenic rocket engine is a rocket engine that uses a cryogenic fuel or oxidizer, that is, its fuel or oxidizer (or both) is gases liquefied and stored at very low temperatures. Notably, these engines were one of the main factors of the ultimate success in reaching the Moon by the Saturn V rocket.
- During World War II, when powerful rocket engines were first considered by the German, American and Soviet engineers independently, all discovered that rocket engines need high mass flow rate of both oxidizer and fuel to generate a sufficient thrust. At that time oxygen and low molecular weight hydrocarbons were used as oxidizer and fuel pair. At room temperature and pressure, both are in gaseous state. Hypothetically, if propellants had been stored as pressurized gases, the size and mass of fuel tanks themselves would severely decrease rocket efficiency. Therefore, to get the required mass flow rate, the only option was to cool the propellants down to cryogenic temperatures (below −150 °C, −238 °F), converting them to liquid form. Hence, all cryogenic rocket engines are also, by definition, either liquid-propellant rocket engines or hybrid rocket engines.
- Various cryogenic fuel-oxidizer combinations have been tried, but the combination of liquid hydrogen (LH2) fuel and the liquid oxygen (LOX) oxidizer is one of the most widely used. Both components are easily and cheaply available, and when burned have one of the highest entropy releases by combustion, producing specific impulse up to 450 s (effective exhaust velocity 4.4 km/s).
| Country | Engine | Cycle | Use | Status |
| RL-10 | Expander | Upper stage | Active | |
| J-2 | Gas-generator | Upper stage | Retired | |
| SSME | Staged combustion | Booster | Active | |
| RS-68 | Gas-generator | Booster | Active | |
| BE-3 | Combustion tap-off | New Shepard | Active | |
| J-2X | Gas-generator | Upper stage | Developmental | |
| RD-0120 | Staged combustion | Booster | Retired | |
| KVD-1 | Staged combustion | Upper stage | Retired | |
| RD-0146 | Expander | Upper stage | Developmental | |
| Vulcain | Gas-generator | Booster | Active | |
| HM7B | Gas-generator | Upper stage | Active | |
| Vinci | Expander | Upper stage | Developmental | |
| CE-7.5 | Staged combustion | Upper stage | Active | |
| CE-20 | Gas-generator | Upper stage | Active | |
| YF-73 | Gas-generator | Upper stage | Retired | |
| YF-75 | Gas-generator | Upper stage | Active | |
| YF-75D | Expander cycle | Upper stage | Active | |
| YF-77 | Gas-generator | Booster | Active | |
| LE-7 / 7A | Staged combustion | Booster | Active | |
| LE-5 / 5A / 5B | Gas-generator(LE-5) Expander(5A/5B) | Upper stage | Active |
Comparison of first stage cryogenic rocket engines[edit]
| model | SSME/RS-25 | LE-7A | RD-0120 | Vulcain2 | RS-68 | YF-77 |
| Country of origin | ||||||
| Cycle | Staged combustion | Staged combustion | Staged combustion | Gas-generator | Gas-generator | Gas-generator |
| Length | 4.24 m | 3.7 m | 4.55 m | 3.00 m | 5.20 m | 4.20 m |
| Diameter | 1.63 m | 1.82 m | 2.42 m | 1.76 m | 2.43 m | – |
| Dry weight | 3,177 kg | 1,832 kg | 3,449 kg | 1,686 kg | 6,696 kg | 2,700 kg |
| Propellant | LOX/LH2 | LOX/LH2 | LOX/LH2 | LOX/LH2 | LOX/LH2 | LOX/LH2 |
| Chamber pressure | 18.9 MPa | 12.0MPa | 21.8 MPa | 11.7 MPa | 9.7 MPa | 10.2 MPa |
| Isp (vac.) | 453 sec | 440 sec | 454 sec | 433 sec | 409 sec | 438 sec |
| Thrust (vac.) | 2.278MN | 1.098MN | 1.961MN | 1.120MN | 3.37MN | 673 kN |
| Thrust (SL) | 1.817MN | 0.87MN | 1.517MN | 0.800MN | 2.949MN | 550 kN |
| Used in | Space Shuttle Space Launch System | H-IIA H-IIB | Energia | Ariane 5 | Delta IV | Long March 5 |
Comparison of upper stage cryogenic rocket engines[edit]
| Specifications | |||||||||||||||
| RL-10 | HM7B | Vinci | KVD-1 | CE-7.5 | CE-20 | YF-73 | YF-75 | YF-75D | RD-0146 | ES-702 | ES-1001 | LE-5 | LE-5A | LE-5B | |
| Country of origin | |||||||||||||||
| Cycle | Expander | Gas-generator | Expander | Staged combustion | Staged combustion | Gas-generator | Gas-generator | Gas-generator | Expander | Expander | Gas-generator | Gas-generator | Gas-generator | Expander bleed cycle （Nozzle Expander） | Expander bleed cycle （Chamber Expander） |
| Thrust (vac.) | 66.7 kN (15,000 lbf) | 62.7 kN | 180 kN | 69.6 kN | 73 kN | 200 kN | 44.15 kN | 78.45 kN | 88.26 kN | 98.1 kN (22,054 lbf) | 68.6 kN (7.0 tf)[5] | 98 kN (10.0 tf)[6] | 102.9 kN (10.5 tf) | r121.5 kN (12.4 tf) | 137.2 kN (14 tf) |
| Mixture ratio | 5.5:1 or 5.88:1 | 5.0 | 5.8 | 5.05 | 5.0 | 5.2 | 6.0 | 5.2 | 6.0 | 5.5 | 5 | 5 | |||
| Nozzle ratio | 40 | 83.1 | 100 | 40 | 80 | 80 | 40 | 40 | 140 | 130 | 110 | ||||
| Isp (vac.) | 433 | 444.2 | 465 | 462 | 454 | 443 | 420 | 438 | 442 | 463 | 425[7] | 425[8] | 450 | 452 | 447 |
| Chamber pressure :MPa | 2.35 | 3.5 | 6.1 | 5.6 | 5.8 | 6.0 | 2.59 | 3.68 | 7.74 | 2.45 | 3.51 | 3.65 | 3.98 | 3.58 | |
| LH2 TP rpm | 90,000 | 42,000 | 65,000 | 125,000 | 41,000 | 46,310 | 50,000 | 51,000 | 52,000 | ||||||
| LOX Tm | 18,000 | 16,680 | 21,080 | 16,000 | 17,000 | 18,000 | |||||||||
| Length m | 1.73 | 1.8 | 2.2~4.2 | 2.14 | 2.14 | 1.44 | 2.8 | 2.2 | 2.68 | 2.69 | 2.79 | ||||
| Dry weight kg | 135 | 165 | 550 | 282 | 435 | 558 | 236 | 550 | 242 | 255.8 | 259.4 | 255 | 248 | 285 |
6.COMPONETS AND COMBUSTION CYCLE
The major components of a cryogenic rocket engine are the combustion chamber, pyrotechnic initiator, fuel injector, fuel and oxidizer turbopumps (including gas turbine), cryo valves, regulators, the fuel tanks, and rocket engine nozzle. In terms of feeding propellants to the combustion chamber, cryogenic rocket engines are almost exclusively pump-fed. Pump-fed engines work in a gas-generator cycle, a staged-combustion cycle, or an expander cycle. Gas-generator engines tend to be used on booster engines due to their lower efficiency, staged-combustion engines can fill both roles at the cost of greater complexity, and expander engines are exclusively used on upper stages due to their low thrust
6.1 Gas Generator
The gas generator is used to drive the turbo by a gas flow. The gas generated produces this energy by pre-burning some amount of liq. Fuel. Use of Gas generator aligned with Turbo pump increases the efficiency of this engine.
6.2 Turbo Pumps
The working of this engine is very easy to understand as it does not involve any complicated cycles or any reciprocating mechanism. The fuel from tanks is firstly passed through the turbo pumps which rotates at a speed of about 14000 rpm by which the mass flow rate of fuel increases to about 2.4 tons before reaching the combustion chamber.
6.3 Injector
Injector plays the most key role in the rocket engine it is like heart of the engine that pumps out the appropriate amount of fuel from the turbo pump to the combustion chamber as per requirement. Injector ensures the stability of the combustion chamber therefore deigning of injector is the most challenging part of the designs department of cryogenic engine even today. The frequency of the combustion chamber is to be maintained between 100-500 cycles per second. If this rate is affected even slightly shifted above or below leads to the failure of engine which has been seen in tragedy of ‘Discovery Spacecraft’. But if injector is so designed to increase the specific impulse more than 700 Space crafts can travel much long distances in the universe. Injector is the only component of this engine which is still under construction yet.
6.4 Combustion Chamber
Finally, when this finely distributed fuel droplets enter the thrust chamber at such high velocities & at their cryogenic temperatures they colloid to each other in the trust chamber, this reaction at such specific conditions increases the pressure of chamber to about 250 bars with a release of huge amount of thrust which is more than 15000 lb. This high amount of trust is then manipulated bay narrow opening towards the nozzle. The opening is kept narrow to follow law of rate of discharge which states that ‘velocity is inversely proportional to area’. By this technique we get the desirable amount of thrust which helps a space craft to achieve its escape velocity. Due this reaction in continues period the temperature of Combustion Chamber as well as nozzle raises up to 3000-4000°C. To withstand such an elevated temperature for extended period of time without any deformation a cooling Jacket is required.
6.5. Cooling Jacket
Cooling Jacket is the necessity of this engine but this facility is provided by the fuel of the engine itself so no external energy is to be used. The mechanism usually used in cooling jackets is active cooling. In this Technique, the cooling jacket is made such that a flow if liq. Proponents is passed through the tubes provided from between the jackets. The liq. propellant passed are already at their cryogenic temperature so provide a very effective cooling. This simple mechanism permits the. Use of this technology throughout its journey without any deformation in Combustion chamber or Nozzle. When all these components work in their perfect algorithm, only then we can achieve our goal a successful launch of a space vehicle for its space mission.
6.6. NOZZLE
The pressure generated in combustion chamber can be used increased thrust by acceleration of combustion gas to high supersonic velocity. Nozzle generally passes parabolic enters. Because when high velocity gases entrance and at exit of the nozzle, pressure of exhaust gas increases with high value and hence velocity and hence velocity reduces
Fig:- Contruction of Rocket Engine
7. WORKING
Cryogenic Engines are rocket motors designed for liquid fuels that must be held at very low “cryogenic” temperatures to be liquid – they would otherwise be gas at normal temperatures. Typically, Hydrogen and Oxygen are used which need to be held below 20°K (-423°F) and 90°K (- 297°F) to remain liquid. The engine components are also cooled so the fuel doesn’t boil to a gas in the lines that feed the engine. The thrust comes from the rapid expansion from liquid to gas with the gas emerging from the motor at very high speed. The energy needed to heat the fuels comes from burning them, once they are gasses. Cryogenic engines are the highest performing rocket motors. One disadvantage is that the fuel tanks tend to be bulky and require heavy insulation to store the propellant. Their high fuel efficiency, however, outweighs this disadvantage. The Space Shuttle’s main engines used for liftoff are cryogenic engines. The Shuttle’s smaller thrusters for orbital maneuvering use non-cryogenic hypergolic fuels, which are compact and are stored at warm temperatures. Currently, only the United States, Russia, China, France, Japan and India have mastered cryogenic rocket technology. The cryogenic engine gets its name from the extremely cold temperature at which liquid nitrogen is stored. Air moving around the vehicle is used to heat liquid nitrogen to a boil. Once it boils, it turns to gas in the same way that heated water forms steam in a steam engine. A rocket like the Ariane 5 uses oxygen and hydrogen, both stored as a cryogenic liquid, to produce its power. The liquid nitrogen, stored at -320 degrees Fahrenheit, is vaporized by the heat exchanger. Nitrogen gas formed in the heat exchanger expands to about 700 times the volume of its liquid form. This highly pressurized gas is then fed to the expander, where the force of the nitrogen gas is converted into mechanical power
Fig:- Working Principle of Cryogenic Rocket Engine
WHY HIGH EFFICIENCY?
According to Newtonian third law of mechanics: ‘Action and Reaction are equal and opposite in direction’. Rocket engine operates through force of its exhaust pushing it backwards. Thrust is in opposite direction and more efficient in lower atmosphere or vacuum (sometimes). It makes the use of liquid oxygen as an oxidizer and liquid hydrogen as fuel. Pure liquid oxygen as oxidizer operates significantly at hotter combustion chambers due to which extremely high heat fluxes are produced which is not available in any jet engines.
Fig:- Propultion Efficiency Curve
8.ADVANTAGES
Storable liquid stages of PSLV and GSLV engines used presently release harmful products to the environment.
The trend worldwide is to change over to eco-friendly propellants. Liquid engines working with cryogenic propellants (liquid oxygen and liquid hydrogen) and semi cryogenic engines using liquid oxygen and kerosene are considered relatively environment friendly, non-toxic and non corrosive. In addition, the propellants for semi-cryogenic engine are safer to handle & store. It will also reduce the cost of launch operations.
This advanced propulsion technology is now available only with Russia and USA. India capability to meet existing mission requirements. The semi cryogenic engine will facilitate applications for future space missions such as the Reusable Launch Vehicle, Unified Launch Vehicle and vehicle for interplanetary missions.
(1)High Specific Impulse.
(2)Non-toxic and non-corrosive propellants.
(3)Non-hypergolic, improved ground safety
9. DISADVANTAGES
(1) Low density of liquid Hydrogen-More structural mass.
(2)Low temperature of propellants -Complex storage.
(3)Transfer systems and operations.
(4)Hazards related to cryogens.
(5)Overall cost of propellants relatively high
(6) Need for ignition system.
Drawbacks of Cryogenic Propellants
- Highly reactive gases
Cryogens are highly concentrated gases and have a very high reactivity. Liquid oxygen, which is used as an oxidizer, combines with most of the organic materials to form explosive compounds. So lots of care must be taken to ensure safety.
- Leakage
One of the most major concerns is leakage. At cryogenic temperatures, which are roughly below 150 degrees Kelvin or equivalently (-190) degrees Fahrenheit, the seals of the container used for storing the propellants lose the ability to maintain a seal properly. Hydrogen, being the smallest element, has a tendency to leak past seals or materials.
Hydrogen can burst into flames whenever its concentration is approximately 4% to 96%. It is hence necessary to ensure that hydrogen leak rate is minimal and does not present a hazard. Also there must be some way of determining the rates of leakage and checking whether a fire hazard exists or not. The compartments where hydrogen gas may exist in case of a leak must be made safe, so that the hydrogen buildup does not cause a hazardous condition.
10. NEXT GENERATION CRYOGENIC ENGINE
If things go as planned, the Indian Space Research Organization (ISRO) will flight-test the semi-cryogenic engine, which uses refined kerosene as propellant, by 2021. With the success of the Geosynchronous Satellite Launch Vehicle Mk-III (GSLV Mk-III), ISRO’s Liquid Propulsion Systems Centre (LPSC) here at Valiyamala is now focusing on the next level – the development of the much-delayed semicryogenic technology. Unlike the cryogenic engine which uses a combination of liquid hydrogen (LH2) and liquid oxygen (LOX) as propellant, the semi-cryogenic engine replaces liquid hydrogen with refined kerosene (Isrosene as ISRO calls it). LOX will be retained as oxidizer.“Various tests are in progress on the engine. Of the four turbo pumps in it, three have undergone tests at the ISRO Propulsion Complex, Mahendragiri. We plan to have the engine ready by 2019 end, the stage by 2020-end and the first flight by 2021,’’ S Somanath, director, LPSC, said. LPSC had developed the cryogenic engine for the GSLV Mk-II and the much powerful one for the GSLV Mk-III. The idea is to replace the second stage of the GSLV Mk-III, which now uses a liquid stage, with the semi-cryo. The rocket will retain the cryogenic upper, third stage. The advantage of inducting the semi-cryogenic stage is the payload capacity of the GSLV Mk-III will increase from four tonnes to six tonnes. Using refined kerosene as fuel has quite a few advantages: It is eco-friendly and cost-effective.
Generally any rocket engine burns their respective fuels to generate the thrust. If any other engine has capacity to generate thrust efficiently then it can be called rocket engine. Currently NASA scientists are working on ‘Xenon Ion Engine’ which accelerates the ions or atomic particles to extremely high to create thrust more effectively and efficiently by usage of electrostatic or electromagnetic force by the principle of Lorentz force or Columbian force.
Fig:- Xenon Ion Engine
11. CONCLUSION
Cryogenic propellants in liquid rocket engine provide high specific impulse which is suitable for use in rocket upper and booster stages. Also, while comparing Rocket engine with jet engine, thrust produced in rocket engine is outwards and that in the jet engine is inwards. Hence this efficiency cannot be achieved by any other engine. From the analysis result it is found that cryogenic rocket engine with the propellant combination of LH2/LOX is suita
Khageswar Badamundi 