26-09-2013, 04:44 PM
Seminar Report on CRYOGENIC ENGINE IN ROCKET PROPULSION
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What is Cryogenics ?
Cryogenics is the study of the production of extremely cold temperatures. This field of science also looks at what happens to a wide variety of materials from metals to gases when they are exposed to these temperatures. Cryogenics is a branch of physics concerned with the production of very low temperatures and the effects of these temperatures on different substances and materials. The temperatures studied in cryogenics are those below -243.67 degrees Fahrenheit (120 Kelvin); such low temperatures do not occur in nature.
These low temperatures have been used to liquefy atmospheric gases like oxygen, hydrogen, nitrogen, methane, argon, helium, and neon. The gases are condensed, collected, distilled and separated. Methane is used in liquid natural gas (LNG), and oxygen, hydrogen and nitrogen are used in rocket fuels and other aerospace and defense applications, in metallurgy and in various chemical processes. Helium is used in diving decompression chambers and to maintain suitably low temperatures for superconducting magnets, and neon is used in lighting.
CRYOGENIC ENGINE INTRODUCTION
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.
CRYOGENIC LIQUIDS:
Another use of cryogenics is cryogenic fuels. Cryogenic fuels, mainly liquid hydrogen, have been used as rocket fuels. Liquid oxygen is used as an oxidizer of hydrogen, but oxygen is not, strictly speaking, a fuel. For example, NASA's workhorse space shuttle uses cryogenic hydrogen fuel as its primary means of getting into orbit, as did all of the rockets built for the Soviet space program by Sergei Korolev. (This was a bone of contention between him and rival engine designer Valentin Glushko, who felt that cryogenic fuels were impractical for large-scale rockets such as the ill-fated N-1 rocket spacecraft.)
Russian aircraft manufacturer Tupolev developed a version of its popular design Tu-154 with a cryogenic fuel system, known as the Tu-155. The plane uses a fuel referred to as liquefied natural gas or LNG, and made its first flight in 1989.
Cryogenics In Space
Cryogenics is the study of low temperatures, from about 100 Kelvin (-280 Fahrenheit) down to absolute zero. In more detail, cryogenics is:
the study of how to produce low temperatures;
the study of what happens to materials when you've cooled them down.
Cryogenics is not: the study of freezing and reviving people, called "cryonics", a confusingly similar term.
What is Cryogenic Engineering
Cryogenic Engineering is a branch of engineering that utilizes cryogenics for various domestic, commercial, industrial, scientific, medical, aerospace and defense applications. For example, the Ground Support Systems at Kennedy Space Center for the Ares-I and Ares-V rockets in support of the NASA manned space program. Another is the DOE's Office of Electric Transmission and Distribution to develop advanced cryogenic refrigeration systems for cooling the next generation of electric power equipment based upon high-temperature superconductors. Cryogenic engineering plays an important role in unmanned aerial vehicle systems, infrared search and track sensors, missile warning receivers, satellite tracking systems, and a host of other commercial and military systems.
CRYOGENIC FUELS/PROPELLANT
In a cryogenic propellant, the fuel and the oxidizer are in the form of very cold, liquefied gases. These liquefied gases are referred to as super cooled as they stay in liquid form even though they are at a temperature lower than the freezing point. Thus we can say that super cooled gases used as liquid fuels are called cryogenic fuels.
These propellants are gases at normal atmospheric conditions. But to store these propellants aboard a rocket is a very difficult task as they have very low densities. Hence extremely huge tanks will be required to store the propellants. Thus by cooling and compressing them into liquids, we can vastly increase their density and make it possible to store them in large quantities in smaller tanks. Normally the propellant combination used is that of liquid oxygen and liquid hydrogen, Liquid oxygen being the oxidizer and liquid hydrogen being the fuel. Liquid oxygen boils at 297oF and liquid hydrogen boils at 423oF.
Components
The major components of a cryogenic rocket engine are: combustion chamber (thrust chamber), pyrotechnic igniter, fuel injector, fuel cryopumps, oxidizer cryopumps, gas turbine, cryo valves, regulators, the fuel tanks, and rocket engine nozzle. In terms of feeding propellants to combustion chamber, cryogenic rocket engines (or, generally, all liquid-propellant engines) work in either an expander cycle, a gas-generator cycle, a staged combustion cycle, or the simplest pressure-fed cycle.
Oxidizer system
The Low Pressure Oxidizer Turbopump (LPOTP) is an axial-flow pump driven by a six-stage turbine powered by liquid oxygen. It boosts the liquid oxygen's pressure from 0.7 to 2.9 MPa (100 to 420 psi). The flow from the LPOTP is supplied to the High-Pressure Oxidizer Turbopump (HPOTP). During engine operation, the pressure boost permits the High Pressure Oxidizer Turbine to operate at high speeds without cavitating. The LPOTP operates at approximately 5,150 rpm. The LPOTP, which measures approximately 450 by 450 mm (18 by 18 inches), is connected to the vehicle propellant ducting and supported in a fixed position by the orbiter structure.
Pre-burners and thrust control system
The oxidizer and fuel preburners are welded to the hot-gas manifold. The fuel and oxidizer enter the preburners and are mixed so that efficient combustion can occur. The augmented spark igniter is a small combination chamber located in the center of the injector of each preburner. The two dual-redundant spark igniters, which are activated by the engine controller, are used during the engine start sequence to initiate combustion in each preburner. They are turned off after approximately three seconds because the combustion process is then self-sustaining. The preburners produce the fuel-rich hot gas that passes through the turbines to generate the power to operate the high-pressure turbopumps. The oxidizer preburner's outflow drives a turbine that is connected to the HPOTP and the oxidizer preburner pump. The fuel preburner's outflow drives a turbine that is connected to the HPFTP.