© 1998 Cetin BAL - GSM:+90  05366063183 - Turkey / Denizli 

Roket Engine

 

Launcher stages (lower stages)
A typical internal equipment complement for a launcher stage is shown in the view of the Ariane 5 first stage. This stage is a crogenic propellant rocket stage using liquid oxygen and liquid hydrogen as the chemical propellants. It essentially consists of two tanks mounted on top of each other (tandem tank arrangement) with a common bulkhead (lower bulkhead of oxygen tank serves as upper bulkhead of hydrogen tank), piping (both external and internal), the thrust generation system (vulcain engine), a pump-fed feed system supported to some extent by Helium tank pressurization. 

Ariane 5 first stage

Typical tank & piping configurations include (see figure below):
 

  • Tandem tanks (with external piping)
     
  • Tandem tanks with common bulkhead (with internal piping)
     
  • Concentric tanks
  • Parallel tanks
     

Typical tank arrangements launcher stages

Through mechanical deflection of engine or nozzle, the direction of the thrust can be changed. Most launcher stages nowadays use mechanical deflection of (part of) the motor to allow for pitch and yaw control during propelled flight. Roll control is than accomplished by a set of 2-4 non-vectorable motors that thrust in circumferential direction. The next figure shows some ways of mechanical deflection of a liquid rocket engine.

 


The Ariane 5 EPS L 9.7 stage propulsion system, see fig. below, has a total stage mass of 11 tons (t) of which 9,7 t. propellant (3,2 t. MMH fuel and 6,5 t. NTO oxidizer). Its dimensions are height 3,56 m and diameter 3,94 m. EPS dry mass is 1,15 t.  The main propulsion system consists of a single 27,5 kN Aestus engine (110 kg dry mass), 4 cylindrical (close to spherical) propellant tanks of diameter 1,410 m (length of cylindrical section is 0,4 D), and 2 He pressurant tanks (0,3 m3 @ 400 bar). The EPS attitude control system (SCA, Système de Contrôle d'Attitude) is designed to provide for spin stabilization. It consists of two spherical tanks containing 35 liter each, feeding six hydrazine thrusters to deliver a thrust of 400 N each. Of these 6 thrusters two are used for spin-up and two for spin-down. The remaining two are to allow tilting the spin axis.
 

Rocket Diagram

General rocket designs all contain the same elements. A rocket needs some form of propulsion to get it flying through the air. This can be anything from a simple toss of a model rocket by human force, to an engine that uses fuel to propel itself. The propulsion is created by two elements: Oxidizer and Fuel. The oxidizer and fuel tanks are located in different parts of the roket. They are forced through a pump down to the cumbustion chamber where they meet. The oxidizer and fuel ignite creating hot gasses that are squeezed out a nozel at the opposite end creating propulsion for the rocket. The outside of a rocket is very aerodynamic. It can very in length and comes to a point at the top. The top is called the 'nose' of the rocket and is very instrumental in the way the rocket flies.

Here are two different diagrams of rockets:

 

Turbopumps on rockets

Turbopumps are used on liquid-fuelled rockets to pressurise the fuel and oxidiser before they reach the combustion chamber. What powers the turbopumps (turbochargers on cars use the car exhaust for power, what does a rocket turbopump use)? — QuantumEleven 14:56, 17 August 2009 (UTC)


The turbopumps are powered by a preburner, which burns a small amount of fuel and oxidizer to run the turbopumps. In the picutre, the preburner is number 6. The preburner provides hot gas to run the turbine (number 5), which drives the turbopumps (numbers 3 and 4). anonymous6494 15:25, 17 August 2009 (UTC)


(ec) There's a fairly extensive discussion in this page linked from our article. For cryogenic fuels and oxidizers (liquid oxygen, liquid hydrogen), some pumps can be driven simply by heating the liquid to ambient temperature or above and allowing the expanding gas produced to drive the turbine. With other fuels, a preburner can be used which combines fuel and oxidizer to generate a small amount of hot, pressurized gas. There are several variations on these themes, which offer different methods of preheating the fuels, and which vent the turbine exhaust in different ways. TenOfAllTrades(talk) 15:27, 17 August 2009 (UTC)


It depends on the design. Sometimes, the turbos are powered by a totally separate source (e.g. a battery or a small separate combustion engine). Other times, they tap off the main propulsion energy source, or use the decompression of a refrigerated fluid to power the pump. All of these scenarios have various advantages and disadvantages to the stability, robustness, and mass budget of the rocket. If mass and flight-time is not an issue, the probable best solution is an electric motor; but this requires a large battery (and suffers from scalability - large mass-flux rockets can't really work off an electric turbo pump) - so more often, the turbo either kicks in later or gets an electric start and eventually draws energy from the primary propulsion source. Nimur (talk) 16:56, 17 August 2009 (UTC)

 

Liquid propellant rocket engines

Liquid propellant rocket engines use a liquid fuel (such as liquid hydrogen or kerosene) and liquid oxidiser (such as liquid oxygen).These are stored in separate tanks and then pumped into the combustion chamber as required. As they are sprayed into the combustion chamber through injection nozzles, they rapidly mix together and react before being ejected.

One advantage of a liquid fuel system is that the amount of thrust can be controlled. This is done by limiting how quickly the fuel is pumped into the combustion chamber.

The three main engines on the tail of the Space Shuttle orbiter are liquid fuel rocket engines. The external tank (ET) is the big orange tank and contains two separate storage tanks – one containing liquid hydrogen and one containing liquid oxygen.

The hydrogen and oxygen are pumped to the three main engines. They are sprayed into a combustion chamber where the hydrogen reacts with the oxygen to form gaseous water. It is the high-speed ejection of this gaseous water that produces the thrust.

Each main engine produces a thrust of 1.8 MN (1.8 million N). It does this by reacting 1340 litres of propellant each second and ejecting the gaseous water at a speed of 3560 m/s (12 800 km/h).

 

CHEMICAL ROCKET LAUNCHER

Gas heated by a chemical reaction provides thrust. Cargo transported by rockets is called payload. The ratio of cargo mass to the total mass of the rocket including its cargo and propellant is called payload fraction. Its value ranges from 6 percent for liquid propellant rockets to 0.2 percent for solid propellant rockets. The minimum mass is 10 tons.

DETAILS

If we ignore gravity and aerodynamic drag, the final velocity of a rocket equals:

 

V = (exhaust_gas_velocity) natural_logarithm (cargo_mass / total_mass)

The total_mass includes structural parts, propellant, and cargo. According to the above formula, which is know as the rocket equation, a high velocity of exhaust gas is needed to launch massive cargo. Rocketeers often talk of specific impulse, which is measured in seconds and is proportional to the exhaust gas velocity. A specific impulse of one second corresponds with the exhaust gas velocity of 9.8 m/s. The maximum velocity of the exhaust gas is about twice its speed of sound:

Umax = A0(2/(G-1))0.5

where:
A0 is the initial speed of sound of the exhaust gas
G is the ratio of specific heat at constant pressure to specific heat at constant volume

The high exhaust gas velocity calls for a hot gas having low molecular mass. The extreme temperature of the exhaust gas is the main cause of the high cost and high failure rate of rocket launchers. To maximize the specific impulse, some researchers attempt to build rockets propelled by pure hydrogen heated either by electric current, or a laser, or microwaves, or a nuclear reactor.

There are five types of chemical rockets:

  1. Liquid propellant rockets burn a mixture of liquid fuel and liquid oxidizer, e.g., hydrogen and oxygen. They have a high specific impulse (350-540 seconds) but require expensive turbopumps to feed fuel and oxidizer at a high pressure to the combustion chamber. The thrust-to-weight ratio of the Space Shuttle main engine is about 70. Russian NK-33 engine's thrust-to-weight ratio is approximately 125.

     

    Profile of liquid propellant rocket engine

 

Rocket engine

 Okay guy's, I am back and this time it's going to be the rocket engine just like I had mentioned in my previous post. Okay, so a rocket engine huh? It must be freaking you out because it's supposed to  be one of the most complex pieces of engineering made by mankind. We'll its complex no doubt, but am going to make it super simple(I did my best guy's)! In very simple words a rocket engine is a jet engine who's complexity is ten folds, so I think going through the description of the jet engine would probably give you a basic idea about a\what a rocket engine is.

 
1) Description: A rocket engine is very similar to the jet engine and  works on the same principle, but                            yet is very different. A rocket engine is capable of producing thrust which is almost equivalent                                        to the thrust produced by 50 jumbo jets, yes it's that powerful. It uses cryogenic liquid 
                       hydrogen as fuel(which is one of the coldest liquids present) and liquid oxygen as the oxidizer.
                       Although these liquids are one of the coldest liquids around, when they combine in the 
                       combustion chamber they go through an intense reaction which produces temperatures of 
                       above 3330 C. The fuel and the oxidizer are known as the propellants and they form a high 
                       speed propulsive jet. The rocket engine basically works by throwing stuff out of the back(In 
                       this case propellant mass), literally. The rocket engine is divided into 7 main parts:

 
                       a) Oxidizer system
                       b) Fuel system
                       c) Pre-burners
                       d) Main combustion chamber
                       e) Nozzle
                       f) Controller
                       g) Helium system

 
                       
                       
 

 
                       These components form a part of the Space shuttle main engine(SSME). Now I will be 
                       explaining to you the different components in the easiest way possible. This might get a little 
                       boring, so you can jump right into it's working if you find this uninteresting.

 
                       a) Oxidizer system: The oxidizer system consists of a Low pressure oxidizer turbopump 
                                                     (LPOT) and a high pressure oxidizer turbopump(HPOT). Don't worry, 
                                                     these are just fancy terms, there basic function is to increase the pressure
                                                      of the oxygen which is the oxidizer. High pressures, allow the high 
                                                     pressure oxidizer turbines to operate without cavitating(cavitating is 
                                                     basically the formation of liquid free zones).

 
                       b) Fuel system: The fuel system consists of a low pressure hydrogen turbopump(LPHTP) 
                                               and a high pressure hydrogen turbopump(HPHTP). The increase in pressure 
                                               of hydrogen by the LPHTP permits the HPHTP to operate at high speeds 
                                               without cavitating. The hydrogen from the HTHTP is seperated and directed 
                                               into three pathways. The first pathway of hydrogen is towards the walls of the
                                               combustion chamber to cool it down. the second flow is directed towards 
                                               low pressure fuel turbopump in the combustion chamber to turn its 
                                               turbines. The first flow is directed to the liquid hydrogen tank to maintain 
                                               pressure. Another part of this flow(Not included in the above three) is a
                                               combined flow of the oxidizer and fuel towards the preburner.
                       
                        c) Preburners: Here the fuel and oxidizer are mixed for efficient combustion. There are 
                                              fuel injectors passing out fuel at whose mouth a spark plug is present the 
                                              ignite the mixture. The spark plug is kept on for a few seconds until this 
                                              process of ignition becomes self sustaining. Its main function is to provide fuel-
                                              rich gases for the turbines to generate power to operate the high pressure 
                                              turbopumps.

 
                        d) Combustion chamber: The combustion chamber receives fuel-rich hot gases. The 
                                                               gaseous fuel enters the combustion chamber through the fuel 
                                                               injector which mixes the propellants(hydrogen and oxygen).
                                                               A spark plug ignites the mixture here as well, and is kept on for 
                                                               about three seconds till this procedure becomes self sustaining.
                                                               The shell of the combustion chamber is made of copper-silver-
                                                               zirconium alloy to withstand the extreme tempertures of 3,315°C
                                                               which is higher than the boiling point of iron.

 
                        e) Nozzle: The nozzle is the part of the main engine, through which the exhaust gases shoot out.
                                       The rim of the nozzle is angled and due to this the pressure of the gases increase at 
                                        rim of the nozzle just before it leaves the rocket increasing the force at which the 
                                        gases shoot out. The walls of the nozzle is lined with brazed stainless steel cooling 
                                        passages through which liquid hydrogen is passes which acts as a coolant.

 
                        f) Controller: Each engine is equipped with a main engine controller which controls all functions 
                                           of the engine. The controllers are designed to be tough enough to withstand the 
                                           force of launch and are extremely resilient to damage.

 
        
                       g) Helium system: The main engine controller operates five main propellant valves which can be 
                                                  fully closed by using the engine's helium system as a back-up in case of an 
                                                  emergency.

 
                                                  
                                               

 
2) Working: The working of a rocket engine is a very similar to the working of jet engine. The rocket uses 
                   propellant mass to produce a high speed propulsive jet. The liquid hydrogen and liquid oxygen is turned gas  
                    and is passed on into the combustion chamber. The fuel(hydrogen) is mixed with the oxidizer
                    (oxygen) through the fuel injectors. The mixture of hydrogen and oxygen is ignited using a spark 
                    plug producing high temperatures(3,315 °C). This burning hot propulsive gas turns the turbines which 
                    in turn generates power for operating the high pressure turbopumps. The gas them passes on to the 
                    nozzle which further increases its pressure releasing the propulsive jet with tremendous force producing
                    very high amounts of thrust(1,890 kN) pushing the rocket upwards.

 
                    
                   
*The rocket engine is a type of jet engine.

 
3) Uses: a) Rocket engines are used during space shuttle lift-off's for producing extreme amounts of thrust. 
             b) Rocket engined are used in space exploration shuttles.

 

 

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 © 1998 Cetin BAL - GSM:+90  05366063183 -Turkiye/Denizli 

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