Of the mechanisms that we have seen until now, all are to facilitate the work to us but in all we must develop some work so that it works. Now we are going to use an energy source so that the man as soon as it uses his energy for the sake of obtaining a work in a Machine. The energy that we are going to contribute will be of the thermal type, that is we are going to use a fuel to generate heat. The Thermal Machines, therefore, are going to turn the thermal energy into mechanical energy.
- If the combustion becomes outside the motor (the one that generates the work) is called Machine of external burning as the steam engine
- If the combustion becomes within the motor is called Machine of internal combustion (the motor of the car)
The steam engine
Although as soon as one is used at present, very educative to be understood how the thermal energy I could become mechanical energy.
To the left we have the furnace in charge to burn the fuel, that is generally coal. The boiler that has been containing the water for of pot under pressure and therefore the steam leaves by the exit valve to enter by the valve of entrance of the cylinder.
The entrance valve opens required time so that the steam pushes the piston the right moving the wheel by means of the system connecting rod-crank.
When it has arrived at the right part, the inertia of the wheel causes that the piston to the left part backs down, opening the valve of exit and passing the aqueous vapour (already without energy) to the condenser.
The condenser is as a deposit where it enters the water and it is cooled by a circuit of external water so that the water that enters of the cylinder leaves in liquid state.
The liquid water enters the boiler again and the cycle is repeated.
|Internal combustion engines. We will see the first gasoline motor of 4 times|
This it is the first time of a complete phase of the gasoline motor. As its name indicates, it is the phase where the cylinder fills of the mixture air-gasoline.
The admission valve is opened so that the mixture can enter air-gasoline. As the piston is lowering, it produces an empty intern who facilitates the entrance in all the camera.
When the piston is in the low zone, the valve closes and finishes 1 time.
|2. Compression. In this time the two valves are closed and the piston begins to raise compressing all the mixture. The pressure is maximum when the piston is almost in the high point but. To comment that when increasing the pressure, the temperature of the mixture has increased considerably. We do not want that the mixture explodes of spontaneous form because it is the spark plug that must issue the order. For that reason to the gasoline lead was added to him (replaced now by another component less polluting)|
|3. Explosion and expansion: Just before the piston arrives at the point superior and with the mixture at high pressure and temperature, the spark plug receives the order and it sends a spark to the mixture. The explosion brings about the reduction of the piston with the accomplishment of the work of the motor. This it is the only moment where the motor contributes work. The first image represents the explosion and 2 the expansion, where the work is realised|
|4 Escape. Once the piston has arrived at the part inferior, it is moment for expelling burned gases. For it, the escape valve is opened and the one of entrance stays closed. According to the piston raises, all the gases are evacuated, using later the exhaust pipe to remove them from the motor||We want to add this image where one is the 4 times. It observes as it incorporates some elements or seen as the connecting rod-crank or the levy that commands the opening of the valves|
We can explain as the diesel engine works, although is very similar to the one of gasoline. The fundamental difference is that in this motor it does not exist spark plugs and the explosion takes place by compression of the mixture air-diesel oil
Before entering the motors of the airplane, he would be interesting to understand one of the laws of Newton on the action-reaction. 3 law of Newton says us that all action has reaction, or what formally this one is due to say that If a body acts on another one with a force (action), reacts against that one with another force of equal value and direction, but of opposite sense (reaction).
In the field of aviation, this is translated that when in a body in balance an exit takes place ofgases on the one hand and those gases have a mass, on the other felt is a push that will be equal to the mass by the speed of exit, that is
m1 * v1 = m2 * v2
In the case of the rocket, the mass of the gases (m1) multiplied by the speed to which they leave the rocket is equal to the mass of the rocket by the speed at which it moves
Several types of motors for airplanes exist that use the action-reaction principle. We are going to see two of them, the Turbojet and they turbofan
One is made up of two parts. The cold Section and I warm up it. In first the air intake takes place that is pushed the combustion chamber by means of the compressor (metallic plates which they push the air when rotating on the main axis).
Those small plates of the compressor, calls blades, cause that the air is compressed and increased its temperature.
In the combustion chamber it is mixed with kerosene to produce the explosion. The explosion causes that the gases leave the combustion chamber at a high speed, happening through other blades of the turbine and later through the exhaust nozzle. Thanks to these gases the push of the airplane takes place.
We have seen before the gases before leaving by the escape, move some blades of the turbine. The turbine rotates the main axis and this one moves the compressor and system of admission of the entrance.
In this type of reactor we can emphasize the following components
- Ventilator: From its name comes here since fan means ventilator. It is located to the entrance of the motor. The air intake divides it in two flows, primary and secondary. The primary current is going away to use in the combustion once it is compressed by the compressors
- Compressors: Metallic disc system that through diverse stages and turning in the same sense that the ventilator, compresses and increases the temperature of the air.
- Combustion chamber: After the stage of compression and with the air to a pressure 30 times superior and a temperature on the 600
- °C, mixes with kerosene, taking place a great explosion.
- Turbines: The gases that leave the combustion chamber to about 1100 C now happen through the blades of the turbine, doing to turn their axis (the same that moves the compressor). Variants exist that we are not going to consider in this subject Escape:
After the turbine the gases are expelled by the nozzle by the part from back from the motor. As the nozzle has conical form, the gases are accelerated here to their exit and of the push that takes place in the motor. Another part of the push comes from the secondary air flow that to the compressed being and soon accelerated when coming out produces another part of the energy of push of the motor.