Engine or Motor....... which is it?????

[jinman]

</font><font color="blue" class="small">( A jet engine is just that, an engine. )</font>

So that raises another point. Does a jet engine get it's thrust by sucking or blowing? I'm not talking about a fanjet. /forums/images/graemlins/smile.gif

 

[em14]

The incoming air supports the combustion which occurs with the ignition of the fuel. The expanding gas exits the combustion chamber and away it goes. Therefore, I would say the "Blowing" createby the expanding gas is the thrust.
Leo

 

[TresCrows]

A jet engine like any combustion engine is really just an air pump. A modern fanjet such as would be seen on all newer airliners identified by the large turbine intake and huge multibladed fan derives the majority of its thrust from that huge fan. Yep, that big fan is an efficient propeller. Depending on the bypass ratio more than 70% of the thrust comes from the fan and the remainder from the expanding gas as thrust. The hot section has a series of turbines that drive the fan through a gearbox and drive shaft, they absorb the energy of the escaping gas turning it into rotating motion to drive the fan and a compressor section. A turbojet has a much smaller fan which acts as a compressor, fanjets have a compressor section behind the huge fan as well, anyway, they derive their thrust from the escaping gas primarily. These are the familiar engines such as seen on older fighter jets such as the F104 Starfighter etc. Modern supersonic aircraft use a plenum that actually slows the incoming air to less than sonic speed and have a smaller bypass section than a typical airliner would have but they are nonetheless fanjet engines. It gets kinda complicated but just consider that one of the engines on a triple seven (twin engine) airliner makes more power than a sizeable city, more power than that which drives the fastest aircraft carriers and it does it effortlessly for thousands of hours with near perfect reliability. That is thousands and thousands of horsepower /forums/images/graemlins/shocked.gif. J

 

[Old_Hickory]

Explain how a rocket engine gets its thrust in 0 gravity...I think I know but I would like to hear your or anyone elses explanantion.

 

[Egon]

For every reaction there is an oposite and equal reaction.

In space the rocket motors/engines are a self contained unit. Releasing the propellent releases energy. The ejected propelant has mass. The rocket has mass. One mass reacts to the other mass.

Now, come on someone; put it in proper terms to explain it properly eehh.
Egon

 

[Egon]

It gets it's thrust by adding energy via the combustion of fuel which has mass and is ejected. Fan jets are very well explained on another post.

Egon

 

[RobS]

Some good explanations here. If I correctly recall some of my college days an engine, or heat engine, is converting heat energy to motion. The heat can be internally or externally generated which explains the steam engine. Internal combustion engines generate the heat within the cylinder. The real power of a heat engine is not pressure or an explosion, it is the transformation of heat energy. The hot combustion gasses give up energy to the piston as they expand during the power stroke. As hot as the exhaust may seem, it has given up substantial heat before it leaves the cylinder. In a steam engine, the steam comes in as "superheated steam" and gives up energy as it expands in the cylinder. It leaves as "normal steam/water" although still plenty hot. Very simplistically, the power of a heat engine can be calculated by knowing the high temperature of the hot gasses and the low temperature of the exhausted products. That difference is the energy potential the engine is working with. Turbochargers work to reclaim even more available heat.

A motor is using energy generated elsewhere and not heat energy. Compressed air, pressurized oil, electicity all have an energy potential that is released in the motor.

Back to tractors... at the Farm Progress Show this year, the Smithsonian had a dispay including an International tractor with a gas turbine engine. Fascinating machine and yes, an engine /forums/images/graemlins/smile.gif

 

[GaryM]

Stand on a wagon with low friction wheels and on a level surface. Arm yourself with a large basket of baseballs. Throw the baseballs off the back of the wagon and the wagon, with you on board, will travel in the opposite direction. Now due to friction we can't eliminate this doesn't work too well, but it does illustrate the equal and opposite reaction. Works even better with a high pressure pump and a tank of water.

Gravity plays no part at all.

 

[TresCrows]

"Explain how a rocket engine gets its thrust in 0 gravity...I think I know but I would like to hear your or anyone elses explanantion. "

What would gravity have to do with it--nothing. I think you mean in the vaccum of space. A rocket engine carries an oxidizer and a fuel. The two react together just as does the air (oxidizer) and fuel (jet A etc) in a jet engine. The oxidizer and fuel are pumped into the combustion chamber by high speed turbo pumps. The oxidizer is usually something like liquid oxygen and the fuel could be liquid hydrogen. There are several liquid fuels and oxidizer other than those. Solid fuel rockets have a propellent "grain" cast which contains the fuel and the oxidizer together in a solid state. Black powder, a rocket fuel in fireworks etc uses potasium nitrate (commonly known in a lesser pure state as saltpeter) as the oxidizer and sulphur and finely powdered charcoal as the fuel. If you think about it in an odd sort of way, a firearm is a rocket engine. Yes, a Glock will fire in outer space, as will a .22 or a shotgun or whatever. J

 

[BIGUN]

For use in space they would have to change the warning on a box of .22 shells to, “CAUTION: RANGE - UMPTEEN MILLION MILES”. /forums/images/graemlins/shocked.gif