Wanted...mobile phone ...subject matter ends way o

Monster-Mat · June 17, 2003

Internal Combustion

To understand the basic idea behind how a reciprocating internal combustion engine works, it is helpful to have a good mental image of how "internal combustion" works. One good example is an old Revolutionary War cannon. You have probably seen these in movies, where the soldiers load the cannon with gun powder and a cannon ball and light it. That is internal combustion, but it is hard to imagine that having anything to do with engines.

A more relevant example might be this: Say that you took a big piece of plastic sewer pipe, maybe 3 inches in diameter and 3 feet long, and you put a cap on one end of it. Then say that you sprayed a little WD-40 into the pipe, or put in a tiny drop of gasoline. Then say that you stuffed a potato down the pipe.

I am not recommending that you do this! But say you did... What we have here is a device commonly known as a potato cannon. When you introduce a spark, you can ignite the fuel. What is interesting, and the reason we are talking about such a device, is that a potato cannon can launch a potato about 500 feet through the air!

The potato cannon uses the basic principle behind any reciprocating internal combustion engine: If you put a tiny amount of high-energy fuel (like gasoline) in a small, enclosed space and ignite it, an incredible amount of energy is released in the form of expanding gas. You can use that energy to propel a potato 500 feet. In this case, the energy is translated into potato motion. You can also use it for more interesting purposes. For example, if you can create a cycle that allows you to set off explosions like this hundreds of times per minute, and if you can harness that energy in a useful way, what you have is the core of a car engine!

Almost all cars currently use what is called a four-stroke combustion cycle to convert gasoline into motion. The four-stroke approach is also known as the Otto cycle, in honor of Nikolaus Otto, who invented it in 1867. The four strokes are :

Intake stroke

Compression stroke

Combustion stroke

Exhaust stroke

Fidgits · June 17, 2003

:D

Thanks Mat...

Monster-Mat · June 17, 2003

Two other things that are good to note:

There are different kinds of internal combustion engines. The gas turbine engine is another form of internal combustion engine. A gas turbine engine has interesting advantages and disadvantages, but its main disadvantage right now is an extremely high manufacturing cost (which means it costs more than the piston engine used in cars today).

There is such a thing as an external combustion engine. A steam engine in old-fashioned trains and steam boats is the best example of an external combustion engine. The fuel (coal, wood, oil, whatever) in a steam engine burns outside the engine to create steam, and the steam creates motion inside the engine. It turns out internal combustion is a lot more efficient (takes less fuel per mile) than external combustion, plus an internal combustion engine is a lot smaller than an equivalent external combustion engine. This explains why we don't see any cars from Ford and GM using steam engines.

Almost all cars today use a reciprocating internal combustion engine because this engine is:

Relatively efficient (compared to an external combustion engine)

Relatively inexpensive (compared to a gas turbine)

Relatively easy to refuel (compared to an electric car)

These advantages beat any other existing technology for moving a car around.

wildrnes · June 17, 2003

matt tell us about the ****el rotary engine

Monster-Mat · June 17, 2003

A rotary engine is an internal combustion engine, like the engine in your car, but it works in a completely different way than the conventional piston engine.

In a piston engine, the same volume of space (the cylinder) alternately does four different jobs -- intake, compression, combustion and exhaust. A rotary engine does these same four jobs, but each one happens in its own part of the housing. It's kind of like having a dedicated cylinder for each of the four jobs, with the piston moving continually from one to the next.

The rotary engine (originally conceived and developed by Dr. Felix ****el) is sometimes called a ****el engine, or ****el rotary engine.

Like a piston engine, the rotary engine uses the pressure created when a combination of air and fuel is burned. In a piston engine, that pressure is contained in the cylinders and forces pistons to move back and forth. The connecting rods and crankshaft convert the reciprocating motion of the pistons into rotational motion that can be used to power a car.

In a rotary engine, the pressure of combustion is contained in a chamber formed by part of the housing and sealed in by one face of the triangular rotor, which is what the engine uses instead of pistons.

The rotor follows a path that looks like something you'd create with a Spirograph. This path keeps each of the three peaks of the rotor in contact with the housing, creating three separate volumes of gas. As the rotor moves around the chamber, each of the three volumes of gas alternately expands and contracts. It is this expansion and contraction that draws air and fuel into the engine, compresses it and makes useful power as the gases expand, and then expels the exhaust.

Fidgits · June 17, 2003

:D

1000 posts..!!!!!

Monster-Mat · June 17, 2003

if anyone finds flaws in what im posting please point it out..... :D

anyone want to know anything else....... :)

is that enough in depth Mat wildrnes.........

rhaines · June 17, 2003

so...

Fidgits 11-April 03 1000 115 23.86%

Supracharged-IS340 26-November 01 3418 56 11.62%

rhaines 10-October 02 478 38 7.88%

wildrnes 21-July 02 948 24 4.98%

TonyGoose 10-December 01 567 23 4.77%

bazza 9-November 02 626 22 4.56%

Zee007 5-March 02 2169 22 4.56%

tony_hetherington 20-November 02 338 20 4.15%

pee.j 19-February 03 431 15 3.11%

Claire G 28-March 02 1283 10 2.07%

Fidgits · June 17, 2003

But thats over the last 24 hours....

Claire G · June 17, 2003

I'm in danger of slipping into obscurity if I don't keep posting...hey, I just want to stay on the list!

Fidgits · June 17, 2003

yeah... but you've done more than 11 over here :P

rhaines · June 17, 2003

It must be my multi-threaded personality :D :D :D

Anyway off to do some fitting :) Have to give myself something to post about :winky:

Zee007 · June 17, 2003

Ian - you have proved to be the fastest person EVER in the history of LOC to get to a 1000.... of which nearly 10% were posted today in half a dozen threads....

Fidgits · June 17, 2003

well ryan... don't forget to post pics... :D

wildrnes · June 17, 2003

Ian - you have proved to be the fastest person EVER in the history of LOC to get to a 1000.... of which nearly 10% were posted today in half a dozen threads....

that is insane

Monster-Mat · June 17, 2003

Ok this ones a biggy, get a hobnob and a coffee

TURBINES

A Little Background

There are many different kinds of turbines:

You have probably heard of a steam turbine. Most power plants use coal, natural gas, oil or a nuclear reactor to create steam. The steam runs through a huge and very carefully designed multi-stage turbine to spin an output shaft that drives the plant's generator.

Hydroelectric dams use water turbines in the same way to generate power. The turbines used in a hydroelectric plant look completely different from a steam turbine because water is so much denser (and slower moving) than steam, but it is the same principle.

Wind turbines, also known as wind mills, use the wind as their motive force. A wind turbine looks nothing like a steam turbine or a water turbine because wind is slow moving and very light, but again, the principle is the same.

A gas turbine is an extension of the same concept. In a gas turbine, a pressurized gas spins the turbine. In all modern gas turbine engines, the engine produces its own pressurized gas, and it does this by burning something like propane, natural gas, kerosene or jet fuel. The heat that comes from burning the fuel expands air, and the high-speed rush of this hot air spins the turbine.

Advantages and Disadvantages

So why does the American M-1 tank use a 1,500 horsepower gas turbine engine instead of a diesel engine? It turns out that there are two big advantages of the turbine over the diesel:

Gas turbine engines have a great power-to-weight ratio compared to reciprocating engines. That is, the amount of power you get out of the engine compared to the weight of the engine itself is very good.

Gas turbine engines are smaller than their reciprocating counterparts of the same power.

The main disadvantage of gas turbines is that, compared to a reciprocating engine of the same size, they are expensive. Because they spin at such high speeds and because of the high operating temperatures, designing and manufacturing gas turbines is a tough problem from both the engineering and materials standpoint. Gas turbines also tend to use more fuel when they are idling, and they prefer a constant rather than a fluctuating load. That makes gas turbines great for things like transcontinental jet aircraft and power plants, but explains why you don't have one under the hood of your car.

The Gas Turbine Process

Gas turbine engines are, theoretically, extremely simple. They have three parts:

Compressor - Compresses the incoming air to high pressure

Combustion area - Burns the fuel and produces high-pressure, high-velocity gas

Turbine - Extracts the energy from the high-pressure, high-velocity gas flowing from the combustion chamber

The compressor is basically a cone-shaped cylinder with small fan blades attached in rows. Then as the air is forced through the compression stage its pressure rises significantly. In some engines, the pressure of the air can rise by a factor of 30.

This high-pressure air then enters the combustion area, where a ring of fuel injectors injects a steady stream of fuel. The fuel is generally kerosene, jet fuel, propane or natural gas. If you think about how easy it is to blow a candle out, then you can see the design problem in the combustion area -- entering this area is high-pressure air moving at hundreds of miles per hour. You want to keep a flame burning continuously in that environment. The piece that solves this problem is called a "flame holder," or sometimes a "can." The can is a hollow, perforated piece of heavy metal.

Compressed air enters through the perforations.

At one end of the engine is the turbine section. Lets say there are two sets of turbines. The first set directly drives the compressor. The turbines, the shaft and the compressor all turn as a single unit:

At the far end of the engine is a final turbine stage, It drives the output shaft. This final turbine stage and the output shaft are a completely stand-alone, freewheeling unit. They spin freely without any connection to the rest of the engine. And that is the amazing part about a gas turbine engine -- there is enough energy in the hot gases blowing through the blades of that final output turbine to generate 1,500 horsepower and drive a 63-ton M-1 Tank! A gas turbine engine really is that simple.

In the case of the turbine used in a tank or a power plant, there really is nothing to do with the exhaust gases but vent them through an exhaust pipe, Sometimes the exhaust will run through some sort of heat exchanger either to extract the heat for some other purpose or to preheat air before it enters the combustion chamber.

The points made here are obviously simplified a bit. For example, I have not discussed the areas of bearings, oiling systems, internal support structures of the engine, stator vanes and so on. All of these areas become major engineering problems because of the tremendous temperatures, pressures and spin rates inside the engine. But the basic principles described here govern all gas turbine engines and help you to understand the basic layout and operation of the engine.

Other Variations

Large jetliners use what are known as turbofan engines, which are nothing more than gas turbines combined with a large fan at the front of the engine.

Imagine that the core of a turbofan is a normal gas turbine engine like the one described in the previous part. The difference is that the final turbine stage drives a shaft that makes its way back to the front of the engine to power the fan. This multiple concentric shaft approach, by the way, is extremely common in gas turbines. In many larger turbofans, in fact, there may be two completely separate compression stages driven by separate turbines, All three shafts ride within one another concentrically.

The purpose of the fan is to dramatically increase the amount of air moving through the engine, and therefore increase the engine's thrust. When you look into the engine of a commercial jet at the airport, what you see is this fan at the front of the engine. It is huge -- on the order of 10 feet (3 m) in diameter on big jets, so it can move a lot of air. The air that the fan moves is called "bypass air" because it bypasses the turbine portion of the engine and moves straight through to the back of the nacelle at high speed to provide thrust.

A turboprop engine is similar to a turbofan, but instead of a fan there is a conventional propeller at the front of the engine. The output shaft connects to a gearbox to reduce the speed, and the output of the gearbox turns the propeller.

Jet Engine Thrust

The goal of a turbofan engine is to produce thrust to drive the airplane forward. Thrust is generally measured in pounds in the United Kingdom (the metric system uses Newtons, where 4.45 Newtons equals 1 pound of thrust). A "pound of thrust" is equal to a force able to accelerate 1 pound of material 32 feet per second per second (32 feet per second per second happens to be equivalent to the acceleration provided by gravity). Therefore, if you have a jet engine capable of producing 1 pound of thrust, it could hold 1 pound of material suspended in the air if the jet were pointed straight down. Likewise, a jet engine producing 5,000 pounds of thrust could hold 5,000 pounds of material suspended in the air. And if a rocket engine produced 5,000 pounds of thrust applied to a 5,000-pound object floating in space, the 5,000-pound object would accelerate at a rate of 32 feet per second per second.

Thrust is generated under Newton's principle that "every action has an equal and opposite reaction." For example, imagine that you are floating in space and you weigh 100 pounds on Earth. In your hand you have a baseball that weighs 1 pound on Earth. If you throw the baseball away from you at a speed of 32 feet per second (21 mph / 34 kph), your body will move in the opposite direction (it will react) at a speed of 0.32 feet per second. If you were to continuously throw baseballs in that way at a rate of one per second, your baseballs would be generating 1 pound of continuous thrust. Keep in mind that to generate that 1 pound of thrust for an hour you would need to be holding 3,600 pounds of baseballs at the beginning of the hour. If you wanted to do better, the thing to do is to throw the baseballs harder. By "throwing" them (with of a gun, say) at 3,200 feet per second, you would generate 100 pounds of thrust.

In a turbofan engine, the baseballs that the engine is throwing out are air molecules. The air molecules are already there, so the airplane does not have to carry them around at least. An individual air molecule does not weigh very much, but the engine is throwing a lot of them and it is throwing them at very high speed. Thrust is coming from two components in the turbofan:

The gas turbine itself - Generally a nozzle is formed at the exhaust end of the gas turbine to generate a high-speed jet of exhaust gas. A typical speed for air molecules exiting the engine is 1,300 mph (2,092 kph).

The bypass air generated by the fan - This bypass air moves at a slower speed than the exhaust from the turbine, but the fan moves a lot of air.

As you can see, gas turbine engines are quite common. They are also quite complicated, and they stretch the limits of both fluid dynamics and materials sciences. If you want to learn more, one worthwhile place to go would be the library of a university with a good engineering department. Books on the subject tend to be expensive, but two well-known texts include "Aircraft Gas Turbine Engine Technology" and "Elements of Gas Turbine Propulsion."

Fidgits · June 17, 2003

Naaaa Tony... I just get a personalised flood message nowadays..

15 a day isn't that many though...

Monster-Mat · June 17, 2003

im assuming your all getting bored of the technical stuff now...............

but now you can all impress your mates down the pub

anyone for how a rocket works?............... :)

sorted avensis · June 17, 2003

If anyone finds flaws in what i'm posting please point it out

The bowline is a fixed loop not a running loop used by sailors

andyhart21 · June 17, 2003

:D

Monster-Mat · June 17, 2003

Space exploration is complicated because there are so many problems to solve and obstacles to overcome. You have things like:

The vacuum of space

Heat management problems

The difficulty of re-entry

Orbital mechanics

Micrometeorites and space debris

Cosmic and solar radiation

The logistics of having restroom facilities in a weightless environment

But the biggest problem of all is harnessing enough energy simply to get a spaceship off the ground. That is where rocket engines come in.

Rocket engines are, on the one hand, so simple that you can build and fly your own model rockets very inexpensively

On the other hand, rocket engines (and their fuel systems) are so complicated that only two countries have actually ever put people in orbit.

The Basics

When most people think about motors or engines, they think about rotation. For example, a reciprocating gasoline engine in a car produces rotational energy to drive the wheels. An electric motor produces rotational energy to drive a fan or spin a disk. A steam engine is used to do the same thing, as is a steam turbine and most gas turbines, as has been discussed in some earlier posts.

Rocket engines are fundamentally different. Rocket engines are reaction engines. The basic principle driving a rocket engine is the famous Newtonian principle that "to every action there is an equal and opposite reaction." A rocket engine is throwing mass in one direction and benefiting from the reaction that occurs in the other direction as a result.

This concept of "throwing mass and benefiting from the reaction" can be hard to grasp at first, because that does not seem to be what is happening. Rocket engines seem to be about flames and noise and pressure, not "throwing things." So here are a few examples to get a better picture of reality:

If you have ever shot a shotgun, especially a big 12-bore shot gun, then you know that it has a lot of "kick." That is, when you shoot the gun it "kicks" your shoulder back with a great deal of force. That kick is a reaction. A shotgun is shooting about an ounce of metal in one direction at about 700 miles per hour, and your shoulder gets hit with the reaction. If you were wearing roller skates or standing on a skateboard when you shot the gun, then the gun would be acting like a rocket engine and you would react by rolling in the opposite direction.......HeHe,ITS FUN

If you have ever seen a big fire hose spraying water, you may have noticed that it takes a lot of strength to hold the hose (sometimes you will see two or three firefighters holding the hose...THATS why they should be paid less). The hose is acting like a rocket engine. The hose is throwing water in one direction, and the firefighters are using their strength and weight to counteract the reaction. If they were to let go of the hose, it would thrash around with tremendous force and everyone would get wet. If the firefighters were all standing on skateboards, the hose would propel them backwards at great speed!

When you blow up a balloon and let it go so that it flies all over the room before running out of air, you have created a rocket engine. In this case, what is being thrown is the air molecules inside the balloon. Many people believe that air molecules don't weigh anything, but they do. When you throw them out the nozzle of a balloon, the rest of the balloon reacts in the opposite direction.

Imagine the following situation: You are wearing a spacesuit and you are floating in space beside the space shuttle; you happen to have a baseball in your hand.

If you throw the baseball, your body will react by moving in the opposite direction of the ball. The thing that controls the speed at which your body moves away is the weight of the baseball that you throw and the amount of acceleration that you apply to it. Mass multiplied by acceleration is force (f = m * a). Whatever force you apply to the baseball will be equalized by an identical reaction force applied to your body (m * a = m * a). So let's say that the baseball weighs 1 pound, and your body plus the space suit weighs 100 pounds. You throw the baseball away at a speed of 32 feet per second (21 mph). That is to say, you accelerate the 1-pound baseball with your arm so that it obtains a velocity of 21 mph. Your body reacts, but it weighs 100 times more than the baseball. Therefore, it moves away at one-hundredth the velocity of the baseball, or 0.32 feet per second (0.21 mph).

If you want to generate more thrust from your baseball, you have two options: increase the mass or increase the acceleration. You can throw a heavier baseball or throw a number of baseballs one after another (increasing the mass), or you can throw the baseball faster (increasing the acceleration on it). But that is all that you can do.

A rocket engine is generally throwing mass in the form of a high-pressure gas. The engine throws the mass of gas out in one direction in order to get a reaction in the opposite direction. The mass comes from the weight of the fuel that the rocket engine burns. The burning process accelerates the mass of fuel so that it comes out of the rocket nozzle at high speed. The fact that the fuel turns from a solid or liquid into a gas when it burns does not change its mass. If you burn a pound of rocket fuel, a pound of exhaust comes out the nozzle in the form of a high-temperature, high-velocity gas. The form changes, but the mass does not. The burning process accelerates the mass.

are we following all this so far......Oi Zee wake up, i know its technical stuff.

Thrust

The "strength" of a rocket engine is called its thrust. Thrust is measured in "pounds of thrust" in the U.K and in Newtons under the metric system (4.45 Newtons of thrust equals 1 pound of thrust). A pound of thrust is the amount of thrust it would take to keep a 1-pound object stationary against the force of gravity on Earth. So on Earth, the acceleration of gravity is 32 feet per second per second (21 mph per second). If you were floating in space with a bag of baseballs and you threw one baseball per second away from you at 21 mph, your baseballs would be generating the equivalent of 1 pound of thrust. If you were to throw the baseballs instead at 42 mph, then you would be generating 2 pounds of thrust. If you throw them at 2,100 mph (perhaps by shooting them out of some sort of baseball gun), then you are generating 100 pounds of thrust, and so on.

One of the funny problems rockets have is that the objects that the engine wants to throw actually weigh something, and the rocket has to carry that weight around. So let's say that you want to generate 100 pounds of thrust for an hour by throwing one baseball every second at a speed of 2,100 mph. That means that you have to start with 3,600 one pound baseballs (there are 3,600 seconds in an hour), or 3,600 pounds of baseballs. Since you only weigh 100 pounds in your spacesuit, you can see that the weight of your "fuel" dwarfs the weight of the payload (you). In fact, the fuel weights 36 times more than the payload. And that is very common. That is why you have to have a huge rocket to get a tiny person into space right now -- you have to carry a lot of fuel.

You can see this weight equation very clearly on the Space Shuttle. If you have ever seen the Space Shuttle launch, you know that there are three parts:

The Orbiter

The big external tank

The two solid rocket boosters (SRBs)

The Orbiter weighs 165,000 pounds empty. The external tank weighs 78,100 pounds empty. The two solid rocket boosters weigh 185,000 pounds empty each. But then you have to load in the fuel. Each SRB holds 1.1 million pounds of fuel. The external tank holds 143,000 gallons of liquid oxygen (1,359,000 pounds) and 383,000 gallons of liquid hydrogen (226,000 pounds). The whole vehicle -- shuttle, external tank, solid rocket booster casings and all the fuel -- has a total weight of 4.4 million pounds at launch. 4.4 million pounds to get 165,000 pounds in orbit is a pretty big difference! To be fair, the orbiter can also carry a 65,000 pound payload (up to 15 x 60 feet in size), but it is still a big difference. The fuel weighs almost 20 times more than the Orbiter.

[Reference: The Space Shuttle Operator's Manual]

All of that fuel is being thrown out the back of the Space Shuttle at a speed of perhaps 6,000 mph (typical rocket exhaust velocities for chemical rockets range between 5,000 and 10,000 mph). The SRBs burn for about two minutes and generate about 3.3 million pounds of thrust each at launch (2.65 million pounds average over the burn). The three main engines (which use the fuel in the external tank) burn for about eight minutes, generating 375,000 pounds of thrust each during the burn.

Solid-Fuel Rockets

Solid-fuel rocket engines were the first engines created by man. They were invented hundreds of years ago in China and have been used widely since then.

The idea behind a simple solid-fuel rocket is straightforward. What you want to do is create something that burns very quickly but does not explode. As you are probably aware, gunpowder explodes. Gunpowder is made up 75% nitrate, 15% carbon and 10% sulfur. In a rocket engine you don't want an explosion -- you would like the power released more evenly over a period of time. Therefore you might change the mix to 72% nitrate, 24% carbon and 4% sulfur. In this case, instead of gunpowder, you get a simple rocket fuel. This sort of mix will burn very rapidly, but it does not explode if loaded properly.

Solid-fuel rocket engines have three important advantages:

Simplicity

Low cost

Safety

They also have two disadvantages:

Thrust cannot be controlled.

Once ignited, the engine cannot be stopped or restarted.

The disadvantages mean that solid-fuel rockets are useful for short-lifetime tasks (like missiles), or for booster systems. When you need to be able to control the engine, you must use a liquid propellant system

Liquid-Propellant Rockets

In 1926, Robert Goddard tested the first liquid-propellant rocket engine. His engine used gasoline and liquid oxygen. He also worked on and solved a number of fundamental problems in rocket engine design, including pumping mechanisms, cooling strategies and steering arrangements. These problems are what make liquid-propellant rockets so complicated.

The basic idea is simple. In most liquid-propellant rocket engines, a fuel and an oxidizer (for example, gasoline and liquid oxygen) are pumped into a combustion chamber. There they burn to create a high-pressure and high-velocity stream of hot gases. These gases flow through a nozzle that accelerates them further (5,000 to 10,000 mph exit velocities being typical), and then they leave the engine.

still with me..............keep up Harty :winky:

For example, it is normal for either the fuel of the oxidizer to be a cold liquefied gas like liquid hydrogen or liquid oxygen. One of the big problems in a liquid propellant rocket engine is cooling the combustion chamber and nozzle, so the cryogenic liquids are first circulated around the super-heated parts to cool them. The pumps have to generate extremely high pressures in order to overcome the pressure that the burning fuel creates in the combustion chamber. The main engines in the Space Shuttle actually use two pumping stages and burn fuel to drive the second stage pumps. All of this pumping and cooling makes a typical liquid propellant engine look more like a plumbing project gone haywire than anything else -- look at the engines on the space shuttle up close.

All kinds of fuel combinations get used in liquid propellant rocket engines. For example:

Liquid hydrogen and liquid oxygen - used in the Space Shuttle main engines

Gasoline and liquid oxygen - used in Goddard's early rockets

Kerosene and liquid oxygen - used on the first stage of the large Saturn V boosters in the Apollo program

Alcohol and liquid oxygen - used in the German V2 rockets

Nitrogen tetroxide/monomethyl hydrazine - used in the Cassini engines

Other Possibilities

We are accustomed to seeing chemical rocket engines that burn their fuel to generate thrust. There are many other ways to generate thrust however. Any system that throws mass would do. If you could figure out a way to accelerate baseballs to extremely high speeds, you would have a viable rocket engine. The only problem with such an approach would be the baseball "exhaust" (high-speed baseballs at that...) left streaming through space. This small problem causes rocket engine designers to favor gases for the exhaust product.

Many rocket engines are very small. For example, attitude thrusters on satellites don't need to produce much thrust. One common engine design found on satellites uses no "fuel" at all -- pressurized nitrogen thrusters simply blow nitrogen gas from a tank through a nozzle. Thrusters like these kept Skylab in orbit, and are also used on the shuttle's manned maneuvering system.

New engine designs are trying to find ways to accelerate ions or atomic particles to extremely high speeds to create thrust more efficiently. NASA's Deep Space-1 spacecraft will be the first to use ion engines for propulsion.