Modern Engines And Energy Conservation (1978)

Whenever an object is moved, work is done. If you happen to be the person doing the moving, you'll probably agree that this is work. Today, much of our work is done by machines. There are machines for pushing, machines for pulling, machines for lifting, and machines for lowering. They all move objects. As you know, energy is needed to operate a machine. Where does this machine get its energy? From gasoline. Like most fuels, gasoline contains stored chemical energy, which scientists call potential energy. But the potential energy cannot move the race car until it has been converted into mechanical energy. The part of a machine that converts the potential energy of the fuel into mechanical energy is the engine. But how does an engine do this? The part of an automobile engine where energy conversion takes place is called the cylinder. Inside the cylinder is a moving part, the piston. When the engine is running, a fine mixture of gasoline and air is drawn into the cylinder. As the piston rises, it compresses the fuel-air mixture and thus increases its pressure. The fuel-air mixture is ignited and burns with explosive force, producing heat. The heat further increases the pressure of the gases in the cylinder. In this way, the chemical energy of the fuel is converted into heat energy. The high pressure of the hot gases forces the piston down. The force of this moving piston is the mechanical energy which turns the wheels of the car. Many engines work on the same principle as the automobile engine, pistons. Although automobile engines and other piston engines are useful devices, they are not perfect. They cannot change all of the chemical energy of the fuel into usable mechanical energy. Piston engines waste most of the chemical energy. But how is this energy wasted? When fuel is burned, some of its chemical energy is converted into light and sound. Some energy is also wasted in friction between moving parts, vibration, or heat radiated from the engine itself. But all of these energy losses are very minor when compared to the loss of energy in the exhaust gases. Since this heat energy has not been converted into mechanical energy, it is wasted. This is the single biggest waste of energy in a piston engine. While the piston engine operates on the up and down movement of pistons, another kind of engine operates on a circular or rotary motion. This jet engine is one kind of turbine engine. The part of the engine made up of curved blades and a shaft is called the rotor because it rotates. The front part of the rotor is called the compressor. While the engine is operating, the blades of the compressor draw air into the engine and compress it. The high pressure air is forced into the combustion chambers where fuel is injected and burned. The chemical energy of the fuel is released in hot expanding gases. The gases rush through the turbine blades of the rotor, forcing it to spin at terrific speeds. Because the spinning of the rotor is smooth and steady, less energy is wasted in vibration than in a piston engine. In addition, the turbine engine has fewer moving parts and so less energy is wasted through friction. Because the fuel is burned in a steady stream, the jet engine, like all turbine engines, develops more heat energy and therefore more mechanical energy than a piston engine of the same weight. But no engine can convert all the potential energy of the fuel to usable energy. The jet's exhaust is very hot. This is heat energy that has not been converted into mechanical energy. It is wasted. The remaining energy spins the shaft of the rotor. Some of the energy which turns the rotor is used to turn the compressor. The rest of the energy can be harnessed to do useful work. For example, the rotor can be used to turn an electrical generator, helicopter blades, or automobile wheels. When a propeller is attached to the rotor of a turbine engine, it becomes a turboprop engine. The turboprop engine is similar to the turbojet engine, except that the turbojet has no propeller. In a jet, the hot gases formed by the burning of the fuel expand and push in all directions with equal force. The gases pushing backward rush out through an opening at the rear of the engines. But gases pushing in the opposite direction are blocked by the engine itself. This results in a strong push against the engine called thrust. Thrust is the force that propels the engine and the airplane forward. Jets often fly best at altitudes of 6 to 8 miles above the Earth, where the air is thin, so there is less drag. Since they perform well at such high altitudes, have you ever wondered why they aren't used for space travel? In a jet engine, the potential energy of the fuel is converted into heat energy by burning the fuel. That is, combining it with oxygen from the air. But about 20 miles up, the air becomes so thin that there is not enough oxygen to burn the fuel. How can this problem be solved? The solution is easy. Build an engine that carries its own supply of both fuel and oxygen. Such an engine is called a rocket engine. Although the basic principle of rocket engines is very simple, space rockets are quite complicated. To prevent explosions, which would occur if the powerful fuels were burned too fast, rocket engines must be designed to carefully control the rate at which the fuel burns. There are two main types of rocket engines, solid fuel and liquid fuel. The liquid fuel rocket contains separate tanks of liquid fuel and liquid oxygen or a chemical that can supply oxygen. Solid fuel rockets contain a solid mixture of fuel and a chemical that will furnish oxygen. In both types of rocket engines, the fuel is oxidized or burned in a combustion chamber. Hot gases are produced which expand and push in all directions in the chamber. Just as in the jet engine, the hot gases rush out an opening in the rear of the rocket engine, while the gases pushing in the opposite direction thrust the rocket forward. Even though there are differences between the engines you have seen, they all must go through the same steps to convert fuel to energy. What are these steps? >> Today, scientists are developing totally new kinds of engines. Engines that do not depend upon chemical energy at all. For example, why doesn't this ship have smoke stacks? It is nuclear-powered. In nuclear engines, fuel is not burned. So, there is no smoke. Instead, a small amount of atomic fuel is converted directly into a great amount of heat energy, which is used to produce mechanical energy. For travel in outer space, the ion engine, a type of electric rocket, is being developed. This engine uses the force of a stream of electrically charged atoms, called ions, rushing out of the engine to drive a spacecraft. Because the ion engine uses only a small amount of electricity, the power it develops is very small. But, in outer space, where there is no air resistance, such engines are able to gradually build up speeds of hundreds of thousands of kilometers per hour. Another kind of engine carries no fuel at all. The solar engine converts the rays of the sun to electrical energy or to heat, which can then be converted to mechanical energy. In the future, it is possible that immense satellite solar power stations will be constructed and placed in orbit high above the Earth. Each satellite might spread out over 20 square miles and weigh millions of tons. Here in space, above the shadows and clouds of Earth, acres of solar panels would capture the solar energy of sunlight 24 hours a day. This energy would be beamed to receiver stations on Earth in the form of radio waves, which would be converted into electrical energy for our homes and factories. The universe itself will become a vast power source as future scientists and engineers develop totally new methods of energy conversion.