Copyright © 2007 Dorling Kindersley
A machine that converts energy from a fuel to do work is an engine. Steam engines were the first engines for transportation and industry. Internal combustion engines power road vehicles and many trains. Jet engines power aircraft, and TURBINES drive ships.
Table 27. ENGINE DEVELOPMENT
Most engines convert heat energy into motion. The heat comes from burning a fuel such as coal, gasoline, or hydrogen gas. The heat makes a gas, such as air, expand rapidly. In a piston engine, the expanding gas pushes a piston down a cylinder. The piston moves down on the power stroke, which drives the machine. The amount of fuel an engine uses to run for a given time is called its FUEL CONSUMPTION.
In this engine, fuel is burned in a cylinder. The cylinder draws in air and fuel through a valve as the piston moves down. As the piston moves up, it compresses the air and fuel, making them heat up. The fuel combusts (explodes), and the gases from the explosion push the piston down, producing power.
In a steam engine, fuel is burned outside the cylinder. Coal heats water in a boiler, which makes steam. Steam is fed into the cylinder, where it expands and pushes the piston. The piston pushes a rod connected to a crank to turn a wheel.
Air entering the front of the engine is compressed by rotating blades and fed to a combustion chamber. Jet fuel injected into the chamber mixes with the compressed air, and burns at a high temperature. This makes a jet of gas shoot from the rear of the engine at such speed that it thrusts the aircraft forward.
Gasoline engines are internal combustion engines. Most modern gasoline engines work on a four-stroke cycle. Fuel and air are drawn into the cylinder; the mixture is compressed and ignited. The expanding gases push down the piston. As the piston descends, power is applied to the crankshaft, and finally the exhaust gases are forced out. Each cylinder operates out of step with the others, so the four work in sequence. This produces a continuous output of power so that the car runs smoothly.
The inlet valve opens. Fuel and air are drawn into the cylinder as the piston descends.
The mixture of fuel and air is compressed as the piston rises. Then the spark plug ignites the mixture and it explodes.
The hot gases expand, which forces the piston down, transferring power to the crankshaft.
Engineer Frank Whittle proposed the idea for jet aircraft in 1928. But it was not until 1937 that he built the first successful engine. His ideas were developed in World War II, and the first Whittle engine jet fighters flew in 1944.
A turbine is an engine that has a set of blades or paddles rotated by a moving liquid or gas. Turbines are used in hydroelectric power stations and ships.
Water mills and windmills are examples of water and air turbines. They are not heat engines because they do not rely on heat to produce motion. Gas and steam turbines are powerful heat engines—the turbine blades are spun by hot gases from burning fuel, or by high-pressure steam from a boiler. They are used to drive large ships and turn power station generators.
The flowing gas or liquid pushes the turbine blades, spinning the shaft. The turbine is connected to a generator. In a modern turbine, the angled blades have a shape similar to aircraft wings to maximize the force generated. The fluid may pass through two, three, or more sets of blades arranged in sequence, to convert as much energy as possible to motion.
A vehicle’s fuel consumption is measured by how much fuel it uses to travel a certain distance. The fuel consumption of a car depends on its engine power, its weight, its aerodynamics (how smoothly it moves through the air), its speed, and how it is driven.
The more fuel a car needs to work, the less engine-efficient it is. Scientists are developing cars that use less fuel, and therefore do not waste energy or pollute the air. They are also making cars that use different sources of energy, such as solar panels, electric motors, or hydrogen fuel, which is pollution-free.