What Makes A Steam Locomotive Work?
When heated, water turns to an invisible vapor known as steam. The volume of water expands as it turns to steam inside the boiler, creating a high pressure. The expansion of steam pushes the pistons that connect to the driving wheels that operate the locomotive.
(1) Coal or oil are the fuels used for heating the water (coal is shown in the diagram). Coal is carried in the tender of the locomotive and is hand-shoveled by the fireman into the firebox. Water is carried in the tender in a tank surrounding the coal. The water passes to the locomotive through a device called an injector.
(2) By spreading the coal evenly throughout the firebox, the fireman creates a level fire above the grates. Air flows up through the grates allowing the coal to burn hotter. The hot gases released from the coal flow forward through a series of flues or tubes to the front of the locomotive.
(3) Water surrounds the outside of the firebox. Heat from the burning coal turns water to steam, which rises to the top of the boiler. The area surrounding the firebox and tubes is the "steam generator" of the locomotive.
(4) Steam gathers at the steam dome, the highest point in the boiler. The engineer uses the throttle to regulate the amount of steam being sent to the pistons. A throttle lever in the cab opens and closes the throttle valve in the steam dome.
(5) Steam passes to the piston valves which control admission of steam to the cylinders. Once in the piston, the steam expands, pushing it in the opposite direction. At the end of the piston stroke, an exhaust port opens, allowing the steam to escape. Then the process is reversed and repeated in the opposite direction. Steam is admitted to either side of the piston so that it is always under power. A lever in the cab allows the engineer to control the action of the piston valves (direction of locomotive movement, and timing).
(6) The pistons push or pull the rods connected to the drive wheels, providing the force needed to move the locomotive.
(7) The steam is exhausted through a nozzle and up through the smokebox into the stack. This action produces the "chuff chuff" sound heard when the locomotive is moving. A draft or vacuum results, pulling air through the firebox grates to induce combustion of the coal. Both exhausted steam and coal smoke travel up through the stack.
What Makes A Diesel Locomotive Work?
The ignition of diesel fuel pushes pistons connected to an electric generator. The resulting electricity powers motors connected to the wheels of the locomotive. A "diesel" internal combustion engine uses the heat generated from the compression of air during the upward cycles of the stroke to ignite the fuel. The inventor Dr. Rudolph Diesel designed this type of engine. It was patented in 1892.
1. Diesel fuel is stored in a fuel tank and delivered to the engine by an electric fuel pump. Diesel fuel has become the preferred fuel for railroad locomotive use due to its lower volatility, lower cost, and common availability.
2. The diesel engine (A) is the main component of the diesel-electric locomotive. It is an internal combustion engine comprised of several cylinders connected to a common crankshaft. Fuel is ignited by the intense compression, pushing the piston down. The piston's movement turns a crankshaft.
3. The diesel engine is connected to the main generator (B), which converts the engine's mechanical power to electrical power. The electricity is then distributed to traction motors (C) through circuits established by various switchgear components.
4. Because it is always turning, whether the locomotive is moving or not, the main generator's output is controlled by the excitation field current to its windings.
5. The engineer controls the power output of the locomotive by using an electrically-controlled throttle. As it is opened, more fuel is injected into the engine's cylinders, increasing its mechanical power output. Main generator excitation increases, increasing its electrical output.
6. Each traction motor (C) is directly geared to a pair of driving wheels. The use of electricity as the "transmission" for the locomotive is far more reliable than using a mechanical transmission and clutch. Starting a heavy train from a dead stop would burn out a clutch in a brief time.