Thermal Machines: Types, Function, and Mechanisms
Thermal Machines: Transforming Energy
Thermal machines convert thermal energy into mechanical energy, or vice versa.
Heat Engines
A heat engine transforms thermal energy (heat) into mechanical energy.
Types of Thermal Machines
External Fuel Sources
- Steam Engine
- Steam Turbines (rotary)
Internal Fuel Sources
- Spark Ignition (Otto cycle)
- Compression Ignition (Diesel cycle)
- Open Cycle Gas Turbines (rotary)
- Wankel Engine
Steam Engine Details
The steam engine primarily consists of a boiler, cylinder, and distributor regulator. The boiler heats water to produce steam, which is then directed to the cylinder via the distributor. This steam exerts pressure on a piston or plunger, causing it to move. A mechanism, through a connecting rod, drives a crankshaft.
Double Acting vs. Single Acting
- Double Acting: Steam is introduced into the cylinder at both ends alternately.
- Single Acting: Steam is introduced at one end only. The connecting rod returns to its original position due to the wheel’s inertia.
Watt Regulator
The Watt regulator controls the speed of the machine. Two heavy metal bowls are attached to a rotating shaft. As the machine accelerates, the bowls are centrifuged outward, closing a valve that reduces steam flow to the cylinder, thus slowing the machine. When the bowls descend, the steam valve opens, increasing speed.
Steam Turbines
Steam turbines are rotary machines that do not use an alternating rod mechanism like steam engines.
Action Turbines
Action turbines require a large boiler to produce steam. The steam is directed through fixed nozzles onto a peripheral rotor, causing it to turn due to the impulse of the steam pressure.
Action and Reaction Turbines
These turbines have multiple fixed and rotating blades. Steam first impacts the fixed blades, then the rotating blades (action), and then passes through another set of fixed blades, which direct it to the next set of rotating blades (reaction), and so on.
Steam turbines can also be part of a closed-cycle system, where steam is condensed and returned to the boiler.
Internal Combustion Engines
Internal combustion engines use fuel that is burned inside the machine. The gases produced exert pressure on a piston, generating mechanical work.
Four-Stroke (4T) Engines
These engines use gasoline and a crankshaft mechanism to convert the reciprocating motion of the piston into rotational motion.
- 1st Stroke: Intake
- 2nd Stroke: Compression
- 3rd Stroke: Combustion (Explosion)
- 4th Stroke: Exhaust
Two-Stroke (2T) Engines
Two-stroke engines are lighter and simpler. They use a mixture of gasoline and oil for lubrication. They complete a cycle in two strokes, performing two functions simultaneously.