What is an aircraft engine and how does it work: Let’s dive deeper into how aircraft engines work, covering both jet engines (turbine engines) and reciprocating engines (piston engines) with greater detail.
1. Jet Engines (Turbine Engines)
Jet engines are highly efficient at high speeds and altitudes, making them ideal for commercial airliners, military jets, and other high-performance aircraft. They operate on the principle of Newton’s Third Law of Motion: “For every action, there is an equal and opposite reaction.” In this case, the action is the expulsion of high-speed exhaust gases, and the reaction is the forward thrust on the aircraft.
Detailed Components and Their Functions:
Intake:
- Role: The intake draws in air from the atmosphere. The design of the intake is crucial as it must smoothly guide the air into the engine at the right speed and pressure.
- How it works: As the aircraft moves forward, air is funneled into the engine. In supersonic aircraft, the intake design often includes mechanisms to slow down the incoming air to subsonic speeds before it enters the compressor.
Compressor:
- Role: The compressor increases the pressure of the incoming air. It is typically made up of several stages, each consisting of a rotor (rotating blades) and a stator (stationary blades).
- How it works: The rotating blades accelerate the air, while the stationary blades convert this kinetic energy into pressure. As the air passes through each stage, its pressure and temperature increase significantly. By the time it leaves the compressor, the air can be compressed up to 30-40 times its original pressure.
Combustion Chamber (or Combustor):
- Role: The combustion chamber is where fuel is mixed with the high-pressure air and ignited to create a high-energy exhaust gas.
- How it works: Fuel injectors spray a fine mist of fuel into the compressed air. Igniters (similar to spark plugs) initiate combustion. The burning fuel-air mixture dramatically increases the temperature of the air, causing it to expand rapidly. This expansion increases the velocity of the air, which is essential for creating thrust.
Turbine:
- Role: The turbine extracts energy from the high-temperature, high-pressure exhaust gases to drive the compressor and other accessories.
- How it works: As the exhaust gases flow through the turbine stages, they cause the turbine blades to spin. The turbine is connected to the compressor via a shaft, so the energy extracted by the turbine drives the compressor. Despite this energy extraction, the exhaust gases still retain enough velocity to produce thrust.
Exhaust Nozzle:
- Role: The exhaust nozzle accelerates the exhaust gases to produce thrust.
- How it works: After passing through the turbine, the exhaust gases are expelled through the nozzle. The nozzle’s design ensures that the gases exit at the highest possible speed. In some engines, the nozzle can adjust its size to optimize performance at different speeds.
Afterburner (in military jets):
- Role: The afterburner is an additional combustion chamber that burns more fuel in the exhaust stream, providing extra thrust when needed.
- How it works: When the afterburner is engaged, additional fuel is sprayed into the exhaust gases after they have passed through the turbine. This fuel ignites, increasing the volume and velocity of the exhaust gases, thus producing a significant increase in thrust. This is especially useful in supersonic flight and combat situations.
Types of Jet Engines:
- Turbojet: A basic jet engine where all the thrust comes from the high-speed exhaust gases. It’s efficient at high speeds but not at low speeds.
- Turbofan: A more advanced type where a large fan at the front of the engine pushes a significant amount of air around the engine core. This bypassed air produces additional thrust, making turbofans more efficient and quieter than turbojets, especially at subsonic speeds.
- Turboprop: Similar to a turbofan but drives a propeller instead of a fan. It’s very efficient at lower speeds and is used in regional and cargo aircraft.
- Turboshaft: Similar to a turboprop but designed to drive a shaft instead of a propeller. It’s commonly used in helicopters.
2. Reciprocating Engines (Piston Engines)
Reciprocating engines are more common in smaller aircraft, such as private planes and some older military aircraft. They operate on the principle of internal combustion, where fuel and air are mixed and ignited inside a cylinder to produce mechanical power.
Detailed Components and Their Functions:
Cylinders:
Role: The cylinders are where the combustion process occurs. A typical reciprocating engine might have 4, 6, or even 12 cylinders.
How it works: Inside each cylinder, a piston moves up and down in response to the combustion of the fuel-air mixture. The movement of the pistons is what generates the mechanical power needed to turn the propeller.
Pistons:
Role: Pistons are the movable components inside each cylinder that convert the energy from combustion into mechanical motion.
How it works: The pistons are connected to the crankshaft via connecting rods. As the fuel-air mixture ignites, the resulting explosion forces the piston downward, which turns the crankshaft.
Crankshaft:
Role: The crankshaft converts the linear motion of the pistons into rotational motion.
How it works: As the pistons move up and down, the crankshaft rotates. This rotational motion is what drives the propeller and generates thrust.
Intake and Exhaust Valves:
Role: These valves control the flow of air-fuel mixture into the cylinders and the expulsion of exhaust gases.
How it works: During the intake stroke, the intake valve opens to allow the air-fuel mixture into the cylinder. After combustion, the exhaust valve opens to expel the exhaust gases during the exhaust stroke.
Spark Plugs:
Role: Spark plugs provide the spark that ignites the fuel-air mixture in the cylinders.
How it works: At the right moment during the compression stroke, the spark plug generates a spark, igniting the compressed air-fuel mixture, causing the explosion that drives the piston down.
Carburetor or Fuel Injection System:
Role: This system mixes fuel with air before it enters the cylinders.
How it works: In carbureted engines, the carburetor atomizes the fuel and mixes it with air in the correct ratio. In fuel-injected engines, fuel injectors directly spray the fuel into the intake manifold or cylinder, mixing with air as it enters the combustion chamber.
aircraft engine
The Four-Stroke Cycle:
Most aircraft piston engines operate on a four-stroke cycle:
- Intake Stroke: The intake valve opens, and the piston moves down, drawing the air-fuel mixture into the cylinder.
- Compression Stroke: The intake valve closes, and the piston moves up, compressing the air-fuel mixture.
- Power Stroke: At the top of the compression stroke, the spark plug ignites the mixture, causing an explosion that forces the piston downward, producing power.
- Exhaust Stroke: The exhaust valve opens, and the piston moves up, expelling the exhaust gases from the cylinder.
aircraft engine Summary
- Jet Engines work by compressing air, mixing it with fuel, igniting it, and expelling the exhaust gases at high speed to generate thrust. There are various types like turbojets, turbofans, and turboprops, each with its specific applications.
- Piston Engines use the four-stroke cycle (intake, compression, power, exhaust) to convert the chemical energy of fuel into mechanical energy that drives a propeller, producing thrust.
aircraft engine
Both types of engines are crucial to aviation, each serving different types of aircraft and flight needs.