Jet propulsion

Rolls-Royce Trent 1000 jet engine

Pump-jet on NatchanWorld 02

Jet propulsion is a means of locomotion whereby a jet engine discharges a fast-moving jet of fluid to generate thrust in accordance with Newton's third law of motion. This broad definition includes both air-breathing jet engines, such as turbojets, turbofans, and ramjets, and non-air-breathing engines, like rocket engines. Jet propulsion is most commonly used in aircraft, enabling them to achieve high speeds and altitudes unattainable by other forms of propulsion.

Principles of Operation

The fundamental principle behind jet propulsion is the expulsion of a high-speed stream of fluid, which can be a gas or liquid, to propel the vehicle in the opposite direction. This is a practical application of Newton's third law, which states that for every action, there is an equal and opposite reaction. In the context of jet engines, the action is the expulsion of the jet of fluid, and the reaction is the movement of the engine, and thus the vehicle it is attached to, in the opposite direction.

Air-breathing Engines

Air-breathing engines intake air from the atmosphere, compress it, mix it with fuel and ignite the mixture. The high-pressure and high-velocity gases then exit through a nozzle, creating thrust. Types of air-breathing engines include:

• Turbojet: The simplest form of jet engine, where air is drawn in, compressed, mixed with fuel, ignited, and expelled.
• Turbofan: Similar to turbojets but with a fan at the front that brings in additional air, part of which bypasses the core engine, providing extra thrust and efficiency.
• Turboprop: A variation where the jet engine drives a propeller, offering efficiencies at lower speeds and altitudes.
• Ramjet: Has no moving parts and relies on the vehicle's speed to ram air into the engine, making it efficient at high speeds but not capable of operating at a standstill.

Non-air-breathing Engines

Non-air-breathing engines, such as rocket engines, carry both fuel and an oxidizer onboard, allowing them to operate in space where there is no atmosphere. These engines expel exhaust gases obtained from the combustion of the fuel and the oxidizer to generate thrust.

Applications

Jet propulsion is primarily used in various types of aircraft, including commercial airliners, military fighters, and space vehicles. Its applications extend to:

• Commercial aviation, where turbofan engines are preferred for their efficiency and ability to cover long distances.
• Military aviation, utilizing turbojets and turbofans for high-speed, high-altitude flight.
• Space exploration, with rocket engines enabling spacecraft to leave Earth's atmosphere and navigate in space.

Advantages and Disadvantages

Jet propulsion offers several advantages, including the ability to travel at high speeds and reach high altitudes. It is also relatively efficient at high speeds compared to other forms of propulsion. However, it has disadvantages, such as high noise levels, significant pollution, and the requirement for sophisticated and expensive infrastructure and maintenance.

Future of Jet Propulsion

The future of jet propulsion may include advancements in engine efficiency, the development of engines capable of operating in both the atmosphere and space, and the integration of new technologies to reduce environmental impact. Research into electric and hybrid propulsion systems could also lead to significant changes in how jet propulsion is applied, especially in reducing the carbon footprint of air travel.