Overview
This lecture explains the fundamentals of turbofan jet engines, their structure, advantages over turbojets, and their importance for efficient, quieter, and more environmentally friendly air travel.
Introduction to Turbofan Engines
- Turbofan engines are widely used in modern commercial and military aircraft.
- They combine a gas turbine core with a large front fan to improve efficiency over older turbojets.
Turbofan Engine Components
- Major parts: gas turbine core (compressor, combustion chamber, turbine) and a large ducted fan.
- The fan at the front pushes a large amount of air backward.
- Two shafts: low-pressure shaft (N1) for the fan and low-pressure compressor, and high-pressure shaft (N2) for the core’s compressor and turbine.
- Shafts rotate independently; some engines have a third intermediate shaft for improved performance.
Operating Principles and Bypass Ratio
- Not all air passes through the core; most bypasses around it, adding thrust efficiently.
- The bypass ratio equals the mass of air bypassing the core divided by the mass going through the core.
- High bypass ratios (e.g., 9:1 or 10:1) are typical in commercial jets, maximizing fuel efficiency.
- Low bypass engines are used in military jets prioritizing speed and power.
Efficiency and Environmental Impact
- Turbofans are more fuel-efficient because they push more air at lower speed, wasting less energy than turbojets.
- Up to 80% of thrust can come from bypassed air, reducing operating costs.
- High bypass ratios lower specific fuel consumption and reduce noise and emissions.
- The fan’s bypass air also dampens noise from the engine core.
Key Terms & Definitions
- Turbofan — Jet engine type with a large front fan and gas turbine core, used for efficiency.
- Gas Turbine Core — The inner engine section: compressor, combustion chamber, and turbine.
- Bypass Ratio — Ratio of air mass bypassing the core to mass passing through the core.
- Specific Fuel Consumption — Fuel used per unit of thrust, lower means higher efficiency.
- Low/High-Pressure Shaft (N1/N2) — Independent rotating shafts in the engine, each driving different components.
Action Items / Next Steps
- Review details on how turbofan engine components interact.
- Watch the upcoming video on afterburners for military jet applications.