Jet Engine Operations

Jet engines operate at temperatures over 1500°C.

Turbojet Performance

Front Fan Performance

• Pushes 13t of air per second
• Compresses 10% of it to 50× atmospheric pressure
• Heats it to ~600°C
• Thrust Generation
• Power Generation
• High-pressure gas expands through turbine blades
• Generates power that drives the fan and compressors
• Engine Design
• Materials Limitations
• Early blades were steel, limited to 780°C and 10-hour life
• Titanium was lighter but lost strength quickly
• Modern Blade Designs
• Use nickel superalloys containing ~10 elements (Cr, Co, Ti, Nb, Ta, V, Mo, Fe, Al, Re)
• Microstructure has γ (disordered) and γ′ phases; dislocations move in pairs and are impeded by γ′ blocks, giving high strength
• Single-Crystal Blades
• Casting Process
• Investment casting: a wax pattern is coated with a ceramic shell, melted to form a mold, and molten alloy is poured
• The mold is cooled directionally from a copper chill plate, with a helical “pigtail” to select a single crystal
• Coatings and Protection
• Metallic Bond Coat
• Protects metal 100–170°C cooler
• Ceramic Top Coat
• Keeps metal 100–170°C cooler
• Protective Coating Materials
• Potassium-sodium hydroxide leaches out core passages with erosion
• Film-cool holes allow compressor air to flow as a protective film
• Engine Efficiency and Reliability
• Carnot Factor Limitation
• Efficiency is limited by the Carnot factor
• Advanced Alloys and Design
• Refine coatings to resist molten dust

link: https://www.youtube.com/watch?v=QtxVdC7pBQM