Combustion Engine Concepts

Oxygen and Combustion Chamber

• Increasing oxygen inside the combustion chamber enhances power output.
• Reducing air speed, while maintaining diffuser function, can impact performance.

Compressor Mechanics

• Types of Compressors:
  • Centrifugal Compressor: Utilizes centrifugal force to compress air.
  • Axial Compressor: Air flows parallel to the axis of rotation, often more complex than centrifugal.
• Stages of Compression:
  • Air rotates and compresses as it passes through compressor stages.
  • Each stage can consist of rotors and stators that control airflow and pressure.

Pressure Dynamics and Stages

• Dual-stage Compression:
  • First stage compresses air by 50%, with a diffuser handling another 50%.
  • Systems may be set for high and low pressure, especially in smaller aircraft.
• Fixed vs. Moving Parts:
  • Stators are stationary, while rotors rotate to compress air.
  • Air pressure decreases before entering the next rotor, helping maintain consistent energy output.

Compressor Performance Factors

• Angle of Attack:
  • Blade angles must be carefully designed to prevent stalling (loss of lift).
  • Excessive angles can lead to compression stall, impacting engine efficiency and affecting the aircraft's performance.
• Material Properties:
  • High temperature-resistant materials (e.g., titanium) are essential due to the extreme conditions in the compressor.
• Compressor Stall:
  • Can occur due to adverse conditions (e.g., bird strikes, blockage) leading to vibrations and performance loss.

Combustion Process

• Burning Fuel and Air Ratio:
  • An appropriate air-fuel mixture is crucial for optimal combustion efficiency.
  • Inadequate oxygen results in incomplete combustion, leading to higher exhaust gas temperatures (EGT).
• Flame Management:
  • Controlling flame speed to avoid backflow into the turbine; maintaining stable combustion conditions is essential to prevent engine stalls.

Engine Management Systems

• Automatic Control Mechanisms:
  • Systems may automatically adjust fuel air mixtures based on power demands to ensure stable combustion and performance.
• Safety Systems:
  • Engines may possess mechanisms to manage excess air pressure through relief systems to prevent compressor overloads.

Additional Concepts

• Rams Air and Engine Performance:
  • As speed increases, the engine may need mechanisms to release extra pressure, impacting efficiency.
  • Air from compressor may also be utilized for aircraft pressurization, enhancing comfort and safety.

Key Terms

• Stator: Fixed component in compressors that help manage airflow.
• Rotor: Spins to compress air in the compressor.
• EGT (Exhaust Gas Temperature): Critical measure indicating combustion efficiency; high EGTs may signify too much fuel or inadequate oxygen.
• Dynamic Stall: Condition where irregular airflow increases vibration, reducing engine efficiency.