Lecture Notes: AGK Series - Piston Engines

Introduction

• Presenter: Grant
• Series: Second class in the AGK series
• Topic: Piston Engines
• Context: Comparing aircraft piston engines to car engines

Types of Piston Engines

• Main Types:
  • Petrol engines (focus of this lecture)
  • Diesel engines (to be discussed in later classes)

How Petrol Engines Work

• Basic Principle: Burn a fuel-air mixture in cylinders
• Mechanism:
  • Increase volume and pressure to push pistons
  • Linear motion converted to circular motion via crankshaft
  • Crankshaft connected to propeller via a gearbox

Four-Stroke Cycle

• Stages: Suck, Squeeze, Bang, Blow

• Induction (Suck Stage):

  • Gases sucked into engine via inlet valve
  • Piston movement decreases pressure and temperature, allowing gas inflow

• Compression (Squeeze Stage):

  • Piston moves up, compressing gas, increasing pressure and temperature

• Combustion (Bang Phase):

  • Spark plug ignites fuel-air mixture
  • Instantaneous combustion increases pressure, pushing piston down

• Exhaust (Blow Stage):

  • Piston moves up, outlet valve opens
  • Exhaust gases expelled due to increased pressure

Other Key Components

• Crankshaft:

  • Converts up-down piston motion into rotation
  • Made from sturdy materials to withstand forces

• Camshaft:

  • Times opening/closing of valves
  • Runs at half the speed of the crankshaft

• Spark Plugs:

  • Ignite air-fuel mixture
  • Two per cylinder for redundancy

Engine Efficiency

• Cylinder Arrangement:
  • More cylinders = more power
  • Types: Inline, Radial, V-shaped, Flat

Summary

• Piston Engine Cycle: Suck, Squeeze, Bang, Blow
• Cylinder Arrangements:
  • Inline: Simple, common
  • Radial: Cylinders in a ring
  • V-shaped: High performance, compact
  • Flat: Streamlined, less aerodynamic drag

Practical Considerations

• Timing adjustments necessary for efficiency
• Engine classifications based on cylinder size and arrangement

Additional Notes

• Learning Aids: 3D animations or models recommended for better understanding of components

This summary provides an overview of the piston engine mechanics, focusing on four-stroke petrol engines used in aviation, their components, and significance of engine design choices.