Introduction to Aerospace Propulsion

Transcription

1 Introduction to Aerospace Propulsion Introduction Newton s 3 rd Law of Motion as the cornerstone of propulsion Different types of aerospace propulsion systems Development of jet engines

2 Newton s Third Law of Motion Newton s Third Law of Motion for every force acting on a body, there is an equal and opposite reaction. Aerospace Propulsion body = atmospheric air that is accelerated as it passes through the engine Newton s Third Law demonstrated in a rotating sprinkler Source: Rolls-Royce, 1986, The jet engine, 5 th edition, Rolls-Royce plc Aero Propulsion Systems Classification

3 Jet Propulsion Development Early 20 th century aero-propulsion systems were internal combustion (reciprocating) engines. First turbojet flown in late 30 s: Superior to the reciprocating engine High power / weight ratio High speed operation Heinkel He 178, the world's first aircraft to fly purely on turbojet power (1939) Source: Jet Propulsion Development Early jet engines: Poor efficiencies Limited to high-speed fighter and reconnaissance aircraft. Messerschmitt Me 262A world s first operational jet fighter Source:

4 Jet Propulsion Development Need to improve efficiency and power: Increasing compressor pressure ratios Increasing turbine inlet temperatures Reduce losses Some major developments: Dual-rotor (spool) configuration Controlled variable-stator blades Improved high-temperature metallurgy and cooling techniques for combustor / turbine section Afterburner Bypass engine (turbofan) Reciprocating Engines Common in small aircraft Pistons turn crankshaft that powers a propeller through a reduction gearbox Typically four-stoke engines - two common types: Otto Cycle Diesel Cycle (new to aviation applications) Picture credit: Soon Kim Tat Video Source:

5 Reciprocating Engines Otto (Gasoline) Cycle Four-stoke cycle Gasoline (petrol engine) High octane fuel e.g. Avgas 100LL Spark plug ignites fuel-air mixture (constant volume) to initiate power stroke Source: Video: Source: Soon Kim Tat Reciprocating Engines Diesel cycle Four-stroke cycle Better power-to-weight Fuel is injected after compression Combustion (constant pressure) due to heat of compression - no spark plugs In aviation, diesel engines run on jet fuel Air Source: Source: Soon Kim Tat

6 Rocket Engine A non-airbreathing jet engine Picture credit: Soon Kim Tat Adapted from Rolls-Royce, 1986, The jet engine, 5 th edition, Rolls-Royce plc (Solar Powered) Electric Engine Solar Impulse Source:

7 Summary How propulsive force is developed using Newton s 3 rd Law of Motion The common aerospace propulsion systems Reflection Question Describe the four-strokes of both the Otto Cycle and the Diesel Cycle and articulate the differences between the two cycles.