1.

Different Types of Engines Used in Aircraft:

Reciprocating (Piston) Engines

1.​ Piston Engines: These engines use pistons moving back and forth within
cylinders to generate power, similar to car engines.
2.​ Inline Engines: Cylinders are aligned in a single row, offering a streamlined
design.
3.​ V-type Engines: Cylinders are arranged in a V-shape, providing a more
compact design.
4.​ Radial Engines: Cylinders are arranged around a central crankshaft,
common in older propeller-driven aircraft.

Turbine Engines (Jet Engines):

1.​ Turbojet Engines: Early jet engines that generate thrust by expelling
high-speed exhaust gases.
2.​ Turbofan Engines: Feature a fan at the front that helps to bypass air,
improving fuel efficiency and thrust, and are widely used in commercial
aviation.
3.​ Turboprop Engines: Combine jet engine technology with a propeller,
offering a good balance of speed and fuel efficiency, commonly used in
smaller airliners.
4.​ Turboshaft Engines: Optimized to produce shaft power, primarily used in
helicopters and other rotary-wing aircraft.

Feature Turboprop Turbofan Turbojet

Rotational Low High High
Speed
Aircraft Type Moderate size Large civil aircraft Military aircraft
aircraft
Airflow / — High airflow rate with Low airflow rate;
Bypass Ratio high bypass zero or low bypass
Efficiency High propulsive Medium / High efficiency Low efficiency
efficiency
Flight Speed Low High High (supersonic
up to Mach 4)
Transmission Geared Ducted fan with geared / —
transmission ungeared transmission

Other Engine Types

1.​ Ramjet Engines: Simple engines that rely on the aircraft's speed to
compress air, suitable for high-speed applications.
2.​ Rocket Engines:Used in space exploration and some military applications,
employing liquid or solid propellants.

Emerging Technologies in Engines

1.​ Electric Propulsion: Electric motors driving propellers or fans, offering a

cleaner and quieter alternative, especially for smaller aircraft.

2. Benefits of Gas Turbine Engines:

1.​ High thrust-to-weight ratio

2.​ Smooth and vibration-free operation
3.​ Higher power output for given weight
4.​ Suitable for high-speed and high-altitude flight
5.​ Continuous combustion process
6.​ Compact design
The gas turbine engine made supersonic flight possible in aircraft.

Reduced the cost of air travel.

Led to great improvements in aircraft safety

3. Why Do We Use Gas Turbines in Aircraft?

1.​ Easy to generate thrust

2.​ High power to weight ratio
3.​ Small frontal area
4.​ High efficiency (almost the highest)
5.​ Few unplanned overhauls(reliable)

4. Principle of Operation of Gas Turbine: (refer 10th que)

●​ Air is compressed → Fuel is added and combusted → Hot gases expand

through turbine → Thrust is produced
●​ Operates on Brayton Cycle

6. Function of a Reciprocating System:

 ●​ Uses pistons to convert chemical energy of fuel into mechanical energy.
●​ Pistons move back and forth (reciprocate) inside cylinders.
●​ Common in small aircraft and light planes.

8. Classify the Gas Turbines:

1.​ Turbojet – All air passes through the core; high-speed jets
2.​ Turbofan – Bypass air + core air; more efficient and quieter
3.​ Propfan – Hybrid between turbofan and turboprop; open rotors
4.​ Ramjet – No moving parts; works at supersonic speeds
5.​ Scramjet – Like ramjet but supersonic airflow through engine
9. Turbopropeller:

✅ Benefits of Turbopropeller Engines:

1.​ High fuel efficiency at low to medium speeds​
Most efficient below ~450–500 mph (720–800 km/h).​

2.​ Excellent for short to medium-range flights​

Ideal for regional and commuter aircraft.​

3.​ Shorter takeoff distance​

Generates high thrust at lower speeds → better for small runways.​

4.​ Lower operating cost​

Lower fuel consumption and simpler maintenance compared to turbojets.​

5.​ Good low-speed performance​

Better control during landing/takeoff phases.​

❌ Limitations of Turbopropeller Engines:

1.​ Speed limitation​
Not suitable for high-speed (>500 mph) or long-haul flights.​

2.​ Less efficient at high altitudes​

Performance drops at cruising altitudes of jetliners.​

3.​ Noise​
Propellers generate more external noise than turbofans or turbojets.​

4.​ Lower cruise speed compared to jets​

Longer travel time on longer routes.

7. Benefit of Turbofan Engine:

1.​ Quieter than turbojets

2.​ More fuel-efficient at high subsonic speeds
3.​ High bypass ratio improves thrust and efficiency
 4.​ Widely used in commercial airliners

8. Turbojet:

1.​ Simplest gas turbine type

2.​ All air passes through core (compressor → combustor → turbine)
3.​ High thrust at high speeds, but noisy and less efficient
4.​ Used in military and high-speed aircraft

9. 8 Components of Turbojet (with purpose):

 1.​ Air Inlet – Directs air into engine
2.​ Compressor – Increases air pressure
3.​ Combustion Chamber – Burns fuel-air mixture
4.​ Turbine – Extracts energy to drive compressor
5.​ Nozzle – Expels hot gases to create thrust
6.​ Shaft – Connects turbine and compressor
7.​ Fuel Injector – Injects fuel into chamber
8.​ Ignition System – Ignites fuel-air mixture

10. Cycle: Brayton Cycle (Ideal Gas Turbine Cycle)

This diagram shows the Air-standard Brayton Cycle, which is the ideal cycle used
to model gas turbine engines like turbojets and turbofans.
🌀⚙️Used In: Gas turbines (turbojet, turbofan, turboprop)​

🔄 Processes (4 steps):
Type: Open cycle (practical), Idealized as closed cycle (theoretical)​

1️⃣ 1 → 2: Isentropic Compression

●​ Ambient air is drawn into the compressor, where it is compressed

(pressure increases).
●​ Adiabatic + Reversible → Pressure ↑, Temp ↑​

2️⃣ 2 → 3: Constant Pressure Heat Addition

●​ In Combustion Chamber
●​ Compressed air is mixed with fuel in the combustion chamber and ignited.​

●​ This produces high-pressure, high-temperature gases.

●​ Fuel burns → Temp ↑, Volume ↑​

3️⃣ 3 → 4: Isentropic Expansion

●​ In Turbine
●​ The hot gases expand through the turbine, spinning its blades.
●​ This rotation produces mechanical work (used to drive the compressor and
generate thrust or electricity).
●​ Adiabatic + Reversible → Pressure ↓, Temp ↓
●​ Produces useful work output​

4️⃣ 4 → 1: Constant Pressure Heat Rejection

●​ Via exhaust gases

●​ The gases exit at high velocity through a nozzle, producing thrust (in jet
engines).
●​ Energy leaves system → Temp ↓

🛠️ Components in Diagram (Top Left)

1.​ Air Inlet → Air enters the system
2.​ Compressor → Increases air pressure (1→2)
3.​ Combustion Chamber → Fuel is added, burned at constant pressure (2→3)
 4.​ Turbine → Expands gases to do work (3→4)
5.​ Exhaust → Gases are expelled (4→1)
6.​ Net Work Out = Work from turbine − Work to compressor​

🌡️ Temperature-Entropy (T–s) Diagram (Bottom Right)-same as 4 processes

●​ Area enclosed = Net work output.

📈 Pressure-Volume (P–v) Diagram (Bottom Left)

●​ Same 4 steps:​

○​ 1→2: Pressure ↑, volume ↓ (compression)

○​ 2→3: Constant pressure, volume ↑ (heat in)
○​ 3→4: Pressure ↓, volume ↑ (expansion)
○​ 4→1: Constant pressure, volume ↓ (heat out)​

🔁 Heat Exchanger Version (Top Right)

●​ Regenerative Brayton Cycle (with heat exchanger)
●​ Waste heat from turbine exhaust is reused to preheat air before
combustion
●​ Increases thermal efficiency​

✅ Summary
●​ Brayton Cycle = basis for gas turbines
●​ Works on air-standard assumptions (ideal gas, reversible processes)
●​ Goal: Produce net positive work (thrust or power) efficiently
●​ Regeneration (via heat exchangers) improves fuel efficiency​

11. Thrust Equation (Rate of Change of Momentum):

12. Rocket Propulsion

Rocket propulsion is the mechanism by which rockets move by expelling mass

(usually hot gases) in the opposite direction. This works on the principle of
Newton's Third Law of Motion:

For every action, there is an equal and opposite reaction.

A rocket engine generates thrust by burning fuel and oxidizer (called propellants)
and pushing the exhaust gases out at high speed through a nozzle.
 ●​ Action: Hot gases are expelled backward.
●​ Reaction: The rocket moves forward.

🚀 Key Components
Component Function
Propellant Fuel + oxidizer that provides energy
Combustion Burns the propellant to generate
chamber high-pressure gas
Nozzle Expels the gas to create thrust
Thrust The force that propels the rocket forward

💡 Important Terms
●​ Thrust: Force generated by the rocket engine.
●​ Specific Impulse (Isp): Efficiency of the engine, measured in seconds.
●​ Delta-v (Δv): Change in velocity a rocket can achieve.

✈️ Types of Rocket Propulsion

Type Description
Chemical Uses chemical reactions (solid or liquid fuel)
Electric Uses electric power to accelerate ions (e.g., ion
thrusters)
Nuclear Uses nuclear energy to heat and expel gases
thermal

🧪 Example: Chemical Rocket (Liquid)

1.​ Fuel: Liquid hydrogen (LH₂)
2.​ Oxidizer: Liquid oxygen (LOX)
3.​ Combustion: Produces steam and energy
4.​ Exhaust: Expelled through nozzle → Thrust