Team 5

Alvin

Jian Ping

Freddie

Content page

• Principles of a jet turbine engine (JP)

• Types of gas turbine engine & comparison (A)

• Modules of a jet turbine engine (JP)

• Engine inlet design (F)

• Conclusion (engine recommendation) (F)

Principles Of A Jet Turbine Engine

• A mechanical device which produces forward thrust by forcing the movement of a mass of gases rearward.

• The compressor to compress the incoming air to high pressure

• Combustion area to burn the fuel and produce high pressure, high velocity gas.

• Turbine to extra the energy from the higher pressure, high velocity gas flowing from the combustion chamber

Types of gas turbine engines

1. Turbofans

Turbofan engines have large diameter main fans to produce great thrust.

They have a bypass ratio (ie. 5:1), which is the mass of air that bypasses the core (goes around the core).

Turbofans have greater fuel efficiency and are more quiet due to the cooler air from the bypass duct cooling down the combusted air.

Turbofans accelerate a large mass of air at lesser speed.

Path of bypassed air

2. Turbojets

Turbojet engines are very similar to turbofan engines, however there are some differences.

Turbojet engines DO NOT have any bypass ratio. All the air enters the engine for combustion.

Turbojet engines have a rather poor thrust specific fuel consumption.

Even modern fighter jets are already using turbofans instead of turbojets (Low bypass ratio turbofans with afterburners e.g : Pratt & Whitney F119 engine used on the F22 Raptor) .

Turbojet engines move a small mass of air at high speed.

3. Turboprop

Turboprop engines are gas turbine engine with a propeller replacing the fan.

There is a gearbox (reduction gear) which is linked to the turbine, reducing the speed of the propeller tips, preventing it from reaching supersonic speeds.

Propeller efficiency drops when it reaches or exceeds Mach 1, this the reduction gear is required.

Turboprops are usually used in smaller low speed aircrafts as propellers lose efficiency when the airspeed increases.

4. Turboshaft

Turboshaft engines are focused on producing shaft power instead of jet propulsion.

A shaft driven by a turbine in the exhaust which is connected to the rotors for a helicopter.

Turboshaft engines are used in applications in which sustained high power is needed, light weight & small size.

Modules Of A Jet Turbine Engine

Subsonic inlet

• When a subsonic airflow is induced into a divergent nozzle, the flow velocity is reduced and the static pressure is increased. The air-intake used for a subsonic flow is composed of a subsonic diffuser, i. e., a divergent nozzle.

Supersonic inlet

• when the airflow is supersonic, the airflow velocity is reduced and the static pressure is increased in the convergent part of a supersonic diffuser. After passing through the throat of the nozzle, the airflow velocity decreases once more in the divergent part.

Conclusion (engine recommendation)

• For today’s conclusion of the problem, we have decided to recommend the turbofan engine to be used in the aircraft.

• The reason for choosing the turbofan for this purpose is because turbofans are more fuel efficient, silent and have a performance envelope suitable to the aircraft. Turbofans also have a higher thrust to weight ratio.