GAS TURBINE INTRODUCTION (POWERPLANT REVIEW) 29/08/23

POWERPLANT - GAS TURBINE INTRODUCTION 29/08/23

WHAT IS GAS TURBINE?

Rotary engine that extracts energy from a flow of combustion gases. 

Primary advantages > power to weight ratio.

Turbine is suit of aircraft propulsion.

Turbine is a true example of Newton 3rd law.

Turbine propel airmass backward in order to move forward.

Formula to calculate the basic force generated on the gas turbine.

F = M.a > Force = mass x acceleration --> Thrust force = M x (Vo-Vi) + Pressure Thrust

Vo> of the air

vi> Inlet Velocity

Propeller drives a large amount of air backward slowly, where gas turbine throws a small amount/ mass of air quicker.

TYPE OF GAS TURBINE

- Turbofan/ turbojet. (Low/ High bypass)

- Turbo shaft.

- Turbo prop.

- Straight Jet.

HOW TURBINE WORKS?

Four stroke cycle > otto cycle (Intake, Compress, Power, Exhaust).

Gas turbine > Brayton cycle (Combustion occurs at constant pressure).

1. Air enters ATM Pressure enter engine.

2. Air is compressed.

3. Fuel is added in combustion chamber > Pressure loss about 3-6 %, but increase in air volume.

4. Exhaust.

TEMPERATURE LIMIT

The higher the temperature, the greater the expansion of gases > more efficient.

APPLICATION OF THE GAS LAW

Boyle = P x V = K

Charles = V/T = K (Most use for turbine engine)

Combine Gas Law = (P x V)/T = K

The product of the pressure and the volume of a quantity of gas divided by its absolute temperature is a constant.

(Philosophy, Prosedur, Callout, Memory item) > is an important thing when you want to fly certain aircraft.

More dense the air, more harder the compressor have to work > Shown slightly RPM drop, however that's will be compensate by the FCU (Fuel Control Unit).

During combustion and addition to fuel burn > Rise in volume but almost constant pressure

During the Air Expansion > Pressure decrease > Temp decrease > Volume Increase

DUCT DESIGN

Duct design affect the air pressure (Potential) and velocity.

Example, on the exhaust > pressure drop, but the velocity increase, Because of the duct exhaust shape

Divergence duct (Membersar) > Velocity drop, pressure increase or as called "Compressor Delivery Air".

Convergence duct (Menyempit) > Velocity increase, Pressure drop ex., for propel the turbine blades.

AIRFLOW

When a compressor and turbine are joined together on one shaft, it's called a spool.

The output from a turbo-propeller engine is the sum of the shaft power developed at the turbine and the residual jet thrust. This is called Equivalent Shaft Horsepower (ESHP).

Major difference between turbofan and turboprop > that in the former almost all the energy in the gas stream into mechanical power.

Reduction gear box > regulate the fan RPM so it's become more normal/ Acceptable than the RPM in the compressor.

In the turboprop > Reverse airflow > air intake enters from the forward side of the engine, but then it will be directed all the way to the back of the engine where the whole gas turbine cycle starts.

Turboshaft > free turbine (not connected to one shaft) > reverse flow > require a centrifugal compressor to be used in high pressure compressor stage, which allow the air to be thrown out radially in order to enter combustion chamber in right direction.

Bypass ratio is the ratio of the airflow between the duct and the hot air.

low ratio is consider (2:1), high (5:1).

Bypass Ratio for fighter jet (0,2:1 - 1:1) > still efficient

The closer the aircraft speed comes to the jet efflux (Speed yang keluar dari engine), the more efficient the propulsion unit becomes.

13.000 is the limit of flying without pressurization.

Modular construction engine method > less expensive to repair, because the engine parts can be separated. (Jadi, tidak perlu ganti semua engine, hanya ganti part yang rusak saja).