Gasturbine Performance Deel 1

Propulsion by Aircraft Gas Turbines

• The principle of propulsion by aircraft gas turbines is the increase of the air's velocity.

Jet Engine Efficiency

• The propulsive efficiency of a jet engine is lowest when the propulsive efficiency is lowest.

Thrust Calculation

• For the calculation of the thrust of an unchoked turbojet, the mass flow and the velocity of the airflow are required.

Reciprocating Engine

• The most common arrangement of the pistons in a reciprocating engine of a propeller aircraft is inline.

Piston Movement

• When the mass of the piston is removed, the piston moves up VERY slowly.

Otto Cycle

• In a petrol engine whose thermodynamics is described by the Otto-cycle, the ignition is spark ignition.

Increasing Efficiency

• To increase the efficiency of a reciprocating engine, the compression ratio can be increased without changing the dimensions of the piston.

Compression Ratio

• In a reciprocating engine, the compression ratio is the ratio of the maximum volume to the minimum volume.

Work Per Second

• If the RPM of a reciprocating engine is increased and the fuel-air ratio remains the same, the work per second increases and the specific work decreases.

Diesel Engine

• A Diesel engine has a higher efficiency than a gasoline engine due to its higher compression ratio.

Turboprop

• The turboprop is driven by the propeller.

Total Enthalpy

• The total enthalpy includes kinetic energy, but not potential energy.

Inlet Temperature

• In the inlet of a turbofan, the temperature of the airflow decreases, but the total temperature remains the same.

First Law of Thermodynamics

• The First Law of Thermodynamics applied to a combustion chamber is ΔE = Q - W.

Thermal Efficiency

• The thermal efficiency of a gas turbine mainly depends on the turbine inlet temperature (TIT).

Total Efficiency

• The total efficiency is the ratio between the power absorbed by the propeller and the power released by the turbine.

Fuel-Air Ratio

• The largest fuel-air ratio is needed in a combustion chamber with a low inlet temperature and a high temperature increase.

Critical Pressure

• If the outlet is replaced by an outlet with a larger opening, the critical pressure decreases.

Isentropic Process

• If the process in the compressor is isentropic, the increase of the total temperature of the air is less than when it is adiabatic.

Increase in TIT

• The increase of the TIT has a beneficial effect on the thermal efficiency.

Thrust

• When cruise altitude increases, the thrust decreases, but the specific thrust increases.

Bypass Ratio

• If the airflow through the bypass decreases and the airflow through the core increases, the BPR decreases.

Geared Turbofan

• The advantage of a geared turbofan is that the turbine can rotate faster than the fan.

Take-Off

• An assumed temperature is determined for the take-off.

Propulsive Efficiency

• The parameters that determine the propulsive efficiency of a turbofan engine are the fuel-air ratio, specific thrust, and specific work.

Compressor

• The casing of the compressor converges to keep the mass flow of the airflow constant.

Drum-Type Rotor

• A drum-type rotor is heavier compared to a disc-type rotor.

Rotor and Stator

• In the rotor of a compressor, the total temperature increases, and in the stator, the temperature stays the same.

Axial Velocity

• In the compressor, the absolute velocity in the rotor decreases, and in the stator, it increases.

Compressor Design

• To design a compressor to transfer a maximum amount of power to 1 kg of air, a combination of a low axial velocity, a high rotational velocity, and a high blade curvature is required.

Blade Stall

• If the relative airflow on half the blade height does not exactly follow the blade shape, blade stall might occur due to a high angle β1.

Multi-Stage Compressor

• A compressor consists of a low- and high-pressure compressor, and the pressure increase in each stage is cumulative.

Velocity Triangle

• The velocity triangle at the entrance of the impeller of a centrifugal compressor differs from that of an axial compressor due to the radial velocity component.

Radial Compressor

• The radial compressor's stage has a relatively high pressure ratio compared to an axial compressor.

Impeller and Diffuser

• In an impeller, the total temperature increases, and in a diffuser, it decreases.

Turbine Blade

• Compared to a turbine blade, a compressor blade has a lower camber angle.

Turbine Passage

• To expand the gas and get a high gas velocity, the passage between blades of the turbine must be convergent.

Centrifugal Compressor

• The velocity triangle at the entrance of the impeller of a centrifugal compressor differs from that of an axial compressor due to the radial velocity component.

Impulse Turbine

• In an impulse turbine, the pressure drop takes place in the nozzle.