Aircraft Gas Turbine: Fuel Effects on Operability of Aircraft Gas Turbine Combustors

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Table of Contents

Introduction
Losses in Parts of Aircraft
Types of Gas Turbine Air Intakes
The Operational Requirements of Axial Compressors
Combustion Chambers
Turbine Stage
Turbine Engines Intercooling
Reference List

Introduction

Gas turbine engines are used in aircraft and industrial applications. They use a combustion process to generate high-temperature gases that power a turbine, which drives a compressor. They consist of several parts that generate power, including the compressor, combustion chamber, turbine, and control systems. This study will discuss the different types of compressors, combustion chambers, and turbines used in gas turbine engines, as we as the losses that occur.

Losses in Parts of Aircraft

Axial compressors are machines that increase the pressure of a gas or a liquid by reducing its volume. The losses in axial compressors are typically caused by air leakage around the compressor blades and by friction between the blades and the incoming air. Additionally, due to the high pressure and velocity, some of the kinetic energy of the air is lost due to viscous forces in the compressor.

Axial turbines are machines that use the kinetic energy of a fluid to generate mechanical power. The losses that occur in axial turbines include friction losses due to the friction between the blades and the incoming fluid, as well as losses due to fluid leakage around the blades (Schobeiri, 2019). Additionally, some of the kinetic energy of the fluid is lost due to viscous forces at the blades.

Fans are machines that move air or other gases from one place to another. The losses in fans are mostly caused by friction between the fan’s blades and the air (Colket and Heyne, 2021), as well as by air leakage around the blades. Additionally, according to Wild (2018) some of the kinetic energy of the air is lost due to viscous forces at the blades.

Losses due to sudden enlargement and contraction in turbulent flow occur when a fluid is forced to flow through a pipe with sudden enlargements or contractions in the cross-sectional area. In such cases, the kinetic energy of the fluid is dissipated due to the turbulence generated, resulting in an overall decrease in the pressure and velocity of the fluid (Jamieson, 2018). Additionally, some of the kinetic energy of the fluid is lost due to viscous forces.

Types of Gas Turbine Air Intakes

Supersonic intakes are gas turbine air intakes designed to operate at supersonic speeds, typically in the range of Mach 1.5 to Mach 3. Due to the high speeds involved, the intakes must be designed to minimize the shock losses when the supersonic air is slowed down to subsonic speeds (Schobeiri, 2019). The design of supersonic intakes requires careful consideration of the duct rating, area ratio, and the methods of diffusion used.

Asymmetric intakes

Asymmetric intakes are gas turbine air intakes that operate at subsonic speeds, typically from Mach 0.5 to Mach 1.5. The design of asymmetric intakes requires careful consideration of the area ratio, the methods of diffusion used, and the aerodynamic considerations for the intake design. Additionally, the intake design must account for the flow separation that can occur when the flow is not symmetric.

Subsonic High-Bypass Fans

The design of subsonic high-bypass fans involves careful consideration of the fan geometry, the area ratio, the methods of diffusion used, and the aerodynamic considerations for the design of the fan. Additionally, the design of the fan must account for the effects of tip clearance losses and the potential for shock losses at the fan inlet (Schobeiri, 2019). Additionally, careful consideration must be given to the fan blade stagger.

The Operational Requirements of Axial Compressors

Operational Requirements

The work done factor measures the work done by the compressor per unit of the air mass and is typically expressed in horsepower or kilowatts. Flow coefficient measures the mass flow rate of air through the compressor (Giampaolo, 2020). The stage temperature rise coefficient measures the temperature rise of the air through the compressor. Finally, surge is a phenomenon that occurs when the operating conditions of the compressor are changed (Korpela, 2019), resulting in an abrupt and large decrease in pressure and flow rate.

Operation Advantages

Axial flow compressors are advantageous due to their ability to achieve high-pressure ratios with a relatively small number of stages. Morever, they are more efficient than centrifugal compressors and can operate at higher speeds (Jamieson, 2018). The inlet is responsible for drawing the air into the compressor, the blades are responsible for compressing the air (Giampaolo, 2020). The outlet is responsible for directing the compressed air out of the compressor, and the shaft is responsible for connecting the blades to the motor.

Centrifugal Compressors

Centrifugal compressors are rarely used in modern gas turbine engines, as they are typically less efficient than axial compressors. The important equations for centrifugal compressors include the Euler turbine equation, the slip factor, the efficiency, and the temperature ratio (Van den Braembussche, 2019). The Euler turbine equation is used to calculate the power required, the temperature ratio is used to calculate the temperature rise of the air through the compressor.

Combustion Chambers

There are three main types of combustion systems found in gas turbine engines: direct combustion, indirect combustion, and dual combustion. Fuel injection is when the fuel is injected into the chamber at the correct time and pressure to ensure a stable and efficient combustion process (Giampaolo, 2020). The stability loop is used to monitor and adjust the fuel injection process to maintain a stable combustion process.

Dissociation is breaking down molecules into their constituent atoms and is a crucial part of the combustion process, the efficiency of the combustion process depends heavily on the extent of dissociation. Finally, flame stabilization is a process that is used to ensure that the flame produced in the combustion chamber is stable and efficient (Korpela, 2019). Flame stabilization can be achieved through the use of flame holders or flame rods.

Turbine Stage

A turbine stage is a component that is used to convert the energy in a pressurized fluid into mechanical energy that can be used to do work. Turbine stages consist of a rotor, a set of blades, and a nozzle. The rotor is responsible for transferring the energy of the incoming fluid to the blades, and the blades are responsible for converting the energy of the fluid into mechanical energy. The nozzle is responsible for controlling the flow of the fluid and directing it towards the blades. The operational requirements of a turbine stage depend on the type of turbine engine and the type of turbine stage being used.

Turbine Engines Intercooling

Cooling requirements refer to the amount of cooling needed to ensure that the engine operates at its optimal temperature. Dilution refers to introducing additional air into the combustion chamber to reduce the combustion temperature and the amount of pollutants produced (Korpela, 2019). Dilution zone performance refers to the ability of the engine to mix the additional air with the fuel to achieve the desired air-fuel ratio. Finally, mixing performance refers to the ability of the engine to effectively mix the fuel and air to achieve the desired combustion process.

Intercooling is a process that improves the performance of gas turbine engines by cooling the air before it enters the combustion chamber. This reduces the air temperature, which reduces the combustion temperature and improves the efficiency of the combustion process (Colket and Heyne, 2021). Additionally, intercooling can reduce the amount of pollutants produced, as lower combustion temperatures lead to less complete combustion and fewer pollutants being produced.

Reference List

Colket, M. and Heyne, J. (edn.), 2021 Fuel effects on operability of aircraft gas turbine combustors. Reston: American Institute of Aeronautics and Astronautics, Inc..

Giampaolo, A., 2020 Compressor handbook: principles and practice. Boca Raton: CRC Press.

Jamieson, P., 2018 Innovation in wind turbine design. 2^nd edn. Hoboken: John Wiley & Sons.

Korpela, S.A., 2019 Principles of turbomachinery. 2^nd edn. Hoboken: John Wiley & Sons.

Schobeiri, M.T., 2019 Gas Turbine Design, Components and System Design Integration: Second Revised and Enhanced Edition. 2^nd edn. Heidelberger: Springer Nature.

Van den Braembussche, R., 2019 Design and analysis of centrifugal compressors. Hoboken: John Wiley & Sons.

Wild, T.W., 2018 Aircraft powerplants. New York: McGraw-Hill Education.

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