08 ATPL Training Gas Turbine Engines 08 Combustion Chambers Part 1 720 X 1280

Summary

The video script delves into the design and function of combustion chambers in turbine engines. It explores how air and fuel are mixed and ignited to generate heat while maintaining efficiency and reducing pollution. It explains the various airflows (primary, secondary, and tertiary) that stabilize combustion and prevent flame extinction, as well as cooling methods to prevent overheating. The script also touches on the role of interconnectors in multi-chamber systems, ensuring continuous ignition across chambers. The overall goal is to balance performance, safety, and environmental impact in engine design.

Takeaways

• 😀 Combustion chambers must generate maximum heat at constant pressure to ensure a steady gas stream for the turbine.
• 😀 Efficient combustion is crucial due to rising fuel costs and growing concerns about atmospheric pollution from exhaust gases.
• 😀 The temperature limit of 1700°C for gases exiting the combustion chamber is determined by the turbine blade materials, which can get damaged if exceeded.
• 😀 Modern turbine materials allow gas temperatures up to 1700°C, with the pre-heated air from the compressor adding an additional 1150°C of heat.
• 😀 Combustion chambers must maintain stable combustion under a wide range of engine operating conditions, with lower power settings requiring lower fuel flows and temperatures.
• 😀 Air velocity needs to be reduced before entering the combustion chamber to sustain the flame, as high-speed air can extinguish it.
• 😀 The air leaving the compressor is slowed down and its pressure increased by passing through a divergent duct before entering the combustion chamber.
• 😀 The combustion chamber's air is divided into primary, secondary, and tertiary flows, each with specific functions to stabilize combustion and manage temperature.
• 😀 The primary air constitutes about 20% of the total airflow and mixes with fuel for combustion, while secondary air forms a vortex to stabilize the flame.
• 😀 Tertiary air, comprising 60% of the airflow, cools the combustion chamber and gas before exiting, ensuring safe operation of turbine blades and nozzle guide vanes.
• 😀 Multiple combustion chamber systems use different cooling methods, including ceramic tiles and transpiration cooling, to manage heat and maintain engine integrity.

Q & A

What is the primary function of the combustion chamber in a gas turbine engine?

The combustion chamber mixes compressed air from the compressor with fuel to generate heat at a constant pressure, creating a heated and accelerated gas stream for the turbine.

Why is efficient combustion increasingly important in modern turbine engines?

Efficient combustion is crucial due to rising fuel costs and growing concerns over atmospheric pollution, as well as the industry's efforts to reduce emissions.

What is the maximum temperature that the gas can reach as it exits the combustion chamber, and why is this limit important?

The maximum gas temperature at the combustion chamber exit is 1700°C, as exceeding this temperature can cause distortion or catastrophic failure of turbine blades and nozzle guide vanes.

How does the design of the combustion chamber help prevent flame extinction in the high-speed airflow?

The airflow velocity is reduced by passing the air through a divergent duct before entering the combustion chamber, and the air is further divided into primary, secondary, and tertiary flows to stabilize the flame.

What role do the swirl veins and flare play in the combustion chamber?

The swirl veins and flare reduce the airflow velocity, promote air recirculation, and help stabilize the flame within the primary zone for efficient combustion.

What is the purpose of the secondary air in the combustion process?

Secondary air, about 20% of the total airflow, enters through secondary air holes and interacts with the primary air to form a toroidal vortex, anchoring the flame and stabilizing combustion.

How is the temperature of the gas reduced after it leaves the primary zone in the combustion chamber?

Tertiary air, about 60% of the total airflow, is introduced into the flame tube to cool both the air casing and the gas, preventing overheating before the gas exits the combustion chamber.

What are some methods used to prevent overheating in the combustion chamber?

Methods include using ceramic-coated tiles inside the flame tube or transpiration cooling, where air flows through laminations in the flame tube to form an insulating air film.

How does the interconnector work in a multiple combustion chamber system?

The interconnector allows the ignition flame to spread between combustion chambers. After lighting one chamber, the pressure differential drives the burning gases through the interconnector to ignite adjacent chambers.

What happens during a 'wet start' in a gas turbine engine?

A wet start occurs when the air-fuel mixture fails to ignite during startup, resulting in excess fuel in the combustion chamber. If not drained before the next attempt, it can cause dangerously high turbine temperatures and a hazardous torching event.