Combustion Chambers and Flammability

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Questions and Answers

What occurs in the Atomization Zone of a liquid propulsion system?

Efficient cooling is necessary to manage turbulent flows

Rapid combustion takes place

Mixing of oxidizer and fuel vapors primarily occurs (correct)

The flame temperature is relatively high

What is a characteristic of premixed flames?

They do not require time for reactant mixing (correct)

They are commonly found in standard liquid rocket engines

They exhibit lower reactivity compared to diffusive flames

They involve mixing of oxidizer and fuel

What is a consequence of diffusive flames in propulsion systems?

They pose a greater danger due to higher reactivity

They reduce the risk of explosive reactions (correct)

They are less common in propulsion systems due to safety concerns

They are characterized by instant reaction without fluid-dynamic slowdown

What is true about the temperature gradient in combustion systems?

It weakens the heat feedback over time Signup and view all the answers

What is a characteristic of the Rapid Combustion Zone in liquid propulsion systems?

It is a highly turbulent environment Signup and view all the answers

What type of flames are commonly found in standard liquid rocket engines?

Diffusive flames Signup and view all the answers

What is a consequence of premixed combustion in confined volumes?

It leads to supersonic flame speeds Signup and view all the answers

What is a key difference between premixed and diffusive flames?

Premixed flames do not require time for reactant mixing Signup and view all the answers

What is the primary concern with nitrous oxide fuel blends in propulsion systems?

Potential for flame back propagation Signup and view all the answers

Why do faster flames tend to stretch the reaction zone?

Because the flame's velocity affects its propagation Signup and view all the answers

What occurs when the reaction zone is excessively stretched?

Incomplete combustion occurs, leading to flame extinction Signup and view all the answers

Where does the highest temperature gradient occur in a premixed flame?

In the reaction zone Signup and view all the answers

What is the purpose of metallic systems in propulsion systems?

To quench back-propagating flames Signup and view all the answers

How do reactants entering the reaction zone experience reduced reaction rates?

Due to reduced heat feedback Signup and view all the answers

What is the primary location of energy loss in a premixed flame?

In the reaction zone Signup and view all the answers

Why do diffusive flames tend to be slower than premixed flames?

Due to the time needed to diffuse and mix Signup and view all the answers

What sustains the flame in combustion chambers?

Heat feedback Signup and view all the answers

What happens when heat feedback is disrupted in combustion chambers?

The reaction halts Signup and view all the answers

What type of flame involves a well-mixed combination of oxidizer and fuel?

Premixed flames Signup and view all the answers

What determines the burning speed in premixed flames?

Global reaction rate Signup and view all the answers

What is the characteristic of diffusive flames?

Separate injection points or ducts for oxidizer and fuel Signup and view all the answers

Why does the flame not propagate downwards beneath the cooking plane in kitchen stoves?

Due to the speed of diffusion of heat Signup and view all the answers

What is the role of the metal plate atop the stove in kitchen stoves?

To act as a flame-stopper Signup and view all the answers

What is the difference between premixed and diffusive flames?

Diffusive flames are slower than premixed flames Signup and view all the answers

Study Notes

Flame Generation

Heat feedback plays a crucial role in flame generation, as it propagates backward, heating incoming reactants and sustaining the flame.
Disrupting heat feedback halts the reaction, similar to blowing out a candle.

Types of Flames

There are two primary types of flames: premixed and diffusive.
Premixed flames involve a well-mixed combination of oxidizer and fuel, where chemical kinetics dictate the reaction speed.
Examples of premixed flames include Otto cycle engines and Bunsen burners.
Diffusive flames entail separate injection points or ducts for oxidizer and fuel, where diffusion governs the reaction.
Examples of diffusive flames include kitchen stoves.

Characteristics of Premixed and Diffusive Flames

Premixed flames have higher reactivity and are prone to explosions, deflagration, or detonation.
Diffusive flames are slower due to the time required for reactant mixing, making them less prone to explosive reactions.
Premixed conditions allow instant reaction without fluid-dynamic slowdown, potentially causing violent combustion.
Diffusive flames are commonly found in standard liquid rocket engines, microscale combustion in composite solid propellants, and hybrid rocket propulsion systems.

Combustion Process in Liquid Propulsion Systems

The combustion process unfolds in three distinct regions: atomization, rapid combustion, and vaporization.
The atomization zone is where liquid fuel is atomized into droplets and mixed with oxidizer vapor.
The rapid combustion zone is where rapid combustion takes place in a highly turbulent environment.

Characteristics of Diffusive Flames in Propulsion Systems

Diffusive flames are slower than premixed flames due to the time required for diffusion and mixing.
Nitrous oxide fuel blends (NOFB) offer promising performance and simplified management in propulsion systems.
Metallic systems are utilized to quench back-propagating flames and ensure safety and efficiency in propulsion systems.

Premixed Flame Profile

The temperature profile of a premixed flame shows a strong gradient in the reaction zone.
Fresh gases enter from the left, while combusted gases exit from the right.
The heat flux moving from right to left is a key factor in the energy balance equation.

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Description

Understanding the role of heat feedback in combustion chambers, where oxidizer and fuel mix, and how it sustains flame generation. Explore the process of continuous reaction and heat propagation.