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Questions and Answers
What occurs in the Atomization Zone of a liquid propulsion system?
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?
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?
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?
What is true about the temperature gradient in combustion systems?
What is a characteristic of the Rapid Combustion Zone in liquid propulsion systems?
What is a characteristic of the Rapid Combustion Zone in liquid propulsion systems?
What type of flames are commonly found in standard liquid rocket engines?
What type of flames are commonly found in standard liquid rocket engines?
What is a consequence of premixed combustion in confined volumes?
What is a consequence of premixed combustion in confined volumes?
What is a key difference between premixed and diffusive flames?
What is a key difference between premixed and diffusive flames?
What is the primary concern with nitrous oxide fuel blends in propulsion systems?
What is the primary concern with nitrous oxide fuel blends in propulsion systems?
Why do faster flames tend to stretch the reaction zone?
Why do faster flames tend to stretch the reaction zone?
What occurs when the reaction zone is excessively stretched?
What occurs when the reaction zone is excessively stretched?
Where does the highest temperature gradient occur in a premixed flame?
Where does the highest temperature gradient occur in a premixed flame?
What is the purpose of metallic systems in propulsion systems?
What is the purpose of metallic systems in propulsion systems?
How do reactants entering the reaction zone experience reduced reaction rates?
How do reactants entering the reaction zone experience reduced reaction rates?
What is the primary location of energy loss in a premixed flame?
What is the primary location of energy loss in a premixed flame?
Why do diffusive flames tend to be slower than premixed flames?
Why do diffusive flames tend to be slower than premixed flames?
What sustains the flame in combustion chambers?
What sustains the flame in combustion chambers?
What happens when heat feedback is disrupted in combustion chambers?
What happens when heat feedback is disrupted in combustion chambers?
What type of flame involves a well-mixed combination of oxidizer and fuel?
What type of flame involves a well-mixed combination of oxidizer and fuel?
What determines the burning speed in premixed flames?
What determines the burning speed in premixed flames?
What is the characteristic of diffusive flames?
What is the characteristic of diffusive flames?
Why does the flame not propagate downwards beneath the cooking plane in kitchen stoves?
Why does the flame not propagate downwards beneath the cooking plane in kitchen stoves?
What is the role of the metal plate atop the stove in kitchen stoves?
What is the role of the metal plate atop the stove in kitchen stoves?
What is the difference between premixed and diffusive flames?
What is the difference between premixed and diffusive flames?
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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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