Liquid Oxygen Tank Pressurization Using Nitrogen Buffer Layer
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Solution Overview
Problem
The existing methods for pressurizing liquid oxygen tanks in rocket engines, such as using helium or gaseous oxygen, lead to heat exchanges at the gas/liquid interface that increase the density of gaseous oxygen and can cause the liquid oxygen to overheat, posing risks to the engine and its components, especially the fuel pump.
Innovation Solution
Incorporating nitrogen as a neutral pre-pressurization gas that forms a stable buffer layer on top of the liquid oxygen, maintaining a higher density than gaseous oxygen, thereby preventing direct contact and heat exchange between gaseous oxygen and liquid oxygen during engine operation, and optionally forming a two-phase nitrogen buffer to manage temperature and pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If gaseous oxygen is injected into the tank for pressurization during engine operation, then the tank pressure is maintained, but heat exchanges at the gas/liquid interface increase the temperature and density of gaseous oxygen, causing liquid oxygen to overheat
Solution Approach 1:
The patent introduces a neutral buffer gas (nitrogen or helium) as an intermediary layer between the gaseous oxygen and liquid oxygen. This buffer gas forms a protective interface that prevents direct thermal contact between the warmer pressurization gas and the cryogenic liquid oxygen, thereby maintaining tank pressure while preventing overheating of the liquid oxygen
Solution Approach 2:
The gaseous headspace is segmented into distinct layers: an upper layer of gaseous oxygen for pressurization and a lower buffer gas layer adjacent to the liquid oxygen. This segmentation creates a thermal barrier that isolates the liquid oxygen from direct heat exposure while allowing pressure maintenance through oxygen injection
2Stress or pressure
If gaseous helium is used for pre-pressurization before engine start-up, then the tank is pressurized effectively, but the helium rises in the gaseous headspace causing oxygen to contact liquid oxygen and heat up
Solution Approach 1:
The patent applies preliminary action by first injecting a buffer gas (nitrogen or helium) to create a protective layer on the liquid oxygen surface before introducing gaseous oxygen for pressurization. This preliminary buffer layer prevents subsequent thermal contact between oxygen and liquid oxygen during engine operation
Solution Approach 2:
The buffer gas serves as a preliminary intermediary that establishes a thermal barrier before the main pressurization process begins, preventing the harmful thermal interaction that would otherwise occur when gaseous oxygen contacts liquid oxygen
3Device complexity
If liquid oxygen is drawn and heated to create gaseous oxygen for pressurization, then pressurization is achieved without auxiliary tanks, but the heated oxygen increases the overall mass of the tank
Solution Approach 1:
The system uses itself to generate pressurization gas by drawing liquid oxygen from the main tank, heating it to create gaseous oxygen, and reinjecting it into the headspace. This self-service approach eliminates the need for separate auxiliary pressurization tanks while maintaining a relatively constant overall mass since the oxygen circulates within the system
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively prevents the increase in mass and temperature of gaseous oxygen in the tank, ensuring the liquid oxygen remains within safe limits for engine operation, reducing the risk of overheating and maintaining efficient propulsion.
Implementation Method 1
its density remains higher than that of gaseous oxygen, whether the gaseous oxygen is at its injection temperature (for example, around 300 K) or at a temperature stabilized in the gaseous atmosphere (for example, around 130 K). Thus, the nitrogen used for pre-pressurizing the tank forms a buffer on the surface of the liquid oxygen
Implementation Method 2
liquid oxygen is drawn, the drawn oxygen is heated to obtain gaseous oxygen, and the gaseous oxygen is injected into the gaseous headspace
Implementation Method 3
liquid oxygen is drawn, the drawn oxygen is heated to obtain gaseous oxygen
Implementation Method 4
The heat exchanges that occur at this interface lower the temperature of the oxygen, which increases its density. As a result, the mass of gaseous oxygen in the tank's headspace increases
Data Source
Figure 1
Figure 2~3
AI summary
According to the invention, after a tank (18) is filled with liquid oxygen (20) to be used to supply a rocket engine (10) with fuel, but before the engine (10) is operated, the tank is pressurized by injecting gaseous nitrogen (N) therein. During the operation of the engine (10), liquid oxygen (20) is collected and heated such as to obtain gaseous oxygen, and the gaseous oxygen is injected into the vapor space (42) of the tank, the pre-pressurization nitrogen forming a nitrogen buffer (40) between the liquid oxygen present in the tank and the gaseous oxygen injected into the vapor space.