Cryogenic Fuel Supply With Pressure Buffering for Boil-Off Gas
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Solution Overview
Problem
The inefficiencies in storing and utilizing gaseous fuels like hydrogen in low temperature liquid gas tanks result in significant boil-off gas losses due to pressure limitations, leading to energy wastage and increased apparatus complexity, especially in mobile applications where refueling intervals are long.
Innovation Solution
A system incorporating a pressure store fluidically connected to the low temperature liquid gas tank and rail, allowing for the buffering and reuse of boil-off gas, which includes a cryopump for converting liquid fuel to gas and a compressor to increase pressure, thereby reducing boil-off gas discharge and enhancing fuel utilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a low temperature liquid gas tank is used to store hydrogen, then the volumetric energy density is improved, but the boil-off gas loss increases due to pressure limitations
Solution Approach 1:
The patent changes the pressure parameter by introducing a pressure store that can maintain higher pressures than the low temperature tank alone. This allows the system to utilize the compressed gas phase of hydrogen while periodically refilling from the liquid phase, thereby reducing boil-off losses while maintaining high volumetric energy density during operation.
Solution Approach 2:
The pressure store acts as an intermediary between the low temperature liquid gas tank and the fuel injection system. It buffers the boil-off gas by storing it under pressure, preventing immediate loss, and allows controlled transfer of gas to the injection system when needed, thus mediating the conflict between maintaining pressure and reducing loss.
2Loss of energy
If thermal insulation is enhanced to reduce boil-off, then the energy efficiency is improved, but the device complexity and cost increase
Solution Approach 1:
The pressure store serves as a mediator that reduces the burden on thermal insulation. By providing a pressure buffer that can accommodate boil-off gas without immediate discharge, the system can operate with less aggressive insulation requirements, as the pressure management function is partially transferred to the mechanical pressure store rather than relying solely on thermal barriers.
Solution Approach 2:
The system uses the unavoidable boil-off phenomenon to its advantage by allowing the boil-off gas to naturally pressurize the pressure store. This self-service mechanism converts what would be a loss into a useful pressurization function, reducing the need for active pressure management systems and simplifying the overall thermal and pressure management architecture.
3Loss of substance
If the pressure resistance of the tank is increased to retain boil-off gas, then the fuel utilization is improved, but the apparatus complexity and weight increase
Solution Approach 1:
The patent segments the storage system into two distinct components: a low temperature tank for liquid hydrogen storage and a separate pressure store for gaseous hydrogen storage. This segmentation allows each component to be optimized for its specific function with appropriate pressure ratings, avoiding the need for a single high-pressure resistant tank while achieving better overall fuel utilization.
Solution Approach 2:
The pressure store acts as an intermediary that handles the high-pressure storage function, allowing the low temperature tank to maintain its lower pressure design. This intermediary component enables the system to retain and utilize boil-off gas at high pressures without requiring the primary storage tank to be designed for high pressure, thus reducing overall apparatus complexity.
4Loss of energy
If a pressure store is added to buffer boil-off gas, then the energy efficiency is improved, but the device complexity increases
Solution Approach 1:
The pressure store is designed to perform multiple functions: it buffers boil-off gas, stores compressed hydrogen for fuel injection, and provides pressure regulation for the injection system. This multi-functionality justifies the added complexity by consolidating several system functions into a single component, improving overall energy efficiency without proportionally increasing complexity.
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 system significantly reduces boil-off gas losses, maintains pressure within the tank, and allows a higher proportion of fuel to be used for its intended purpose, improving energy efficiency and reducing apparatus complexity.
Implementation Method 1
a cryopump (7) integrated in the low temperature liquid gas tank (2) for the removal of fuel gas from the liquid aggregate state
Implementation Method 2
a compressor (10) whose lower pressure side is connected to the outlet of the boil-off valve (9) and whose upper pressure side is connected to the pressure store (5)
Implementation Method 3
the permanently occurring partial evaporation, the so-called boil-off, exerts a very great influence on the handling. This inter alia relates to the need for a very effective and thus complex thermal insulation.
Data Source
AI summary
The invention relates to a system for supplying a gaseous fuel that comprises a low temperature tank for receiving the fuel in its liquid aggregate state achieved by cooling and comprises a rail that is fluidically connected to at least one injector device for discharging gaseous fuel into a combustion space. The system is characterized in that it has a pressure store that is configured to receive gaseous fuel and that is fluidically connectable to both the low temperature tank and the rail to buffer fuel coming from the low temperature tank and to supply it to the rail.