Supercritical CO2 Heat Engine Isothermal Expansion
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Solution Overview
Problem
Current heat engines face inefficiencies and short service life due to reliance on high-speed processes, high compression work, and sealing issues, particularly in high-compression Stirling engines, which hinder thermodynamic efficiency and longevity.
Innovation Solution
A supercritical cycle with isothermal expansion and isochoric pressure build-up, utilizing an intermediate heat storage device for thermal energy recuperation, and a two-cylinder design with a thermally conductive oscillator piston for isothermal heat input, achieving high expansion ratios and reduced mechanical pre-compaction work.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high-speed processes and high compression work are used to improve power output, then productivity increases, but wear and corrosion increase significantly reducing service life
Solution Approach 1:
The patent changes the operating parameters by using supercritical CO2 instead of conventional gases, operating at supercritical conditions (above 31°C and 73.8 bar) to achieve high density and compressibility while enabling slower stroke frequencies. This parameter change allows high power density without the wear and corrosion associated with high-speed conventional engines
Solution Approach 2:
The patent employs hydraulic energy extraction where the expanding supercritical CO2 directly drives a hydraulic motor, converting thermal energy to mechanical energy through fluid pressure rather than traditional mechanical linkages. This pneumatic-hydraulic system reduces mechanical wear while maintaining high power output
2Use of energy by moving object
If isothermal expansion is used to maximize thermodynamic efficiency, then energy conversion efficiency improves, but cycle time increases reducing productivity
Solution Approach 1:
The patent uses supercritical CO2 whose thermodynamic properties near the critical point enable extremely rapid phase changes and heat transfer. This allows near-isothermal expansion to be achieved much faster than with conventional gases, reconciling high efficiency with acceptable cycle times
Solution Approach 2:
The patent implements a cyclic process with repeated compression and expansion strokes, where the working medium is periodically heated and expanded. The oscillator piston creates controlled periodic motion that maintains near-isothermal conditions during expansion while keeping overall cycle time practical for power generation
3Power
If high working pressures are used to improve power density, then power output increases, but sealing problems worsen particularly in Stirling engines
Solution Approach 1:
The patent uses the supercritical CO2 itself as both the working medium and hydraulic fluid, eliminating the need for separate sealing systems. The high-pressure CO2 is contained in a closed loop where it directly actuates hydraulic motors, reducing sealing interfaces compared to traditional piston-crank mechanisms
Solution Approach 2:
The patent introduces a hydraulic motor as an intermediary between the expanding gas and the generator shaft, allowing the high-pressure gas to drive the system without direct mechanical contact requiring seals. The hydraulic fluid transmits the energy while the generator can be positioned separately, simplifying sealing requirements
4Use of energy by moving object
If internal combustion is used to achieve high-speed heat input, then heat input rate improves, but compression work and wear increase significantly
Solution Approach 1:
The patent extracts the combustion process from the working chamber, using external combustion to heat the supercritical CO2. This separates the high-temperature combustion zone from the working medium, allowing rapid heat input without subjecting the CO2 to corrosive combustion byproducts that cause wear and corrosion in internal combustion engines
Solution Approach 2:
The patent uses a heat exchanger as an intermediary to transfer thermal energy from the combustion gases to the supercritical CO2 working medium. This allows efficient heat transfer while preventing direct contact between the corrosive combustion products and the working medium, eliminating wear and corrosion issues
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 approach enables nearly complete conversion of heat into mechanical energy with high recuperation rates and extended service life by minimizing mechanical energy requirements and maintaining high pressures at slow stroke frequencies, while reducing cooling losses and wear.
Implementation Method 1
a working medium in a working space being supercritically expanded isothermally at a predetermined upper working temperature with heat supply external to the working space
Implementation Method 2
a thermally conductive oscillator piston for isothermal heat input
Implementation Method 3
utilizing an intermediate heat storage device for thermal energy recuperation
Implementation Method 4
with the cyclic process always taking place above the critical pressure of the wet vapor curve of the working medium
Data Source
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AI summary
Supercritical cyclic process, which enables an almost complete conversion of heat into mechanical energy, and reciprocating piston device in order to convert same. The isothermal expansion of the gaseous working medium is carried out by supplying heat via the cylinder wall and an oscillator piston which has turbulator slots, which oscillator piston oscillates in a linear manner in the expanding working chamber. The external heat is almost entirely supplied during the isothermal expansion at a slow stroke frequency, while all other steps – isochoric pressure build-up, isobaric expansion and isobaric reliquefaction – are almost completely carried out by means of the internal recuperator. The working piston is designed as a hollow free piston having sealing rings on the cold end and, just as the oscillator piston drive, follows the stroke profile of control piston, which is driven by the external master drive. All external piston drives are operated in a largely force-neutral manner with hydraulic pressure equalisation and require only little mechanical supply of energy as a result of the process. Owing to the elongated design, the device has a high thermal resistance in the direction of the hydraulic pressure chambers and/or cold poles and requires relatively little external cooling as a result of the process.