CO2 Gas Expansion Engine Subcritical Cycle
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Solution Overview
Problem
Gas expansion engines using CO2 as a working fluid face inefficiencies due to high compressor work requirements and emission of CO2 into the atmosphere, particularly when operating above the critical point, which limits the utilization of heat energy at low thermal ambient temperatures.
Innovation Solution
A regenerative closed circuit method for CO2 gas expansion engines that operates below the critical point, utilizing a two-stroke process with a reciprocating piston and integrated condensation, where CO2 undergoes heat exchange as a two-phase fluid to generate mechanical work, keeping the thermodynamic state subcritical and allowing for efficient energy recovery from low-thermal sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If gas expansion engines operate above the critical point of CO2, then mechanical work can be generated, but high compressor work is required for gas compression which reduces injected useful work
Solution Approach 1:
The patent changes the thermodynamic parameters by operating below the critical point of CO2 (temperature below 31.1°C and pressure below 73.8 bar) instead of above the critical point. This parameter change allows the system to utilize the two-phase region of CO2 for expansion work while avoiding the high compressor work requirements associated with supercritical operation.
Solution Approach 2:
The patent exploits the phase transition characteristics of CO2 in the two-phase region (liquid-vapor equilibrium) below the critical point. By operating in this phase transition region, the system can generate mechanical work through expansion while the condensation work integrated into the cycle compensates for the compression work, reducing net energy consumption.
2Power
If gas expansion engines operate above the critical point, then gas expansion work can be performed, but heat energy utilization from low thermal environmental temperatures is largely excluded
Solution Approach 1:
The patent changes the operating temperature parameter to be below the critical temperature of CO2 (31.1°C), which enables the system to utilize heat energy from low thermal environmental temperatures. This parameter change allows heat exchange with ambient sources to drive the expansion process, converting previously unusable low-temperature heat into useful work.
Solution Approach 2:
The patent converts the previously harmful effect of low thermal environmental temperatures (which were considered waste heat) into a beneficial resource. By operating below the critical point, the system can use ambient heat to drive the CO2 expansion cycle, transforming environmental heat into useful mechanical work.
3Use of energy by moving object
If CO2 is used as working fluid in gas expansion engines, then large amounts of thermal energy can be transported, but CO2 is emitted into the atmosphere causing environmental harm
Solution Approach 1:
The patent implements a feedback mechanism through the integrated condensation work and closed cycle operation. The CO2 that would otherwise be emitted is condensed and returned to the expansion chamber, creating a closed loop that recycles the working fluid and eliminates atmospheric emissions while maintaining thermal energy transport capability.
Solution Approach 2:
The patent recovers the CO2 that would normally be discarded as emission. Through the integrated condensation process, the CO2 is recovered from the expansion chamber and returned to the heat exchanger for reuse, transforming a waste product into a valuable working fluid resource.
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 method enables the energetic utilization of low-thermal heat energies from ambient temperatures, transforming them into environmentally neutral drive energy for mobile and static systems, providing regenerative energy potentials that are usable anywhere and at any time, reducing energy losses and emissions.
Implementation Method 1
the inlet volume of the gas liquefies before the second piston reversal point is reached by the reciprocating piston
Implementation Method 2
integrated condensation, where CO2 undergoes heat exchange as a two-phase fluid
Implementation Method 3
via a heat exchanger, isobaric heat transfer is carried out on gas drawn from the storage tank in a liquefied state until it evaporates
Implementation Method 4
In the adiabatic expansion case, the mechanical work delivered by a gas expansion engine originates from the enthalpy stored in the CO2 gas
Implementation Method 5
its volume can be altered by changes in pressure and/or temperature, undergoing mass transition phases from gaseous to liquid and solid, and vice versa
Data Source
Figure 1~3
Figure 4~5
AI summary
The main feature of the invention is an energy method for using low-grade thermal heat sources, preferably from natural ambient temperatures, such as in air, water or the ground, to generate, by heat exchange, usable environmental energy for carrying out useful mechanical or hydraulic work and to transform said energy in an environmentally friendly manner using a non-critical CO2 working cycle process in gas expansion engines with integrated condensation work, for mobile and static drive systems.