Split Cycle Engine with Regenerator for Compression Work Reduction
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Solution Overview
Problem
Split cycle engines face inefficiency due to heat loss from the expansion cylinder, which reduces brake thermal efficiency, as the hot expansion cylinder experiences greater heat loss compared to the Otto cycle engine.
Innovation Solution
Incorporating a liquid-phase coolant, such as liquid nitrogen, into the compression cylinder to absorb heat during compression, maintaining quasi-isothermal conditions, and using a regenerator to capture exhaust heat and increase net torque, while managing exhaust heat through a second working fluid system to enhance torque production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the expansion cylinder is maintained at higher temperature to improve combustion efficiency, then brake thermal efficiency is improved, but heat loss to atmosphere increases
Solution Approach 1:
The patent captures the harmful heat loss from the expansion cylinder exhaust and converts it into a beneficial resource by directing it through a heat exchanger to preheat the compressed working fluid before it enters the expansion cylinder. This transforms waste heat into useful thermal energy, improving overall brake thermal efficiency while reducing atmospheric heat loss.
Solution Approach 2:
The system recovers heat that would otherwise be discarded to the atmosphere through the exhaust. By implementing a heat recovery mechanism where exhaust heat is transferred to the compressed working fluid, the patent prevents energy waste and reuse it to enhance the thermal state of the working fluid entering the expansion cylinder.
2Device complexity
If compression is performed adiabatically as in traditional engines, then the process is simple, but the work required for compression is high
Solution Approach 1:
The patent introduces a coolant as an intermediary substance in the compression cylinder that absorbs heat during the compression process. This mediator enables quasi-isothermal compression by maintaining a more constant temperature, significantly reducing the work required for compression compared to adiabatic compression, while the heat is subsequently recovered and utilized.
Solution Approach 2:
The coolant undergoes phase transition from liquid to gas during compression, absorbing substantial heat in the process. This phase change mechanism enables effective heat absorption during compression, maintaining quasi-isothermal conditions and reducing compression work, while the heat is later recovered through the heat exchanger.
3Use of energy by moving object
If a coolant is injected into the compression cylinder to achieve quasi-isothermal compression, then compression work is reduced, but the system complexity increases
Solution Approach 1:
The coolant serves multiple functions: it cools the compression cylinder walls, absorbs compression heat through phase transition, and its heated vapor becomes part of the working fluid mixture. The heat exchanger also serves dual purposes by cooling the exhaust and preheating the compressed working fluid. This multi-functionality reduces the need for separate systems and justifies the added complexity through enhanced efficiency.
Solution Approach 2:
The patent merges the coolant system with the working fluid system, where the coolant vapor mixes with the compressed working fluid and both enter the expansion cylinder together. The heat exchanger also combines exhaust cooling and working fluid heating in a single component. This integration reduces overall system complexity despite the addition of the coolant injection 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 approach reduces the work required for compression, enhances brake thermal efficiency, and increases torque production by effectively utilizing heat that would otherwise be lost, leading to a more efficient engine operation.
Implementation Method 1
the coolant boils from its liquid phase to its gas phase in the compression cylinder and passes, with the working fluid, into and the expansion cylinder. The coolant may be liquid nitrogen, for example. As the coolant boils it absorbs heat that is produced as a result of the compression so that the compression is at least quasi-isothermal.
Implementation Method 2
the cold (or relatively cold) fluids in compression side of the system are separated from the hot expansion cylinder by a recuperator. Following combustion, the exhaust valve of the expansion cylinder is opened and the hot exhaust product is released from the expansion cylinder and directed through the heat exchanger, thus providing the heat source that increases the temperature of the high pressure working fluid supplied to the expansion cylinder.
Implementation Method 3
Fuel, typically diesel fuel or natural gas, is then injected into the heated compressed working fluid and burnt. Combustion of the fuel/working fluid mixture drives the power stroke of the working piston to produce torque.
Data Source
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AI summary
A split-cycle engine (4), comprising a compression cylinder (10) having a first volume (12) for a first working fluid and a second volume (14) for a second working fluid, the first volume and second volume being separated by the compression piston (20), an expansion cylinder (50) having a first volume (52) for the first working fluid and a second volume (54) for the second working fluid, the first volume and second volume being separated by the expansion piston (60), and a fluid coupling (90) between the second volume 14 of the compression cylinder (10) and the second volume (54) of the expansion cylinder (50), wherein the two second volumes (14, 54) and the fluid coupling (90) provide a closed volume for the second working fluid, wherein the fluid coupling (90) comprises a regenerator (92) arranged such that the two second volumes (14, 54) are thermally decoupled.