Split-Cycle Engine Regeneration for Expansion Heat Loss
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Solution Overview
Problem
Split cycle engines face inefficiency due to high heat loss from the expansion cylinder, leading to reduced brake thermal efficiency, as the hot expansion cylinder loses heat to the atmosphere and engine components.
Innovation Solution
Incorporating a liquid-phase coolant, such as liquid nitrogen, in the compression cylinder to absorb heat during compression, maintaining quasi-isothermal conditions and reducing work required for compression, while utilizing a regenerator to capture and redirect exhaust heat for increased torque production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the expansion cylinder is maintained at high temperature to improve combustion efficiency, then power output is improved, but heat loss to atmosphere increases
Solution Approach 1:
The patent captures the harmful heat loss from the expansion cylinder exhaust and redirects it through a regenerator to preheat the compressed working fluid before it enters the expansion cylinder. This converts the waste heat into a beneficial resource, reducing the energy required for heating the working fluid and improving overall thermal efficiency while maintaining power output
Solution Approach 2:
The patent implements quasi-isothermal compression by injecting liquid nitrogen coolant into the compression cylinder, fundamentally changing the compression temperature profile from adiabatic to near-isothermal. This parameter change reduces compression work requirements and allows the expansion cylinder to operate at optimized temperatures for power production while the regenerator recovers heat that would otherwise be lost
2Use of energy by moving object
If liquid coolant is injected into the compression cylinder to achieve quasi-isothermal compression, then compression work is reduced, but device complexity increases
Solution Approach 1:
The patent utilizes the phase transition of liquid nitrogen to gaseous nitrogen during compression. The liquid nitrogen is injected into the compression cylinder where it absorbs heat and evaporates, becoming part of the working fluid mixture. This phase change process enables quasi-isothermal compression by continuously absorbing compression heat, reducing the work required while the nitrogen itself becomes a useful component of the expanded gas mixture
Solution Approach 2:
The liquid nitrogen serves multiple functions simultaneously: it acts as a coolant to enable quasi-isothermal compression, it becomes part of the working fluid mixture for expansion, and it can serve as an oxygen-free atmosphere for certain types of fuel combustion. This multi-functionality reduces the need for separate systems and justifies the added complexity
3Loss of energy
If exhaust heat is captured and redirected through the regenerator, then thermal efficiency is improved, but device complexity increases
Solution Approach 1:
The regenerator captures the harmful waste heat from the exhaust and redirects it to preheat the compressed working fluid before expansion. This heat recovery process converts energy that would be lost into useful thermal energy, improving brake thermal efficiency by reducing the fuel energy required to achieve the necessary expansion temperature
Solution Approach 2:
The regenerator acts as an intermediary heat exchanger between the hot exhaust stream and the cold compressed working fluid. It facilitates heat transfer from the exhaust gases to the working fluid without requiring direct mixing, enabling efficient heat recovery while maintaining separate fluid paths and allowing the system to achieve improved thermal efficiency with a single added component
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 enhances brake thermal efficiency by minimizing heat loss and optimizing energy recovery, resulting in improved engine performance and reduced fuel consumption.
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
Implementation Method 2
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 3
the cooled compressed working fluid then flows through the outlet port of the compression cylinder into the first path of the heat exchanger, or recuperator, in which it is heated to a substantial temperature before flowing into the expansion cylinder
Implementation Method 4
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 5
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
AI summary
A split-cycle engine includes a compression cylinder having a first volume for a first working fluid and a second volume for a second working fluid, the first volume and second volume being separated by the compression piston, an expansion cylinder having a first volume for the first working fluid and a second volume for the second working fluid, the first volume and second volume being separated by the expansion piston, and a fluid coupling between the second volume of the compression cylinder and the second volume of the expansion cylinder, wherein the two second volumes and the fluid coupling provide a closed volume for the second working fluid, wherein the fluid coupling includes a regenerator arranged such that the two second volumes are thermally decoupled.