Cryogenic Engine HEF Timing for Expansion Efficiency
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Solution Overview
Problem
The efficient operation of cryogenic engines is hindered by the ineffective control of Heat Exchange Fluid (HEF) introduction during the expansion stroke, leading to reduced volumetric efficiency due to valve flow limitations and inefficient expansion.
Innovation Solution
The HEF is introduced into the cylinder no less than 5 degrees after the exhaust valve opens and maintained until the exhaust valve is fully closed, with the introduction continuing until 2-10 degrees after closure, and ceasing no later than Top Dead Centre (TDC), allowing for controlled reverse heat transfer and optimal expansion conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If HEF is introduced during the first phase of the expansion stroke, then heat transfer to working fluid is enhanced, but volumetric efficiency is reduced due to valve flow limitations
Solution Approach 1:
The exhaust valve is closed before Top Dead Centre (TDC) to preliminarily trap the working fluid and heat exchange fluid mixture in the cylinder. This preliminary action creates a sealed environment that allows efficient heat transfer during the subsequent expansion stroke without the need for early HEF introduction that would limit valve flow
Solution Approach 2:
The patent dynamically adjusts the timing of exhaust valve closure relative to TDC, optimizing the balance between heat transfer efficiency and volumetric efficiency. By making the valve timing dynamic rather than fixed, the system can adapt to different operating conditions and achieve both efficient heat transfer and high volumetric efficiency
2Productivity
If HEF introduction timing is optimized for efficient expansion, then expansion ratio increases, but temperature spikes occur
Solution Approach 1:
The heat exchange fluid acts as an intermediary between the working fluid and the cylinder walls. By introducing HEF into the cylinder before expansion, it mediates the heat transfer process, allowing controlled heat exchange that increases expansion ratio while preventing extreme temperature spikes through the thermal buffer capacity of the HEF
Solution Approach 2:
The patent changes the thermal parameters of the system by introducing a heat exchange fluid with specific thermal properties. This parameter change allows the system to achieve higher expansion ratios while controlling temperature excursions through the thermal characteristics of the HEF
3Use of energy by moving object
If HEF is introduced early in the cycle, then heat transfer is improved, but hydraulic locking may occur
Solution Approach 1:
The exhaust valve is closed before TDC as a preliminary action to seal the cylinder contents. This timing ensures that HEF is trapped inside the cylinder rather than being introduced through open valves, preventing hydraulic locking while maintaining heat transfer efficiency during the expansion stroke
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 the through-flow ratio, increases the effective expansion ratio by up to 30%, and improves indicated efficiency by 17%, while preventing hydraulic locking and reducing temperature spikes, thereby increasing power density and engine efficiency.
Implementation Method 1
employs a source of working fluid (WF), normally comprising a gas derived from a liquid cryogenic source, which is introduced into a chamber of the engine in combination with a heat exchange fluid (HEF) which transfers heat to the working fluid (WF)
Implementation Method 2
The working fluid is exposed to the heating effect of the heat exchange fluid (HEF) and expands and the pressure in the cylinder rises such as to cause the piston to undertake an expansion stroke
Data Source
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AI summary
The present invention provides a method of operating an engine (14) having one or more cylinders (16) each having a piston (18) within the cylinder (16) and each piston (18) having an expansion stroke and a return stroke and a top dead centre (TDC) position and a bottom dead centre position (BDC) and said engine (14) employing a working fluid (WF) and a heat exchange fluid (HEF), comprising the steps of: introducing the HEF during the return stroke of the engine; introducing the working fluid (WF) during the expansion stroke of the engine; causing the exhaust valve to be opened at or near bottom dead centre of the piston BDC; delivering the HEF to the cylinder (16) after the exhaust valve has been opened; and closing the exhaust valve before TDC, such as to allow the working fluid to be compressed by the piston within the cylinder. The invention also provides an engine (14) capable of being operated in accordance with the method.