Fuel Cell Ejector Sizing With Bypass Valve Flow Control
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Solution Overview
Problem
Fuel cell systems face challenges in maintaining optimal fuel flow and entrainment ratios across a wide operating range, leading to inefficiencies and potential damage due to improper sizing and operation of venturis or ejectors, particularly at varying current densities.
Innovation Solution
The implementation of a by-pass valve in parallel with a sized ejector, allowing for proportional control of fuel flow, enables the fuel cell system to achieve a target primary fuel flow rate and entrainment ratio by adjusting the size of the ejector based on efficiency, geometry, and operational conditions, including fuel composition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single ejector is used for fuel flow control, then the system structure is simple, but the system cannot maintain optimal fuel flow and entrainment ratios across a wide operating range
Solution Approach 1:
The fuel flow control system is segmented into two parallel paths: one through the ejector and another through the bypass valve. This segmentation allows independent control of fuel flow through each path, enabling the system to maintain optimal entrainment ratios across a wide operating range while managing complexity through modular design
Solution Approach 2:
The bypass valve is implemented as a proportionally controlled dynamic component that can adjust its opening degree continuously. This dynamic control capability allows the system to adapt fuel flow distribution in real-time based on operating conditions, achieving versatile operation across different current densities while maintaining manageable system complexity through electronic control
2Quantity of substance
If the ejector size is increased to handle maximum fuel flow, then the maximum fuel flow capacity is improved, but the entrainment ratio becomes improper at lower current densities
Solution Approach 1:
The ejector is sized specifically for optimal performance at maximum current density, while the bypass valve handles the local requirement of excess fuel flow at lower current densities. This local quality differentiation allows each component to be optimized for its specific operating condition, ensuring proper entrainment ratio across the entire operating range
Solution Approach 2:
The system changes the flow distribution parameter dynamically by adjusting the bypass valve opening degree. At lower current densities, the bypass valve opens to reduce the effective fuel flow through the ejector, maintaining proper entrainment ratio. At maximum current density, the bypass valve closes completely, allowing the full-sized ejector to handle the maximum fuel flow capacity
3Quantity of substance
If a larger ejector is used to accommodate maximum fuel flow, then the fuel flow capacity is improved, but the parasitic load from recirculation pumps increases
Solution Approach 1:
The recirculation pump is extracted from the fuel flow control system and replaced with a proportionally controlled bypass valve. This elimination of the recirculation pump removes the associated parasitic energy load while maintaining the ability to control fuel flow distribution through the bypass valve's proportional opening degree
Solution Approach 2:
The ejector utilizes the kinetic energy of the incoming fuel flow itself to create the suction effect for secondary fuel entrainment, eliminating the need for external recirculation pumps. The bypass valve complements this self-service mechanism by providing additional flow control capability without requiring additional energy-consuming components
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 configuration enhances the fuel cell system's operational flexibility and efficiency by maintaining optimal fuel flow and reducing the need for recirculation pumps, thereby minimizing parasitic load and extending the operating range while preventing damage from improper fuel distribution.
Implementation Method 1
The sized ejector may include a primary nozzle. A size of the sized ejector may be determined by decreasing the primary nozzle area.
Implementation Method 2
the by-pass valve may be a proportionally controlled valve
Data Source
AI summary
The present disclosure generally relates to fuel cell systems and methods of sizing a venturi or ejector by using aby-pass valve for determining or controlling fuel flow through the venturi or ejector.