Cathode Inlet Humidity Sensing via Differential Pressure Airflow Meter
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Solution Overview
Problem
Fuel cell vehicles face challenges in accurately measuring and controlling humidity at the cathode inlet of the fuel cell stack, which affects performance and longevity, as existing sensors like UEGO sensors require complex calibration and are not suited for the harsh conditions within the fuel cell system.
Innovation Solution
A fuel cell vehicle system incorporating a differential pressure airflow sensor, mass airflow sensor, and temperature/pressure sensors to measure relative humidity and control the humidifier and fuel cell stack operations, using a controller to adjust airflow and compressor speed based on differential pressure signals, allowing for precise humidity control at the cathode inlet.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If UEGO sensors are used to measure humidity, then humidity measurement capability is provided, but calibration complexity increases and reliability decreases under fuel cell operating conditions
Solution Approach 1:
The patent replaces the UEGO sensor (electrochemical system) with a differential pressure sensor system that uses fluid dynamics principles. The differential pressure sensor measures pressure differential across a flow metering orifice, and combined with mass flow rate measurements, calculates humidity without requiring complex electrochemical calibration. This substitution eliminates the calibration complexity while maintaining measurement capability.
Solution Approach 2:
The patent introduces an intermediary calculation approach where humidity is not measured directly by a humidity-sensitive sensor, but rather derived from intermediate measurements of differential pressure and mass flow rate. This intermediary method using fluid dynamics relationships provides a reliable humidity measurement pathway that avoids the calibration issues of direct humidity sensing in fuel cell environments.
2Measurement precision
If UEGO sensors are used to measure humidity, then humidity measurement capability is provided, but reliability decreases under harsh fuel cell conditions
Solution Approach 1:
The patent replaces the unreliable UEGO sensor with a differential pressure sensor system that uses robust fluid dynamics measurements. The differential pressure sensor and mass flow sensor are both well-established, reliable technologies that can operate reliably in the harsh temperature and pressure conditions of fuel cell systems without the electrochemical degradation issues that plague UEGO sensors.
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
The system provides simple and effective humidity control with reduced calibration complexity, maintaining optimal humidity levels to enhance fuel cell performance and longevity, avoiding the limitations of traditional sensors like UEGO sensors.
Implementation Method 1
a differential pressure airflow sensor positioned between the airflow outlet of the humidifier and the cathode inlet of the fuel cell stack
Implementation Method 2
a mass airflow sensor disposed within an intake airflow upstream of the cathode inlet of the fuel cell stack and upstream of the airflow outlet of the humidifier
Implementation Method 3
The differential pressure airflow sensor may include a flow metering orifice upstream of a pressure differential sensor
Data Source
AI summary
A fuel cell system includes an air compressor having an inlet fluidly coupled to ambient, a humidifier fluidly coupled to an outlet of the air compressor, a mass airflow sensor disposed downstream of the air compressor and upstream of the humidifier, a fuel cell stack having a cathode inlet fluidly coupled to an outlet of the humidifier, a differential pressure flow sensor disposed downstream of the humidifier and upstream of the cathode inlet of the fuel cell stack, and a controller programmed to control at least one of the air compressor and the fuel cell stack in response to humidity of airflow to the cathode inlet of the fuel cell stack as indicated by signals from at least the mass airflow sensor and the differential pressure flow sensor.