Fuel Cell Hydrogen Recirculation System​

The hydrogen supply system significantly impacts vehicle safety and operational lifespan.

The hydrogen recirculation system serves as a core component of the fuel cell engine's hydrogen supply system. Its primary function is to recirculate high-humidity gas from the anode outlet back to the stack inlet. This process not only enables the reuse of unreacted hydrogen but also humidifies the incoming hydrogen stream, eliminating the need for an external humidification system and thereby simplifying the fuel cell system architecture. Currently, the mainstream hydrogen recirculation pumps include Roots-type, claw-type, scroll-type, and vane-type, with vane-type pumps being relatively uncommon in domestic markets.

A high-performance hydrogen supply system must exhibit substantial hydrogen storage capacity, operational stability, and high safety standards to ensure extended driving range and durability of fuel cell vehicles. The onboard hydrogen supply system comprises pressure/flow regulation components, hydrogen leakage sensors, supply pipelines, control systems, and hydrogen recirculation systems (typically excluding the hydrogen storage vessel). The operational workflow consists of three phases: refueling, storage, and delivery.

1.Refueling: Hydrogen refueling stations deliver hydrogen to onboard storage tanks via check valves.

2.Storage: The tanks maintain high-purity (99.999%) hydrogen at 35 MPa or 70 MPa pressures. 

3.Delivery: During fuel cell operation, hydrogen passes through pressure-reducing/regulating valves to achieve operational pressure before entering the stack via electronically controlled valves, pressure sensors, flow meters, and humidifiers. Excess hydrogen either enters the recirculation system or undergoes treatment before atmospheric release.

​​Critical System Requirements:​​

1.Stable hydrogen supply enhances fuel cell durability​​:

Storage tank outlet pressure (35/70 MPa) substantially exceeds stack operational requirements.

Improper pressure regulation may cause irreversible proton exchange membrane damage, necessitating precision pressure control.

2.Intrinsic safety is mandatory​​:As a highly combustible gas, hydrogen systems require comprehensive monitoring of pressure, temperature, and flow parameters.

Implementation of safety components (e.g., sensors, relief valves) prevents leaks, overpressure, overheating, and flow anomalies.

​​Hydrogen Recirculation Device: Optimizing Utilization and Water Management​​

The hydrogen recirculation device significantly improves hydrogen utilization while addressing stack water management challenges, directly influencing fuel cell engine longevity. Standard practice involves extracting water generated during operation through gas-liquid separation, with recovered hydrogen reintroduced into the system. This process:

Provides inherent humidification via water vapor in recirculated gas

Increases anode flow velocity to prevent water accumulation ("flooding")

Enhances overall hydrogen utilization efficiency

​​Recirculation System Configurations:​​

Current implementations primarily utilize hydrogen recirculation pumps and ejectors, either individually or in combination:

1.Hydrogen Recirculation Pump​​:

Employs variable-frequency motor control for dynamic flow adjustment

Advantages: Enhanced hydrogen circulation flexibility across power ranges

Disadvantage: Additional electrical power consumption

2.Ejector​​:

Passive operation without auxiliary power requirements

Advantages: Simple construction, operational reliability, extended service life

Limitation: Fixed recirculation rate constrains effective operating range