Polymer Electrolyte Membrane Fuel Cells for UAVs By Aza Walker, - - PowerPoint PPT Presentation

Polymer Electrolyte Membrane Fuel Cells for UAVs

By Aza Walker, Ashwin Bhojwani, Rohan Kalyani, Abhinav Goli NPRE 470 April 26th, 2018

Introduction

• UAV - Unmanned Aerial Vehicle

○ No human pilot required; directed by GPS ○ Used in military surveillance applications

• UAV surveillance missions typically are

about 40 hours

○ Attains altitude of 60,000 - 65,000 ft ○ Flight speed: 560 km/hr

• Current UAVs use internal combustion

engines

○ Fuel source: petro-based (jet fuel) ○ Low efficiency ○ Results in production of greenhouse gases ■ Harmful to environment

• Proposal: Design a UAV using hydrogen

and oxygen gas as fuel and oxidizer, respectively, in a PEMFC.

Engineering Requirements for UAV’s

• Long range and lightweight

○ Low weight to high power output → High gravimetric power (W/kg)

• Can function at high altitudes and velocities
• Fuel management system

○ Can compactly store and dispense fuel

• Thermal management system

○ Minimize losses by maintaining fuel cell op. temp. range

• Air management system

○ Filter and pressurize supply air at the correct humidity ■ Air humidity can affect fuel cell performance

Diagram of PEMFC

Electrochemical Reactions of the fuel cell

• Reaction at Anode

2H2 4H+ + 4e-

• Reaction at Cathode

O2 + 4H+ + 4e- 2H2O

• Overall Reaction

2H2 + O2 2H2O

Design and Structure

Specification Value Peak Power Output (W) 5000 Number of Cells 320 Cell active area (cm2) 64 Operating temperature (°C) 60 Hydrogen storage pressure (MPA) 30 Mass (kg) 49.6 Gravimetric Power (W/kg) 100.8

Thermal management system Air management system Fuel management system

Design and Structure

• Fuel cells would be

located in the front of the UAV just before the wings

• Other parts would be

similar to usual UAVs

Fuel Cell Stack Engine

Hydrogen Storage in UAV

• Storage methods:

○ Pressurized hydrogen gas ○ Liquid hydrogen ○ Metal Hydride (e.g. Sodium Borohydride)

Hydrogen Storage in UAV cont.

Liquid hydrogen is the best storage option; Gives longest runtime

Characteristic features of FCs compared to

• Batteries (Lithium)

○ Converts the fuel and oxidant but does not store any energy. Because air is used as the oxidant and is not stored with the fuel. ○ Runtime is ~5x greater for H2(g) and ~10x greater for H2(liq) ○ For endurance missions, only fuel storage is necessary while FC system mass constant to increase range. However if batteries are used, more batteries are necessary.

Characteristic features of FCs compared to

• Internal Combustion Engine (ICE)

○ Superior in small-scale engines as they are noisy and polluting, give off high thermal signatures in situations where stealth is necessary ○ Due to higher energy density, ICEs can provide longer endurance ○ Higher altitude flexibility - FCs have positive control of air flow so power reductions can be adapted without oversizing propulsion systems

Benefits of PEMFCs w/ H2 Storage

• System

○ Higher power efficiency ○ Higher Energy density up to 5x more (gas H2) 50x more ( liq H2) and than ICE- 200 Wh/kg ○ Stability rating 1 on Cooper-Harper scale(1 best - 10 worst)

• Surroundings

○ Friendly to the environment( No greenhouse emissions ) ○ Very low thermal, vibrational, and acoustic signatures

Conclusion

• While time of flight and cost is an issue, with more research and development

a fuel cell powered UAVs could be a very viable alternative to currently used methods to power UAVs.

• Fuel cell powered UAVs will be better for the environment and they’ll be more

efficient.

References

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.466.1837&rep=rep1&typ e=pdf http://www.unmannedsystemstechnology.com/wp-content/uploads/2017/02/White- Paper-Fuel-Cell-Energy-Systems-for-UAVs.pdf

Q&A