easyJet unveiled plans for a revolutionary zero emissions hydrogen fuel system for its aircraft which could save around 50,000 tonnes of fuel and the associated CO2 emissions per year. The hybrid concept utilizes a hydrogen fuel cell stowed in the aircraft’s hold. This zero-emissions system allows energy to be captured as the aircraft brakes on landing and is used to charge the system’s lightweight batteries when the aircraft is on the ground.
The energy can be used by the aircraft – for example when taxiing – without needing to use jet engines. Due to the high frequency and short sector lengths of easyJet’s operations, around 4% of the airline’s total fuel consumed annually is used when the airline’s aircraft are taxiing. easyJet’s aircraft average 20 minutes of taxi time per flight – the equivalent of around four million miles a year.
Each aircraft would have electric motors in their main wheels and electronics and system controllers would give pilots total control of the aircraft’s speed, direction and braking during taxi operations. The system would therefore reduce the need for tugs to maneuver aircraft in and out of gates, delivering more efficient turnaround times and increased on time performance. The only waste product is fresh clean water which could be used to refill the aircraft’s water system throughout the flight.
The idea of using fuel-cells is novel. So far so good. But once again we see the e-taxi idea being applied to the main wheels. This is similar to the EGTS system which we have written about before. For those who don’t recall what the challenges are, we recommend another read. The questions we have not seen answered yet – how safe is it to place electric motors next to hot brakes? How can one be sure the braking of the aircraft is not compromised? These are questions have certainly been asked by others.
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Regenerative braking seems far from ideal for an aircraft. The energy dissipation has got to be in the ballpark of 1000 kW or more for an A320 (Heat rate ~= 1/2mv^2 / t). A motor/generator and battery system that could absorb more than a small fraction of that so fast would be vastly oversized to the task of taxiing (not to mention, fitting in such small space). Your other article mentioned mere 50 kW motors.
A fuel cell to power it also seems like an odd choice. Fuel cells have high initial cost relative to their power output, and depend on high utilization to justify that cost. They also introduce another consumable to your gate operations, and one which is more difficult to handle than almost anything else currently used on aircraft due to the extremely high pressures involved. This really sounds to me like an application for batteries. I wouldn’t normally call lithium ion batteries cheap, but they’re practically free compared to fuel cells of similar power output. Those batteries could be charged at the gate via shore power extremely efficiently and cleanly, or slightly less efficiently using spare aircraft power in cruise, so the only logistical change is the maintenance of the batteries, which would be minimal.
So, I question what EasyJet actually has going on. It sounds like they’re planning on testing the landing gear motors (perhaps even from one of the existing developers – EGTS or Wheeltug) with a realistic expectation to reduce fuel consumption, engine run time, and potentially also turn-around time, and are using the university student concept for fuel cells and regenerative braking as something to mention to, not a path they’re actually pursuing.
Say Billy Blaze, how you doing? EGTS yeah, you will DOOM not Billy!