# Pneumatic Regenerative Braking

1. Mar 28, 2009

### copria

Does anyone know of a pneumatic regenerative braking system (applied to any type of vehicle)?

2. Mar 28, 2009

### OmCheeto

Nope. But they talked about it over at http://www.halfbakery.com/idea/Regenerative_20Brake_20Bike" [Broken] way back in aught 2.

It is an interesting idea, but I've not spent enough time researching it. Here are a few numbers I've run across and a few more I've calculated:

Wiki claims that a 5 liter tank charged to 2900 psi has an energy content of 0.16 kwh.
This is 576,000 joules of energy, or about as much kinetic energy as a 3500 lb car traveling at 60 mph, or the amount of energy the same vehicle descending 120 feet at a constant velocity could generate.

Since the energy from regenerative braking is usually recouped in less than a minute, the system would not tend to lose as much thermal energy as purely pneumatically powered vehicles, so it can be approximated to be an adiabatic system. Of course, regenerative systems almost always run in parallel with primary motive systems which generate heat(ICE, electric), so any heat which is lost in the regeneration process can more than be made up for with the use of a simple heat exchanger. By scavenging heat from these primary motors, it could theoretically generate more energy than would be thought possible by simply looking at the physics involved with the regeneration system alone.

Please do not consider me as an expert in this area. I've only considered this as a thought experiment, and have not worked out any of the dirty details of actually implementing such a silly idea. I will leave that for you.

Last edited by a moderator: May 4, 2017
3. Mar 30, 2009

### minger

a professor at my university last time I checked was doing this. I believe he was using it for large industrial applications (e.g. garbage trucks especially). I can't remember his name for the life of me, but from what I understand this is the ideal application.

4. Mar 30, 2009

### Topher925

You won't find to many pneumatic braking systems as you can never have a very efficient regen braking system with a compressible fluid. Hydraulic drive trains with regen brake system are starting to become quite common in commercial vehicles.

http://auto.howstuffworks.com/hydraulic-hybrid3.htm

5. Mar 30, 2009

### mgb_phys

Couple of problems with it.
First you don't have many pneumatic driven vehicles - so you need to have an entirely separate pneumatic drive to reuse the energy stored in the braking system.
Of course on a non-hybrid ICE vehicle you would need to fit a separate electrical system.

But mainly the braking is the wrong way around. With a simple pnuematic system you have the least braking power at the start when there is no pressure in the tank and then the brakes gradually become more effective as the pressure builds up - exactly the opposite behavior you want from brakes. You could fit a more complicated governing system but that adds weight and complexity.