Author Options:

Why dont they use alcohol in closed system steam engines? Other than safety? Answered

By closed system i mean constant mass of working fluid.  i.e. no steam leaving system, like an air conditioner.

My point is that alcohol has a lower boiling point that water, (some kinds can boil from the heat of your hand!). SO other than the safety problem of alcohol being flamable, alcohol could operate with a lower heat input than water.    With the addition of a cold resivoir, the closed system alcohol steam engine could work right?

Or why not use a refridgerant gas in a closed system steam engine cycle,? >Which would effectively absorb the heat input
any ideas?

addition*  I mean for use in any steam engine with a closed loop cycle, like the Rankin cycle   http://en.wikipedia.org/wiki/Rankine_cycle


 Everyone has given good answers to your good question. Some approaches have actually been used to power an engine.  

I'll add one more point for you to consider: because it is easy to boil alcohol makes it hard to condense--you need a colder condenser.  Don't forget, cooling a gas requires energy too.

A precise answer to you question can be found with thermodynamics.  Look up "heat engine" on wikipedia.  It pretty much explains it all.

Cheapness, availability & and physical properties are why. If you could be more specific about the engines you're thinking of I might be able to give more details.



8 years ago

"Other than safety?"  That's a little like asking why you can't use nitro-glycerine to fuel a piston engine.
Theoretically, its probably feasible, but, other factors excluding the obvious safety issues, concern cost. 
Engineering difficulties regarding containment of the pressurized alcohol or whatever liquid you choose, (you probably wouldn't be permitted to vent over-pressurized alcohol into the atmosphere as you can H2O), the cost difference and availability of water versus some other liquid,  and most likely, H2O steam engines work, safely, efficiently and are proven systems.

Aside from flammability issues associated with safety (which is a prime motivator in most steam engines...) there are other fluids which do the job more efficiently... and with significantly lower flammability. I think it's simply a matter of "economy".

Working fluids are chosen based on their availability and their chemical and physical properties within the method and temperature range of the "engine". Why not use liquid sodium as your working fluid? Because your temperature differential isn't high enough. Why not use Freon?  because the temperature differential is too high...

I suppose it's the range in which you want it to work that's the problem. Alcohol would be more suited to use in a geothermal distribution schema rather than a traditional fired steam plant simply because of it's potential for explosive catastrophe, but although I am unsure, it may be that with temperatures of several hundred degree, it may not be as efficient as other working fluids...How about ammonia?. Ah, but ammonia is nasty too, for other reasons...so let's investigate something that isn't chemically active...hmm..perhaps a liquified noble gas...oops, we've been there... Water is easy....

You might be able to get away with a diultion of alcohol to increase efficiency.