Liquid Air Engine

[brian eiland]

Again, I don't think the folks at Ricardo would consider investing time in such a notion if it were so clear that the termondynamics of the situation were so obviously wrong as expressed by some on this subject. Refer my posting at #15

I will say the discussion has gained momentum, with lots of interesting and informative replies.....thanks to all.

BTW, I was NOT really thinking of this as a vessel usage technology. I've just always been interested in alternative technologies for our autos, so we can save some of that oil for the other products we build our boats with

[Mr Efficiency]

The price of the cheapest available liquid air needed to run this thing would be a pretty fair index of what this idea's possibilities are, by comparison to the fuel cost of a conventional IC engine doing the same work. The opinions of several here suggests it wouldn't be in the ballpark.

[TeddyDiver]

Originally Posted by brian eiland

Again, I don't think the folks at Ricardo would consider investing time in such a notion if it were so clear that the termondynamics of the situation were so obviously wrong as expressed by some on this subject.

Just for reference to see what's needed to make this "fuel" http://www.uigi.com/new_cryo_plants.html Anyway while we are waiting someone to send us some from Titan

[RonL]

Originally Posted by TeddyDiver

Just for reference to see what's needed to make this "fuel" http://www.uigi.com/new_cryo_plants.html Anyway while we are waiting someone to send us some from Titan

Thanks for the link,
Some very useful material there, commercial plants make use of the things I am referring to. Namely cross flow preconditioning of temperatures and the use of expanders to produce work, in order to dump pressure.

The prohibitive costs that everyone tacks on to an idea of using a refrigerant as a heat gatherer to produce a small amount of power, is the expense of removing the first round, heat, water, and impurities that result in a finished product ready for market, and at very large volume.


The exotic products needed to handle liquid air at such cold temperatures (things become brittle like glass) drive the cost up.
The pressures that develop at atmospheric temperatures, mean expensive materials to resist pressure even beyond most hydraulic systems hardware.

If on the other end, high temperature super-heated steam should catch attention, here most materials are weakened and deterioration accelerates in most products, due to extreme heat.

The most cost effective range of a system, that allows use of most over the counter hardware, would be -50 F through maybe 300 F degrees temperature.

The important specs on liquid propane are,
-44 F degrees @ zero psig
90 F degrees gives a pressure of 149 psig
130 F degrees gives a pressure of 257 psig

With only a 40 degree delta of temperature, 100' of 1" copper pipe, will transfer the equivalent of 1.413 horsepower of Btu's per minute. Consider a Stirling Engine, a Heat Pump, and a Refrigerator unit, blended together and each supplying a needed function of the others. An over simplified statement but I'm just trying to build a mental image.

5 to 10 horsepower should be in most peoples price range, 50 horsepower would be a strain, going on up would require a healthy bank account and a good sized boat.
It all boils down to how and where you use heat. Put the heat inside the propane tank and you better have something transferring the pressure. A cycle that reacts between 0 psig and 150 psig, will be quite exciting.

RonL

[Yellowjacket]

Originally Posted by RonL

5 to 10 horsepower should be in most peoples price range, 50 horsepower would be a strain, going on up would require a healthy bank account and a good sized boat.
It all boils down to how and where you use heat. Put the heat inside the propane tank and you better have something transferring the pressure. A cycle that reacts between 0 psig and 150 psig, will be quite exciting.

Ok, so now we have pressurized propane as a working fluid, and WHEN you have a leak (notice I didn't say IF), you are going to quickly accumulate propane gas in the bottom of your hull. This is hugely dangerous for any marine application.. You need another working fliud. And OBTW it has to be someting that won't kill people if they breathe it.

There were some companies pushing a supercritical CO2 bottoming cycle for the Navy. CO2 is safe, right? Well of course it's safe, it's used in fire extinguishers, people use it all the time, right? RRRRIIIIIIGHT!!!! Problem is, in a warship, there is always going to be battle damage. Release a huge amount of CO2 into a closed compartment in a ship and everybody in the compartment dies if the concentration gets above 17%. Watch training films on CARDOX releases and it becomes clear that CO2 isn't a good thing to have a lot of in a closed space. Propane is not going to be acceptable as a working fluid in any ship or boat.

The selection of a working fluid for any energy production cycle in the marine environment isn't just themodynamics (although that's the law), it's about how safe the system is and what are the failure modes and effects (FMECA). Back to the old drawing board.

[RonL]

Originally Posted by Yellowjacket

Ok, so now we have pressurized propane as a working fluid, and WHEN you have a leak (notice I didn't say IF), you are going to quickly accumulate propane gas in the bottom of your hull. This is hugely dangerous for any marine application.. You need another working fliud. And OBTW it has to be someting that won't kill people if they breathe it.

There were some companies pushing a supercritical CO2 bottoming cycle for the Navy. CO2 is safe, right? Well of course it's safe, it's used in fire extinguishers, people use it all the time, right? RRRRIIIIIIGHT!!!! Problem is, in a warship, there is always going to be battle damage. Release a huge amount of CO2 into a closed compartment in a ship and everybody in the compartment dies if the concentration gets above 17%. Watch training films on CARDOX releases and it becomes clear that CO2 isn't a good thing to have a lot of in a closed space. Propane is not going to be acceptable as a working fluid in any ship or boat.

The selection of a working fluid for any energy production cycle in the marine environment isn't just themodynamics (although that's the law), it's about how safe the system is and what are the failure modes and effects (FMECA). Back to the old drawing board.

I agree with almost everything you said, with one exception, a leak proof design can be built, by making use of magnetic couplings. I know accidents happen, but I don't throw things when I get upset, not planning to go to war anytime soon, and a complete system with an output only sufficient to charge a battery bank, could float like a buoy, just outside the confines of the boat.

I don't understand your point about breathing, I have breathed Propane, gasoline and diesel fumes and still I'm here pecking away slowly at my keyboard, but YES I do understand why you said it.

I am aware of the potential danger, that is why a large tank is not in full scale operation just outside my home.

I have pushed and pulled a fair number of barges in my younger days, so the idea of a complete power unit acting as a tiny tug or pusher, operated like an RC airplane or ROV, UAV, or whatever one would call it, is not such a speculation.
But yes, rules are rules and codes are codes, most make sense but some are just flat out stupid.

I have the utmost faith that good engineers could work around the knee jerk objections of most people. I see everything I have mentioned safely at work in other systems on their own, but not in a multi-blend package.

Looking at all the propane tanks spread over the planet, I would speculate that there are less accidents related to propane tanks, than accidents related to home shop air compressors or compressor systems in the work or marine fields. Has anyone had a hot water heater fail lately (explosively) ?

Safety is what one makes it.

RonL

[Boston]

propane conversions were all the rage a while back before bio diesel came along. They went out with the Dodo when people realized they were a big pain in the ass and didn't get as good a mileage as petrol.

Bio diesel on the other hand gets the same or better mileage as diesel. Which is better than gas any day.

If you want to explore propane conversions on a commercial scale check out these guys and notice all the disclaimers, I think they mention a roughly 10% drop in mileage when you make a propane conversion.

http://www.gotpropane.com/p11.html

[Yellowjacket]

When propane leaks from a tank sitting on a slab in Iowa, somebody finds the leak and fixes it. It's no big deal. When you have a leak in a system in a boat, the propane, being heavier than air sinks to the bottom of the hull, just like gasoline fumes. It doesn't dissipate like it does around your above ground tank, it sinks to the bottom of the hull and stays there unless you pump it out, or you light it of. All it takes at that point is a spark. Building codes won't let you put propane tanks in your basement for the same reason, and that's why they are always above ground.

You are thinking about rotating seals and yes you can address those with magnetic shaft couplings. I'm talking about every flange coupling and joint in your system between the heat exchanger, the engine and the power source. Lots of places to weap a small amounts of highly combustable gas. No ship, however large is rigid. The Navy had huge problems with leakage of high pressure air in their destroyers and cruisers and have removed the majority of those systems and relaced them with lower pressure systems. Leakage occurrs, just the same a "DO DO Happens". You are working with piping with significantly different temperatures, the thermal expansion and contraction will eventually result in working fluid leakage.

Your home air conditioner is sitting on a slab of concrete and it doesn't move, it contains an intert gas, and it eventually leaks that gas out and you have to replace the hardware from corrosion and metal fatigue in the heat exchanger. How is your system different? Oh, my AC system operates between 35 F and 120 F, any your cyro system is going to operate over what temperature range? You cannot assume you are going to always contain your working fluid. To assume that is going to cost somebody his life.

[Boston]

oh and I think the auto insurance industry pretty much killed the propane conversion craze when they discovered propane tanks make a great blow torch under the right conditions.

[P Flados]

Back to the product that started this.

After re-reading the article I see that the basic premise is to use cryo air (both nitrogen and oxygen) as a ZERO emissions fuel. The key to this discussion is that overall thermodynamic efficiency and low cost are probably secondary to the zero emissions requirement.

Compressed air as energy storage has been discussed at length. It is not efficient to compress and high pressure tanks are heavy and expensive. Going with a cryo solution gets all the potential energy of very high pressure compressed air (as long as you add heat back in during use which can be easy / cheap if you do it right), but allows for low pressure bulk storage.

Where ZERO emission is a must, the concept could be useful.

If zero "bad" emission is OK, a liquid nitrogen solution may be simpler. This would only be OK where there are no confined spaces that could become dangerously oxygen deficient.

If low emission is OK, consider a separate liquid nitrogen and liquid oxygen cycle. The cryo process makes separating the two very easy. Now you can go with oxygen for combustion and nitrogen to convert combustion waste heat to power. Your combustion can be MUCH more efficient and/or very high power density with pure or enriched oxygen.

For any of the above, the basic production of the cryo liquids become a cost concern. The cost is high due to both the type of equipment required but more importantly due to the low efficiency of compressing gas (unavoidable - basic law of thermodynamics).

Only where you can get your raw energy for compression dirt cheap does this have any real interest to me.

This is where I keep coming back to stuff like wind, hydro, and tidal energy. These are plentiful sources, but they have issues with availability (location and/or sporadic in nature). Cryo production with these types of sources could fix both the energy storage and transportation issues.

[kerosene]

Originally Posted by Boston

oh and I think the auto insurance industry pretty much killed the propane conversion craze when they discovered propane tanks make a great blow torch under the right conditions.

You can buy a Honda civic that runs on gas (not gasoline) and can fill it at home from same pipe as your stove works.

[rasorinc]

A lot of cars, busses, trucks are being converted to natural gas these days.So can boats because natural gas is lighter than air and rises if leaked. One problem is the size of tanks and the strength of the steel because to compress natural gas you have to go to 3300-3500 psi and propane compresses at 300-400 psi.

[RonL]

Hey Brian,
Guess I'm going to have to throw in the towel here, hope I didn't mess your thread up, talking about propane instead of liquid air.
On a 100 F degree day, propane boils @70 F and reaches a pressure of close to 100 psig with no involvement from me......It seems that this is close to free stuff based on the sun having done some work for me.

This is clearly an eye to eye, white board discussion involving different types of engineers.
Exactly what got Charles E Tripler into production of liquid air.

What I have tried to propose is a method of system design, that works on the principle of continual non equilibrium, for those that understand that concept.

Small power, low temperatures and pressures that allow over the counter hardware (generally 150 psi and lower).

I'm not smart enough to describe things better, so I'll drift back into the background.

RonL

[Boston]

while I'd agree there is a power source involved with just the pressure of the propane, in a car at least its used as a fuel injection source. That way you only have a regulator and don't have to deal with the pump.

If your using propane anyway then might as well also use the combustion to help with the vapor pressure. But that becomes kinda dangerous as well.

as far as in a boat is concerned I think its been adequately pointed out that propane just isn't safe in a a boat. Even for a stove it s really not a great idea.

The alternative fuel being considered in this case is liquefied air, I suppose we drift around a little but propane is pretty well known and there seems to be already a system out there that puts its natural pressure to work. From what I can see your just suggesting we use it in the cylinder itself rather than use it to drive the injection process. Might work since you've already got the pressure in the tank, but that pressure is variable so your going to have to have a compressor in that system somewhere. I suppose it could run like a turbo off the exhaust gasses but then you've got to keep the heat down somehow. Whole things gets way complicated which is why Hydrogen is not even remotely an option.

Deal is compressing air down to a fluid state is ragingly complex, very expensive, and dangerous. Now put that into a car doing 75 mph and hit a chunk of concrete. Something is bound to give. Picture the end of that terminator movie when Arnie freezes the bad guy.

[pdwiley]

Originally Posted by Boston

Deal is compressing air down to a fluid state is ragingly complex, very expensive, and dangerous. Now put that into a car doing 75 mph and hit a chunk of concrete. Something is bound to give. Picture the end of that terminator movie when Arnie freezes the bad guy.

Another issue (this is a boating forum).

I pull into West Bumf**k in my sailboat with one of these fancy cryogenic engines in company with my unreconstructed friend who has a diesel engine.

He refuels from 200l drums of diesel, bio-diesel or whatever that were dropped off by the last supply ship some 4 months ago, next one due in 2 months time, maybe. He can filter out the water, sediment and other crap at some cost to his filters so doesn't require perfection.

Where's my tank of cryogenic air and how do I refuel?

I wouldn't have a tank of LN2 anywhere on my boat. We used to take dewars of the stuff to sea with us in research vessels and had storage & handling protocols to deal with it which wouldn't work on a small boat. The stuff is really dangerous, probably no more so than propane but IMO no less so.

Who stores propane tanks below decks?

There's lots of engines & fuels that satisfy special purpose niche requirements and this may well be another one. General purpose replacement for an IC engine, no way. Even mass produced electric cars have serious problems if you look at the total energy input over their life when compared with the latest generation of small diesel engines - 2l/100km claimed consumption with refuelling ranges in 600+ km and 5 minutes or less to refuel.

PDW