Liquid Air Engine

[RonL]

Originally Posted by 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.

Hi Boston,
It baffles me a little, that it seems no one appears to have understood my comments about the entire air compression system being inside the propane tank, completely submerged in liquid propane. The intake line is ported through the tank shell and the exhaust is also ported through the shell. Everything related to compressing air takes place inside the propane tank.

A 250 gallon propane tank can house a lot of power transfer equipment, I won't try to describe it, just rest assured it will fit.

The short version is, warm air in, colder air out. Almost all the heat from the air moves into the liquid propane, no wasted heat of compression.

Compressed air and high pressure propane both perform mechanical work on a single power shaft, that power is divided as needed to carry out recycling of system states, and a sum (work) has to be moved out of the system in order to bring about another cycle.

As an example only, lets call air motors "expanders", if three are used in series for air, and three in series for the propane gas, they can all (6) be set to turn the same power shaft. (two separate systems working in unison)

More heat comes from sea water as liquid propane can be circulated through some form of ex-changers.

Well I'm getting carried away again, just let me say it's a mind bender, but it can be done. (SAFELY)

RonL

[brian eiland]

Just for reference there was a long subject thread that developed over here on the subject of 'compressed air' driven engines

http://www.yachtforums.com/forums/te...ve-system.html

[brian eiland]

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. Refer my posting at #15/

Another Ricardo project
Super car, super engine
F1 teams with a string of world championships to their credit demand the absolute best, and no less. That’s why McLaren turned to British engineering consultancy Ricardo for help in the design, development, and manufacture of a landmark V8 engine for its brand new MP4-12C road-going supercar
http://dev.designfax.net/opens/artic...earticle&pn=01

[philSweet]

1.413 horsepower of Btu's per minute

Ron- I'm not sure what it does do, but I'm quite sure it doesn't do this. This brings unit abuse to new lows. Power is already per unit time. You can't have HP/ min. unles you are talking about the rate of change of power.

[cthippo]

To me this is reminiscent of the old fireless kettle steam engines. Basically they were a normal steam engine but with a pressure tank instead of a boiler. They worked well in applications where lots of steam was available and range wasn't an issue, such as switchers at industrial plants. Advantages included lower maintenance requirements and being safer to operate. Some of these engines were in service at steam electric power plants well into the 1990s. The same limited range of applications would apply with this technology, but within that range it could be viable.

I'm also thinking about the SCBA bottles we use at my fire department and the range of uses they have. In addition to breathing air, we also use them to power air tools and lifting bags for rescue work. While they lack the energy density of gasoline, they are easier to store and safer to handle. We mostly use 2250 psi carbon fiber and aluminum bottles, but we also have a 4000 psi carbon fiber bottle on our RIT pack which is rated at an hour and doesn't weigh any more than the lower pressure bottles. It would be interesting to hook one of these up to a small air motor in a dinghy and play with it

When considering these sorts of technologies, you have to adopt the mindset of current fossil fuel systems no longer being viable. It's not a matter of "is this better than what we have now" so much as "Is this viable if or when what we have now becomes unavailable or uneconomic"

[RonL]

Originally Posted by philSweet

Ron- I'm not sure what it does do, but I'm quite sure it doesn't do this. This brings unit abuse to new lows. Power is already per unit time. You can't have HP/ min. unles you are talking about the rate of change of power.

Hi Phil,
I'll go back and check my numbers

RonL

[RonL]

Originally Posted by RonL

Hi Phil,
I'll go back and check my numbers

RonL

Here is the link I used,

http://www.engineeringtoolbox.com/co...loss-d_19.html


Heat loss from 1/2" to 4" copper pipes or tubes at various temperature differences between the pipe and the surrounding air, are indicated in the diagram and table below:



Nominal bore Heat loss for the fluid inside pipe
(W/m) Heat loss for the fluid inside pipe
(Btu/hr ft)
Temperature difference (oC) Temperature difference (oF)
(mm) (inches) 22 38 55 40 68 99
15 1/2 21 32 45 22 34 47
22 3/4 28 43 60 29 45 64
28 1 34 53 76 36 56 79
35 1 1/4 41 64 89 43 67 93
42 1 1/2 47 74 104 49 77 108
54 2 59 93 131 62 97 136
67 2 1/2 71 111 156 74 116 162
76 3 83 129 181 87 135 189
108 4 107 165 232 111 172 241

The graph won't copy.

I used the 40 degree difference, which shows 36 Btu/hr per/foot, for 1" pipe.

100' X36 = 3,600/60 = 60BTU/42.4BTU/min = 1.415 hp

My books give hp to BTU/min.......hp X 42.44 = BTU/min

if heat is being lost at this rate, it is waste heat or lost power.
if it is being absorbed it is power gained, heat drives pressure up in a refrigerant, right ??? pressure dispersed through a motor/expander over a time should equal a measure of power/work.

Consider two tanks, valve closed on each.
Tank 1, has propane in it @ 60 F, it will show 92 psig
Tank 2, has water in it @ 315 F, it will show about 95 psig

To maintain temperature in tank 2, fuel of some kind will have to be burned.

I might be a little off on the water, because of conversion from metric (I'm a pretty old geezer ,)

I'll accept correction if I'm completely wrong, but if it is just a slight miscalculation in the numbers, please look at the concept which is a goal of developing pressure, without the burning of fuel of any kind.

RonL

[P Flados]

Originally Posted by brian eiland

Just for reference there was a long subject thread that developed over here on the subject of 'compressed air' driven engines

http://www.yachtforums.com/forums/te...ve-system.html

Based on the dates, it looks like this effort went no-where. It is a shame. Before internal combustion ruled transportation, compressed air was being used in urban settings.

An "air car hybrid" make a lot of sense to me. However, the key is not the car (the car is the easy part).

The key is the charging station. A straight electric compressor rejects a bunch of heat as waste energy. There is so much waste heat that overall cost is high unless you find a thermo legal way to beat the second law. Some options that could improve things include:

• Integrate the compressor into a system that that also does home HVAC and water heater. Use the compression waste heat for hot water and/or home heating in the winter.

• In a small business/industrial setting, integrate the compressor with a process requiring heat. Actually, you would go out looking for a business that has high energy usage for process heating and go in business "selling" them heat at a discount while producing "cheap" compressed air that you would then use or sell. This kind of stuff has been done before with "co-gen" electric stations.

• Negotiate a contract for really cheap off-peak electricity.

• Use green energy (wind, wave, tidal, geothermal, etc) to drive your compressor.

Once you find a way to produce high pressure air with one or multiple of the above (or any other similar), traditional storage options are not great. Large high pressure stationary tanks are expensive and are regulated for safety (registered, relief valves, periodic inspections). This adds cost and complexity.

A recent twist on storage came to my attention (liquid air engien thread) could help drastically improve your storage options. However, it comes at the price of even more complexity with the compression piece. If your compression goes all they way to produce cryogenic liquid air, storage options become much easier.

The real problem with all of the above, is that pulling everthing together to make a viable buisness venture is probably beyond the proivate sector, and governments just do not have the vision to push stuff like this.

[Yellowjacket]

The problem with using compressed air is that, as you expand and use the stored air, the left in the tank cools, leaving you with less pressure and work capability in the tank the further you go. This is the primary reason to go to liquid, using the air in the tank doesn't reduce the energy of what's left.

Still, all things considered, it's a very, very expensive way to store energy. Even when you are sitting still you are losing energy to boil off. If you wanted to use it in a coal mine, where ambient temperatures are high and you can't allow any type of sparks, then it could make sense. But otherwise it's simply a novelty.

You can make a vehicle run for a little while using any number of systems, from electricity, to flywheels, to compressed air, to C02, to hydrogen and I am sure countless others. The bottom line is that lots of these things will produce useful power for a little while, but the reality is that it's very very hard to contain energy in almost any form. All of these forms of storing and then re-extracting energy are very heavy, expensive and complex and for the most part very inefficient.

The easiest and most efficient way to store and extract energy is in the form of a fossil tank and heat engine. It has been such for the last 100 years, and the bottom line is that this isn't going to change in the foreseeable future. It's interesting to look at these systems, but until we have the nuclear reactor in a backpack (like the Ghostbusters did), the amount of energy that can be stored in a mobile system is going to limit all of these energy storage approaches to being a curiosity.

That's not saying that you can't store some energy for a few minutes in stop and go traffic and help yourself out. Recovering energy from one stop to be expended in the next acceleration is viable, but that's not a lot of energy, and it doesn't apply to something like a boat.

[P Flados]

Yellowjacket,

You are right about the efficiency problem of compressing air.

You are wrong about cryo storage. We have some huge LN2 storage tanks at my place of employment and the losses are not that bad at all. They have double walls with vacuum insulation and this technology is proven and it works fine.

The other thing about this type of storage is the effective energy density.

Shop air has a density of about 0.6 lb/ft^3. This gives you about 1.6 lbs of air in a 20 gallon tank.

Air is like 80% nitrogen. As a liquid, LN2 has a specific gravity of 0.8 compared to water. This allows you store about 100 lbs in a 20 gallon tank. This is a 60X increase in storage. The effective pressure is also much higher.

As an example, if you pump a small stream of LN2 as a liquid into a small 3500 psig tank that you keep at ambient temp you get 3500 psig gas when the liquid vaporizes. Nitrogen at 3500 psig can do a lot more work than air at 100 psig. Note that a positive displacement LN2 pump takes very little power to pump the liquid.

The above shows that as you vaporize and expand the fluid, you have the opportunity to transfer heat into your engine from surrounding air (or water). This recovers some of the energy lost as "waste heat" during compression. This trick was used long ago when compressed air was first being explored for transportation use.

You are also wrong about using the energy. Recovering energy as you expand a gas is at the heart of most engines. Doing it with a clean cool gas as compared to combustion products is a piece of cake. Doing it in stages with the ability to extract heat from ambient air / water is just normal engineering, not rocket science. Yeah, there is room for some innovation to get the most out of the process, but it is no where near as complex as the technology behind todays automotive engines.

Again, the problem is pulling together a compressing scheme that makes sense and then just working out the details on how to use the stored energy.

[Yellowjacket]

Cryo storage loss rates for a 50 liter dewar are on the order of 1% per day. That means if you fill up every 10 days you are going to have a 90% storage efficiency.

The manufacturing efficiency of liquid air is 50%, according to wikipedia., so you are looking at 45% efficiency and you haven't even started to do any expansion work.

You need to compress the fluid to 3500 psi (a couple of percent) and then you have to perform the expansion. At some point you have to try to add heat to the fluid. This is obviously done best in the expander, but there isn't enough time to do it there. If you don't get the fluid hot first, when you do the expansion it will recondense and your expansion efficiency will be zero, or you can only do a small amount of expansion and then reheat it again. If you do it before the expansion, you have to valve high pressure gases at higher mach numbers so there are additional losses there, or there are going to be throttling losses (like in a steam engine). If the gas was well heated (to room temp) you need an expansion ratio of 240 to one. That means you need a multi-stage expander. Multi-stage steam systems have expansion ratios of about one third of that, with heat addition between, so you are looking at some complex machinery here.

I'd bet you would be lucky to see expansion efficiency of 70%, assuming the valving and losses in the heat exchanger were kept to a minimum.

Overall energy efficiency is now looking closer to 33%, and you haven't taken into account transmission losses or anything else...

The recoverable liquid nitrogen energy density is about 97 watt hours per kg. Lithium ion batteries are between 100 and 250 watt hours per kg. The complexity and weight of the expansion system is going to be a lot greater than an electric motor, and that assumes the expansion efficiency is 100%.

Electric motors and control systems have an efficiency of greater than 90%. So where is the incentive to use liquified air if the energy density of the storage system alone is worse than a good lithium ion battery? To have a range equal to a 13 gallon gas tank you would need 92 gallons of liquid air and a whole lot more complex expansion system.

Sorry but I don't see a system here that is viable unless you really need to have no electricty or fumes.

[philSweet]

Ron, I get it now. I read

(1.413 horsepower of Btu's) per minute. (and was really pulling my hair out with the units mismatch)

you meant for me to read-

1.413 horsepower of (Btu/minute). (Which is consistent unit-wise).

Thanks for taking the time to clear that up. We could easily have gone on arguing two different points and talking past one another.

[P Flados]

YJ

Lithium Ion batteries are great compared to lead acid. However:

• What is the cost of a full sized set for a car with a practical range.

• How long does the battery pack last.

• Regardless of what the batteries cost as part of the initial manufacture, what will an owner have to fork out for a replacement set.

• What is the disposal cost.

Electric car technology has made huge advances with better controls and batteries, but they still have their problems. Even when cars are being sold with adequate range, bullets 2 -4 above are what I see as my biggest concerns.

My desire to see something like compressed air make a go, it partly that it gets you back to just machines that can be made to last. I do not ever expect this from batteries.

The other part is that the poor compression efficiency is something than can be dealt with. I have never said to just compress the air with full priced regular electricity.

One example would be as follows. A homeowner sized wind turbine can generate enough compressed air to at least give you a Hybrid approach where your first 30 miles or so after leaving home is with stored energy from the wind. Advances are such that an automated system would be almost entirely made from building blocks that are already being produced. One configuration could be a wind turbine coupled to a high efficiency generator, a high efficiency motor driven compressor, a heat recovery system to use compressor waster for your hot water heater and the real key - a modern computer control system. It is just that they have not been integrated and optimized.

Going for more than just a hybrid approach using compressed air is what interested me in the thread about cryo powered engines. I am convinced that cryo can store a lot of effective energy. However, a "show me" attitude for getting this energy out of a drivetrain is well warranted at this point.

When I seen test data on how much energy a cryo powered engine will deliver from a reasonable quantity for an automotive tank, more real world comparisons can be made.

For example I currently burn around 14 gallons of gas a week. At an assumed $4 a gallon this will be around $2800 for 2012. This does not keep me from eating, but it is more than I like to pay. I also do not like funding the oil producers of the world, and I know that the long term does not look good if we can not reduce consumption.

I will admit that any ability for this to be practical is as of yet unproven in the real world. I just try to be optimistic and I look for any potential for ways to start getting us off of our fossil fuel reliance.

[RonL]

Originally Posted by philSweet

Ron, I get it now. I read

(1.413 horsepower of Btu's) per minute. (and was really pulling my hair out with the units mismatch)

you meant for me to read-

1.413 horsepower of (Btu/minute). (Which is consistent unit-wise).

Thanks for taking the time to clear that up. We could easily have gone on arguing two different points and talking past one another.

Hi Phil,
You now seem to understand at least one part of what I'm doing a poor job of putting into proper words and correct terms. Thanks

Brian,
The thread seems to have divided into discussions of things other than liquid air, however I can still blend liquid air into my comments, but I'm as resistant to extreme cold and it's affect on materials, as some are about the dangers of propane. I'll back off from making comments until I hear if you are OK with my postings.

Brian,
Also thanks for the link to YachtFourms.com, seeing the quality of so many ships and the level of sophistication of engineering and wealth they represent and how abundant throughout the world they are, I'm a bit embarrassed that I make my comments sound as if I might be promoting the reclaiming of aluminum cans from along the roadside a big business.

Craft of such size and accommodation potential, along with a movement through the water that makes heat transfer a perfect fit, I see not only the piddly 5 or 10 hp that I have been talking about, but placing a system of 500 or more horsepower on existing boat structure, would not be difficult at all.

If boat design from the drawing board to completion, were to take into consideration a heat transfer system as I'm proposing, at speed I see possibilities of 1000 hp or more. I think that what I now see, money is always a concern, but not an issue for a proper and working system.

Well, let me know if you think I have messed your thread up.

RonL

[philSweet]

Having gone back and reread the thread, A few random impressions.

1. The waste heat argument is not being properly characterised. If the power extraction cycle reabsorbs environmental heat to augment the stored potential energy, this should be subtracted from the waste heat of the compression cycle. (It's not simple subtraction, it's the change in enthalpy that occurs in the fluid as a result of the transfer.) This is akin to an HVAC economiser cycle running in reverse. There are losses associated with this, but since the equipment is simple it can have a very long life. Its cost in terms of tons-of-steel/MW production is very high, though. I keep thinking of a paddle wheeler with plate heat exchanger blades feeding an outrunner air motor in the hub.

2. Running a cold hull though warm water may significantly change the ship's resistance. I can't find any info on this. Anyone looking for a study problem? What is the best way to arrange a large heat suck in the hull with regards to hull resistance?

3. The primary power source for compression is just plain irrelevant. Power is nearly 100% fungible when you are talking about up converting a low grade power source to one that is as high grade as LAIR. The only time it matters is when you can avoid having to convert to a higher grade power source or are only upgrading a little bit. So as far as wind turbines go for LAIR, they either work or they don't based on the cost of electricity production. If you want to water some cattle from a ten foot deep well, the answer might be different.

4. Comparing a LAIR powered system to a battery powered system is a bit of a mystery at this point. If I replace my batts every three years, how does that compare to the cost of regular tank inspections and reapproval? As a move towards independence, I think it's a loser vis a vis batts. I don't need any blankety blank inspectors for a batt system at present. Of coarse that just reflects the current state of regulations. Any serious challenger to the oil business from the outside will doubtless find themselves buried in a regulatory hell by those who stand to lose the most.