compressed air to run 2000w petrol generator

[J.P.M.]

Funny you brought that up. Earlier I was recalling some USN archive footage I seen when I was in the USN The footage was testing of catapults. Now mind you it was not At Sea testing on a ship, but at a USN Airbase (land). The film was more for humor break from sub training. It had out takes in which the public would never see. Designers and engineers are boys at hearts and could resist launching a VW Beattle's, Trucks, and all kinds of weird stuff which had no greater value other than amusment of the engineers. One that sticks in my mind is VW bug. First attempt failed, ripped the front end off , Reinforced what was left of rear half and launched it. It had to clear a 1/4 mile before crashing onto the ground exploding into a shower of parts, bits and everywhere.

Understood. Boys will be boys. An idle mind is the devil's workshop. Similar but also other interesting technical items and insights about steam power were recounted to me. Any mention of mannequins occasionally appearing, wearing O6/higher rank and piloting/strapped to caissons and smoking cigars, etc. ? Stories I heard were from the era way before crash test dummies.

[Sunking]

BTW, but off topic, a late good friend, mentor, univ. engineering dean and retired naval officer spent a lot of time and summers with the Navy in the late '40's and 50's helping to develop and get steam catapults up to speed as a reserve officer after yachting around the pacific with the USN in WWII. I learned a lot of good steam/power engineering from him long after graduation and also lots of good stories about things like launching concrete caissons of about 80,000 lbm or so with some interesting perspectives on proof testing I used later on.

Funny you brought that up. Earlier I was recalling some USN archive footage I seen when I was in the USN The footage was testing of catapults. Now mind you it was not At Sea testing on a ship, but at a USN Airbase (land). The film was more for humor break from sub training. It had out takes in which the public would never see. Designers and engineers are boys at hearts and could resist launching a VW Beattle's, Trucks, and all kinds of weird stuff which had no greater value other than amusment of the engineers. One that sticks in my mind is VW bug. First attempt failed, ripped the front end off , Reinforced what was left of rear half and launched it. It had to clear a 1/4 mile before crashing onto the ground exploding into a shower of parts, bits and everywhere.

[J.P.M.]

JPM compressed air machines are stil in use today and will be tomorrow. How many mechanics are going to give up Air Powered Tools, Artist give up Air Brushes, Euro Adults and US Kids giving up Air Riffles, Navy giving up on catapults (OK that is steam) or Aerospace giving up jet engine starters. You know what I am saying; air powered machines have their place and will be around forever. Good lesson in Potential Energy efficiency.

Understood and agreed. Air power has some advantages that will not be easily replaced. Never meant to imply otherwise. I designed quite a few inter/aftercooler systems for Ingersoll-Rand and others back in the day. It's just that things are changing and compressor companies are planning ahead, and also that compressed air systems, while convenient for intermittent/short term tasks, are not an efficient means of a lot of energy transfer or as a long term or continuous mode means of supplying power, such as continuous power generation from steam turbines for example.

BTW, but off topic, a late good friend, mentor, univ. engineering dean and retired naval officer spent a lot of time and summers with the Navy in the late '40's and 50's helping to develop and get steam catapults up to speed as a reserve officer after yachting around the pacific with the USN in WWII. I learned a lot of good steam/power engineering from him long after graduation and also lots of good stories about things like launching concrete caissons of about 80,000 lbm or so with some interesting perspectives on proof testing I used later on.

[Sunking]

I can think of one more air engine that will be around as long as there are kids and balloons.

[Mike90250]

And air power starters for large and giant diesel engines.
An air engine is basically a steam engine running on compressed air instead of steam. A 4-cycle ICE could be converted by changing the camshaft to make it into an air motor.

[Sunking]

JPM compressed air machines are stil in use today and will be tomorrow. How many mechanics are going to give up Air Powered Tools, Artist give up Air Brushes, Euro Adults and US Kids giving up Air Riffles, Navy giving up on catapults (OK that is steam) or Aerospace giving up jet engine starters. You know what I am saying; air powered machines have their place and will be around forever. Good lesson in Potential Energy efficiency.

[J.P.M.]

Compressed air systems are among the least efficient methods to provide motive power to anything. That was OK when energy was cheap, with the energy used to compress the air being removed during interstage or aftercooling cooling and either recovered for use as heat (not often), or simply rejected.

Most of the energy used to compress the air is already relatively low entropy shaft mechanical energy (work) input at the compressor, with that energy already coming from probably some fossil, nuclear or renewable (hydro ?) source. The idea of compressing air is usually done in industrial applications where the medium (compressed air) has the advantageous property of being able to transport the energy of compression in the gas over relatively short distances through pipelines, say in an industrial plant, and then having that available energy that was added at compression extracted at some other location by expansion in, say a tool of some sort - maybe even a device that will extract shaft work - i.e. a compressor in reverse (but not in a reversible cycle of course).

Compressing air (or other gasses) is a way of transporting power (or storing energy) that increases entropy more than a lot of other, and most common ways to get the job done. There is a relatively large segment of American industry that grew up and thrived on making equipment that compressed air for such uses in the days of cheap energy and when there was less concern for the environment. That segment is now trying to readjust itself to the new realities of not so cheap energy and more environmental awareness, regardless of the validity of those realities.

[Sunking]

You cant just put air into the intake of an engine, so you would need to replace the petrol engine with an air motor that has a governor that will run at 3000rpm. You will also need a 5hp motor to run a high pressure air compressor. So work out the logic of how much solar you need to run a 5hp electric motor long enough to compress enough air to run a 5hp air motor for any given length of time.

Thus is why is an exercise in futility. That is why Air Powered cars went bankrupt before they went on sale. Pretty stupid if you know one gallon of gasoline in an ICE gets you down the road 30 miles, or that same gallon of gas used to compress air only gets you 3 miles down the road. Once you understand that then you are no longer call yourself Dan.

[Bala]

You cant just put air into the intake of an engine, so you would need to replace the petrol engine with an air motor that has a governor that will run at 3000rpm. You will also need a 5hp motor to run a high pressure air compressor. So work out the logic of how much solar you need to run a 5hp electric motor long enough to compress enough air to run a 5hp air motor for any given length of time.

[SunEagle]

yeah thats trivial.
and then there is the low storage power of the compressed air. according to this page https://en.wikipedia.org/wiki/Compressed_air_car , about 50Wh per liter of compressed air at 4,500psi (which is a lot of pressure).

Would be a lot simpler, more efficient and practical to just split water to hydrogen and oxygen, then run your generator on that at night.

The surprising thing, is that even with the low efficiency of using compressed air I read somewhere that they are going to build a 1200MW CAES up in Delta Utah next to an existing coal powered generating plant that will soon be retired. The plan is to use wind power out of Wyoming and the HV distribution lines that are already in place.

[J.P.M.]

so the heat loss during the compression is most of the energy? , so to make this efficient there needs to be heat capture during the compression stage, and heat returned during the decompression stage.

The heat of compression is removed and usually rejected by intercoolers for multistage compressors and aftercoolers for all compressors. The gas is then stored at something closer to ambient temp. the compressed gas is then cooled, usually when expanded either in a thermodynamic cycle (and work extracted), or a throttling process (unrestrained expansion). Otherwise, the storage tanks and to a lesser extent the piping in compressed air systems would need to be larger and also more robust. Additionally, inter/aftercooling removes moisture that would otherwise accumulate in the system and/or cause problems.

[ButchDeal]

so the heat loss during the compression is most of the energy? , so to make this efficient there needs to be heat capture during the compression stage, and heat returned during the decompression stage.

yeah thats trivial.
and then there is the low storage power of the compressed air. according to this page https://en.wikipedia.org/wiki/Compressed_air_car , about 50Wh per liter of compressed air at 4,500psi (which is a lot of pressure).

Would be a lot simpler, more efficient and practical to just split water to hydrogen and oxygen, then run your generator on that at night.

[almac]

so the heat loss during the compression is most of the energy? , so to make this efficient there needs to be heat capture during the compression stage, and heat returned during the decompression stage.

[SunEagle]

Ah the kinetic kick start option. I remember seeing that.

[ButchDeal]

WWII Submarine engines (diesel electric boats) start their big engines on compressed air.
Some old planes used to use shot gun shells to start radial engines (with no shot of course).