Hi DG Air. There are a few interesting areas of development. If you don't mind, I'll change your topic just slightly from "air" compressor to "gas" compressor, meaning any gasseous state.
I think that in order for a new/novel kind of compression system to develop, there has to be a niche for it in industry. Generally, a compressor will fill that niche if the compressor can either:
- Perform some compression task that was previously impossible.
- Perform the compression task at a cost which is lower than conventional machinery. Here, cost can be broken into initial capital costs, maintenance costs and energy costs.
One might think that this cost issue is valid regardless of the 'niche' in which a machine is placed, but what you'll find is that different types of machines dominate in the industry depending on things such as pressure ratio, flow rate and media. For example, reciprocating machinery dominates the lower flow, high compression ratio needs while centrifugal machinery dominates the higher flow, lower compression ratio markets. Similarly, corrosive media, oxidizers and other fluid types are commonly compressed using diaphragm machines. The point being that there isn't a 'one type fits all' machine that can dominate in all areas of the compression industry. Compression equipment will have advantages and disadvantages depending on the process.
If you're interested in recent developments, I can tell you about 2 areas I work in. One is isothermal compression and the second is cryogenic gasseous compression. Machines that can do this are being developed for the hydrogen industry.
Linde has developed something they call an "Ionic Compressor" which uses an ionic fluid instead of a conventional piston. The liquid is forced into a sealed cylinder to compress the gasseous hydrogen and force it out at high pressure. By doing this, they can produce a process which aproximates an isothermal process, and the ionic fluid is used so they can easily separate out any vapors using an electric field. I work for a competitor and recently got a patent on a similar isothermal compressor which is in the development phase.
A second area of development is cryogenic compression of gas. Because hydrogen is commonly distributed as a cryogenic liquid, and because it will slowly boil off inside a vacuum insulated container, there is a need for cryogenic compression which takes advantage of the high density of the cryogenic gas. Rix is a company in California that came up with a two stage machine with no intercooling that could compress gas H2 from 100 to 3000 psi. It was successful and they've been marketing it for about 8 years now. It probably won't go too far because it failed to reach the higher pressures needed for the emerging hydrogen econemy due to very high discharge temperatures. I've recently developed a similar two stage reciprocating compressor that takes cryogenic H2 gas from 100 to 7000 psi for use in hydrogen systems and have a few patents on it.