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turbopneumatic hybrid

Gas turbine + Pneumatic hybrid
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A combination of a pneumatic car and a gas turbine engine. A gas turbine is used to drive an air compressor. Compressed air is stored in a high pressure tank. No attempt is made to cool the compressed air. Furthermore it is insulated and the exhaust of the gas turbine is passed trough a heat exchanger and heats the stored air. The compressed and heated air is used to drive an air motor.

Rationale: Gas turbines are known to be more efficient than regular engines, however they are only efficient at certain ranges of RPM and a lot of energy is lost in the exhaust. The heat exchanger recovers heat from the turbine and stores it in the compressed air tank. The compressed air tank provides a reservoir of energy so the engine can use a lot or a little as needed, while the turbine is runnning always at optimal rpm or stopped.

Purely pneumatic cars have a problem of autonomy (compressed air has low energy density, so large tanks are required). By providing a turbine a smaller air tank can be used.

In crowded streets the turbine can be stopped and no emissions are produced.

Compressed air engines are known to work (mdi air car).

Gas turbines are known to work (For example in tanks, and they can use practically any fuel)

Drawbacks: Too many parts. Air compressor probably heavy. Weight of the compressed air tank. May be made lightwieght using composite materials. A possible problem is the resistance of materials in compressed air tank (at high temperature most materials are not as strong).

Pro: Compressed air can be used to start the turbine.

atomico, Apr 17 2008

Compressor-Turbine Tandem Engine Layout Perfect_20Engine_20...omotive_20X_20PRIZE
A ceramic rotary engine much like a gas turbine engine in lay-out but with intermittent thermodynamic cycle. [rotary, Apr 18 2008]

A detailed diagram http://nanoquimica....urbixair/Aircar.htm
Fictional description of concept, with nice drawing [atomico, Dec 31 2009]

[link]






       You don't need the turbine to RUN a compressor; just use the compressor that is already an integral part of the turbine engine: oversize it and tap off air at the pressure you need, before the combustion chamber. Chuck in some regenerative braking (use air motors as compressors - easy) , and you might actually be on to something here.
The main problem could be the efficiency of using compressor/airmotors (as opposed to, say, hydraulic) to transmit power, but I don't know what sort of percentages a system like this might get...
neutrinos_shadow, Apr 17 2008
  

       Yeah, the front end of a turbine is a compressor, and a damn good one. In jet airplanes, air is bled off and used in many ways.
baconbrain, Apr 18 2008
  

       I used to think of compressed air to start my rotary engine much like [neutrinos_shadow] proposed until I found a more compact, powerful and efficient hydraulic system. My rotary engine layout is much like a gas turbine with compressor and turbine sections. Are you interested having your gas turbine made of ceramics? You are right that an ordinary gas turbine is only efficient at certain RPM, so I would like to introduce you to my positive displacement rotary engine that can hold the working fluid even in much slower RPM and yet efficient still.   

       You are particularly interested in chemical engineering. Do you have other alternatives aside from boric acid or diamond-like carbon films for ceramic engine lubrication? Hope you can give me some insights too in ceramic engine innovation particularly zero-thermal expansion (ZTE) composite and the net-shaped ceramic engine production developed in Ohio State University, and how can these two be combined into one fabrication. Is it best to have a ceramic core and a tensile-stressed metallic skin for turbines?
rotary, Apr 18 2008
  

       Jesus, there he is again.
elhigh, Apr 18 2008
  

       I like this. That says a lot considering my opinion of hybrids in general. [+]   

       The great advantage of pneumatics here is that air is compressible. That precludes a direct hydraulic equivalent, unless one incorporates a spring-loaded hydraulic accumulator or some such: but what about a pneumatically-loaded accumulator, like a high-powered version of a Citroën suspension sphere?   

       Subsequent drive would be hydrostatic. I suppose pure pneumatic drive would have the same problem as hydrostatic, namely that the equipment becomes extremely heavy as soon as one is dealing with a decent amount of power. But for a very light vehicle either would be cool.
Ned_Ludd, Apr 18 2008
  

       What kind of pressure can you pull as bleed air off the compression stage? I thought Ford had a cool concept with their hydraulically assisted launch hybrid idea in the Tonka show truck, but that used captive nitrogen and shuttled hydro fluid from high-pressure storage to low-press catchment. I would think that your storage tanks would have to be either big (and therefore very heavy and of course bulky) or numerous (still heavy, but you can pepper them around the vehicle in otherwise unused spaces).   

       I think the biggest advantage this has over the Tonka idea is that no catchment tank is needed - just vent the used air. Even better, since it's likely to have cooled quite a bit, having given up a great deal of its kinetic energy to the drivetrain: blow the exhaust over the AC condenser coils.
elhigh, Apr 18 2008
  

       I like it (+). The problem with regular pneumatics are are compression heat loss. You embrace that and add in waste engine heat.   

       As you have said, you have to use a separate compressor. The pressures needed to store a decent amount of pressure energy are orders of magnitude larger than seen in a turbine engine. I think the MDI uses 1500psi tanks.
MisterQED, Apr 18 2008
  
      
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