Gregory's ServerIn fact, when run in reverse and with different solenoid timings, the engine can work as a fairly high pressure ratio compressor. The adiabatic efficiency wouldn't be great, but the system could theoretically recharge an air reservoir.
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...by the waste heat from the shuttle return solenoid. At the beginning of the power piston downstroke, this reheated air flows into the low pressure expansion volume, helping to push the shuttle piston and power piston down past top dead center. Once the power piston passes bottom dead center, the exhaust valve opens and the expanded air is pushed out of the engine. Solenoids help pull the shuttle and power piston to their top positions to reset the cycle. How useful an engine like this is really depends on the availability of compressed air and electricity. It would likely be a lot quieter and cleaner than an internal combustion engine, but given how affordable and efficient electric motors are, you'd need a strong case not to just use one of those. There's no rare-earth minerals in this engine though, which is a possible selling point in extreme resource constraint scenarios. Ok, looks like I was a bit off on the compressor angle. It wouldn't take running it in reverse, it just requires offsetting the valves (in purple) by 180 in the cycle. If you have a mechanism that can do that, then the engine can switch into "regenerative" mode mid-operation. That's got a bit of potential for vehicles with regenerative braking. Just to elaborate a bit on that possible use case, let's imagine a relatively low speed vehicle that has a hybrid electro-pneumatic drive train. It's overall air storage capacity isn't huge, but it takes the acclerative power demand off of the electric system which is there to recharge the air tank and augment the engine through different power modes. Overall vehicle weight could be lower, and cost could probably be lower too, given less batteries. Because the electric system wouldn't be providing all the torque, you could get away with batteries which are energy dense but aren't as power dense. The vehicle would still be rechargeable like a purely electric system. Range wouldn't probably be fantastic, but could probably be adequate for certain kinds of applications where high torque, start and stop driving, and frequent opportunities to recharge could be possible. A bus or trolley comes to mind.  @skyfaller Feel free to use the concept! Compressed air storage is great if you can spare the space for the tanks and are okay with the quirks pneumatic systems have. |
In terms of operation, high pressure air enters into the first expansion volume, and is heated by the solenoid waste heat as the volume is moved into an optimal crank position by the shuttle piston. Once there, the heated air is allowed to expand, driving the power piston down through bottom dead center. The intake valve switches at this point to direct the high pressure exhaust gasses up into an intermediate chamber, where they are trapped and reheated...