Combined Cycle Engine v2.0

[Dave]

Some of you may have read my earlier post about the Brayton cycle engine I built. Upon greater contemplation of the thermal cycle that takes place in the engine I have come to the conclusion that it is not exactly a Brayton cycle engine, but more a blending of the Brayton and Ericsson cycles.

Here is a more complete description. If I had a Digital Camera I would post pictures.

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[*]Air is drawn into the system via a twin scroll compressor that is driven by the main shaft. The air is compressed into the cold chamber.

[*]Inside the cold chamber there is a heat exchanger where the fuel (LNG) is decompressed, drawing heat from the intake air as it expands inside the exchanger’s tubing. This super-cools the intake air, dropping the temp by approximately 200°.

[*]The air is then moved by a second compressor from the cold chamber through another heat exchanger which takes heat from the exhaust and preheats the air, raising the temp 300+°.
After passing through this second heat exchanger, it enters the combustion chamber where the NG is injected and burned, raising the temperature by aprox 1000°.

[*]The super heated gas is then piped into an expansion motor (in this case a boxer 6). The temp of the gas drops 500° during the expansion, and another 300° when it passes through the second exchanger, and then it exists the tail pipe.
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I’ve placed Pyro sensors at each stage along the engine to monitor these temps.

Now to the reason for my Post. I keep loosing compression, leading to gas blow by around the cylinder rings. I know the reason why. The engine is able to rev up to 26,000 RPMS, much like a formula 1 engine, the high piston speeds are taking their toll on the cylinder walls and rings, and after a short while, gaps begin to form.

I can solve this problem by using more exotic materials, but that’s way outside my budget. I can afford to CNC parts out of aluminum casting I’ve done myself, so I have. So, I thought I would pick your brains a bit and see if any one has any better ideas for an expansion motor?

Ideally it would be a motor that can more efficiently extract mechanical work from the high pressure gasses, without developing sealing issues at high rpms.

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