Combined Cycle Gas/Steam Piston Engines?
So I've been looking to work on somewhat of a home project to keep myself entertained and keep my engineering concepts fresh in my head long after college. I've been looking towards using 1 or 2 turbochargers and and axial turbine hooked up to a generator to design some sort of combined gas-powered electricity/steam generator. As far as practicality goes, the project would be damn expensive and not worth it when considering efficiency, required tooling, etc.
So I've been considering the idea of going with a piston engine instead. Piston parts can be cheaply purchased from old compressors, etc, or even manufactured cheaply via a home aluminum foundry. Design/simulation processes will also be significantly easier than using turbines. The goal is a piston engine with either 2 or 4 gas pistons in V or in-line configuration, and a separate steam piston. The steam would be obviously generated via the exhaust gases from the combustion pistons, as well as additional gas feeding to the boiler as necessary.
So that brings me to my question: why has this not been done before? Exhaust gases are pretty damn hot, even after their pressure and kinetic energy are extracted in a turbocharger. A steam piston operates as a power stroke in both directions of piston movement, so I'm sure there's power to be extracted.
My guess would be that the size/weight of having even a small water boiler would make it impractical to put in an automobile when weighing added weight/size vs the amount of additional power the steam would provide. My application is not for transportation, it would be used strictly for power generation, or to power a fan, compressor, etc, maybe even just for fun or to have a cool project.
Another idea I've weighed is changing the cycle from a 4-stroke Otto Cycle to a 6-stroke gas/steam cycle, where after combustion, the steam is allowed to work the same piston. There's obviously cons to this concept as well as you'd have to design a system where the parameters and materials can use both gas and steam.
So what are your guys' thoughts? There's obviously a reason this has not been done, patented, and researched heavily if this were practical. Trying to get some good advice here.
Submitted June 26, 2017 at 11:43AM by ME_2017
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