The Brayton thermodynamic cycle, used in gas turbines, makes it possible to build an engine where the combustion chamber doubles as a furnace. It is also possible for it to run on solid fuels, such as
wood. This is all possible due to the use of a regenerative-cooling air duct around the combustion chamber that recycles the heat, so the engine can burn cleanly and produce more power at a higher (cycle) efficiency. The engine may even be able to achieve temperatures hot
enough to recycle scrap metal without melting itself. At those temperatures, it
should also be possible to cleanly fuel the engine on non-recyclable plastics, most of which convert to just
water and
CO2 when burned completely. A filtration system may be required for plastics that contain other elements.
The engine is equipped with a water bath to filter out unwanted substances from the exhaust, such as unburnt hydrocarbons (which would not form under optimal combustion), carbon monoxide, and NOxs, without the need for expensive catalysts. Catalytic converters get clogged with
ash, which does not get filtered out like it would in a bath. The filter could also remove halogens and heavy metals from certain plastics. The removed ash and NOxs undergo a chemical reaction in the bath to form powerful oxidizers, which when mixed with fuel, makes combustion cleaner and more efficient. The water bath further improves efficiency converting otherwise wasted heat into steam power.
The furnace should be able to create steam power from various chemical or culinary processes such as boiling or dehydration, which could extend to wet fuels, such as other sources of biomass or biological waste. Where boiling is required, the elevated pressures should serve to reduce cook times at a higher temperature, similar to a pressure cooker. The furnace itself, with some skill by the operator, could control the temperature for more delicate chemical or culinary processes, such as roasting or baking.
With the addition of a condenser after the expander, it is entirely feasible that the engine could also be used to generate clean water from water formed during combustion or evaporated in the bath or furnace. By changing the contents of the bath, it should also be possible to distill liquid fuels such as ethanol, cellulosic butanol, or other hydrocarbons, formed from the destructive distillation of solid fuels within the engine, controlled by the air-fuel ratio. Lastly, the heat released upon recondensing could be used for radiant heating which is more efficient than convective heating and does not expose occupants to cold air sucked in from outside like traditional fireplaces do.
In the worst-case scenario, all of the components of this engine could be forged or fabricated. I have designed a rotary compressor-expander mechanism, similar to turbomachinery used in a gas turbine, with a flexible housing that seals against the rotor along flat edges, thus eliminating the need for machine tools (though a milling machine would greatly improve productivity). This all-in-one engine creates a minimalist manufacturing paradigm where the engine, and tools that can be derived from it (including machine tools), are sufficient for building an identical engine.
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