confused readers, or get me laughed out of here for conceiving a new
Rube Goldberg machine. Since I'm not sure which yet, I'll go ahead and
talk about my Crazy Idea of the Week(TM). I'm not really sure if this
is a new idea or if it's been tried before, so I'll let those of you
with more experience answer that for me.
One of the biggest problems in using power producing Stirlings is that
much of the thermal energy is lost before it can be transmitted to the
engine. This results in much poorer engine performance than is
possible in the Stirling cycle.
As I considered this problem, I wondered if there was any way in which
the excess thermal energy could be recovered and used. In cars, excess
thermal energy can be put to good use by driving a turbo-charger. The
turbo-charger compresses the air coming through the intakes, then
feeds that to the engine for better performance. I began to think
along those lines, but I needed a configuration that could capture a
bit more power than most turbo-chargers. So I followed along the lines
of a Brayton cycle engine.
In the Brayton cycle, the excess pressure is captured in an exit
turbine and used to power both the drive mechanism and the air
compressor. This cycle is extremely efficient and compact.
Unfortunately, in Gas Turbines (the most common form of the Brayton
cycle) the combustion produces so *much* heat that it stresses our
material sciences to the max. As a result, Gas Turbines are very
expensive to own and operate. However, I think there may be a
compromise between the Stirling and Brayton cycles.
Here's a crude diagram of my idea:
(If you can't see the image, Click
Here)
The idea I have is this: Air flows into the air compressor on the
right. The air is compressed on the way through, and is fed into the
combustion chamber. The fuel flows in tandem with the air flow.
Combustion occurs as the mixture enters the pressure chamber, creating
a flame-thrower against the Stirling engine. (Note that the Stirling
engine presented is just an example. I'm not advocating any particular
model.)
Now some of the heat will power the Stirling, but some of it will want
to escape with the combusted air, lowering the efficiency of the
Stirling engine. The key is that the combusted air is not allowed to
escape so easily. Instead, pressure is retained by a turbine at the
back. When the pressures are sufficient, they drive the turbine fast
enough to maintain the operating pressure of the vessel. The energy
produced by the turbine both assists the Stirling and drives the air
compressor. Surplus energy can then be siphoned off for power
production.
That's my idea, anyway. I'm not yet certain if adding the energy back
to a direct drive train makes sense, or if it would be more efficient
to break up the two cycles and use the extra energy only to drive the
compressor. In theory, attaching it to the Stirling drive train
shouldn't be a problem as any overdrive in the Stirling cycle will
merely make the hot side hotter (and the cold side colder) until an
equalibrium is reached between the energy produced by the turbine and
the energy produced by the Stirling. That is, in theory. (Famous last
words, right?)
Thoughts? Comments? Criticisms of a wacky idea? (It's so crazy, it
might just work!)
Thank you in advance for your comments. I'm sure they'll be very
insightful.
> It looks to me that you are burning fuel to turn a turbine,More or less. The flame is directly applied to the Stirling engine in an attempt to provide the highest Stirling power capacity possible. However, the turbine acts as a secondary waste heat recovery system. i.e. Heat that would normally exit with the exhaust is converted to greater volume in the combusted gas. The greater volume results in higher pressures that then drive the turbine. The worst case scenario is that the Stirling Engine is 100% efficient (not bloody likely) and the compressor costs are partially recovered. Since that's effectively impossible for a variety of reasons, it's a fair certainty that there will be excess energy to extract from the system. No energy is extracted during the gas expansion phase.> like a diesel engine. So... if you hooked sirling engine to the > casing of a diesel engine, then you would be all set. Not quite the same thing. What you're proposing is a secondary recovery system for an internal combustion engine. This is slightly different in that the Stirling is intended to be the primary engine while the turbine is the secondary recovery system.Just to be clear (since I'm sure many people are wondering why I don't just use a Gas Turbine) what I'm trying to design here is an efficient engine that can power a car at high thermal efficiencies. Now GM and STM power already tried that once with a converted Lumina hybrid car, but GM wasn't very happy with the thermal efficiency of any of the delivered engines. Their next experiment was with a Gas Turbine hybrid (a modified EV-1) that managed 60 miles to the gallon. (Although the true efficiencies haven't been disclosed. The 60MPG figure was a full 6.5 gallon tank of gas and fully charged batteries via the EV-1's charger.) Still, the Gas Turbine engine managed to produce about half of the emissions of a comperable gasoline engine through more efficient combustion. Unfortunately, GM seems to have abandoned the technology.The reason for GM's abandonment is unclear, but it may have something to do with the cost of a proper Gas Turbine. The temperatures at which the exit turbine must operate make the required materials very expensive. Chrysler spent some 30 years on the problem attempting to come up with a way of bringing Gas Turbine prices in line with gasoline engines. They never succeeded and had to give up the technology.The idea in my engine is that the pressure built up from the exhaust gases would drive the turbine and not the temperature/expansion spikes of intial combustion. We want to move as much of the thermal energy through the Stirling engine before allowing the exhaust gases to escape through the turbine (hopefully) generating extra power in the process. If I'm correct (and not just pushing wishful thinking) then the turbine could be manfactured of lighter, less expensive materials than a Gas turbine.