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2 stroke engine's have a theoretically superior power to weight ratio, but they suffer from exhaust back-pressure, especially at high RPMs. "Tuned" exhaust systems can help, but typically result in a narrow power band.
My idea is for a supercharger type engine driven fan in the exhaust system. Creates
a nice vacuum to suck that nasty exhaust gas right out of the cylinders, consequently also helping to pull more fuel-air mixture in.
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this would worsen the two stroke's problem with fuel efficiency (by pulling more unburned fuel-air mixture into the exhaust system). And the weight of the contraption would kill your precious power/weight ratio. And the hot, dirty and corrosive exhaust would destroy the seals in the supercharger. But I guess thats why this is on the HALFbakery... |
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for more jollies, add an afterburner instead. |
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Fully baked and in use in many large two-stroke diesels. It's called a scavenging blower. |
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elhigh: That's incorrect. A scavenging blower of
the type used in large diesel engines is fitted to
the INTAKE side of the engine. It supplies
positive pressure intake air while the inlet and
exhaust valves are both open to make sure all the
exhaust gasses are out of the cylinder before the
next injection of fuel. |
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This idea implies an engine-powered pump to
create a partial vacuum on the exhaust. Which,
isn't as good. But hey, it's easier to retrofit. |
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but pusher-scavenger 2-strokes are totally baked....
Ha! I wonder if you could power the scavenger pump
by putting a turbine in the inlet manifold.... like a
reverse-turbo. Really pushing the inefficiency
envelope there.... |
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Exhaust pressure could start the turbo spinning, then momentum would keep it spinning, ie: extracting, when the pressure dropped, to pull in fresh air. |
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The old Detroit Diesel two strokes all had a gear driven blower on the intake side, no intake valves, just exhaust valves, and often on marine applications a turbo charger to increase power.
Intake ports in the cylinder liners were covered/uncovered by the moving pistons. |
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1)the idea is ass before cart
2) the risk of a single backfire destroying the blower would be hard to summount
3) the engine now "pays even more" for waste heat
4) the issues with thermal expansion would be profound
5) lubrication would be very hard to maintain
6) the accumulation of coke would rapidly destroy the lobes of the blower
7) the lack of intake pressure still limits the engine to a narrow power band
8) the massive increase in exhaust manifold surface area and hot side heat retention is going to cause novel engine and cylinder head overheating problems.
9) 2 stroke diesels don't currently pass stringent emissions standards, and this isn't going to solve that
10) you are pumping heat/work in the wrong direction. |
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