Superchargers and turbochargers have been around for many decades, once it was figured out that if you force feed an engine it will produce more power. And swapping the factory exhaust manifolds for less restrictive exhaust headers is a proven way to make more power by evacuating the exhaust better, thereby making more room for the intake charge. So how about a system which acts like a supercharger, only it "super-exhausts" the engine? I'm thinking of a small fan or turbine placed at the end of the collector (on an exhaust header) which will pull the exhaust out of the engine forcibly. It in essence will be a header on steroids. It would have to somehow be "self-powered" otherwise if it was running off of the engine the power to operate it might cancel out the gain in the power it makes. The second issue would be if it needs to be in synch with the exhaust pulse, rather than a constant pull on the exhaust. But I think there's a million dollar idea in this one!
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Why? You will gain no performance really. You will lose power somehow that will need to run the device.
I would like to hear from anyone who knows the thermodynamics of engines as to why this shouldn't work, but I know that "tuned" exhausts that set up a standing wave such that the pressure at certain pulse frequencies is actually negative have been used. In fact, these are called "extractors" I think. It seems to me that a very small amount of energy applied to lowering back-pressure could leveage to a large increase in power. I don't think it would be zero-sum.
On the other hand, if it's this easy, it would have been done by now ...
I think it could be run on electric power like any other accessory rather than mechanical (crankshaft) power. I can't imagine it would take that much power even to run this turbine/fan at a very high speed. My biggest concern would be whether or not the Super Exhauster would need to be in synch with the exhaust pulses of the engine. Also, I wonder if it's possible to "over-exhaust" an engine so that you're pulling out the exhaust charge too quickly.
But where would the electric power come from? All the power in existing auto electrics are eventually derived from the engine's crankshaft anyway.
Well, yes and no. Yes, the electrical power ultimately is derived from the work the engine is doing, but many accessories such as a cooling fan, headlights, stereo, get their energy from the alternator. Adding another electrical accessory to the alternator does not put additional load on the crank.
The high volume of the exhust gas requires high capacity pumps/fan that requires considerable energy. Variable valve timing has taken care of scanvenging exhaust gases by taking advantage of the mementum of exhaust gases as they flow out of the cylinder due to intially high pressure following combustion and then the upward movement of the piston. As the exhuast gas flows out at very high speed it continues to do so. A late exhaust valve closing while having early inlet valve opening help draw in fresh air for the next cycle. Opening the two valves at the same time called the Over Lap Angle which can exceed 90degrees on racing cars. Engines with variable valve timing and variable inlet manifold are very effective at naturaly getting rid of exhaust gas.
Some engines won't run right or at all without at least some exhaust back-pressure.
You dont want to suck more air through the cylinder than necessary. Some flow control is needed to get decent power. If less restrictive was the way to go and there were no restraints, then race cars wouldnt even run headers. The trick is to force as much air as possible into the combustion chamber. There is a "mechanical" solution to this already. Its called an expansion chamber. It uses exhaust pulses to cram more air into the cylinder at the end of the exhaust stroke. Basically it takes the pressure wave from the previous pulse and bounces it back against the upcoming pulse, momentarily reversing the flow of the gassses coming out of the engine thereby pushing more air into the chamber.
Releasing to much backpressure reduces low end power (torque). But gives top end improvement. Exhaust valves are open when the intake valve opens (overlap).A certain amount of spent air/fuel is still in the chamber when the exhaust valve closes, mixing with the new air/fuel. This also helps reduce combustion temps. With a exhaust scavaging system you could pull fresh air/fuel out the exhaust valve during overlap wasting fuel and confusing air flow and exhaust sensors and overheating the cataylist. However perhaps on a direct fuel injected engine, injecting fuel right before ignition in the camber, when the valves are closed. On a side thought I think this method was able to get air/fuel mixture into the neighborhood of 40 parts air to 1 part fuel.