New hair brained idea...

[Clev]

Originally Posted by SuperTrooper

GM hybrids use a belt driven alternator/starter, operating at 36 volts.

I'm thinking about replacing the alternator entirely with one of these:

Robot MarketPlace - Mars Brushless PMAC Motor with 250A Controller Kit

and throwing 72V worth of batteries in the trunk. With the right kind of controls, it could do regen for long downhills, instant engine restarting after EOC or auto-stop at a light, up to 15hp power boost for hybrid capabilities... Install a DC/DC for the 12V stuff, a small PM motor to drive the A/C compressor and/or PS pump, and you've got 75% of an IMA solution.

[metromizer]

Originally Posted by TheTopher

However, what if this hydrogen system was powered by one of the new "turbine alternators" (I don't remember the actual name for it).

I read the same thread, good sounding stuff. google TIGER alternator, I think the investigators/inventors are UK based.

Originally Posted by TheTopher

Since it doesn't take any added stress on the engine to power this type of alternator, would this make the hydrogen boost idea feasible?.

The web page I looked at said TIGER does require a microprocessor or controller of some sort, since some phases of ICE operation are beter than others to recoup exhaust gas pumping losses, and turn them into gain. I am not sure zero added stress is right, but maybe reduced effort to drive this alternator is closer to right?

I'd like to see this TIGER alternator work, first, as a replacement for the standard alternator. After than, I don't see in theory at least, why you couldn't 'on board' generate brown's gas on some small scale. Weather or not you'd realize any gains would have to be experimented with.

Just clear your mind first, chanting "in physical science there's no free lunch, no free lunch... "

[Formula413]

Originally Posted by jamesqf

No, because the exhaust gas isn't really (or mostly) pushed by the piston, but by the power of its own expansion. (Think for instance of the difference in the noise level of an unmuffled exhaust and an air compressor.) The power captured by the turbine comes from the waste heat in the exhaust gas stream. It will be hotter upstream, cooler (and thus lower pressure) downstream.

But isn't the power of the expansion used to move the piston in the firing stroke? How would just heat (and not pressure) turn the turbine?

[metromizer]

Originally Posted by Formula413

But isn't the power of the expansion used to move the piston in the firing stroke? How would just heat (and not pressure) turn the turbine?

Jumping in here...

Yes, but it's a little more complicated a story. Heat forces the gas to expand, the expanding gas' energy (mostly) stops pushing the piston down the bore once the exhaust valve opens, which happens near the middle of the ignition or power 'stroke', piston not yet to the the bottom (I think about mid-stroke). This residual positive pressure just gets vented to atmosphere via the tail pipe. A well designed turbo system takes advantage of that fact, and uses it to turn a compressor wheel. Why not turn a generator with that same shaft? At least, that's the idea.

Contrary to popular belief, zero restriction in the exhaust path (to atmophere) hurts the performance of most ICE's. Said another way, some carefully controlled backpressure is actually a good thing for gasoline engine efficiency.

[johnmyster]

Originally Posted by Formula413

But isn't the power of the expansion used to move the piston in the firing stroke? How would just heat (and not pressure) turn the turbine?

You are both right.

If you put a turbo in the exhaust stream, yes, the piston has to push the exhaust gasses out of the cylinder against the back pressure of the turbo.

However, the opposite is also true. Think of the piston at BDC after the intake stroke. Now think of it at BDC after the power stroke. After the power stroke, the gasses have combusted and expanded due to the increase of temperature. Typically, this expansion is large enough that even at the bottom of the power stroke there is still pressure within the cylinder. As soon as the valve opens this pressure is released and the potential energy is lost.

Thus, the turbo has the advantage of being fed by a higher volume of gasses than simply that displaced by the exhaust stroke. See, the gain comes from the pulse of exhaust gasses that jets out as the exhaust valve opens and the piston is still stationary.

So yes, backpressure increases the work that the engine must do. However, a portion of the engine gained by turbines would have been lost anyhow. This is why intercooled turbos win compared to intercooled superchargers, even at the same operating parameters. Turbos are partially driven by otherwise uncaptured energy.

[johnmyster]

Originally Posted by metromizer

After than, I don't see in theory at least, why you couldn't 'on board' generate brown's gas on some small scale.

I'd rather used any energy recouped by a turbine (mechanical energy) to power things that presently place a mechanical load on the motor. Electrical, power steering, A/C, etc. Once you did this, you'd be far ahead of trying to convert your mechanical power source to electrical to chemical and back to mechanical.

[TheTopher]

Originally Posted by johnmyster

I'd rather used any energy recouped by a turbine (mechanical energy) to power things that presently place a mechanical load on the motor. Electrical, power steering, A/C, etc. Once you did this, you'd be far ahead of trying to convert your mechanical power source to electrical to chemical and back to mechanical.

I agree, this would definitely be the first, and a very large step in the right direction, especially since you could stop having to only use AC while you're coasting with the fuel cutoff to avoid the major impacts on your FE.

But still, I found the idea of taking the recouped energy one step further pretty intriguing.

[jamesqf]

Originally Posted by Formula413

But isn't the power of the expansion used to move the piston in the firing stroke? How would just heat (and not pressure) turn the turbine?

When it comes to gasses, heat & pressure are pretty much the same thing. Here's a link to a wikipedia article: Gas laws - Wikipedia, the free encyclopedia

Bottom line is that unless the exhaust gas is coming out the tailpipe at ambient temperature & pressure (which it certainly isn't, especially just back of the cat), it's still got energy in it that can be extracted.

[MechEngVT]

Starter/generators are still used on almost all gas golf carts. And they are generators, not alternators (alternators generate AC, generators DC). They work in golf carts and are quiet because they are so low-powered they can be driven from a v-belt without too much problem. A generator powerful enough to start a high-compression V8 would have to be gear or chain driven and that's where the noise comes from.

Honda has developed under-flywheel starter/generators for single-cylinder industrial engines (the iGX440 I think?). It works by using the flywheel magnets as both a magneto generator and a brushless starter motor and since it's directly connected to the flywheel it's silent. It starts the engine with lower power requirements by first indexing the engine to TDC (either stroke, doesn't matter) and then applying starting current, and it starts in a fraction of a second with the push of a button. This technology is scalable to automobiles but generally requires the increase of system voltage from 12-36 (or from 14-42 to use prevailing high-voltage terminology). There is a reason that automotive system voltages stopped at 12VDC and it has to do with higher voltages arcing at the ignition but I'll have to dig to find the specifics...all I know is there were safety concerns with higher DC voltages and distributor ignitions. Most modern engines are distributorless so hopefully this hurdle is gone now.

metro, backpressure is bad for engines. The reason that engines don't do better exhausting straight to open atmosphere is that acoustically-tuned exhaust pipes can do *better* to improve performance than zero backpressure. When an exhaust pipe comes into tune with the engine's pulsing the exhaust port will actually see a vacuum near the end of the exhaust valve event that improves scavenging. Having an exhaust pipe to achieve this tuning inherently provides backpressure, but it isn't the backpressure that helps the engine it's the absence of backpressure during certain designed operating parameters that helps the engine.

[metromizer]

Originally Posted by MechEngVT

metro, backpressure is bad for engines. The reason that engines don't do better exhausting straight to open atmosphere is that acoustically-tuned exhaust pipes can do *better* to improve performance than zero backpressure. When an exhaust pipe comes into tune with the engine's pulsing the exhaust port will actually see a vacuum near the end of the exhaust valve event that improves scavenging. Having an exhaust pipe to achieve this tuning inherently provides backpressure, but it isn't the backpressure that helps the engine it's the absence of backpressure during certain designed operating parameters that helps the engine.

very well put, thanks.

I have played with tuned exhaust headers and mufflers on an engine dynomometer... (normally aspirated gas engine) Exhaust theory is not as well understood as some would think (I barely grasp some of it...).

Are you saying that adding a turbine wheel might negate the positive effects of a 'tuned exhaust'? <trying to answer my own question here...> Thinking more, I bet it would. Perhaps a well designed system with turbine wheel could be tuned? i get a little confused since the only exhaust turbine wheel engines I'm familiar with to date, have the turbine mated to a compressor that adds power, a completely different animal than the idea being floated here.