Exhaust Heat Recovery - Steam Power

[Dr. Jerryrigger]

all good points, I am also skeptical of this working, but I like to be skeptical of most things I try, it results in more accurate findings.
The problem of over spinning the alternator could be addressed with either a RPM sensitive let off valve or a simple governor, like the one is a music box (I don't know if you've ever taken one apart...) It's a shaft with a sheet metal "fan" that forms a T, as the T spins it has air resistance which increases at a rate of RPM^3. If properly sized it would make it imposable for it to spin out of limit, and would add very little extra load an normal speeds.

[Phantom]

Using a "waste gate" would work and can work to limit and reduce the RPM. Yes normally the waste gate is used to blow off excess pressures going to the intake, but place a waste gate before the turbo and you can slow the turbo by now sending gas to it. See : QTP » Electric Exhaust Cutouts

Instead of bumping the gas in to the air have a pipe run to a Y collector and rejoin the exhaust path just after the turbo.

[Big Dave]

Compounding is an idea that has been tried a number of times.

It actually works quite well for aircraft engines. The reason that B-29s could hit nearly all of Japan was the super-efficient R-3320 engine. It was also very temperamental and probably more B-29s were lost to engine failures than Zeros.

Also the Napier Sabre was considered very efficient.

Airplane engines often cruise at a high percentage of rated power. Even running "Lindbergh lean" those R-3320s were running at 65% of rated power just to keep the heavily-laden planes at altitude.

But on cars, not so much. Especially cars driven in the low-power, low speed(efficient) part of the envelope. Most cars run around 10% of rated power. Lower fuel burn at lower perecentage of rated power leaves you with not much available energy.

My truck barely makes any boost (turbocharger = turbocompounded air compressor) at all at 70 MPH. At lower speeds the needle is super-glued to the peg. Very little compounded power being recovered.

For ground vehicles, you rapidly hit the point that all the weight & complexity of the compoinding exceeds the recouped energy.

[jdgFirefly]

Originally Posted by C3H8

what i am now asking is, how would you prevent the alternator from over revving and blowing its self up under high heat and low electrical load conditions.

One of the nice things about a steam system is that it can easily store energy (for a short time). The boiler is a pressure vessel that acts just like the storage tank on your air compressor. If you want to regulate your power output you only have to add a control valve just before your steam motor. The unused steam will only build up pressure in the boiler until its needed.

If a low mass / flash boiler design is used than a separate tank may need to be added just for storing pressure.

The boiler can only hold the pressure as long as it can maintain temperature so adding insulation may help it hold pressure for longer, if that becomes a problem.

[Dr. Jerryrigger]

Originally Posted by jdgFirefly

If you want to regulate your power output you only have to add a control valve just before your steam motor. The unused steam will only build up pressure in the boiler until its needed.

If a low mass / flash boiler design is used than a separate tank may need to be added just for storing pressure.

The boiler can only hold the pressure as long as it can maintain temperature so adding insulation may help it hold pressure for longer, if that becomes a problem.

I was imagining a flash boiler thus far, but greater pressure holding capacity would be useful. It adds a lever of danger, as just about any energy storage method does.
I'm thinking that it will be quite complicated and or expensive to regulate the steam flow, in comparison to regulating the water entering the system. Just a thought. A well insulated, and beefy flash boiler could potentially hold heat for some time, but it would be nice to not add 300kg to ones car... the water will likely weigh quite a lot already.

[jdgFirefly]

Controlling the steam or water would both use a valve and some sort of electric or mechanical controls so the complexity would be the same. However its off the shelf stuff as apposed to some of the other ideas so far that would involve building governors.

The problem with controlling the water flow to the boiler is that you don't want to starve it of water as it will be damaged if it starts to run dry. Also it doesn't give the flexibility of having some stored energy.

I agree that storing the steam energy would be more dangerous, but I would also like to point out that any steam system we make could be dangerous. In any case safety precautions like pressure relief valves should be considered, and the construction of any boiler should not be taken to lightly. But that being said I like the idea of having some storage to make the system run at a more constant rate despite the ICE engines erratic behavior. And like i said it doesn't necessarily mean you need a bigger boiler with a larger volume of water. you could still use a low mass boiler but have a separate pressure tank, the tank could even be mounted in a remote location, as long as any condensate is able to flow back to the boiler.

Another way to control the system (and probably the safest) would be to control the source of heat (the exhaust). Add a pipe in the exhaust to bypass the boiler and have a bypass valve. This valve could be a crudely made butterfly valve, it wouldn't need to seal perfectly just divert most of the exhaust flow.

[Dr. Jerryrigger]

With a T of some kind spiting the exhaust, one could have the butterfly valve on a light spring so if exhaust pressure increased more would go to the muffler and a similar amount would go to the boiler. Also the exhaust coming out the boiler would likely not need much muffling anyway.

[basslover911]

Right... Aaaaaaand with all this how much backpressure would form?? Because that's an inefficiency that must get outcompeted by the gain of having said boiler.

[ConnClark]

The big safety problem with using a steam pressure boiler in a vehicle is the risk of a rupture. Once ruptured the pressure will drop quickly and any water remaining in a boiler will flash to steam. This can quite easily equal a small bomb going off.

[jdgFirefly]

Originally Posted by basslover911

Right... Aaaaaaand with all this how much backpressure would form?? Because that's an inefficiency that must get outcompeted by the gain of having said boiler.

"Backpressure" would be a factor that needs to be considered but I can't see it being to hard to build it with the same or less pressure drop as a muffler or cat.