Turbo-Charged Alternator

[Zerohour]

"When this baby hits 88mph you're gonna see some serious ****" - Doc Brown


Or quit possibly when this baby hits the top of the rpm range, you're gonna have to run like a mother ****er who just dropped an unpinned grenade in the fox hole.

[t vago]

Originally Posted by Zerohour

I knew there was a reason I hesitated on posting this up. I know there are alot of nay-sayers about such an idea. But there are 50+ other variables that go into the rate of rotation...

Hey, don't give up. I have my own idea about installing a variable displacement system on my truck, and many here have also said it was not feasible for one reason or another (including a few here who tried their own form of variable displacement without doing their homework first, then throwing up their hands when their experiment failed to work).

Are you sure that you must deal with rotations north of 100K RPM? Perhaps lower would be better. After all, you don't need much more than 2 HP (assuming an alternator rated at 120 A) to drive an alternator at its rated capacity, and you're not going to need rated capacity all of the time.

[markweatherill]

Would it be any more efficient to have an exhaust driven turbocharger driving an accessory which would normally be driven by the engine,

or to have the turbocharger attached to the engine and thereby assist in driving every accessory...

[Zerohour]

One of those options requires a complete engine replacement, turbo installation, and complete fuel management and ecu alterations, and when tuned for economy will still require more costly premium grade fuel and will only result in a power up which most likely will yield identical FE but faster drive times. One of those options requires the relocation of parts already provide with the vehicle and utilizes an unused engine by-product. Tell me which one costs less, frees up rotational mass, and could maybe eek a tiny bit of FE back out of an engine? :-)

[t vago]

Originally Posted by Zerohour

One of those options requires a complete engine replacement, turbo installation, and complete fuel management and ecu alterations, and when tuned for economy will still require more costly premium grade fuel and will only result in a power up which most likely will yield identical FE but faster drive times. One of those options requires the relocation of parts already provide with the vehicle and utilizes an unused engine by-product. Tell me which one costs less, frees up rotational mass, and could maybe eek a tiny bit of FE back out of an engine? :-)

It'd be interesting to see an alternator driven by exhaust gases. Assuming the mechanism is in place and operational, how would you account for increased loading on the alternator? For instance, how would you account for turning on the exterior lighting when driving at night? That is a load of several amps, and represents a fairly substantial load transient when the lights are turned on.

Another thought - have you considered installing an electrohydraulic power steering pump? Preferably, one that is able to sense steering demand and turn on as required? That might relate to the thought about about load transients, but it would also be another parasitic load removed from your engine.

And another thought - When you remove this parasitic load from the engine, you realize that for a given throttle setting, more engine power will be available to push the car forward than if the parasitic load was there. Assuming that your turbine captures the work available in the exhaust to drive this otherwise parasitic load, and assuming a small amount of backpressure that effectively loads your engine to a fraction of what the parasitic load did before, it is likely that your throttle plate will be shut more than it was previously, in order to maintain the same cruising speed as before. This will also have the effect of raising your engine vacuum higher than before. Won't that increased throttle plate closure and higher vacuum hurt your fuel economy?

[Zerohour]

Actually getting up to speed is what kills the mileage in the subaru. All rotating mass will greatly effect TP and engine load required to get up to speed. The "back pressure" is a mythical creature, you can run a car on open headers. Back pressure could become an issue with there were cam changes, head porting, time changes, etc that would effect the duration in which the valve is open to exhaust. But there is nothing that requires such a change from a small difference. Plus, the exhaust already has the factory muffler replaced with a two chamber, adding a bit of back pressure at this point won't account for as much that was eliminated to begin with.

As for the "load" placed on the alternator, most modern units are equipped with regulators. The "dim" of a headlights is actually the rate which your alternator responds to adjust to compensate for the load. If you idle is changing when the alternator dims you most likely experiencing a soon to be failed alternator, poor grounding of the electrical system, or some other variation in the ignition system of the car which was greatly effected by a change in electrical demand (aged battery, old coil, etc).

Of course issues might arise of this change, but the simple fact still remains no one has procured a unit which does or does not work. Or has/has not effected FE in a good/bad effect.

And guinea pig numero uno will not be the Subaru.

[markweatherill]

I don't mean to be a nay-sayer as I do appreciate the gain of taking the alternator's load off the engine.
However I'd hope the goal is better than 'a tiny bit of FE' as more conventional alternator modifications, like simply turning it off and on at appropriate times already yield that.
Please aim for 'a large amount of FE'! :-)

[t vago]

I'm not entirely sure you understood what I'm saying... I will try to clarify.

I will agree that backpressure is generally considered to be a bad thing, so when I mention it, you realize that you will have a slight amount of backpressure that is caused by the turbine housing. It's unavoidable, because the turbine housing requires a pressure differential to convert the heat energy in the exhaust into flow energy that can be captured as work. Higher backpressure will mean a larger amount of drag on the engine itself, even a perfectly stock engine.

As for your mentioning regulators, that's all good what you mentioned, but you also realize that if the alternator is called upon to provide more amperage, it has to take more work from whatever's moving it. That isn't noticed while the alternator is mechanically powered by the engine, because the alternator is simply a small parasitic load that could be essentially ignored. However, in the case where the alternator is powered by something like your turbine, where that's the only thing it's moving, then you have to have some mechanism in place to keep the turbine spinning. Otherwise, you'll find that your turbine will stop altogether at a certain alternator loading.

I am, of course, assuming that you're going to use some sort of wastegated solution or variable nozzle solution to limit your turbine speed. I still don't think you need to spin as fast as what is mentioned here.

[some_other_dave]

Has anyone mentioned the deleterious effects of heat on alternators? Most turbos get very very hot, and I would imagine that unless you mounted the turbine separately from the alternator, you'd limit the lifespan and possibly the output of the alternator. That would argue for a pulley and belt, or maybe a long shaft between the turbine section and the alternator section.

-soD

[Zerohour]

I would like to point out something at this point. Different parties are claiming opposite ends of the spectrum.

Maxwell Mk I also says you may be wrong. :-)