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Old 01-05-2008, 06:57 PM   #21
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OK you're half right... yes people put turbos in old engines BUT they also modify the engine or get a new one and build it up so it doesn't blow up. My car shares the drivetrain with the supras so people try to work on it all the time so I do know a thing or two about it. people that put turbos on stock engines run very little boost or blow it up. Turbocharged engines ARE built differently to handle the additional heat/load from both the exhaust resistance and additional charge pressure.

Nobody's saying you can't put a turbo-alternator on the car. We're just saying you don't get something for nothing and the power to charge the battery has to come from somewhere. Using a turbo-alternator would be somewhat inefficient in a non-turbo engine. look at the fluid dynamics of it. Turbocharged cars don't care about it because the losses are more than made up for in the additional intake charge but a non-turbo car is fairly dependant on exhaust velocity and pipe tuning. drive a car with the stock wrinkle press bent exhaust with the stock cast manifolds then drive one with free flowing headers and open mandrel bent exhaust....10-15% increase in power is normal. put a turbine wheel in there nice and close to the ports for the most velocity and you'll be at the stock level with a belt alternator or therabouts. IF you can set up a valving system with a well set up exhaust (for both aspects...free flowing and turbo electrical charging...you will see gains. but getting it right will take a while AND will cost more than you'll save on gas in 5 years. (valves that withstand gasoline exhaust heat=$$$$)
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Old 01-05-2008, 08:41 PM   #22
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Quote:
Originally Posted by kamesama980 View Post
Turbocharged engines ARE built differently to handle the additional heat/load from both the exhaust resistance and additional charge pressure.
I have a strong suspicion that the additional heat and load associated with turbo systems come primarily from burning more fuel and the associated increase in engine power output. Without the compressor side of the turbo, there's no pressurization of the intake charge. Without additional air being forced into the engine, you can't burn any additional fuel, produce additional power or additional waste heat.


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We're just saying you don't get something for nothing and the power to charge the battery has to come from somewhere.
Agreed - You'll get power out of the turbo-generator at the expense of exhaust stream temperature and noise, but I never said the turbine should charge a battery.


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drive a car with the stock wrinkle press bent exhaust with the stock cast manifolds then drive one with free flowing headers and open mandrel bent exhaust....10-15% increase in power is normal.
I don't see how exhaust system design could be important when we're talking basic theory, but for the sake of argument, those sound like manufacturer advertised numbers. Actual gains from aftermarket I/H/E upgrades vary greatly from model to model since the quality of flow through stock components can vary greatly. Take the typical mid to lake '90s era performance-minded Honda or Acura 4-cylinder. They generally come stock with a decently flowing air intake, a 4-2-1 header and a decently flowing mandrel-bent exhaust system. Yes, you can improve the flow with larger aftermarket components, but you'll probably only see a 5% gain in power output.
Look at a V8 pickup from the same time period and you'll likely find a restrictive intake, blocky log-style exhaust manifolds and a crush-bent exhaust like you described. In those cases, I have little doubt that better flowing aftermarket parts could net 10-15% if not more.


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put a turbine wheel in there nice and close to the ports for the most velocity and you'll be at the stock level with a belt alternator or therabouts.
That's pure speculation.


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Originally Posted by kamesama980 View Post
IF you can set up a valving system with a well set up exhaust (for both aspects...free flowing and turbo electrical charging...you will see gains. but getting it right will take a while AND will cost more than you'll save on gas in 5 years. (valves that withstand gasoline exhaust heat=$$$$)
I agree that proper R&D is expensive, but post-turbine exhaust systems on turbocharged cars aren't nearly as important as you seem to think, and the great majority of turbochargers have an exhaust bypass valve built into the turbine housing, commonly referred to as a waste gate.
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Old 01-06-2008, 05:53 AM   #23
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Put an AC compressor Clutch with a toggle switch on your alternator.

When off its like removing the belt. With just the flick of a switch.
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Old 01-06-2008, 07:08 AM   #24
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A turbine alternator isn't going to be worth it. I will admit that this is pure speculation but here are a couple things that make me come to this.

First, turbine speeds - turbos typically run many tens of thousands of rpm. Most chargers reach a point of diminishing returns at about 120k. Others won't make it to 100k but they all spin fast. The only reason they even get that fast is because they begin making a little boost and that makes more exhaust gases and so forth and so on. Can you get up to efficient turbine speeds with an N/A engine? Especially an engine that isn't even under heavy load? and yes, you want those turbine speeds because without it you might as well clamp the end of your exhaust shut.

Second, gearing - Unless you are going to make your own lightweight, high speed alternator you aren't going to find one that's going to last long at much over 15k rpm. Does the gearing to go from 60-100k turbine speeds to 8-12k alternator speed save or use more energy to run? You have more bearings and the added inertia of not only an alternator but the gears or belts needed to make the reduction. On top of that. Without any boost you'll need some way of monitoring turbine speeds so you can actually activate the waste gate when it starts turning too fast.

Third, boost lag and back pressure - Ever ridden in a car that has a turbo put on it that's too big and has serious boost lag? That car will be beat off the line in a race every time and will have worse mileage in town guaranteed. The turbine is going to cause back pressure, serious back pressure. And back pressure is always an engine's worst enemy. It causes lowered performance and extra work that the piston has to do when it's pumping out on it's exhaust stroke. The piston engine is an air pump, and an inefficient pump at that. There is a reason miller cycle engines get better mileage than their normal otto cycle counterparts even though they must drive a supercharger at all times.

Anything you do need to take less power to run to save energy. This, doesn't. Plus, the more load you place on an alternator the less efficient it becomes. The alternator running only part-time means when it is on it'll likely be close to full capacity just trying to charge the battery, then you have the EFI system and ignition system and lights it has to run on top of that.
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Old 01-06-2008, 09:05 AM   #25
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First, turbine speeds - turbos typically run many tens of thousands of rpm. [...] Unless you are going to make your own lightweight, high speed alternator you aren't going to find one that's going to last long at much over 15k rpm.
That assumes you would simply attach an alternator to a turbocharger shaft. If you look at the link I posted earlier, they talk about using a switched reluctance generator specifically because it can handle high RPMs.
Further, if you follow my original system description and direct-drive a pair of wheel-motors, there's no point in restricting the generator output to 12 volts, or even to DC current... Higher voltages make it easier to transmit wattage around the car, anyway.
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Most chargers reach a point of diminishing returns at about 120k. Others won't make it to 100k but they all spin fast. The only reason they even get that fast is because they begin making a little boost and that makes more exhaust gases and so forth and so on. Can you get up to efficient turbine speeds with an N/A engine? Especially an engine that isn't even under heavy load?
Yes and yes. The gas volume it takes to spool up a turbine is a function of it's A/R value. Lower values spool the turbine up at lower flow levels, but present a flow impediment at higher levels. Higher values present little high flow restriction, but don't spool properly at low flow levels. An ideal solution would be to use a stepper motor controlled variable geometry turbine.

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Without any boost you'll need some way of monitoring turbine speeds so you can actually activate the waste gate when it starts turning too fast.
If the turbine were to direct-drive a switched reluctance generator, determining input shaft RPM should be trivial.

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Third, boost lag and back pressure - Ever ridden in a car that has a turbo put on it that's too big and has serious boost lag? That car will be beat off the line in a race every time and will have worse mileage in town guaranteed. The turbine is going to cause back pressure, serious back pressure.
See the VGT link above.

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Anything you do[, you] need to take less power to run [in order] to save energy.
That's only true if you have a 100% efficient system. Gasoline engines are horribly inefficient... This generator is making use of existing waste energy, improving the efficiency of the system rather than drawing useful energy from an existing source.
Take peltier module based power generation for example.
Peltier modules are solid state thermoelectric heat pumps - when current is applied, one side gets hot and the other gets cold. Similarly, if one side is heated and the other cooled, a current is generated.
Some have suggested attaching these to the exhaust manifold of the car, and cooling the opposite side with a heat sink. This would certainly generate power (though peltier modules are very inefficient, so not a whole lot), but the only affect on the engine would be a slight cooling of the exhaust manifold. How would cooling the exhaust affect the engine's normal power output?
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Old 01-06-2008, 09:36 AM   #26
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It doesn't have to be a 100% efficient system.

So, we have an engine that creates say 20hp on the freeway to maintain 70mph. That's stock, alternator connected with a belt and the alternator alone uses lets say 2hp of that to keep the efi system going and headlights on with radio and a/c load. This engine is at 16% thermal efficiency and uses 2 gallons per hour to accomplish this or 35mpg.

Now, we've removed that alternator and put it on a turbine in the exhaust system. Created a source of back pressure but relieved the strain on the engine from running a belt across one more pulley. The alternator still takes 2hp to run everything, that doesn't change. What does change is that the exhaust isn't as free anymore(there is nothing you can do about this). You will end up with more exhaust gases in the camber now and that will dilute the air fuel mixture in the chamber. This will cause less power to come from that air fuel charge that would have been there had the exhaust not been there. It's going to slow flame propagation and reduce engine efficiency even further. Like taking off a performance ignition part like this.

So, we still use 20hp, 2 of which runs the electric stuff and we are trying to scavenge exhaust gases to create the power because we know it's a loss. BUT we've just reduced engine thermal efficiency to 14% and it now takes 2.04 gallons to go 70 miles or 34.3mpg.

Thermal efficiency is REALLY easy to hurt on an ICE.

http://www.gassavers.org/showthread.php?t=5668
Look what his exhaust restriction test resulted in.
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Old 01-06-2008, 10:03 AM   #27
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I think you're misunderstanding how the exhaust turbine works. It extracts energy primarily from velocity and heat, not static pressure.
A stopped turbine provides very little resistance to flow. Just for the sake of messing around, I've fired a roughly 1/4" diameter stream of 100 psi air into the exhaust turbine of a turbocharger and got zero backpressure. In fact, the air surrounding the stream was pulled into the turbine inlet as if it were a simple pipe. I know those conditions aren't the same as a running engine, but I think you're grossly overestimating the flow restriction a turbine presents. That is, unless you're thinking of using a turbine the size of a golfball.
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Old 01-06-2008, 10:16 AM   #28
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Well if you want that thing to pull any sort of load at part throttle it will have to be small. Not much air moves out of a part throttled engine.

Your typical turbo isn't expected to make any power unless the engine is wide open and a lot more air flows then than an engine just cruising down the freeway.
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Old 01-06-2008, 10:21 AM   #29
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Nothing we say will convince you otherwise. Yes a few things I said aren't proven but DK and I come from other forums where adding power is the standard and we have some idea of what turbochargers, turbines, and exhaust systems do to an engine.

after the turbo, your right, exhaust design is irrelevant because you've already destroyed linear flow. I was suggesting parallel systems, not serial.

If you're not going to use the alternator you've just spend hundreds if not thousands to design, why are you even arguing it?

are you aware that your 100 psi air compresser blowing through the turbine wasn't impeded because of the volume? engines can intake 50x your compressers CFM easily...exhaust is a LOT more . Try doing the same thing with a .1" dia port and see how much backpressure you get. As for turbine size....have you ever seen a turbocharger? or maybe you're thinking of using one the size of a softball so it can take 10 minutes to spool up.

You've got a good idea going on but you need to hang out on some performance forums and see what things produce power and what things kill it fastest. non forced induction power comes from efficiency and v8 muscle cars without forced induction are actually capable of impressive numbers when you don't give into the heavy foot.
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Old 01-06-2008, 10:36 AM   #30
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Quote:
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Put an AC compressor Clutch with a toggle switch on your alternator.

When off its like removing the belt. With just the flick of a switch.
I was thinking about something along those lines as well, but then you add the electrical load of the electric clutch, the weight of it that is always spinning, and suddenly you have more spinning mass when it's turned off then you have in the alternator,and if the coils in rhe alternator are not energized, then it's just the spining mass, load of the bearings, load of the belt, and the poor ballance of the alternator.
as I see this you could improve the belt drive, improve the bearings and impprove the ballance.
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