Different twist on forced induction

[rjwoods77]

http://www.scania.com/products/newtruckrange/technology...how_does_it_work.asp (http://www.scania.com/products/newtruckrange/technology/turbocompound/how_does_it_work.asp)

[rjwoods77]

http://www.scania.com/products/newtruckrange/technology...how_does_it_work.asp (http://www.scania.com/products/newtruckrange/technology/turbocompound/how_does_it_work.asp)

[Andrew Nabb]

I have heard of an old Renault F1 turbo car having a similar setup. They had a gear drive coming off of the turbo whcih was used to transmit power to the engine. There was an extra injector in the turbo which made the car mroe or less a pistion engine turbine powered hybrid.

[Erich Ohlde]

Wonder what the judges would say if a team came with that to competition. Pretty cool idea though, i wonder if it would have any dampening effects on engine torque pulses (cryptic I know, but I'm talking about the sinousidal wave that can be found from measuring torque at high sampling frequencies).
Rob do you actually do any design work or just oogle at what someone else came up with? http://fsae.com/groupee_common/emoticons/icon_wink.gif

[Chris Davin]

I'm fairly certain that turbo-compounding would be considered illegal under the current rules. The engine is no longer purely a piston engine. Give the piston engine component a compression ratio of one and now you have a turbo-shaft.

[KU_Racing]

Seems like a waste of energy to me. I was talkin to Newton the other day. He told me that there is no free energy. Seems to me any benefits you gain by driving the crank with a system like that is burned in the huge pumping losses to create that extra drive. Add up the frictional, inertial (?), and gear drive efficiency losses of the system, and It seems like you would have more heat and less power than you started with.

[Matt Gignac]

I think the principle that makes this make more power is that you are extracting more energy from the hot exhaust gasses, which would otherwise just be expelled to the atmosphere. They claim a 100degree drop across the second turbine. Figure out the mass air flow through the system, multiply by the entropy difference btwn 500 and 600, and you have the extra power you'd put into your engine.

You'd for sure lose some of that in pumping power, spinning the various hydraulics couplers they're talking about and heating all these components, but odds are this amounts to less than what you're gaining.

More importantly, I think it would be quite difficult to have a driveable powertrain with such a setup. I imagine it would be difficult to design a coupling that would map each power turbine rpm to the equivalent engine rpm, as I do not think that there can be a linear or even close to linear relationship between the two, thus such a system could probably only be used for a relatively small rpm range, tuned for whatever driving you want to be doing. So in F1, probably very high in the rpm range to get massive top end power at the expense of low rpm response, and in the Scania engine down low to have better torque for hauling more weight. Other than for acceleration, I think such a technology would not be good for FSAE.

Matt Gignac
McGill Racing Team

[drivetrainUW-Platt]

Isn't this just sequential turbos, but the second one is a reverse supercharger....thats a loooot of extra crap, more tubing, another turbo, all those gears...yeks!

[Chris Davin]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by KURacing:
Seems like a waste of energy to me. I was talkin to Newton the other day. He told me that there is no free energy. Seems to me any benefits you gain by driving the crank with a system like that is burned in the huge pumping losses to create that extra drive. Add up the frictional, inertial (?), and gear drive efficiency losses of the system, and It seems like you would have more heat and less power than you started with. </div></BLOCKQUOTE>

Turbo-compounding for improved power and efficiency does not violate the first law. The advantage comes from the fact that you're extracting power from the expansion of your exhaust gas all the way down to atmospheric pressure. In contrast, the Otto cycle loses power and efficiency in the blow-down (transition from 4 to 1 on a P-V diagram).

One of your design parameters for a turbo-compound engine is the fraction of turbine power that goes to the crankshaft as opposed to the compressor. The limiting case of a ratio of 0 is the well-known turbocharged engine. A ratio of 1 would be an over-expanded Atkinson cycle with no forced induction (boost). As you move between 0 and 1, you basically trade efficiency for power.

Of course, there are obvious disadvantages in weight, friction, etc. I think turbo-compounding has been used successfully in some World War 2 era fighter aircraft, although I might be mistaken. Turbo-compounding also has some interesting, although perhaps somewhat impractical, benefits to a modern gas turbine. Modern turbine engines are mostly limited by their turbine inlet temperature - turbine blade material technology will not allow a near-stoichiometric air/fuel ratio at desirable compressor pressure ratios, so the combustors typically run very lean. If intake air were first passed through a piston engine (or equivalent) and burned stoichiometrically, and then passed through a turbine, equivalent thrust or power could be attained with a physically smaller engine. Again, probably impractical, but a good thought experiment in thermodynamics and engine design.

[Nick McNaughton]

I read about this somewhere, years ago. I think it was about a WWII-era piston engined plane, and one of the factors that made it worthwhile was the fact that at altitude, atmospheric pressure is lower and ambient temps cooler so the geared turbine stage is more efficient... and offered a fuel economy advantage under high altitude cruising conditions. Don't quote me on it...

[PatClarke]

Nick, the Wright Cyclone R 3350 turbo compound engines were a last ditch effort to stave off the jet turbine engines in aircraft. The most powerful version developed about 2750KW
The Lockheed Constellation flown by the Historical Aircraft Restoration Society (based at Albion Park near Wollongong)is powered by 4 of these monsters.
A description and picture can be seen here
http://en.wikipedia.org/wiki/Wright_R-3350

Another picture is here: http://www.enginehistory.org/Gallery/JimBuckel/Wright%2...o%20compound%201.JPG (http://www.enginehistory.org/Gallery/JimBuckel/Wright%20R-3350-42%20turbo%20compound%201.JPG)

I love these old prop driven aircraft :-)
Pat

[cieutag]

I know its been discussed and explained, but don't you think someone did some calculations before they designed/built any of these. Its obviously got some advantage or else they wouldn't have designed/built any of these. Just cause you don't understand the finer details doesn't mean it doesn't work.

[John Bucknell]

I have these papers somewhere (can't look at them now for detail), but a review of these SAE papers will show you how to extract ALL of the heat energy of diesel or gasoline fuels. The Wright and Napier papers below are AWESOME if you like old warbird engines.

830124 : A Review of Engine Advanced Cycle and Rankine Bottoming Cycle and Their Loss Evaluations

550239 : Napier Nomad aircraft diesel engine

540239 : Development of the turbo compound engine

[PatClarke]

Thanks John =]
Pat

[murpia]

Just to throw in an idea, what about turbine-powered ancillaries?

A turbine-oilpump might be a bit risky but a turbine-alternator or turbine-waterpump could work. I'd be interested in the calculations either way...

Ian

[UQ Turbo]

erm...restrictor limits max power anyway. You could have as many turbo-fed supercharger hybrids as you'd like, there still only going to be 0.074 kg/s of air getting into your engine! :P

The concept is kind of cool though! I know in Hugh Macinnes's turbo book, theres a 3-stage turbo diesel that runs 250 psi boost! I'd be interested if anyone's done better than that now (the book is quite old).

[BeaverGuy]

The idea behind using one of these on an FSAE car, or any engine really, isn't that you can get more air. But you can use the air you get more efficiently. If FSAE engines were 100% efficient we could put out around 400 HP but they aren't. This is just a way to increase efficiency.

[UQ Turbo]

my mistake, noted!

[CornellGixxer]

The BMW Turbosteamer system works on a similiar concept, by extracting otherwise wasted exhaust gas energy to turn water into steam. The steam is then routed to an expansion unit connected to the crank to help power the car. Apparently they are able to extract 80% of the exhaust gas thermal energy and use it to raise fuel economy by 10-15%.

This second turbine idea is just another way of extracting that energy from the exhaust. Im not sure which one is more efficient on the whole (weight, power, complexity).