Exhaust idea

[manchild]

I'm sort of lazy to make the drawing right now, so I'll explain it in few lines.

There is a rule saying that engines can't be turbocharged, right? Not a word that car can't be fitted with turbocharger if it remains naturally aspirated.

Speaking of turbocharger, blown turbine itself (without a compressor), generates certain amount of power.

The initial idea of mine, more like thinking out-loud question is - would the performance of the car increase IF drive-shafts would be used as the axles of two separate turbines attached on them?

Another option would be to have a bigger single turbine blown by both banks, aiding gearbox's shaft.

Perhaps a turbine could even attached to crankshaft of the engine.

With automated variable geometry of the turbine, it could be set to engage only when desired.

I know that it's a bit farfetched and daydreaming kind of idea, but at least technically, it could be done and remain in compliance with current regulations.

It would be interesting to hear is someone has idea how much HP a turbine could generate, and would obvious weight and aero losses be lower than overall gain.

[Jersey Tom]

So you're saying to use a turbine to draw shaft power directly rather than compressing air going into the engine?

TERS - Thermal Energy Recovery System. Seems like a smart thing if F1 wants to stick to its "green" (LOL!) racing image.

[ringo]

Intially i thought Mclaren were doing this with their exhuasts during testing.
my concept had the pipes going into the gearbox with the turbine mounted on the back of the crank though.


I'd say it's legal. Though the turbine is technically an extension of the engine, so it would be illegal by strict definition of the allowed engine, since the engine is to be a 2.4lt V8 otto cycle engine and nothing more.

[manchild]

That's it ringo. I think that the engine is considered only as far as the clutch, so having a turbine just after the clutch or at the end of gearbox would be as legal as having two separate turbines on drive shafts.

[riff_raff]

manchild,

That's a clever bit of thinking, but it seems to be a bit fuzzy with the rules:

"5.2.1 The use of any device, other than the 2.4 litre, four stroke engine described in 5.1 above and one KERS, to power the car, is not permitted."

riff_raff

[Michiba]

I thought the exhausts have to be symmetrical, hence Ringo's drawing would not be allowed.

[manchild]

manchild,

That's a clever bit of thinking, but it seems to be a bit fuzzy with the rules:

"5.2.1 The use of any device, other than the 2.4 litre, four stroke engine described in 5.1 above and one KERS, to power the car, is not permitted."

riff_raff

Thanks for the compliments. I agree that FIA might not allow it, but it is debatable. If we consider turbine as part of the exhaust system than what powering the car is the 2.4 litre, four stroke engine's exhaust.

Allowing it or not would be more political decision by FIA rather than anything else, and if their goal is lower consumption, more silent engines than this would fit in that policy.

[marekk]

As i've suggested it already on exhaust energy use 2011 thread, you can use 2 turbos designed to act as a source of high pressure /high mass flow air.
There is lot of thermal energy in exhaust gases, most of it being just blown away and wasted.
Once you have significant amount of this not to hot compressed air, you can build mclaren's octopus with any materiall and blow as many points as you want from it. Even blown rear wing is possible this way. Even front wing.
And it will be perfectly legal IMO.

[010010011010]

Strangely enough I was wondering about the legality of this exact system only a few weeks ago. I saw it in a book about unusual engines, and some aircraft engines used this around WW2 if I recall. Its been proven to work, but I agree that it would be a judgement call in the part of the FIA whether to allow it or not.

[Giblet]

It's sort of like the downstream half of a parallel turbo compounding setup if I understand correctly. Putting all the exhaust energy into the driveshafts, instead of just the scavenged energy that would be picked up after the primary turbo.

[Ciro Pabón]

Well, to answer the question, something that nobody ever does in this forum of deranged and vagarious souls (exception made of 747heavy but he is also Spaniard, olé, viva Alonso and King Juan Carlos!) I will try some numbers, you hippies.

I am making a lot of guesses and assumptions that I know are not correct, sure, but I have a few minutes. This caveat/lame excuse/temptation is for my many pedantic, yet dear friends: correct me if you dare!

Simple:

You have a 18.000 rpm, 2.4 liters engine. This means (not taking in account the delay in valve opening between TDC and actual opening of valve, gimme a break, will ya?) that at the intake you have, if you are at full throttle:

9.000 rev/min x 2.4 liters/60 seg/m = 360 liters/second

A liter of air weighs around 1.2 grams. So thin and yet so refreshing!

I'll assume that the track is at 300 Kelvin, that is, 27 degrees Celsius, which is a relatively hot day in the "land of pretty and beautiful women", where I stand shirtless right now, but it is also a similarly pretty and beautiful round number.

I also will assume that exhaust gas temperature (EGT) is around 1500 Fahrenheit from what I know of EGT vs air to fuel ratio.

I'd say EGT it goes from 1250 to 1800 Fahrenheit, but 1500 is a nice round number and it has a 5 in it, a number I like so much that I will take a rum because of it.

That is around 1100 degrees Kelvin (give or take).

I don't like to use calculators nor computers, only my trusty slide rule, as everybody in this forum does, so let's round it to 1200 Kelvin.

I will assume that the exhaust pressure is 4 bars. This is a huge assumption as I actually have no idea and the calculations are really complicated, but since when have engineers been deterred of assuming things they have no idea? Let's toast again to that.

I will also assume that after the turbine you have 1 bar, no major discussions here. I will also assume things are adiabatic (like they always are in books) and that isentropy should be around 85% (another 5!).

So:

The temperature at the exit of the turbine is given by Texhaust/Tintake = (1 bar/4 bars)^(1-1/Gamma)

Gamma should be around 1.4. So, if the intake is at the 1200 Kelvin I assumed, then:

T exhaust = 1200 * (1/4) ^ (1-1/1.4) = 1200 * (1/4) ^ (0.3)

This is around 795 Kelvin (it must be right, as it has a 5 in it).

So, the ideal temperature change is around 400 Kelvin (1200-795).

As the isentropy I assumed is 85%, then the real temperature change is about 400 * 0.85 = 350 degrees Celsius.

Let's toast to that, again. Hip. Actually, I will take another rum every time I get a 5.

Now, as Phi plus P is equal to change in enthalpy, and I assumed it is an adiabatic process, then Phi is zero.

So, P = flow of air * Cp * Change in temperature.

The mass of air is 360 liters per 1.2 grams/liter, this is 432 grams per second. So, let's round it to 500 grams per second. Another rum for that!

Now, Cp is about 1000 Joules per degree Kelvin per kilogram, isn't it?

So, P = 0.4 kg/s * 1000 Joules/ degree-kg * 350 degrees = 140.000 Joules/s

This is around 140.000/746 = 185 HP, give or take.

A fourth of the power goes out of the engine through the exhaust? No wonder the Poles are melting.

Where did I make a mistake?

My god, this was too much rum and I still have to make lunch. Your fault, Manchild. This means I'm going to raise my Spanish flag right now and hum (it has no lyrics!) the Spanish anthem, in vengeance. Viva el rey! Hip.

[marekk]

As the isentropy I assumed is 85%, then the real temperature change is about 400 * 0.85 = 350 degrees Celsius.

So, P = 0.4 kg/seg * 1000 Joules/ degree * 350 degrees = 140.000 Joules

This is around 140.000/746 = 185 HP, give or take.

A fourth of the power goes out of the engine through the exhaust?

Where did I make a mistake?

Exhaust is still at 850K after turbine (note digit 5, so must be ...).
550 degree over ambient and 295 hp for further use (ok, 294,9 hp, but this number has no 5).

[Ciro Pabón]

marekk, dear friend, if the turbine doesn't change the temperature of the gas, then the work is zero. In the enthalpy equation goes delta T, not T.

Don't blame me, blame Carnot. I admit the guy wasn't Spaniard, so... I am not that sure, but mechanical engineers believe him, apparently. Let's give him the benefit of doubt: even mechanical engineers are sometimes right.

Look, adiabatic expansion (the way of the turbine!):



See? It says adab.. adiabatacal... adiab... darn rum!

Besides, 294.9 has a 29 in it and that's a prime number. Very suspicious, it raises a flag for me, although I must say that I admire your mastery in rounding it to 295. Flawless rounding!

[manchild]

Thanks for the math Ciro. BTW, If I was right now (ok, ok... recently) shirtless, with a beautiful woman, I'd be laid-back as well, sipping rum or some other drink. Writing formulas and humming anthem is the only thing I wouldn't be doing.

[marekk]

marekk, dear friend, if the turbine doesn't change the temperature of the gas, then the work is zero. In the enthalpy equation goes delta T, not T.

Yeah. 1200K-350K=850K. Lots of 5's.