Renault Power Unit Hardware & Software

[wuzak]

Tommy is right in describing the layout of the V-1710-E27 (-127).

The turbine used for this application was a modified version of the turbine from a C-series turbocharger. The C series was the larger of the two main turbo units used by the US in WW2, and was coupled to the R-2800 in the P-47 (main application). The smaller B-series turbos were used with the V-1710.

Despite having a higher rated temperature than the standard item, the exhaust temperature was too hot for the turbine. Further developments would have involved Allison developing an air cooled urbine, but they gave up on teh project to concentrate on gas turbines.

The difference between the turbo-compound and the turbo engine was that the latter was able to maintain constant power rating up to the turbo's critical altitude - roughly 25-30,000ft. The former's power fell away as more power was required to drive the 2 stage compressors as altitude increased.

The core engine, the 2 stage V-1710, had a maximum war emergency power of ~2000-2200hp (depending on version), while the turbo-compound's maximum was 2900-3000hp. So, as much as 50% more power was recovered from the turbine.

For perspective, the turbine made more power than the early V-1710s had done, just 7 or 8 years earlier.

[Tommy Cookers]

but power recovery increases with altitude, as the decrease in ambient pressure increases the pressure difference across the turbine
so for our purposes we should look at recovery performance at sea level

[lio007]

Remi Taffin on the big PU upgrade using all of the remaining 12 tokens:
http://en.f1i.com/news/23577-renault-co ... grade.html

Regardless of whether we have it in Russia or later...

So unfortunately it seems that Russia is not set in stone.

[bergie88]

but power recovery increases with altitude, as the decrease in ambient pressure increases the pressure difference across the turbine
so for our purposes we should look at recovery performance at sea level

So 50% is a too high number of revovery, could it be 25% maybe? Then we are already talking about ~650*0.25 = 162.5 bhp, which is the full power of the MGU-K (!).

[Tommy Cookers]

with increasing exhaust recovery beyond a certain level there is some loss of crankshaft power
iirc 1940s NACA research showed roughly 1-for-1 loss (at lowish boost, and inconveniently for us, a 10000' altitude)
so imo you could get 25% but that % won't be all 'free' and won't be a fair measure of the benefits in PU efficiency
ie 'free' power won't be enough to max the mu-k action whenever desired

but ....
raising the exhaust 'back' pressure should reduce the pressure losses in blowdown, improving efficiency ie crank and recovered power
(by increasing the density ie the inertial load resisting expansion and so reducing peak flow velocity and choking)
further, the NACA work showed this improved efficiency eg with a -dP ie an EP greater than MAP (when EVC was eg only 20 deg atdc)
afaik gg attributes this entirely to improved fuel trapping in-cylinder, ie of no benefit here with DI
but would this engine with such early EVC show (the most) improved trapping ?
our everyday driving is mostly at high -dP, of course,
and race exhaust systems help by briefly lowering EP around EVC anyway, so there's no exhaust flow back into the cylinders

[PlatinumZealot]

http://www.enginehistory.org/Wright/TC%20Facts.pdf . . . Page 12 and 13

That does not apply to car turbines though. Thats a pure impulse turbine with a very small recovery that works from pulses... As you say these pulse pressures are so high dorectly after the exhaust port that the impulse from the turbine buckets will never preduce a higher pressure.

What is happening is that the buckets are simply lime moving vanes.... There is negligible ressure change across them just energy transfer velocity change....

No one makes this anymore for gas turbines. There is more emergy to be had by designing your turbine to be a mixture of impulse and reaction. Just by looking at the external shape of the a typical automotive turbine housing.. It is clearly both impulse and reaction. There will be back pressure.

If there was not any backpressure that honda turbo would be very inefficient...

[gruntguru]

Nobody claimed there is no backpressure. With careful design, a substantial amount of additional turbine energy (blowdown pulses) can be recovered with no increase in backpressure.

[ringo]

......Back Pressure must exist, if there is any form of load. Be that mechanical or electrical.
.....the F1 engine. It's just a motor generator on a gas turbine, just like any power station. Back pressure is there for sure.

it's not a generator on a gas turbine because by gas turbine you/we mean steady flow and so a constant (modest) pressure aka pressure working of the turbine

blowdown working imo .....

the exhaust flow from the cylinder is (massively) choked flow
(unavoidable in a piston engine or similar)
so conditions just upstream of the turbine have no effect on the conditions in the cylinder
ie the piston does not 'see' the generator load, so the generated power is free
(as long as the load exists only during expansion ie is insufficient to raise the exhaust pressure in the scavenge stroke)

I linked in the TERS thread 21 July to thermodynamic reasons why blowdown working allows more recovery than pressure working
the essay writer's source seems to be the 1982 Watson book 'Turbocharging the IC Engine'

I think this applies only to the reference engine, the wright turbo. It may be somewhat loose to apply it to an automotive engine. The conditions and whatever takes place in that particular engine are very different. I wouldn't readily apply it's observations to these F1 engines. Can you link me to the articles?

[ringo]

Nobody claimed there is no backpressure. With careful design, a substantial amount of additional turbine energy (blowdown pulses) can be recovered with no increase in backpressure.

You don't have any support for this outside of the wright TC do you?
I respectfully disagree.

[trinidefender]

http://www.enginehistory.org/Wright/TC%20Facts.pdf . . . Page 12 and 13

That does not apply to car turbines though. Thats a pure impulse turbine with a very small recovery that works from pulses... As you say these pulse pressures are so high dorectly after the exhaust port that the impulse from the turbine buckets will never preduce a higher pressure.

What is happening is that the buckets are simply lime moving vanes.... There is negligible ressure change across them just energy transfer velocity change....

No one makes this anymore for gas turbines. There is more emergy to be had by designing your turbine to be a mixture of impulse and reaction. Just by looking at the external shape of the a typical automotive turbine housing.. It is clearly both impulse and reaction. There will be back pressure.

If there was not any backpressure that honda turbo would be very inefficient...

As GG said. Nobody claimed no back pressure. All that was claimed was that blowdown energy can be recovered with little to no (increase in) back pressure. We were just discussing how much energy can be obtained through the use of an impulse stage of a turbine.

[trinidefender]

Nobody claimed there is no backpressure. With careful design, a substantial amount of additional turbine energy (blowdown pulses) can be recovered with no increase in backpressure.

You don't have any support for this outside of the wright TC do you?
I respectfully disagree.

Read.
http://encyclopedia2.thefreedictionary. ... wn+turbine

It appears you have the concept of the turbine working on the pressure of the gas. Speaking about a pure blowdown turbine here, the blowdown turbine uses the kinetic energy from the velocity of the gas. Not the pressure that the gas is under.

[gruntguru]

Nobody claimed there is no backpressure. With careful design, a substantial amount of additional turbine energy (blowdown pulses) can be recovered with no increase in backpressure.

You don't have any support for this outside of the wright TC do you? I respectfully disagree.

In which case you didn't understand the explanation given in the link. The graph on p12 is most instructive. You see a large pulse of exhaust pressure after EVO (66* BBDC) but this pressure spike (about 8 psi) has no effect on flow through the valve or pressure in the cylinder because flow across the exhaust valve is choked (supersonic) and changes in downstream pressure make no difference to flow rate. Choked flow exists whenever the downstream pressure is less than half (approx) of the upstream pressure. (both abs)

It is true that there is backpressure (about 2 psig average) showing in the graph but this does not affect the pumping work of the piston due to the timing of the pressure pulses as mentioned above.

There are many references around (https://www.google.com.au/search?source ... own+energy) but the Wright document has the simplest explanation I have seen.

http://naca.central.cranfield.ac.uk/rep ... rt-822.pdf

[PlatinumZealot]

OK.

Gruntguru and Trini are saying that "blowdown" pressure pulses can be utilised to add energy to the turbo without increasing back pressure substantially... on an average of pressure over time.. maybe..(exhaust valves might be closed when the pulse reflects too).. but these blowdown pressure pulse just aint gonna happen in a modern car engine. I will gladly accept humbling up if there was some paper detailing this effect being created utilized in present day car engines. (it is certainly possible to create, but I can't see the benefit).

This is the first time I am hearing the term "blowdown" when it is not related to a steam boiler. You learn something new everyday I guess.. I can see how it translates and I get what the aviation paper is describing. I think this will never apply to a current formula 1 engine though.

Even in a boiler, you get that huge blowdown pulse because the extreme pressure difference across the blowdown valve. For example you will have 120 psi for your typical steam boiler (and even more for water tube boilers!) blowing down to atmosphere in a very short distance. The result is sudden pulse of flash steam blowing out - It sounds like an billowing explosion.

In your plane engine a similar thing is happening. The K-factor for the exhaust valve is very small (valve is small compared to the chamber size too).. there is a poor transition after the valve and you have a huge pressure difference between the combustion chamber and the atmosphere. It is made even worse by the fact that you have bucket blades (low pressure difference across them). So you have "blow down" effect happening after the exhaust valve. (high pressure loss at ex valve then low pressure loss at turbo) This is very contrasting to modern automobiles whose engines have large exhaust valve to chamber size and have very smooth low restriction ports AND then significant pressure drop across these modern turbines. (low pressure loss at valve then high pressure loss at turbo). Blowdown effect will never happen in these f1 engines unless you did something like remove the exhaust pipes or had a gigantic extra retarded explosion.. the exhaust valves and ports are just too good flowing for that effect. Not to mention the turbo is there.

[PlatinumZealot]

Here is a modern "blow down" paper.

http://kth.diva-portal.org/smash/get/di ... TEXT01.pdf

I will read it another time. It is very detailed. Guys read this.

[gruntguru]

OK.
Gruntguru and Trini are saying that "blowdown" pressure pulses can be utilised to add energy to the turbo without increasing back pressure substantially... on an average of pressure over time.. maybe..(exhaust valves might be closed when the pulse reflects too).. but these blowdown pressure pulse just aint gonna happen in a modern car engine.

In a reciprocating ICE, "blowdown" is what happens when the exhaust valve opens near the end of the power stroke. It happens at WOT in every Diesel and SI engine ever made. It happens because the pressure in the cylinder is still much higher than the pressure in the exhaust. Blowdown is what you hear from an exhaust with no muffler fitted. Blowdown generates a brief, high pressure pulse in the exhaust port and travels at the speed of sound (ie faster than the gas itself) down the exhaust runner. Blowdown energy is "free" because the piston is almost stationary during the process and In most engines on earth, the blowdown energy is wasted. Attempts to capture this energy include engine designs with increased internal expansion (Atkinson, Miller) and engines with external expansion devices - usually a turbine.

If this high-pressure wave can be preserved until it reaches a turbine, it can impart useful energy to the turbine without increasing the pressure in the pipe throughout the remainder of the 4 stroke cycle.

If instead, it feeds into a plenum or larger diameter pipe, it will expand, increasing the average pressure in the exhaust. This means that all cylinders feeding into that common exhaust will have to push against that higher pressure during their exhaust stroke and reducing the MEP. This is the reason that no more than three cylinders (with even firing spacing) can share a turbine inlet. More than three would mean that the arrival of a blowdown pulse at the shared duct must coincide with some point in the exhaust stroke of another cylinder.

The paper you have linked is discussing two things.
1. Capturing blowdown energy as described above.
2. Providing a "shuttle" valve to allow each cylinder to exhaust to atmosphere after the blowdown energy has been captured and routed to the turbine. This would give the best of both worlds - capturing blowdown energy yet allowing the exhaust stroke to be performed with near atmospheric back pressure.