Renault Power Unit Hardware & Software

[bergie88]

I think there will always be a little bit extra exhaust backpressure, but exhaust energy can be considered as lost in a na engine, so every bit recovered from it is profit. I'm sure the balance between generating power by the MGU-H and losing ICE power due to increased backpressure will be far in the advantage of generating with the MGU-H.

[godlameroso]

I think that with the proper design back pressure under MGU-H loading becomes essentially a non-factor, especially in consideration of what you gain.

[gruntguru]

recovery powers above this blowdown power will only be available by raising exhaust pressure generally such powers can loosely be seen as power moved from the crankshaft source to an electrical source

Although raising EBP has a penalty in crankshaft work lost to exhaust stroke pumping, the increase in energy available for recovery by the exhaust turbine is far greater. You are familiar with the Wright document which discusses pressure turbines as an alternative to blowdown turbines on their turbocompound engine.

[trinidefender]

Blowdown energy is a result of the pressure pulses created in piston and then transferred in an exhaust system to the turbocharger.

You cannot think of a turbocharger turbine in the same way as a constant pressure turbine used in something like a gas turbine or turbofan used in aviation. There the combustion process is constant and therefore no significant pressure changes and pressure pulses except through changes of airflow or fuel flow.

In an internal combustion engine each cylinder will have a pressure pulse coming out of it when the exhaust valve is opened. This pressure pulse then travels down the exhaust manifold and into the turbocharger helping to spin it (assuming that the pressure pulse doesn't interact negatively with other pressure waves (probably a better word) from other cylinders). That is why exhaust design is seen to be so critical.

If you were to somehow measure the pressure at the entry to the turbocharger turbine you will see that it increases and decreases depending on the rpm of the ICE. You cannot think of it as a constant.

Therefore when you want to think of the energy available to a turbocharger turbine you have to think in terms of how much energy can it extract from these pressure waves and how much from the exhaust massflow flowing through the turbine. With a correctly designed exhaust manifold you can design a turbocharger that very efficiently transfers this blowdown energy (pressure waves) into rotational energy with very little (on the negligible end of the scale) to no increase in back pressure as a result of constricting the actual massflow of the exhaust.

This brings in my point about compression ratios. The more energy that an ICE can directly extract to the crankshaft via the pistons means there is less blowdown energy when the exhaust valve opens.

[gruntguru]

When reduced CR is used to increase blowdown energy, the extra power recovered by the turbine is less than the crankshaft work lost by the reduction so this is a poor tradeoff.

When placed in the exhaust of a reciprocating ICE, the turbine normally recovers a combination of blowdown and "constant pressure" heat energy. Measurement of pressure at the turbine inlet would reveal a significant positive pressure with significant fluctuation above and below the average - due to blowdown and other cyclic events. Exceptions include the right TC which utilised blowdown energy almost exclusively.

OTOH many turbocharged engines utilise very little blowdown energy - certainly those where more than three cylinders feed each turbocharger scroll. In this case, measurement of the pressure at the turbine inlet would reveal a relatively constant pressure at a much higher level than any individual pulse which may survive.

The exhaust energy recovery levels present in current F1 engines (especially in "self-sustaining" mode with no draw on the ES) are not possible using blowdown energy alone. If you take the hypothetical example of an engine running at 3 bar MAP and 2 bar EABP there is unquestionably a large "constant pressure" (2 Bar) component which will produce significant turbine work in addition to the superimposed, fluctuating-pressure (blowdown) component. In fact this example could operate without blowdown energy - turbine power = approx. 90 kW, compressor work = approx. 70 kW, surplus to MGUH = 20 kW.

[Tommy Cookers]

recovery powers above this blowdown power will only be available by raising exhaust pressure generally such powers can loosely be seen as power moved from the crankshaft source to an electrical source

Although raising EBP has a penalty in crankshaft work lost to exhaust stroke pumping, the increase in energy available for recovery by the exhaust turbine is far greater .....

NACA work seemed to show power moving on a roughly 1-for-1 basis from crankshaft to recovery turbine with raising of EBP

anyway I have always advocated maximising both blowdown power and constant pressure power
we all seem to agree on this

turbine and compressor efficiencies have a huge effect on recoverable power
won't efficiencies obtainable in typical race use be degraded by the ever-changing rpm and boost ?
18% rpm drop on shifting and fuel rate constant/boost varied throughout 10500-12400 rpm
VGT etc being banned the race situation is rather different from a steady state testbed situation
eg afaik even at gg's favoured 3.3 bar the constant pressure recovery falls to 23 kW if/when the actual efficiencies are 72%

[Abarth]

If MAP = BP the turbo machinery is a simple Brayton cycle - the combustor being replaced by the piston engine as its heat source.

In the F1 case, the heat input to this Brayton cycle (Gas Turbine) is relatively fixed wrt PR. The surplus work (Wt - Wc) however, is dependent on PR. The theory behind this is well established.

There are useful calculators here https://www.engineering-4e.com/calc4.htm for compressor and turbine power (you can use the isentropic compression calculator for expansion as well or use the expansion calculator further down the page). The calculators are for 100% isentropic efficiency so the actual turbine work will be about 0.8 times the output from the calculator and the compressor work will be equal to the calculator output divided by 0.8.

Have fun playing. Don't forget to adjust the massflow and turbine inlet temp when you change the PR (boost).

SIMPLE EXAMPLE.
Compressor Massflow = 0.55 kg/s
Turbine Massflow = 0.578 (AFR = 19.6:1)
PR = 3.3
T comp inlet = 298 K
T turbine inlet = 1000 K

Calculator gives Wcomp = 66.8 kW and Wturb = 161.9 kW (Need to use 57.8 kg/s to get 3 significant figures into calculator)
At 80% eff for comp and turb Pcomp = 66.8 x 1/0.8 = 83.5 kW and Pturb = 161.9 x 0.8 = 129.5 kW
Pnet = Pturb - Pcomp = 129.5 - 83.5 = 46 kW surplus.

Now try it at PR = 2.5 and compressor massflow 0.5 x 2.5/3.3 = 0.378 (assuming intercooling to ambient)
Turbine massflow is 0.406 and AFR = 14.5:1
T turbine inlet will be higher - say 1220 K

Calculator gives Wcomp = 33.8 kW and Wturb = 114.5 kW
At 80% eff for comp and turb Pcomp = 33.8 x 1/0.8 = 42.3 kW and Pturb = 114.5 x 0.8 = 91.6 kW
Pnet = Pturb - Pcomp = 91.6 - 42.3 = 45.4 kW surplus.

So interestingly, at 80% isentropic efficiency for the turbine and compressor, changing the PR has little effect on surplus energy to the MGUH. At lower efficiencies lower PR will be favoured and at higher efficiencies, higher PR will produce more surplus energy.

Gruntguru did some constant pressure calculations in another thread, see above quoted.
Between roughly 43 to 83 kW are needed just to drive the turbine, depending on PR 2.5 to 3.3.
If the kinetic energy from the pulses at turbine shaft is say 8% of the ICE power, this energy would suffice to compress the charge air at PR is 2.5, at 3.3 not.

About pulse to pressure conversion, I wrote last year:

I looked a bit around for pulse-to-pressure converters, which are essentially converting the pulse velocity of the single cylinder outputs into pressure by joining them into a diffuser.

According to a paper (from Basshuysen IIRC) in best case a pressure increase of 1.4x cam be achieved in the diffuser without negative effects on backpressure to the single cylinders.

Here are two quickly found articles about this:

http://road-transport-technology.org/Pr ... 20Yang.pdf


https://books.google.ch/books?id=AzTFSH ... er&f=false

[ringo]

sorry ringo, I can't understand which bits (if any) in my post you accept and which you don't

in my post earlier 1147 am yesterday I refer to earlier posts of links to the source material
the NACA source material shows migration of power from crankshaft to recovery turbine as turbine load (& exhaust pressure) is raised
I thought people were anyway taking that position as common sense

Back Pressure must exist, if there is any form of load. Be that mechanical or electrical.
I think there is some confusion with the turbo compound being geared to the crank, which the momentum of the crank may have an effect on the second turbine it's connected to, which then may have some effect on the main turbine.

However there is no such thing on the F1 engine. It's just a motor generator on a gas turbine, just like any power station. Back pressure is there for sure.
Could you point me directly to the article that suggest there is no back pressure?

[gruntguru]

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

[Tommy Cookers]

......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'

[Blackout]

A bit OT: what is that part that looks like a compressor? and what is that pipes coming from it? (the shorter big pipe)

[Tommy Cookers]

a compressor (first stage) supercharging the engine via that pipe (and the other standard 'engine(driven)-stage' supercharger)
not a turbocharger because it's not driven directly by the turbine but by a variable speed coupling
the turbine being directly coupled to the crankshaft for recovery (turbo-compounding)
3090 hp with WI - but never in production (Allison 1710 E22 aka 127)

try this also
http://www.missbardahl.com/engine/tech/ ... fficen.pdf

[gruntguru]

Interesting plumbing. Current layouts invariably seek to minimise length of the exhaust plumbing to the turbine (to preserve heat energy). I guess because the early turbines were limited to much lower turbine inlet temperatures.

Also because aircraft applications are less sensitive to transients. Long pipework takes a few seconds to heat up when transitioning from light load to full power with dreadful turbo lag being the result.

[Blackout]

a compressor (first stage) supercharging the engine via that pipe (and the other standard 'engine(driven)-stage' supercharger)
not a turbocharger because it's not driven directly by the turbine but by a variable speed coupling
the turbine being directly coupled to the crankshaft for recovery (turbo-compounding)
3090 hp with WI - but never in production (Allison 1710 E22 aka 127)

try this also
http://www.missbardahl.com/engine/tech/ ... fficen.pdf

Great. Many thanks.

[Blackout]

Interesting plumbing. Current layouts invariably seek to minimise length of the exhaust plumbing to the turbine (to preserve heat energy). I guess because the early turbines were limited to much lower turbine inlet temperatures.
Also because aircraft applications are less sensitive to transients. Long pipework takes a few seconds to heat up when transitioning from light load to full power with dreadful turbo lag being the result.

The exhaust plumbing is not very long on the Renault, (still longer than the Merc and Honda) but charge air plumbing is ridiculously long