TERS : Thermal Energy Recovery System

[Moose]

If you stick a turbine in the exhaust why wouldn't you connect it to a compressor?

Well, the question is, why would you - can you extract more power by connecting it to a compressor, by connecting it to a generator, or by connecting it to both? It's entirely possible (though I think unlikely), that connecting it straight to a generator, and powering the wheels with it is more efficient than connecting it to a compressor.

[pgfpro]

If you stick a turbine in the exhaust why wouldn't you connect it to a compressor?

Well, the question is, why would you - can you extract more power by connecting it to a compressor, by connecting it to a generator, or by connecting it to both? It's entirely possible (though I think unlikely), that connecting it straight to a generator, and powering the wheels with it is more efficient than connecting it to a compressor.

IMO I think that you will have to have the turbine connected to a compressor to keep good engine delta pressure (dp).

From experimenting on my staged turbo compound Talon, I have notice that engine delta pressure plays a big role in controlling knock and making power.
On my high pressure small turbo in this pic before the waste gate opens (around 14 psi intake pressure) and by passes most of the exhaust to my mid- mount large low pressure turbo, second pics, I see a good amount of knock and power loss.
Before the waste gate opens I see around a -3psi to -4psi engine delta pressure. When the gate opens and the low pressure turbo comes on line at 14 psi inlet or 42 psi intake my engine delta pressure drops to 1psi to 2psi engine delta pressure with no knock and great flow through the engine.
On my system I can change both small and large turbo's waste gates opening points, and the way I tune for this is by data-logging exhaust back pressure verse intake pressure or optimum "engine delta pressure".




Full write up link.
http://ecomodder.com/forum/showthread.p ... 28776.html

[PlatinumZealot]

@ wuzak. The proposal is that turbo is not continuous duty. It only serves to charge the EStore. And it would be much smaller than a turbocharger.

Sticking the compressor could be an option, but this is like having a car running NA for part of the lap then Turbo for other parts, sorta confusing to fans in a way.

[gruntguru]

I guarantee the power (thermal efficiency) of a compounded NA will be way less than the current engines. Something lie the Wright Turbocompound would be a good comparison (Turbine added to existing engine design - albeit supercharged)

[Tommy Cookers]

If you stick a turbine in the exhaust why wouldn't you connect it to a compressor?

Well, the question is, why would you - can you extract more power by connecting it to a compressor, by connecting it to a generator, or by connecting it to both? It's entirely possible (though I think unlikely), that connecting it straight to a generator, and powering the wheels with it is more efficient than connecting it to a compressor.

you could extract more electrical energy connecting the turbine to generator only (ie on an NA engine designed to F1 fuel limits)
but while the rules allow unlimited real-time use of that electrical energy, they limit its power to the 120 kW of the MU-K function

this because the rules are written to support the compounded turbocharged type of engine not the compounded NA type
fair enough for the road car spending 99% of its time in part power operation
the turbo engine being smaller, it tends to have lower losses at partial powers

16000 compounded aircraft engines optimised for running supercharged 15% over atmospheric (mechanical supercharging)
used at sea level 0.36 lb/hp-hr in the later versions (equivalent to 0.35lb on good car fuel, or 0.33 lb on MBs Petronas stuff)
at this boost the supercharging power was only about 2% of the engine power
and the free recovered power from the turbines was 6%, without raising the exhaust pressure or costing crankshaft power
ie all done by blowdown

over a limited rpm band a race NA engine will develop at least 15% over atmospheric pressure from its tuned length induction system

the first compounding research the NACA did was on NA engines, iirc giving via the compound train 8-9% free recovered power

research (lightly supercharged) showed best efficiency from real back pressure (eg 30% of total power via the compound train)
often in research the exhaust pressure was 0.25 bar more than the induction pressure
0.25 bar bp was specifically stated to be problem-free (typically the engines having anyway small valve overlap eg 40 deg)
there is a relationship between exhaust valve closure timing and useable BP, this would still apply in an NA compounded engine
though bp would reduce massflow with NA, this is not a killer problem unless rules prevent a suitable displacement
best efficiency would similarly be with high bp and a high % of recovered power (ie far more than the permitted 120 kW)

btw
we have little idea of the exhaust pressure of the current engines
the required compressor power becomes very high if seriously lean mixture (extra air) is used
ie an apparently high boost can imply quite a low recovery

iirc gg's view is that the turbine/compressor will always give a net work output from exhaust heat for any/all extra air use
I don't know if he has produced figures for different levels of leanness
fwiw - remember early gas turbine 'engines' gave no output
(their compressors and turbines were not vastly worse than F1's and their turbines had a higher heatsource energy state)
the first successful gt (Brown Boverei) was nominally a blowing system (pump) with partial recovery from in-process combustion
but the recovery was more than partial, so BB had an engine and the world beat a path to their door

EDIT
@ pgfpro
regarding your interesting account of experience of detonation with rising exhaust pressure .....
F1 is using super DI with 400-500 bar pressure and injection timing(s) only microseconds ahead of need ?
and fuel of unlimited octane number
presumably you were momentarily getting under-scavenge
NACA seemed to find this at their high bp in Allison (76 deg overlap) engines but not with P&W (40 deg overlap) engines


@ self
yes (NACA) research on backpressure running (all at less than full boost) was maybe helped by a CR margin available
the CR being set for full boost operation it seems to be sub-optimal at lower boost
but the recovery is likely to be higher with this sub-optimal CR

[gruntguru]

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.

[Abarth]

Interesting, thanks for the link and the calculations.

However, the published data from Cosworth about their simulations as well as some bits, AFAIR from Magneti Marelli, do hint that the electrical motor/generator is well in another power league than these figures. We heard about at least 90 kW.

So can we assume that the kinetic energy of the exhaust (i.e. the part which doesn't show in static backpressure) would contribute to at least another 45 kW to be extracted from the generator?

I think TC provided numbers based on the N/A aviation engine, which produced compund power without (almost) loading the engine with backpressure, i.e. no power loss.

[Tommy Cookers]

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

thanks to gg for these calculations and the useful source/calculator

to me they seem to indicate essentially no benefit from particularly high AFRs
(which would anyway need a somewhat larger compressor, turbine and charge cooler ?)

though in principle AFR need not be limited by considerations of combustion speed/stability in-cylinder
as combustion could continue post-cylinder, to the benefit of turbine power
low AFRs (close to stoichiometric) would post-cylinder reverse any in-cylinder dissociation and so tend to benefit turbine power

iirc gg has suggested a compression ratio of less than 10:1 ? , this would benefit turbine power (but cost crankshaft power) ?


@ Abarth
8-9% gain free via recovered (kinetic) power with NA is my recollection of the first NACA note, this appears alone in some searches
iirc the (mechanically supercharged) 'Turbo-Compound' version of the Wright Duplex Cyclone (cr 6.7:1) measured at sea level .....
6% gain when in low mep 'endurance' running (map about 1.15 bar abs and very lean mixture)
18 % gain when in high mep takeoff running (map about 2.25 bar and very rich mixture)

the aviation case runs at steady rpm and mep, allowing more efficient turbines and compressors than possible in F1 ?
even with the mgu-h actions is 80% a realistic efficiency in F1 conditions ? (importantly regarding compressor power demands)

'real' backpressure (EP greater then MAP) seems tolerable, and increases turbine power recovery at the expense of crankshaft power
ie tolerable when exhaust valve closure is appropriately timed

further benefits (increased efficiency suggested by NACA) may be, as gg has said, an illusion due to better trapping of fuel
though with a lean mixture any fuel escaping the cylinder would usefully be burned ahead of the turbine, NACA never did lean runs
recent compound engine patents eg by Ilmor and Caterpillar might imply that real backpressure does increase efficiency ?

whatever the mixture used at 10500 rpm, we don't know is done to massflow and mixture at 11000 rpm and 12000 rpm etc
what is done will have effects on combined (PU) power and on gu-h power

[Abarth]

Thanks for looking up these figures.
Well, with high single digit numbers of kinetic energy recovering we would be in the ballpark..

[gruntguru]

There are a few possibilities for the discrepancy in recovery numbers - 45 kW vs 90 kW.
- Blowdown energy recovery as already mentioned. If 8% of crankshaft power as suggested by TC, this alone would account for the missing 45kW.
- Compressor and turbine efficiencies. Recovery is quite sensitive to these, so anything over the 80% assumed will have an effect.
- Exhaust temperature. The example above uses conservative numbers. An increase of 100 degrees improves recovery by about 20 kW. Provided detonation can be controlled, exhaust temp could be increased simply by reducing intercooling. Of course that would change massflow and require adjustment of

TC. I don't believe CR is less than 10. Total guesswork, but perhaps 11?

Burning fuel in the exhaust is much less efficient than in the cylinder. Energy recovered is about 14%, 19% and 26% for PR = 2, 3 and 4.

[Tommy Cookers]

blowdown recovery of 8% was for NA (and maybe this first work is less reliable)
the Wright TC recovery figures were checked in flight with torque meters
6% at lowest mep, 18% at highest at sea level (this literally a vital check for takeoff)
CR was eg 6.7 later 7.25 (always 115/145 fuel)
a RR Merlin 24 study for a Lincolnian showed on 7:1 CR a bsfc of 0.41 - 0.425 lb at 10000' improved to 0.36 - 0.37 with turbine
P96 in that Crecy book and in an Aeronautical Research Report in 1946

so apparently 11.5% recovery (at 10000')

given that EV opening will be fixed according to downstream conditions regardless of CR (and so is quite early with any turbine)
the gas state into the turbine will be relatable to Wright's at appropriate boosts
imagine Wright had designed for cruise only, with such a boost limit they could have used eg a CR of 10

so my guesstimate is that a blowdown recovery of 10% is happening in F1

btw
most TCs were military, and most of those used WI, the last giving around 4250 hp
(to incorporate WI ?) the military engines seem to have replaced the DI of the civil engines with the conventional 'injector carburettor'

[pgfpro]

blowdown recovery of 8% was for NA (and maybe this first work is less reliable)
the Wright TC recovery figures were checked in flight with torque meters
6% at lowest mep, 18% at highest (this literally a vital check for takeoff)
CR was eg 6.7 later 7.25 (always 115/145 fuel)

given that EV opening will be fixed according to downstream conditions regardless of CR (and so is quite early with any turbine)
the gas state into the turbine will be relatable to Wright's at appropriate boosts
imagine Wright had designed for cruise only, with such a boost limit they could have used eg a CR of 10

so my guesstimate is that a blowdown recovery of 10-12% is happening in F1

btw
most TCs were military, and most of those used WI, the last giving around 4250 hp
(to incorporate WI ?) the military engines seem to have replaced the DI of the civil engines with the conventional 'injector carburettor'

TC

Were the turbos axial or radial?
Did they use a blow down exhaust manifold to reduce back pressure?

Also On my setup in which I know its not close to what a DI F1 engine is, but my engine cams are design for a high boost turbo charged application, with only 8 degrees over lap.

I do see knock with a poor delta p on pump premium (400whp limit), but not on race fuel VP C16 (650whp limit) but, I do see power fall off from high exhaust pressure before the high pressure turbo starts by passing the exhaust around it to the low pressure turbo. This is my question with the F1 engines loading the turbine for power to feed the MGUH I would expect them to have to keep the intake pressure equal to or more then the exhaust pressure?

[Tommy Cookers]

the Wright Power Recovery Turbines (and those in all the NACA tests) were axial
the superchargers were the standard mechanically driven centrifugal ones as in the conventional version of the engines
the name Turbo-Compound has got at least one textbook wrongly saying it's a turbocharged engine

Wright in their brochure show a plot to prove that there's no backpressure
it looks as if they help this by having 12 exhaust headers of tuned length and 6 not
quite close to an ideal layout for blowdown

NB see my next post to find the links to their brochure and other stuff from earlier in this thread

[pgfpro]

the Wright Power Recovery Turbines (and those in all the NACA tests) were axial
the superchargers were the standard mechanically driven centrifugal ones as in the conventional version of the engines
the name Turbo-Compound has got at least one textbook wrongly saying it's a turbocharged engine

Wright in their brochure show a plot to prove that there's no backpressure
it looks as if they help this by having 12 exhaust headers of tuned length and 6 not
quite close to an ideal layout for blowdown

I shall try to post here a link to their brochure, it might even be earlier in this thread

Thanks TC. I was trying to find it last night but couldn't these threads are crazy long now;)

[Tommy Cookers]

the links are all in my post made at 520 April 27 2014 on P15 of this thread

the Wright brochure, the relevant NACA papers and the Mazda man's demon work (look at what he does, not everything he says)
iirc early in this thread WB says 72% efficiency for the turbine Wright used (I will check and change if this is a wrong recollection)