F1technical.net

If scavenging is being achieved with these engines via wave tuning, then what use is supercharger mode?

The use is a drastic reduction in pumping losses.

Wave tuning is a critical part of a naturally-aspirated engine’s efficiency, since it is the only way to create ‘charge’ motion o0ther than – and sometimes in spite of – piston motion. Wave-tuning is what made the huge jump from engines that only had effective filling in the 40 – to – 70 – percent volumetric efficiency range to the common 110 – to – 130/140 – percent numbers. Once artificial pressurization of the intake system is added/used. You have a source of charge motion other than piston movement or wave tuning. With a supercharger (electric supercharger mode/free load mode). You have a higher pressure on the inlet side, and a lower pressure on the exhaust side. So that can be used to initiate air flow, even before the piston starts moving away from TDC. With a supercharger application (electric supercharging mode/free load mode). The intake side of the engine is pressurized to around 4 atmospheres of pressure – but the exhaust side remains at 1 atmosphere, creating a 4:1 pressure ratio on the intake side. While there are similarities between supercharging and turbocharging on the intake side - mainly the pressurization of the intake tract to assist in-cylinder filling – there are significant differences on the exhaust side between the two applications. Which lead to an entirely different set of camshaft specification needed between the two applications. When it comes to camshafts there is no such thing as “boost is boost”.
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godlameroso wrote: ↑

11 Jul 2019, 02:41

The use is a drastic reduction in pumping losses.

That's my understanding as well--the exhaust stroke essentially becomes easier. My question poorly phrased. If wave tuning is relied upon to reduce cylinder pressure, then: to what degree? How would a wave induced pressure drop compare to wastegate operation?

roon wrote: ↑

11 Jul 2019, 06:47

godlameroso wrote: ↑

11 Jul 2019, 02:41

The use is a drastic reduction in pumping losses.

That's my understanding as well--the exhaust stroke essentially becomes easier. My question poorly phrased. If wave tuning is relied upon to reduce cylinder pressure, then: to what degree? How would a wave induced pressure drop compare to wastegate operation?

A quick search found me this:



If true, it would lower the pressure to half an atmosphere.

“How would a wave-induced pressure drop compare to waste-gate operation?”.
From my previous post:- “With these modern and highly developed turbochargers there is still an exhaust restriction – there is no getting around that fact – but they bring the restriction level to that of the amount of boost they are providing the intake tract. That 1:1 pressure ratio is what allows wave-tuning into play”.
The exhaust pressure drop with waste-gate/s operation (waste-gate/s open), (electric supercharging mode/free load mode) differences will be ‘ZERO’ pressure to whatever level of exhaust restriction is incurred with waste-gate/s closed.
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saviour stivala wrote: ↑

11 Jul 2019, 06:45

Wave tuning is a critical part of a naturally-aspirated engine’s efficiency, since it is the only way to create ‘charge’ motion o0ther than – and sometimes in spite of – piston motion. Wave-tuning is what made the huge jump from engines that only had effective filling in the 40 – to – 70 – percent volumetric efficiency range to the common 110 – to – 130/140 – percent numbers....

well ... and sincerely ....
what charges all NA engine other than/in spite of piston motion is 'Bernoulli' - kinetic energy changing into pressure energy
wave 'tuned-length' effects can be added to supplement this (for racing) - or be deliberately kept trivial (for your parents' car))
because wave tuning works essentially near to a fixed rpm (unless it's variable geometry) - and is also noise-generating
anyway all WT'd engines are simultaneously using Bernoulli

Bernoulli tells us when a moving column of gas is stopped the pressure rises according to the square of the gas speed
this means that eg the inlet valve can usefully be opened before tdc and closed after bdc and so help the VE
Be can give a VE close to 100% - but only where gas speeds are high ie peak at c.800 mph the 'speed of sound'
this means rather large ports and valves - to keep peak gas speed subsonic even at 100% rpm
but eg at 50% rpm Be is only giving 25% benefit (and cams designed for Be at 100% rpm are wrong for 50% rpm)
road engines of course had small ports/valves to get max Be at rpm well below 100%
so the charging/rev fell at high rpm as the ports 'choked' via losses in attempting supersonic peak gas speeds
the result was a practical though unexciting torque/power curve
even race engines were compromised in this - different designers having different ideas
eg the Cosworth DFV chose/had unfashionably high gas speeds from seemingly (to some) 'small' ports and valves

the trend-setting pre WW1 GP Peugeot had huge ports and seemingly no appreciation of Bernoulli (or wave tuning of course)
judging by the designed valve timings
it chose very low gas speeds for laminar flow 'to minimise flow losses' (wrote L H Pomeroy Jnr)
ironically the size of the porting to atmosphere is important in WT and Be (it controls pressure differences of course)
eg the 1967 McLaren F1-destroked Ford Detroit Indy V8 had lacked power at high and low rpm
until the intake (porting to atmosphere) diameter was reduced (increasing pressure differences)

early post WW1 GP winners had extended valve timings and WT (on the induction side anyway)
invented by motorcycle racing then car racing on ovals in the UK and USA
inlet port and valve sizes for Be helped power curve (eg 1923 Fiat-clone GP Sunbeam had 3 gears vs preWW1 Peugeot 5 gears)
European inter-war NA motorcycles developed extreme WT incl megaphone exhaust but had good Be by not over-porting
this drove later NA F1 design though most compromised on exhaust and/or inlet side for power curve reasons
till liberated by intelligent injection/fbw throttles, vg induction tracts, and 7 speed paddle shift gearboxes


when I claimed a NA VE of 125% was possible proof was demanded (not from s s) - so doesn't 130%-140% seem high ?
of course the car's forward speed can increase VE and power
and increase the power from exhaust thrust power (this at max speed about 3% of current F1 PU ?)

and of course the exhaust process at high % powers in all piston ICEs is choked
(even if the valves were infinitely large and opened infinitely quickly it would be)
choked by the high loss of pressure as some/much of the flow necessarily is supersonic
in current F1 the potential of the exhaust gas is thereby degraded - the process is in part thermodynamically irreversible
presumably somewhat limiting the recovery potential by further expanders
though usefully choking and its losses are reduced according to the density (exhaust pressure) upstream of the turbine

rscsr wrote: ↑

11 Jul 2019, 08:19

A quick search found me this:

http://www.topplocksverkstan.se/bilder/ ... iagram.jpg

If true, it would lower the pressure to half an atmosphere.

That is a wonderful illustration I haven't seen before - thank you rscsr. I recommend anyone should spend some time to try and understand what is happening there.

The following image shows instantaneous pressures in the cylinder and exhaust port of the Wright TC aircraft engine which extracted up to 500 bhp (18% of crankshaft power) from the exhaust. Note that average exhaust pressure is about 3 psi but cylinder pressure when exhaust valve closes is about 1 psi below atmospheric, enabling significant scavenge during valve overlap. (intake pressure is several psi above atmospheric).

Also note the similarity of the exhaust pressure trace to the image posted by rscsr.

rscsr wrote: ↑

11 Jul 2019, 08:19

http://www.topplocksverkstan.se/bilder/ ... iagram.jpg

Gauge or absolute?

The main factors seem to be the relationship between cylinder pressure at EVO and exhaust runner/manifold pressure at EVO. I'll call this exhaust pressure differential, EPD. There may be an established term.

Scenario 1: low or negative EPD, WG closed. Maximal expansion in cylinder before EVO. Piston pushes exhaust gases out.
Scenario 2: high EPD, WG closed. Pressure wave assists exhaust gas evacuation, may reduce piston work.
Scenario 3: high or very high EPD, WG open. Backpressure maximally reduced. Expected operation for supercharger mode. Increased scavenge may demand more compressor flow.

These my speculation. Scenario 1 would be a sort of atkinson mode.

The flow out of the narrow
wastegate pipes must be incredibly fast, perhaps supersonic?

rscsr wrote: ↑

11 Jul 2019, 08:19

If true, it would lower the pressure to half an atmosphere.

half an atmosphere at the valve
it (the pressure reduction) would be a lot less than half an atmosphere in the pipe
.05 - .08 relative (ie bar) in the pipe is shown in the Smith & Morrison book (though apparently with an artificial wave)
presumably the wave has in the pipe less pressure reduction (than it would in the valve region)
and varies anyway according to the relative speed of valve opening and relative size of the valve

btw
the Wright plot in gg's post is at rated power
afaik this is cruise power where the recovery is about 100 hp
Wright stated that for practical reasons only 12 exhaust pipes were of a length that assisted scavenge as we expect

The 1.6-litre V6 turbo-supercharged ICE/engine part of the present power unit design is a first in formula 1 being designed to run as a turbocharged as well as a supercharged forced induction engine, two forced induction systems between which there are substantial design different needs.
Is RSCSR supplied image of pressure events of a well-tuned racing engine pertains to a forced induction or a NA engine?.
GG’s image of instantaneous cylinder pressure of the Wright TC engine doesn’t say of which of the at least 15 variants of the 2200 to 3700 HP it belongs too. The R-3350 3700hp two stage supercharged engine had three exhaust driven turbine from six cylinders exhaust with each turbine being geared to the crankshaft through a fluid coupling.

isn't the F1 engine a turbo-compound engine not a turbocharged engine ?

you seem unaware that Wright is a Turbocompound TC18 version (14000 made) of the Wright Duplex Cyclone aka Cyclone 18
far more of the conventional versions of the Duplex Cyclone were made
there was never a TCDC offered at such a low power as 2200 hp (and never a conventional DC at 3700 hp)
(btw R-3350 is the pan-military designation for any radial engine of 3345 - 3355 cubic inches displacement)

the pressure plot is from the Wright brochure
like the 1954 paper this predates the later TC that had 7.2 CR and improved DI - for this no bsfc figures seem to exist
1954 paper gives energy balances at TO and at max sl endurance (hence my 100 hp recovery - airline cruise 240 hp recovery)
the bsfc everyone quotes is for the earlier TC engine with 6.7 CR
all DCs and TCs were 115/145 fuelled

Is a present formula 1 engine a ‘turbo-compounded engine?’. The present formula I engine is designed to be used as a forced induction engine by two substantially different pressurizing systems. A turbocharger OR an electric supercharger.
A turbo-compounded engine employs a turbine to recover energy from the exhaust gases. Instead of using those exhaust gases to drive a turbocharger. The energy of the exhaust gases is instead sent to the output shaft (crankshaft) to increase total power. The turbine is mechanically connected to the crankshaft. As on the Wright R-3350 DUBLEX-CYCLONE.
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saviour stivala wrote: ↑

14 Jul 2019, 07:58

Is a present formula 1 engine a ‘turbo-compounded engine?’. The present formula I engine is designed to be used as a forced induction engine by two substantially different pressurizing systems. A turbocharger OR an electric supercharger.
A turbo-compounded engine employs a turbine to recover energy from the exhaust gases. Instead of using those exhaust gases to drive a turbocharger. The energy of the exhaust gases is instead sent to the output shaft (crankshaft) to increase total power. The turbine is mechanically connected to the crankshaft. As on the Wright R-3350 DUBLEX-CYCLONE.
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you're saying the F1 PU can't use concurrently in MGU-K motor action electrical energy produced in MGU-H generator action
it can
exhaust recovery turbine powered G-H to M-K (electrical to mechanical) energy transfer gives second expander action
(the piston being the first expander)
having a second expander (downstream of the piston expander) is what makes the PU a compound engine
the Mercedes efficiency claims of c.50% are made on this basis - ie sustainable power vs fuel heat rate
any other basis would be false
how can these engines not be classified as some kind of compound ? (eg a part-time compound)

the Wright Duplex Cyclone was not a compound engine because it had no exhaust recovery of power to the output shaft
about 50000 were made - initially and famously for the B-29 Superfortress
the Wright Turbo-Compound (a version of the Duplex Cyclone) was a compound engine
because it had added to it exhaust recovery by PRTs mechanically connected to the output shaft
Turbo-Compound was a name registered by Wright (incl potentially Turbo-Compound versions of other Wright engines)

about 7 years ago in this thread a priceless link was posted - to what I call the Wright brochure (afaik gg's source)
the lavish explanation and vindication of the Turbo-Compound to a sceptical world was and is priceless
handy for me when I seemed to be the only person in the world saying there was free power in the exhaust
ie power can be recovered from the exhaust as Wright did without any so-called 'back pressure'

people should move beyond Wikipedia