Renault Power Unit Hardware & Software

[Tommy Cookers]

.... wastegate open ......The exhaust pulsation can maybe also be better utilisied as in a NA engine...

if the wastegate is open the mean exhaust pressure is maybe 1.05 bar
if the wastegate is closed the mean exhaust pressure is maybe 4.05 bar

even with an active turbine surely the 4.05 bar stream has bigger pulse reflections available than the 1.05 bar stream does ?
what did the 80s F1 turbo engines do ? (though they might have had no use for the benefit as they didn't recover power)

ok the 4.05 bar stream the pulse energy has less energy relative to the steady flow energy (than does 1.05 bar stream)
because less of the 4.05 stream's flow will be choked as the gas acceleration will be less due to the higher density

[djos]

.... wastegate open ......The exhaust pulsation can maybe also be better utilisied as in a NA engine...

if the wastegate is open the mean exhaust pressure is maybe 1.05 bar
if the wastegate is closed the mean exhaust pressure is maybe 4.05 bar

even with an active turbine surely the 4.05 bar stream has bigger pulse reflections available than the 1.05 bar stream does ?
what did the 80s F1 turbo engines do ? (though they might have had no use for the benefit as they didn't recover power)

Iirc they had blown diffusers in the 80's turbo era.

[henry]

.... wastegate open ......The exhaust pulsation can maybe also be better utilisied as in a NA engine...

if the wastegate is open the mean exhaust pressure is maybe 1.05 bar
if the wastegate is closed the mean exhaust pressure is maybe 4.05 bar

even with an active turbine surely the 4.05 bar stream has bigger pulse reflections available than the 1.05 bar stream does ?
what did the 80s F1 turbo engines do ? (though they might have had no use for the benefit as they didn't recover power)

ok the 4.05 bar stream the pulse energy has less energy relative to the steady flow energy (than does 1.05 bar stream)
because less of the 4.05 stream's flow will be choked as the gas acceleration will be less due to the higher density

So the wastegate opening impacts 3 areas of performance?

It reduces the pressure in the exhaust stream by providing a freer flow route than solely going across the impeller. ICE crank output goes up, turbine output goes down.

It changes the tuned pressure wave reflections in the exhaust system that aid cylinder filling (I believe this is what you are referring to). ICE performance goes down?

It changes the kinetic energy of the exhaust stream (density down) that drives the blowdown stage in the turbine. Turbine output goes down.

[godlameroso]

.... wastegate open ......The exhaust pulsation can maybe also be better utilisied as in a NA engine...

if the wastegate is open the mean exhaust pressure is maybe 1.05 bar
if the wastegate is closed the mean exhaust pressure is maybe 4.05 bar

even with an active turbine surely the 4.05 bar stream has bigger pulse reflections available than the 1.05 bar stream does ?
what did the 80s F1 turbo engines do ? (though they might have had no use for the benefit as they didn't recover power)

ok the 4.05 bar stream the pulse energy has less energy relative to the steady flow energy (than does 1.05 bar stream)
because less of the 4.05 stream's flow will be choked as the gas acceleration will be less due to the higher density

Are pressure waves affected by higher inertia due to increased mass flow?

[dren]

Wave velocity increases when exhaust gas velocity increases, if that's what you're asking, assuming density and temperature stays the same.

[63l8qrrfy6]

Pretty sure wave velocity is always local speed of sound.

[PlatinumZealot]

The fact that all the Manufacturers spent time redesigning their waste-gates each season certainly shows they are integral for performance. The Ferrari and Mercedes has very noticeable waste gate sounds over the course of the lap.Whatever trickery they do with them besides boost control and electric supercharging beats me.

[Tommy Cookers]

So the wastegate opening ......
It changes the tuned pressure wave reflections in the exhaust system that aid cylinder filling (I believe this is what you are referring to). ICE performance goes down?

imo
2x 3 tuned length headers should work equally well (gains proportionate to exhaust pressure) for either exhaust pressure
ie wastegate closed the F1 engine would have free supercharge potential of eg (1.25 -1) x 4 atm
and wastegate open would have free supercharge potential of (1.25 -1) x 1 atm
(but a pipe with the turbine upstream of the tuned length point only (1.25-1) x 1 atm free supercharge wastegate closed)

EDIT (and tbf some the 25% tuned length benefit is from the inlet side)
ie wastegate closed the free supercharge reduces substantially the compressor work needed from the turbine and H motor
substantially increasing H recovery

[e36jon]

Pretty sure wave velocity is always local speed of sound.

Greetings Mudflap

I believe it works like this: If you're in an airliner going 700mph, the speed of sound inside is what it is (Driven by temp, pressure, etc.). Seen from the outside though, the speed of your sound inside the airplane is + or - 700mph.

Same thing in an intake or exhaust manifold: The bulk air is moving, and the speed of sound is what it is within that bulk air, but is seen by external elements as + or - the speed of the bulk air.

Or I am completely wrong and must go sit in the corner...

Jon "Blowing hot air"

[godlameroso]

So the wastegate opening ......
It changes the tuned pressure wave reflections in the exhaust system that aid cylinder filling (I believe this is what you are referring to). ICE performance goes down?

imo
2x 3 tuned length headers should work equally well (gains proportionate to exhaust pressure) for either exhaust pressure
ie wastegate closed the F1 engine would have free supercharge potential of eg (1.25 -1) x 4 atm
and wastegate open would have free supercharge potential of (1.25 -1) x 1 atm
(bit a pipe with the turbine upstream of the tuned length point only (1.25-1) x 1 atm free supercharge or worse wastegate closed)

ie wastegate closed the free supercharge reduces substantially the compressor work needed from the turbine and H motor
substantially increasing H recovery

Ties in very nicely with balancing ICE power and MGU-H power.

[Big Tea]

Pretty sure wave velocity is always local speed of sound.

Greetings Mudflap

I believe it works like this: If you're in an airliner going 700mph, the speed of sound inside is what it is (Driven by temp, pressure, etc.). Seen from the outside though, the speed of your sound inside the airplane is + or - 700mph.

Same thing in an intake or exhaust manifold: The bulk air is moving, and the speed of sound is what it is within that bulk air, but is seen by external elements as + or - the speed of the bulk air.

Or I am completely wrong and must go sit in the corner...

Jon "Blowing hot air"

Is it not Dependant on air (or medium) density?

[Tommy Cookers]

the thing we call the speed of sound in air is driven by temperature not pressure

btw and imo
blowdown is a choked process
that is why they can use both wastegate open and wastegate closed with the same EVO timing
dropping mean exhaust pressure from 4 bar to 1 bar makes little difference to blowdown ie doesn't demand later EVO timing
(and blowdown would still be a choked process if the exhaust valves were infinitely large and opened instantaneously)
because it takes a disproportionate pressure for the gas to accelerate itself to scavenge the cylinder in less than 1 millisec
the early velocity (of this pressure pulse aka 'shock wave') is supersonic

[PlatinumZealot]

Define blowdown...

I have only seen this word in very old PV graphs... for turbocharged 2 strokes? But never saw a good explanation. Granted, I have not really tried researching that term too much.

[henry]

Define blowdown...

I have only seen this word in very old PV graphs... for turbocharged 2 strokes? But never saw a good explanation. Granted, I have not really tried researching that term too much.

Fortunately there’s a whole thread on the topic

viewtopic.php?f=4&t=20312

[PlatinumZealot]

Define blowdown...

I have only seen this word in very old PV graphs... for turbocharged 2 strokes? But never saw a good explanation. Granted, I have not really tried researching that term too much.

Fortunately there’s a whole thread on the topic

viewtopic.php?f=4&t=20312

Nope! I remember that thread! I won't re-enter!

There was no clear answer.. I have a Pressure-Volume graph with blow-down featured on it, which I might post if anyone is interested.. and some other very old references. But I would like a clear definition for everyone to be able to join the discussion. It's mostly the old-heads you hear with this blow-down term.