F1technical.net

toraabe wrote:Don't forget that the shorter the manifold is, the higher the temperature is when the gasses enters the turbine. Although the log manifold takes around 15 hp from the engine, you are able to harvest more energy through the MGU-H and deliver it direct to the MGU-K than you are loosing...

Valve timing needs to coordinate with blowdown at the exaust valve to retain high back pressure. High back pressure reduces losses at exhaust valve. And as stated, mass flow is basically the same regardless of exhaust layout, so you want to retain as much discarded energy in the exhaust as possible. The log exhaust helps with reducing temperature/pressure drops.

The log mainfold might not take anything from the ICE because you likely are running higher boost pressures with it as has been stated earlier.

trinidefender wrote: Just thinking this through in my head. Blowdown energy is energy captured from the kinetic energy of the mass of the exhaust gasses. Usual Kinetic energy formula applies KE = .5*m*v^2.
So in the exhaust the mass of gasses is relatively constant throughout each cycle so that is fine. What we can alter is the velocity (v). The velocity of the exhaust gasses is created by the pressure differential in the cylinder vs in the exhaust. The greater the pressure differential, the greater the velocity. The greater the velocity the greater the kinetic energy available to be converted to blowdown energy.
If we increase the exhaust back pressure then we reduce the pressure differential and reduce the speed and hence KE of the exhaust gasses.
Feel free to tell me that I am talking out of my ass but please explain what would actually happen then.

at our mep or even a brisk road speed mep the blowdown is a choked process
ie exhaust velocity is sonic or partially supersonic, so cannot be significantly increased with any pressure differences available to us
all conventional engines opening the EV at around 7 - 8 bar when at max mep (so that the exhaust pressure has fallen by bdc)
much pulse pressure energy being turned to heat, tending to increase mean exhaust pressure

if we engineer for a raised mean exhaust pressure the exhaust will be denser
so the blowdown will give less acceleration and choking, so convert less pulse pressure to heat (and more to recovered power)
the mean exhaust pressure can be raised even to exceed the boost without problem if the EV closure is suitably timed for this
shown to be the most efficient PU way (migration of power from crank to turbine), but recovered power would breach F1 rules

in principle we could vary mgu-h load to give mutual independence of compressor rpm/boost and exhaust pressure
allowing all sorts of massflows (for various AFRs) and all sorts of mean exhaust pressures


@ mr luke
up to the 1950s road cars typically had a crude exhaust manifold, a straight length of tube running along the side of the head
the changes in flow direction were brutal and the path lengths varied greatly, as the flow exited at the manifold end
a system not tuned for cylinder filling, but at least quite quiet (a tuned system is a noisy system before silencer/muffler)
like a log it conspicuously had no branches
race manifolds up to the 1950s had multiple branches serially joining the runner ie giving a small variation in path length
(unlike the modern race manifold where pipes meet at 1 point to give equal path lengths)
were regarded as the opposite of the derided log-like basic road manifolds

and drift was originally called 4-wheel drift
a desirable state of substantial slip angle on both axles engineered in 1938 by Nuvolari and Colombo ? (said Rene Dreyfus)
where previously front slip angles had been trivial or even reversed (oversteer)
now drift is a meaningless term like turbo

Thanks TC I always enjoy your post's!!!

Tommy Cookers wrote:the mean exhaust pressure can be raised even to exceed the boost without problem if the EV closure is suitably timed for this

It is highly advantageous to operate with a positive pressure differential. Thermal stress and detonation tendancy increase rapidly as exhaust pressure rises above intake pressure causing scavenge during overlap to reduce to zero (or negative ie EGR).

shown to be the most efficient PU way (migration of power from crank to turbine), but recovered power would breach F1 rules

F1 rules do not limit MGUH power. A maximum of 120kW can be used directly in the MGUK and the rest sent to the ES.

No teams appear to be harvesting more than 120kW as yet, requiring some period of reduced power operation to increase ES charge. This does appear to be the area of Mercedes superiority, requiring less time to charge the ES and more time at max output from a given ES charge.

the evidence suggests that appropriate EV closure timing prevents any problems when running at exhaust pressure exceeding boost
ie the valve motions isolate the in-cylinder conditions from the exhaust
(supported by later EV closure timing showing its best performance with less relative exhaust pressure)

ok the level of exhaust pressure for optimal PU efficiency probably doesn't suggest more mgu-h recovery than F1 can use .......
it does seem to depend on how much turbine power is consumed by the supercharger, eg this will be high at high AFR
(my evidence is for engines supercharged from the crankshaft, and using only traditional AFR)

depending on the track we need to harvest 130-140 kW ? throughout driver WOT demand time to reach the full potential of the rules

Tommy Cookers wrote:the evidence suggests that appropriate EV closure timing prevents any problems when running at exhaust pressure exceeding boost

Not "problems" as such - just a big performance advantage when boost pressure exceeds back-pressure. Combustion products are completely removed and chamber components get some cooling air applied to their hottest surfaces.

Ron Dennis just said on the BBC that Honda will run 2 different engine concepts at the Abu Dhabi test.

Split turbo/no split turbo?

mikeerfol wrote:Split turbo/no split turbo?

Possibly, but I think it has to do with the xhausts, MHPE's log-style is quite different from conventional wisdom in that regard.

xpensive wrote:

mikeerfol wrote:Split turbo/no split turbo?

Possibly, but I think it has to do with the xhausts, MHPE's log-style is quite different from conventional wisdom in that regard.

I think the log exhausts were done for purely packaging reasons. They were a late edition, apparently, being tested just befor the homologation deadline.

Both the Ferrari and Renault could easily adopt the log exhausts.

So why didn't Ferrari and Renault apply logs in the first place Wuz?

xpensive wrote:So why didn't Ferrari and Renault apply logs in the first place Wuz?

Maybe because they didn't consider them, or if they did they thought that the disadvantages outweighed the advantages.

Sorry I was a bit slow in noticing the comments below and joining them up to Merc's comments in the press.

Richard wrote:

xpensive wrote:Au contraire, it has everything to do with their superiority, I'm still certain that they have a clutch, which the spannerman (Whiting) mindlessly approved upon some years back. This way they can disconnect the turbine to reduce inertia and speed up the compressor with the MGU-H only, which in turn allows the use of log-xhausts, all in all dramatically improving throttle-response and packaging.

Andy Cowell is on record as stating that their (Merc's) compressor and turbine are on the same shaft and that the clutch is used to disconnect the MGU-H from the turbo under certain circumstances.

As this is what the rules require/allow, it is not a total shocker.

But the point is that if you disconnect the MGU-H on a split turbo, the turbine and compressor will no longer turn at the same speed.

xpensive wrote:But the point is that if you disconnect the MGU-H on a split turbo, the turbine and compressor will no longer turn at the same speed.

They could still be on a common shaft and the mguh could be concentric with but not attached to that shaft.