Mercedes Power Unit Hardware & Software

[bill shoe]

I have been on tests in Barcelona and Mercedes powered cars sounded quite different from others, particularly on start-finish straightline in DRS zone. They sounded in higher frequency like older V8s.

That frequency is the result of aggressive ignition timing, the closer the piston fires to TDC the higher the pitch. The further from TDC the piston is when it fires, the lower the pitch. Much like in a sliding trombone, the further you move the slide the deeper the pitch. Or the longer pipes on an organ resulting in deeper lower pitch sound than the shorter ones.

That doesn't make sense to me. Piston engines typically ignite some amount before TDC, so aggressive ignition timing would be more advanced before TDC and thus lower-pitch according to the trombone analogy. Also, not sure if I buy the trombone analogy.

[PhillipM]

I will say on almost everything I've worked on, generally (I'm excluding strange timing events such as anti-lag or boost building) it does hold across many engines that the note will be deeper with less timing advance and higher pitched with more.

[Brian Coat]

(1) That trombone stuff is incorrect.

(2) Faster combustion will inherently have more high frequency content but that does not mean this is why the Merc sounds the way it does.

[godlameroso]

I have been on tests in Barcelona and Mercedes powered cars sounded quite different from others, particularly on start-finish straightline in DRS zone. They sounded in higher frequency like older V8s.

That frequency is the result of aggressive ignition timing, the closer the piston fires to TDC the higher the pitch. The further from TDC the piston is when it fires, the lower the pitch. Much like in a sliding trombone, the further you move the slide the deeper the pitch. Or the longer pipes on an organ resulting in deeper lower pitch sound than the shorter ones.

That doesn't make sense to me. Piston engines typically ignite some amount before TDC, so aggressive ignition timing would be more advanced before TDC and thus lower-pitch according to the trombone analogy. Also, not sure if I buy the trombone analogy.

The reason you time ignition events before TDC, is because the combustion event isn't instantaneous. Full combustion happens slightly after TDC on the down or power stroke. If you were to have full combustion before TDC you'd be wasting power as you'd be slowing the piston on it's compression stroke and there wouldn't be any power left on the power stroke. In fact having a misfire on the compression stroke is a good way to destroy rods.

[Facts Only]

Funny that we all thought they were geniuses in 2014 after coming out with the log exhaust manifold. They definitely backtracked on that.

Choosing the correct solution for each season isn't backtracking, it's optimisation. Seeing as how Merc have been untouchable since the V6T's started none of their choices could be called wrong and needed backtracking on.

[Brian Coat]

"Seeing as how Merc have been untouchable since the V6T's started none of their choices could be called wrong and needed backtracking on."

I see what you mean ... but this is clearly not true.

[godlameroso]

(1) That trombone stuff is incorrect.

(2) Faster combustion will inherently have more high frequency content but that does not mean this is why the Merc sounds the way it does.

I should have made the distinction between ignition and combustion clearer from the get. For that I apologize.

[roon]

Probably they are allowing the cylinder liners to be well lubricated before ignition. Can be down to " smart" scaverning rings

If oil pressure in these power units is variable apart from engine speed, via valving or variable drive, then seals & gaps could be designed to work in conjuntion.

High oil pressure + plus low engine speed might provide some of the oil smoke we're seeing.

I speculated in another thread that the pistons & conrods in these engines could be pressurized components, with internal oil channels. If so, piston ring action could be active or controllable, to the extent of controlling oil pressure feed to the rotating assembly.

[toraabe]

I will say on almost everything I've worked on, generally (I'm excluding strange timing events such as anti-lag or boost building) it does hold across many engines that the note will be deeper with less timing advance and higher pitched with more.

Mercedes start.. https://www.youtube.com/watch?v=3gAhmqs0_f0

Same rpm ( idle 4000 rpm) when the car begins to move.
This can be crucial with these wide tyres out of low speed cornes when the driver can put the pedal down

[PlatinumZealot]

I have been on tests in Barcelona and Mercedes powered cars sounded quite different from others, particularly on start-finish straightline in DRS zone. They sounded in higher frequency like older V8s.

That frequency is the result of aggressive ignition timing, the closer the piston fires to TDC the higher the pitch. The further from TDC the piston is when it fires, the lower the pitch. Much like in a sliding trombone, the further you move the slide the deeper the pitch. Or the longer pipes on an organ resulting in deeper lower pitch sound than the shorter ones.

That doesn't make sense to me. Piston engines typically ignite some amount before TDC, so aggressive ignition timing would be more advanced before TDC and thus lower-pitch according to the trombone analogy. Also, not sure if I buy the trombone analogy.

For TJI you can fire very close to TDC because the combustion is so rapid, if you advance your TJI timing too much your peak pressure will be miss-timed and you will do work against the engine - as I know you know - but just saying. At the end of the day it is all about getting the peak pressure of the explosion to happen at the maximum mechanical leverage angle of the crank. TJI is rapid flame spread, you have to fire it later much later. So your base timing is pretty retarded compared to regular spark ignition. As the rpms go up your timing will advance just the same of course. I don't know what to say about Goldie's post on the pitch... it makes sense in a way.. like wine glass.. but I guess it would have to be a like rpm to like rpm comparison between the two ignition timings to really tell if this is true.

[Juzh]

I will say on almost everything I've worked on, generally (I'm excluding strange timing events such as anti-lag or boost building) it does hold across many engines that the note will be deeper with less timing advance and higher pitched with more.

Mercedes start.. https://www.youtube.com/watch?v=3gAhmqs0_f0

Same rpm ( idle 4000 rpm) when the car begins to move.
This can be crucial with these wide tyres out of low speed cornes when the driver can put the pedal down

That's a few starts now I've seen from mercedes when they seem to launch incredibly well. More so than any other car.

[toraabe]

I will say on almost everything I've worked on, generally (I'm excluding strange timing events such as anti-lag or boost building) it does hold across many engines that the note will be deeper with less timing advance and higher pitched with more.

Mercedes start.. https://www.youtube.com/watch?v=3gAhmqs0_f0

Same rpm ( idle 4000 rpm) when the car begins to move.
This can be crucial with these wide tyres out of low speed cornes when the driver can put the pedal down

That's a few starts now I've seen from mercedes when they seem to launch incredibly well. More so than any other car.

This is due to the superiour drivability of the engine. From this article http://www.auto-motor-und-sport.de/form ... 32406.html the Merc engine respons like a normal car engine...

[hurril]

What is so fascinating is that we've known from the start of 2014 that the Mercedes engines are very good. But for each year it's like we learn just how flippin awesome it is judging by how hard it is for other very competent manufacturers to get it right and also how hard it is to get the Mercedes concept working.

[gruntguru]

At the end of the day it is all about getting the peak pressure of the explosion to happen at the maximum mechanical leverage angle of the crank.

No - for best thermodynamic efficiency you need peak pressure to be as close to TDC as possible.

[Tommy Cookers]

At the end of the day it is all about getting the peak pressure of the explosion to happen at the maximum mechanical leverage angle of the crank.

No - for best thermodynamic efficiency you need peak pressure to be as close to TDC as possible.

well, as close to TDC as possible would seem (in some prechamber engines anyway) to include peak pressure at TDC
PP at TDC means dumping more heat to coolant as expansion is suspended while cooling is continuous

surely there will always be a compromise between throwing heat away to coolant and throwing heat away in exhaust ?
the faster the combustion the clearer this compromise will be eg even if a prechamber does give super fast combustion eg to very lean mixtures ?