Mercedes Power Unit Hardware & Software

[dren]

I'd say you'd want to run as hot as possible then, and also move towards dumping heat out the exhaust rather than the radiators, with optimizing towards transferring the most of the pressure increase to the crank.

Any idea on how far in advance you have to ignite the jet before the jet is igniting the in cylinder mix?

[Singabule]

Surely it is variable. I think about 15 degree btdc in corner exit and up to 35 degree at full throttle 11k rpm. Who knows, merc engine is Just like a living creature with the best AI. That their major strength. STRAT2 mode maybe very destructive to them since its bypassing their AI logic.

[PhillipM]

PP at TDC means dumping more heat to coolant as expansion is suspended while cooling is continuous

Your exposed chamber wall surface at that point however is at it's smallest, so the slight heat loss may not me much issue.

[PlatinumZealot]

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.

Hmm could be the same thing since the piston dwells a bit at the top. My order of magnitude is less than 14 ATDC. Close enough?

[godlameroso]

In a perfect world you'd want full combustion asymptotically after TDC.

.00000000000000000000000001 degrees after TDC if you could. The closer you get, the more power you make. Simple in principle, almost impossible to reach because reasons. Having combustion instability probably being the biggest hurdle. The closer you get, the easier it becomes to have a catastrophic misfire.

[PlatinumZealot]

In street cars is about 14 ATDC for most power. U have to advance spark timing maybe 30 odd degrees to get it there... at higher rpms I'm talking. I couldnt tell you a out thermal efficiency and spark timing,never learned or read so will have to take guru's word for it.

[Singabule]

Agree, surely you dont want to waste 18:1 CR by retarding the ignition. It is just for retarded people please also consider their CC need time to react, so the ignition timing maybe faaarrrr earlier than you think

[Brian Coat]

PP as close as possible to TDC will not give best efficiency in any real world SI engine - it's always after.

[godlameroso]

Close is not the same as equal to. Immediately after TDC is not the same as exactly at TDC.

[FW17]

Close is not the same as equal to. Immediately after TDC is not the same as exactly at TDC.

http://performancetrends.com/Definition ... re-Lrg.gif

Dont think that TJI works anything like that. It will be more in line with diesel injection, fuel and spark together at TDC

[Singabule]

Close is not the same as equal to. Immediately after TDC is not the same as exactly at TDC.

http://performancetrends.com/Definition ... re-Lrg.gif

Dont think that TJI works anything like that. It will be more in line with diesel injection, fuel and spark together at TDC

Nope, not as easy as that. There is still lead time prior to ignition inside and outside jet chamber

[FW17]

Close is not the same as equal to. Immediately after TDC is not the same as exactly at TDC.

http://performancetrends.com/Definition ... re-Lrg.gif

Dont think that TJI works anything like that. It will be more in line with diesel injection, fuel and spark together at TDC

Nope, not as easy as that. There is still lead time prior to ignition inside and outside jet chamber

Any info on the speed of the plasma? that could determine time before TDC

[J.A.W.]

Close is not the same as equal to. Immediately after TDC is not the same as exactly at TDC.

http://performancetrends.com/Definition ... re-Lrg.gif

Now kindly present a 'blown' engine graph, for a more realistic view..

[Singabule]

Dont think that TJI works anything like that. It will be more in line with diesel injection, fuel and spark together at TDC

Nope, not as easy as that. There is still lead time prior to ignition inside and outside jet chamber

Flame front for high CR lean burn engine is Hard to better than 20m/s, meanwhile in hydrogen burning is about 48m/s. Depend on fuel, they May approaching 27m/s. In 12000rpm, the piston speed about 21m/s, and length between crown and valves let say 3 mm minimum, it means 6mm for build up pressure to CC. Because TDC is approaching faster than BDC, i think with the fastest burst TJI of merc, 35 degree BTDC ignition point is more likely

[Singabule]

You now what? It is more than likely merc has dual anchor TJI, imagine that vertical jets should be not a problem, and the big problem is the horizontal and diagonal one, since the length of jets should cover 80 mm of bore, and if this True, first anchor is ignited in 70 degree BTDC, and the second one in 35. Just WOW! How can they avoid detonation?!!!