NL_Fer wrote:Frank_ wrote:gruntguru wrote:They are common rail DI - Yes. Spraying the fuel as it burns - No.
You need to read the last few pages of this thread including Mahle TJI.
ahh, thanks gg, i had assumed that in order to achieve 45%+ thermal efficiency they had to keep the flamefront away from the cylinder walls, like a small swirling ball of fire continuously fed with fuel from tdc onwards (that was my understanding of current diesel engines)
No, the key is an (ultra)lean fuel/air mixture and TJI to properly burn it. A lean mixture with classic spark ignition would burn slow or not ignite at all.
It is still a mystery though, how much fuel is injected during intake and how much before TDC. The orginal implementation of TJI has also a separate port fuel injector, but this is not allowed in F1.
all types of engines seem to do some burning btdc
this is not wholly bad - most of that heat is still available for relatively efficient conversion to work
judging by the many schemes for lean homogeneous charge the heat 'insulating' benefits of charge stratification per se are more PR than actual
ie the overall AFR is the significant factor and the nominally homogeneous charge works just as well
lowering cycle temperature by increased air massflow is beneficial in-cylinder without disbenefit to the exhaust recovery
(and remember all cars used lean mixture till mandatory 3 way catalysts forced most/all running 4% rich)
but N/A the Mahle TJI shows roughly 40% bte with a stoichiometric mixture and at best leaning (raising AFR) to 1.7x equivalence 44%
don't tell the FIA, they like to pretend that N/A is only good for 29%
and of course they banned multiple sparkplugs, a traditional means of getting distributed ignition sites and leaner running etc
(gas fuelling of the TJI unit allows further raising of the AFR, as does, greatly, gas fuelling of the engine)
in boosted engines TJI might support (F1 full power) leaning beyond 1.7x equivalence ratio
but isn't this1.7x the sort of equivalence ratio currently used, judging by the boosts used ?