WhiteBlue wrote:
You have not answered my question there, TC.
I believe that combustion efficiency is much improved by direct injection versus carburettor or port injection. At least that is what we see in high performance sports cars, F1 regulations ...... Pressure is going up from 200 bar to 500 bar. This leads me to believe that the fuel efficiency advantage enjoyed by the DI systems will also be experienced by the 2014 F1 cars.
I understand that for fuel efficiency it is best to compress the air without fuel because you can prevent early combustion much better. In order to do this you need a fuel delivery system that work in microseconds. You need to be able to have the fuel delivered into the fully compressed air, atomised and evaporated in a very short time. This process also fully exploits the cooling effect of the evaporating fuel only that it looses no cooling to the surrounding metal parts of the engine because the effect is contained in the compressed air charge.
I might add that DI was also identified as one of the crucial fuel efficiency technologies by people like Gilles Simon when the engine project was first discussed in 2009. Those sources are not in this thread but in it's predecessor.
thanks for the Simon reference (STEEL pistons though ?)
again my answer is that 100% DI prevents any cooling in the supercharging process, which IMO our 2 fellow posters who are experienced turbo engine builders/users incorporate in their engines
the issue is how many or few of the efficiency gain routes with DI in road use will be equally valuable in racing
combustion efficiency should mean eg does all the fuel get burnt, and does it get burnt at the right time for best thermal efficiency
if DI keeps fuel away from the cylinder etc it will save a tiny amount of fuel going unburnt, tiny in race power but emissions-significant for road use
for DI to minimise cooling of cylinder etc there must be stratification ie an overall lean mixture that tends to disadvantage in racing, again DI scores in road use (partial power leaning to avoid throttling losses) rather than in racing
DI helps VE by not displacing the 3% of induction air that PI does, and it cools entirely in the combustion chamber
(carburettors giving large droplet size at open throttle do the same, and can give more power than PI according to David Vizard)
IMO the crucial thing is thermal efficiency, which we assume relates (when combustion speed is not an issue) rigidly to CR
DI (as I have been posting for 6 months) aids CR by reducing time exposure at high temp, so deterring detonation
I suspect that combustion speed in SI engines is not dominated by droplet size ie DI vs PI
combustion speed was not a big issue with 20000 rpm 107 mm bore NA engines (albeit with fuel optimised for combustion speed)
2014 fuel will be optimised for energy content and detonation resistance (the Octane limit has been scrapped)
anyway, if DI speeds combustion that will demand some (relative) lowering of the CR
dissociation also impedes efficiency gains with raising CR, particularly in race engines
(at high powers/temperatures combustion CO2 temporarily changes to CO (witholdng heat), then reverts to CO2 on expansion, the returned heat arriving too late in the stroke to be used efficiently)
by chemistry rich mixtures deter dissociation (but 2014 won't be using them), can the fuel companies work on this property ?
IMO race engine designers have not been stupid or lazy and left a mess for DI to clear up
if DI improves best efficiency on the road from eg 31% to 33%, its advocates won't rush to say that the gain in F1 will be less