Quote:
Originally Posted by cRiPpLe_rOoStEr
Sure cooling the water prior to injecting it might render some benefit, but would it offset the energy eventually spent in order to provide such cooling? And the weight of the cooling setup too.
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David Vizard tends to ..er.. 'carry on' and lose the plot a bit now that he's older
but a good video on water injection none-the-less:
From what I have read; evaporative cooling does not care what temperature the water is at:
If you add almost boiling water to a swamp cooler, it cools the air just as effectively as ice water but uses way more water.
"Physics..?!"
NB that boiling point increases with pressure, so not much of that going on during the compression stroke.
Then there's the pressure of combustion... so steam likely only forms after the main combustion event, when pressure drops enough.
(And when the crank-conrod is at a better angle for producing torque..!)
In Short:
Evaporative cooling is the greater effect by far vs plain old conductive cooling. IMHO.
Cool water means less air/oxygen space-taking evaporation during the intake stroke so that it happens/cools more during compression when the gas volume is trapped.
There may be a maximum threshold or optimum temperature for that..?
But it's not used in std water injection systems like that used on the BMW M4 GTS.
(Also NB the Steam Reformation Reaction:
HC+H2O=H2+CO (CO also burns but weakly/slowly)
This reaction, used in the industrial production of Hydrogen. is likely to occur at the higher pressures and temperatures at the end of compression and during combustion.
Pity it has so little time, but I wouldn't be surprised to find a slightly increased H2 concentration just before and during the combustion stroke.
Catalysts help.
)
With a pre chamber we are interested in cooling the much richer, closer to stock AF ratio charge in the pre chamber only.
Not the super lean, needs lots of pre heating/temperature just to catch fire mixture in the main chamber.
The rich mixture in the chamber is due to the fact that the piston is moving very slowly at/around TDC.
Only ~4mm for 40 degrees, including a very brief dead stop at TDC.
ie; As the same amount of fuel is being inject at this slow air intake point in the stroke the mixture is much richer during this pre-chamber filling time.
So a small quick squirt of (cooled?) water at this point will cool the pre chamber charge during compression avoiding the ...er... 'pre-knock' plaguing pgfpro. Hopefully!
Easy for him to try... if the water injector is (aimed) in the right place in the intake tract..?
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