Fuel Atomisation

[Greg Hermann]

>> Most port EFI designs deliberately injects the fuel onto the back
>> side of the _closed_ intake valves (or somewhere in that vicinity,
>
>They do so to meet emission requirements; specifically HC. There is
>a finite probability that some fuel droplets survive the combustion
>process and will only go out the exhaust pipe as they vapourize.
>Regardless of the mode of fuelling.

The bigger the droplets, the higher that probability. Try taking a peek at
the HC emissions of a properly tuned engine equipped with DCOE's. at WOT.
It would appear that not many droplets survive , at all, in this case !!
>
>If you don't have to comply with emission standards, you can open
>your injected whenever it pleases you.

True. But only because typical injectors give terrible atomization.
>
>> if they are lucky) at a point in time when there is little, if
>> any, air velocity in the port. This is done so that the heat in
>> the valve, combined with the reversion of exhaust gas into the
>> intake during overlap will _vaporize_ the fuel, and thus
>> _compensate_ for the (conventional) port injector's inability to
>> atomize it very well at all.
>
>Droplet sizes?

Vary all over the place. Sometimes relatively huge. (100 micron, at least)

Do your own research!!
>
>> The heat that is taken from the intake valve to vaporize the fuel
>> is robbed from the next cycle. Thus the deterioration in thermal
>> efficiency. The vaporized fuel displaces a great deal more O2 in
>> the inlet charge than atomized liquid fuel does--thus the
>> deterioration in volumetric efficiency.
>
>Oh, it's robbed, is it? Basic thermal efficiency (Carnot) is
>determined by the hottest and coldest phases of the cycle. The
>greater the difference, the greater the amount of work that can be
>done and hence the greater the power output of the engine.

Gee --Sounds as though you took a course in basic thermo after all !! But
cut the class where they explained that the cycle would fall below the
theoretical efficiency if the processes were not perfectly adiabatic !

>
>Furthermore, injecting onto the back of the inlet valve cools the
>valve, reducing that as a being a catalyst point for detonation.

B.S. !! You are blowing smoke, trying to sound knowlegeable without having
a clue. The intake valve is one of the cooler parts of the chamber to begin
with !!

Greg


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