Fuel atomization and fuel pressure

toon1 · Post by **toon1** » Tue Feb 12, 2008 4:05 pm

What is the lowest fuel pressure that can be run before it starts affecting atomization??

Keith

toon1 · Post by **toon1** » Thu Feb 14, 2008 9:08 pm

anyone??

AR 67202 · Post by **AR 67202** » Fri Feb 15, 2008 1:12 am

atomisation is always affected by a change in fuel pressure... the question you should be asking is when does the atomisation become too poor...

But isn't that like asking how long a piece of string is? What engine/manifold/Injection system are you using. What is the distance of the injectors from the intake valves etc.. All these will affect the minimum pressure you can run....

Regards,
Steven

toon1 · Post by **toon1** » Fri Feb 15, 2008 7:09 am

The engine is a 992cc, 2cyl. V twin.

The intake is hard to describe. It is on the tall side and from what I can tell is made to create lots of air velocity for low end torque. the openings are about 30mm.

The inj. will be mounted approx. 3 inches above the head (best location I can find for the conversion).

Inj's I would like to use are 21lb./ hr at 43psi. If I'm not mistaken , they are a disc style. they have 4 small holes in the tip.

The engine only nees 9.5lb/hr. In my estimation, this inj. could be made to work if I ran the fp in the 20psi range.

Thank's for the help, Keith

AR 67202 · Post by **AR 67202** » Fri Feb 15, 2008 12:50 pm

any reason they wouldn't work at 43 psi or there about? the only trouble they might give you, and even that remains to be seen, is idling when hot. As long as your minimum injector opening times stay in the vicinity of 2ms you should be fine. If you run your injhection as 2 squirts/alternating you can nearly double your injector opeing times vs 2 squirts/simultaneous..

I'd give it a go as is, maybe you are worrying for nowt... 20 PSI seems low to me though, but there's always the possibility to fabricate something so you can safely watch the influence of the fuel pressure on your injector...

toon1 · Post by **toon1** » Fri Feb 15, 2008 2:11 pm

Thank's guy's,

Lance, the reason I am trying to do this is to reduce the current draw of the fuel pump.

I do have inj's. that are a lower flow rate and are better suited for this app. but would require running the pump at 40psi.

Just trying to weasle around my engine perameters

Keith

AR 67202 · Post by **AR 67202** » Fri Feb 15, 2008 2:18 pm

Lance wrote:AR 67202,

I suspect you mean "injector pulse widths" when you say "injector opening times". In MegaSquirt, the "opening times" are the period during which the signal is applied, but no fuel is flowing yet. It is relatively constant, depending only on supply voltage, and not the number of squirts, etc.

Lance.

I did, but for the life of me couldn't remember the "pulse widths"... thanks for making this clear though...

AR 67202 · Post by **AR 67202** » Sat Feb 16, 2008 1:22 am

toon1 wrote:Thank's guy's,

Lance, the reason I am trying to do this is to reduce the current draw of the fuel pump.

I do have inj's. that are a lower flow rate and are better suited for this app. but would require running the pump at 40psi.

Just trying to weasle around my engine perameters

Keith

Wouldn't you be better off with throttle body injection then? they use much lower fuel pressures, iirc around 20 psi...

or move your injectors as far away from the intake valve as possible. Does the manifold/header get hot when running? It should if this was a carbed manifold/header first...

toon1 · Post by **toon1** » Tue Feb 19, 2008 7:18 am

I looked into Tb injection, this engine is an exposed A/C engine on a boat.

the intake man. has long runners to the head and in cold condtions (which it sees all the time for it's type of use), it will ice up.

The way the engine is set up, there is no problem with intake heating.

Keith