Ways to make the fuel evaporate right after the intake valve closes

[ELS]

I know this is like asking how do I pull a rabbit out of the empty hat. But maybe you have some good ideas for this.

So at low rpm the air flow will be somewhat lower in the intake, and the fuel will have more time in the intake, so the fuel should enter the intake closer to the combustion chamber, but at high rpm there's not enough time for the fuel to vaporize so the fuel should be injected farther away.
I've seen many sport bike engines have 2 sets of injectors for this.
But what if instead you change the physical position of the fuel injectors? something like a system where the injectors are on rails inside the intake runners and move depending on the rpm,temps, etc.

Another idea is "loosely" heating the intake manifold, so at high rpm the air and fuel will cool the intake so the fuel would naturally evaporate less, but at low rpm low load it would heat back up. This would not respond quickly tho, maybe if the intake was made out of thin polymer it would have little enough thermal mass to be usable but idk.

Is there a variable spray pattern fuel injector? sort of like the thing you get on spray bottles where you can adjust the orifice size to change the particle size. If that was then motorized it could be used to adjust the droplet size and would fix the problem.
Or maybe a variable pressure injection system, and then pair that with injectors that change the particle size depending on the pressure, so less moving parts.

[ELS]

A variable particle size booster could probably be also implemented in a carburator, Have for example an annular booster, then add a spring loaded sleeve inside the booster with the fuel exit holes, taper them.
When the air flow trough the booster increases it pulls that sleeve down and reduces the droplet size.
But then there's the problem with the booster signal which a design like this would nearly keep constant so fuel metering gets shut down.

I was thinking of trying to undervolt an injector, it most likely will work poorly but I'll see if it does produce a finer mist as expected.

[rgalajda]

A variable particle size booster could probably be also implemented in a carburator, Have for example an annular booster, then add a spring loaded sleeve inside the booster with the fuel exit holes, taper them.
When the air flow trough the booster increases it pulls that sleeve down and reduces the droplet size.
But then there's the problem with the booster signal which a design like this would nearly keep constant so fuel metering gets shut down.

I was thinking of trying to undervolt an injector, it most likely will work poorly but I'll see if it does produce a finer mist as expected.

For a carburetor all you need to do is run an annular booster in the primary with a dogleg booster in the secondary. Already been done long ago on some of the OEM factory carbs including the Ford 4100 carb in the 60's and again in a Holley carb by Ford in the 80's.

[ELS]

A variable particle size booster could probably be also implemented in a carburator, Have for example an annular booster, then add a spring loaded sleeve inside the booster with the fuel exit holes, taper them.
When the air flow trough the booster increases it pulls that sleeve down and reduces the droplet size.
But then there's the problem with the booster signal which a design like this would nearly keep constant so fuel metering gets shut down.

I was thinking of trying to undervolt an injector, it most likely will work poorly but I'll see if it does produce a finer mist as expected.

For a carburetor all you need to do is run an annular booster in the primary with a dogleg booster in the secondary. Already been done long ago on some of the OEM factory carbs including the Ford 4100 carb in the 60's and again in a Holley carb by Ford in the 80's.

That's the reverse of what you want for ideal evaporization time.
That is tho the ideal setup for descent booster signal which is probably gonna give you more gains on a carburator anyway, more than making sure the fuel is properly atomized

[juuhanaa]

You must have already considered changing the injector spray timing?



-juhana

[ELS]

You must have already considered changing the injector spray timing?



-juhana

But that's such a band-aid. It also would add a ton of other problems.
Of course you could get a very fine mist injector with a lot of flow capacity and then just time it when you want it.

But I'm talking about actually making/modifying an injector to give varying particle sizes, depending on some input signal.
It would give you godly control over the engine's performance, think of not needing to enrich the afr at cold temps, no need for heated intake/throttle body, no double-sets of injectors to have more-optimal high rpm performance, less carbon deposits because of better evaporation, ability to tune the combustion speed (because you can make it so barely any fuel atomizes so when combustion happens, for the flame to spread it first needs to evaporate it by the increasing combustion pressure and temp, effectively a very shitty way to slow down combustion)

I mean the benefits are endless, the problem is probably how to implement it.
Also pair this with a changing length intake runners, like an ITB setup with the velocity stacks changing size automatically, together with the air filters for each throttle body. You could optimize the engine to have intake ram tuning at every rpm, also fix dips in the torque range from wacky flow by changing the fuel particle size or runner length to get that wackyness out of there.

[juuhanaa]

What if the port injector is positioned so that droplet size is altered as the port velocities changes with lift?

Im thinking about what happens if fuel is injected into the vena contracta, and its some distance from the valves after mid lift and up Thanks for reply,



-juhana

[ELS]

You could maybe make the inner sleeve for the booster somewhat like this

booster idea.png

When the inner booster part gets sucked down by the air friction at high load and rpm, the inner sleeve fuel holes get bigger, but the outer booster part body restricts the flow. The inner holes getting larger are to account for the booster signal loss when this happens.
So the area of the fuel holes stays around the same, but the shape of the fuel holes changes from an almost square hole, to one that's a very short but wide rectangle.
So the fuel particles get smaller but since the area stays the same, the booster signal doesn't diminish.

The orange thing is the spring that will keep the inside part up. It will resist the air friction induced force on the inner booster part so you could tune the flow at which the particle size starts getting smaller by changing that spring.
(I forgot to draw the part that blocks the top holes, so it should be just a band of fuel around the fuel exits

[ELS]

I just realized carburator boosters do this already.
The higher the air velocity across them the more the fuel breaks up.

Also my design wouldn't work, the area doesn't actually stay constant.

Does this mean that technically a carburator could be tuned to give a overall higher VE than with fuel injection? Maybe... There's still the fact that there would need to be SOME restriction as a venturi so "static" VE would be lower but when you count in the fact that a carburator may be tuned so that fuel almost always atomizes at the preferred time, the "dynamic" VE could be higher... quality of burn could be better... etc.

I'll rig up some jig to test the injector particle size at different solenoid voltages next.
The response will probably be unusable at a reduced voltage but maybe if you first drive it with a higher voltage on the "attack".. then reduce the voltage so the needle moves slightly back and restricts the nozzle to break up the fuel more and lead to a smaller particle size.
Consequently the lowered fuel flow could be addressed by higher duty cycle, Doing it automatically at lower voltages then fine adjust with the O2 sensor feedback as usual.

[ELS]

Nope, can't undervolt injectors. It's just an on/off switch, with lower voltages it wont trigger, if I trigger it with a higher voltage then go back to a lower one, either the voltage is too low and it turns off, or it sprays the exact same way as normally.

Maybe I could talk a fuel injector company into making injectors with adjustable particle sizes?

[juuhanaa]

I dont understand where are you going with this, i mean cant we alter the droplet size already like we want by choosing the injectors, theyr location, fuel pressure, and timing?

Further all of these also have some effect on how the engine runs, which again changes the droplet size in the intake track.

What if the port injector is positioned so that droplet size is altered as the port velocities changes with lift?

The above comment was not about designing of a new hardware, rather could we perhaps use the existing one in a new way? What happen if we apply pressure or vacuum in a liquid form into a vena contracta where mostly air flows? Does it increase the mass flow / velocity and thus affect the droplet size? Just a thought, thanks.



-juhana

[ELS]

I dont understand where are you going with this, i mean cant we alter the droplet size already like we want by choosing the injectors, theyr location, fuel pressure, and timing?

Further all of these also have some effect on how the engine runs, which again changes the droplet size in the intake track.

What if the port injector is positioned so that droplet size is altered as the port velocities changes with lift?

The above comment was not about designing of a new hardware, rather could we perhaps use the existing one in a new way? What happen if we apply pressure or vacuum in a liquid form into a vena contracta where mostly air flows? Does it increase the mass flow / velocity and thus affect the droplet size? Just a thought, thanks.



-juhana

You can't change injectors, their location on the go.
a high pressure injector wont be affected by the intake runner air velocity, droplet size is nearly constant.
It only is optimal for 1 condition, at higher rpm fuel isn't evaporated in time, at lower rpm it evaporates too quickly and you loose VE.

I already said, it doesn't work. I just tried it. a standard injector wont allow it.
Maybe if you modify the solenoid or something idk...

I figured out how a constant flow rate with varying droplet size could be achieved. like this:

injector idea.png

So as the injector opens, the more the magnet moves the needle the bigger the particle size.
To maintain constant flow rate the other end of the needle starts to restrict the supply flow.
Or the other versions which does the same thing just a bit differently.


You might be able to get a carburator-like effect by putting something in front of the injector, so at low air velocity it sort of like flows around the obstruction, but at high velocities the fuel gets sheared on some sharp edge...

[juuhanaa]

Think something extreme like the venturi air blower principle, but powered by a fuel injector. More revs / more fuel and more flow. The fuel injector now makes the port flow more, which i dont think can be done with a carburetor / EFI advantage; we can just give it fuel, if it works with liquid



-juhana

[ELS]

Think something extreme like the venturi air blower principle, but powered by a fuel injector. More revs / more fuel and more flow. The fuel injector now makes the port flow more, which i dont think can be done with a carburetor / EFI advantage; we can just give it fuel, if it works with liquid



-juhana

Well yeah the velocity of the fuel could increase VE...
Perhaps pointing the injector right at the top part of the valve, boosts air velocity a bit. also decreases pressure at the back of the valve which could promote tumble in the cylinder.
Btw the injector I was testing was an early 90s subaru injector. It is a cast aluminum body, quite large, 5 holes at the tip. high impedance
I'll try a standard type injector later, the plastic body needle type.

[jsgarage]

Not voltage changes but varying fuel pressure to change droplet size. I've noticed in the YouTube films that at 40 psi, the same injectors seem to create a coarser looking mist than at 55 psi. And changing fuel pressure with voltage seems easy since nearly all EFI injectors are already electric-fed. But maybe there's something funny going on, as D Vizard and others have noted a very fine gas mist changes power levels- sometimes up, sometimes down. More testing!