FUEL INJECTION, Petrol

[Lakc]

We know that banked mechanical fuel injectors work, although not that efficiently (but more efficiently than carbs). We have systems that control high impedance PWM injectors for full sized engines. Is it possible to use the PWM control to bank fire a solenoid on the front end of a very high pressure fuel pump (like the bosch mechanical fuel injection uses) which feeds simple carb type sprayers? Then the electronics and valving don't have to be scaled, just the orifices in the mechanical injectors and feed lines.

Sure, there are plenty of ways to skin that cat, so to speak. It really boils down to personal preference and familiarity, as well as how much of your time budget you want to spend on the engineering.

 

[keith5700]

I did think of a system along those lines,where a single solenoid opens and feeds 8 nozzles, each having a spring loaded non return valve. After pondering for a while I decided it wouldn't work very well at low engine speeds and idling. The quantity of fuel at these times would be miniscule and possibly even the flexibility in the feed line sidewalls would absorb the fuel pulse, rather than the valve actually opening.
Even if the spring valves did open then the chances of them opening at the same time/rate would be virtually zero.

My current thinking is to keep the solenoid as big as I can, to negate the effects of scale as much as possible.
This means using just one or 2 injectors, hidden away inside a plenum chamber, like my full sized motor.

They would have to spray fuel just behind the throttle body at the front, hopefully keeping the fuel atomised as it gets sucked in.

8 injectors would be great but the more I think about it, the less realistic it looks.

Thanks for replies so far.

 

[mu38&Bg#]

I see nothing wrong with a TBI system. It would still be very unique.

 

[milotrain]

Lakc, what I meant was that the custom EFI systems that are already designed for us could be used to trigger solenoids rather than injectors and therefore be scalable without having to reinvent an ECU.

Microsquirt/Megasquirt works with TBI systems as well (not trying to shill for the electronics, just that they really seem to fit your needs). For small engine systems I think TBI makes a lot of sense.

 

[Lakc]

I dont want to come off as a buzz killer in this thread. In general, yes, but in practice, megasquirt might have its cells hard coded into a bunch of totally unusable rpm ranges for a specific engine. Thats kind of the way it is with fuel injection, where some of the simplest things have unforseen consequences.

 

[milotrain]

That's the cool thing about MS, it's not hardcoded at all. It's opensource so if you have any programming acumen then you can make it do whatever you want, but it's got the hardware handled for you so it's not as roll your own as coding your own pic.

I'm not trying to defend it or anything, it may very well be a horrible solution, but it's worth looking at.

 

[Lakc]

I am not trying to knock it, playing devils advocate is sort of an occupational hazard with me. :

 

[LongRat]

I'm still unsure whether the solenoids are even required, in the most basic configuration. Certainly Schillings doesn't use them. What about using and airbrush type nozzle for the injectors? They can deliver a tiny amount of fluid when set to their minimum opening.

 

[keith5700]

I've not read the Megasquirt manual yet but I'm sure it'll control anything I can throw at it.
The problems are the injectors and the fuel pump.
I'm saying they're a problem, but I've not had time to look into it yet, so they may be doable.
I think the best spray pattern at this sort of scale will be a single small hole, airbrushes use a large hole with a tapered needle to regulate the paint flow. I guess the nice atomisation comes from the air rather than the paint nozzle.

 

[Billzilla]

Hi Keith.
(bump time)

I have mucked around with fuel injection on full-sized cars a fair bit and the easiest way to get the fuel scheduling right for you engine is to just use throttle position Vs rpm for load sensing. It's as simple as you can get and works fine; I used it on a couple of engines a while back.
Here's an example of a load map. It's for the Motec M4 ECU that was I using at the time.

I can help with most things you want to know about EFI as well ....... ( I hope!)