General > General Technical Chat
Getting an electronic fuel injector to only open partially
langwadt:
--- Quote from: ELS122 on June 04, 2023, 05:13:44 am ---
--- Quote from: bdunham7 on June 04, 2023, 04:39:01 am ---
--- Quote from: ELS122 on June 04, 2023, 04:16:06 am ---The reason I want this is to be able to adjust the fuel particle size on-the-go. To maximize engine efficiency over the entire rpm range.
I'm not very concerned about the impact of fuel flow when the injector is partially open, since I can compensate for that later and I just want something that gives me an adjustable particle size first.
--- End quote ---
What effect on fuel droplet size do you anticipate from various pintle positions? I'm just curious...
As for hanging a solenoid valve in an intermediate position, I think it would be pretty tricky. You would have to do something like using a PWM signal and then somehow measuring the pintle position (via a change in inductance) in between the pulses using some sort of test signal. Or something like that. I don't think typical port injector changes inductance much during the intermediate phase that you are looking to stabilize, so...
--- End quote ---
Well a big difference, smaller outlet orifice = higher velocity = more breakup, atomization.
The problem is that fuel injectors are already meant for PWM, they are PWM driven to control the fuel flow by changing the duty cycle, and at 8000rpm, the whole intake cycle happens in around 2 miliseconds, and in that time span they're PWM controlled... who knows how extremely fast you'd have to drive them to control the position... 10khz? 100khz?
Oh and btw they are normally triggered at a much higher current, triggered around 11 amps then held with 500mA. presumably to make them open faster, and when they're open lower the current so they dont melt
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what type of injectors is that? direct injection gasoline?, they are surely not the usual injectors used in port injection gasoline engines
mendip_discovery:
I dont have my usual contact to ask about this (ford fuel injection nerd).
But my 2p, it takes a given time to open completely could you only pulse long enough for it to open a small amount. Even dropping the current so it opens slower.
Alternative idea is to add some extra smaller injector for the lower speeds and swapping over to larger ones.
bdunham7:
--- Quote from: ELS122 on June 04, 2023, 05:13:44 am ---Well a big difference, smaller outlet orifice = higher velocity = more breakup, atomization.
The problem is that fuel injectors are already meant for PWM, they are PWM driven to control the fuel flow by changing the duty cycle, and at 8000rpm, the whole intake cycle happens in around 2 miliseconds, and in that time span they're PWM controlled... who knows how extremely fast you'd have to drive them to control the position... 10khz? 100khz?
Oh and btw they are normally triggered at a much higher current, triggered around 11 amps then held with 500mA. presumably to make them open faster, and when they're open lower the current so they dont melt
--- End quote ---
You're making a lot of assumptions that you should consider more carefully. There are a lot of different specific types of injectors and they all have different designs and drive requirements. I'm pretty sure that there are many that will behave pretty much the opposite of your stated expectation. Also, not that it matters to your original question, but the injector on-time is typically not correlated with the 'intake cycle'; the specifics of that are the subject of quite a bit of research and testing when an engine is designed.
Gregg:
It certainly is difficult to out engineer large companies that specialize in trying to gain fuel economy in order to achieve government mandated regulations.
But maybe you could consider adding compressed air ahead of the injector to make an air-fuel emulsion similar to the way air bleed orifices worked on carburetors.
Miyuki:
Most fuel injectors are not spraying from the needle but from an array of tiny precisely machined orifices in a plate on its tip
Opening the valve just partially will decrease the spray pressure, so it will just make big droplets
Such ancient injector construction was used on throttle body injector with very low pressure spraying at the throttle plate and just evaporating the fuel in the long intake manifold
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