P Mack

iTrader: (6)

Is it better to have your injectors close to maxed out so they spray fuel evenly throughout the whole intake charge, or if it would be better to have oversize injectors so you can spray the majority of the fuel at a certain time, like when the intake valve opens.

Or put another way, is it better for fuel atomization to have high injector duty cycle or low duty cycle?

RedHardSupra

iTrader: (1)

great question! i think this is mostly a question of balance, you dont want it too low on atomization, but you dont wanna overwork the injectors either. at the same time, you gotta remember that at lower rpm your duty cycle is gonna show much lower numbers, but it doesn't mean it's atomizing it less because of it, the pressure supplied is still the same. gotta remember that rpm's dont change the duration of the fuel injection itself, but only changes the 'window of opportunity' to do the injection in. the actual flow is dependent only on size of the injector and the fuel pressure. so i'd guess atomization has to do a lot more with fuel pressure than the duty cycle.

or i might be completely wrong, i'm just 'thinking out loud' here

Fedge

iTrader: (3)

good question...my 42s are at 60% DC right now, but i planned on some FI...

GIGAPUNK

iTrader: (2)

I've only heard of atomization being dependent upon pressure.

P Mack

iTrader: (6)

The pressure in the port is changing with the movement of the air and the intake valve. But maybe "atomization" was a bad choice of words. Seems like you would end up with a different distribution of fuel in the cylinder if you injected the fuel in one short burst instead of the injector staying open the whole time.

Old Geezer

iTrader: (3)

The "pattern" will change as the pressure is increased/decreased. As most injs are rated at 3 bars, that's where I flow test them. [Unless specified by the customer.]
The duty cycle, usually, has no effect on the pattern. [I can choose cycles from 3ms/800rpm, to as much as 12ms/10,000 rpm.
I do see some "lazy" patterns on the very large injectors, such as 160#... But, those injs are showing a "fire hose" type spray, anyway.

Back to

RednGold86Z

And just to dispel a possible myth that you may believe, Sequential injection is designed to spray on a CLOSED intake valve. The fuel that reaches the valve will absorb some heat (vaporize too), and then when the valve cracks open, there is a nice blast of exhaust to blow the wet fuel into iddy biddy pieces also. If you spray mostly at an open valve, your atomization will suffer greatly, and the burn will be terrible. Yes, I've tested it.

cantdrv65

iTrader: (3)

Sounds like a high duty cycle itself has nothing to do with efficency....as long as the injector can provide enough fuel.

P Mack

iTrader: (6)

In that case wouldn't it be better to have an injector that's large enough to spray all the fuel before the intake valve opens?

cantdrv65

iTrader: (3)

It probably does that from the factory. Injector timing is more important than duty cycle. At least thats what I make of it.

RednGold86Z

A typical factory sequential injector is sized to be about 60-65% (or even less) max duty cycle. Guess what the "duty cycle" is of the closed-time of the intake valve?

But, injector timing becomes LESS important at full throttle. It's still a little important, but there's tons of flow and turbulence/swirl/etc to get OK mixing. The batch fire systems of the 80's and early 90's didn't have too much problem with it, but sequential is better from an emissions and combustion stability standpoint throughout all operating ranges.

Another good reason for larger injectors is the cold starts at -40°C (or °F), where the PW is ginormous. But, probably no one on here will really want to try that with their sport car.

Bink

P Mack - I dug up these old threads. Might help a little - I've forgotten most of this!



https://ls1tech.com/forums/pcm-diagnostics-tuning/201234-when-does-injector-pulse-start.html

https://ls1tech.com/forums/pcm-diagnostics-tuning/125236-tuning-ace-s-c-mon-debate.html