IGN-1A

Many here ask about the Fuel Injector Flow Rate AND none ask about the size of the fuel particles.
What is the best size ?

G Atsma

And on the heels of that question, how does one achieve said droplet size?

TrendSetter

Doesn’t matter.

Ben.

And on the heels of that, how does one MEASURE droplet size?

For the sake of starting discussion, I'm going to say definitively the the smallest droplet size possible is best for maximizing serfuace area and change of state from liquid to gas, hopefully generating perfect homogenisation of the charge mixture. I have nothing scientific to back this up and would love to hear why I am wrong.

TrendSetter

if your droplet size is too big (but still the correct volume overall) will it not vaporize during combustion?

Che70velle

iTrader: (6)

I haven’t tested this, but I would think you could change the size of the fuel spray (droplets) with varying fuel pressure. More pressure should create a smaller droplet (finer mist) and a lower pressure should create a bigger droplet (heavier mist). Just thinking out loud here really…

Ben.

Not efficiently. I believe it leads to richer and leaner spots in the cylinder, just obviously on a fairly small scale.

All the OE's have gone the way of high pressure direct injection, this would lead me to believe that GENERALLY speaking, smaller droplet size is better on all fronts. I do vaguely recall David Vizard speaking on the topic, there was some situations where it may have been advantageous to have bigger droplet size but from memory it was oddly specific to his Mini race engines.

Full Power

Test Case 1) LQ4 in 1500HD with wrecker boom, 3.73 gears and TOO much cam ( 220/228 ) Stock 25 pound GMT800 injectors, carefully tuned, well sorted VE table: All is well with the world. Cold starts at ZERO degrees, smooth fast warm-up, Defrost action in 3 or 4 minutes from COLD start, great driveability, no problem but obviously TOO Much Cam for 7000 pound truck..
Install crudely DE-Capped injectors ( Bench grinder ) input 70# for injector flow rate: Truck starts immediately, runs well.
Some VE map adjustments here and there.....
Went from 2 immeasurably tiny micro-pinholes to OPEN PINTLE injectors, with ZERO change in driveability, idle quality, no perceptible change in character..
.
Test case 2)
Stock 5.3 LM7 with 188,000 miles, OEM 25 pound truck injectors.
Change to Deatschwerks 60# open pintle injectors: input 60# to flow rate, didn't change another thing: Starts right up, drives fine. slight tweaks to PE and BE tables. No change in exhaust smell, idle character, driveability. part thrttle, full throttle, all the same story. Two tiny little microscopic pinhole injectors are functionally equivalent to an OPEN Pintle in idle quality, driveability, cold start, warm up, etc.
simple answer: Open pintle port injection does the job, and atomization across an open intake valve does in practice occur very nicely.

G Atsma

Looks to me that in spite of decapping, you were STILL getting good (maybe not great, but ???..) atomization. A GOOD injector maybe is the difference here.
Hey, just speculation....

TrendSetter

theres a big difference between DI at 2000+ psi and 3-4 bar as far as atomization goes, and thats not even getting into the chamber distribution advantages of DI.
anything port injection on any engine that a mere mortal owns, gains or improvement from droplet size will be in the margin of error for however you decide to test it. assuming you are injecting the correct amount of fuel, it will vaporize and absorb the same amount of heat by the time combustion happens whether it absorbs that heat in the plenum, intake runner or the cylinder.