Injector Spray Patterns

[Neal H]

Hi all,

Some more questions from me! I have just seen some on-line video footage of different types of injector "in action" so to speak. There appears to be different types of spray pattern from different OE injectors for different applications, according to the website by design. For example, some injectors that spray in a distinct V shape (supposedly for multi-valve engines with a jet aimed down each inlet tract), some where a fine mist is produced, and some others that have a single almost straight jet. My questions are:

Is this true that there are different, deliberately designed spray patterns for different intake designs?
If there are injectors designed for specific applications, is there one design that is superior to others, or would turbulence in the inlet tract completely negate any specific spray patterns?
Are there any performance advantages to running low impedance injectors over high impedance injectors if given the choice between them?

Thanks as always in advance for any advice,

Neal.

[Neal H]

Now, I have been thinking about this a bit over the festive period, and also trying to find some more information on the internet. From what I have read, and my assumptions, injectors that provide the finest mist of fuel should ensure the inlet charge has the most even mix and help efficent clean combustion.

As per this thread on GCRE viewtopic.php?f=13&t=914&st=0&sk=t&sd=a ... y&start=15 it appears that people have had better results running smaller injectors at higher pressure - I would assume to be because the fuel would be forced out faster, and in a finer mist. Also, at higher engine speeds, the air will be flowing faster than the fuel coming out of the injector (approximately twice as fast at 6500 rpm if the info in this post is correct viewtopic.php?f=4&t=1109&hilit=injector+spray). I would assume that the faster the fuel comes out of the injector, the less it will slow the incoming airflow, even if this is only a tiny amount.

Regarding the injector spray patterns I have seen, I would like to post a link to the videos here to illustrate the footage I have seen, but I am unsure about copyright etc so I won't. In summary, the injectors that spray in a V pattern may be suitable if the injector is close enough to the ports to actually direct the fuel where it is intended, however, if the injector is too far away the fuel would be directed towards the port walls, probably not desirable. I would also expect a well designed and fettled multi-valve cylinder head to draw the same volume of air towards each valve, therefore a fine mist would still be distributed evenly.

As I stated earlier, these are only thoughts and assumptions, but from a common sense perspective these would make sense to me. If anyone can help clarify my thinking, or qualify with experience that would be very much appreciated.

Thanks again,

Neal.

[Guy Croft]

Sorry Neal,

injector spray patterns are not one of my strong points! I have heard various reports from folk more expert than I, but nothing definitive re the effect of different injector patterns has yet been put forward.

If anyone has indisputable proof from their own in-house back-back tests that one or other setup makes a difference good/bad (on the same engine naturally) you're welcome to comment.

GC

[CraigAPD]

Generally spray pattern in modern OE petrol engines is biased towards emmision reduction. I would hazzard a guess that the actual nozzle design would be tailored to port shape. Consider an injector pattern which sprays a large diameter "fan", if this diameter is too large, a large portion of the fuel will be deposited directly on the port walls. Obviously this isnt good for atomisation, and thereofre not for power or emmisions.

As Guy says there is little factual "this is best" type proof, alot of it is suck it and see and personal preference (for whatever reason).

As for impedence, this will depend on the driver in the ecu and its ampage capability.

[Neal H]

Would a fine mist that spreads in the fast moving airstream in an inlet port "stick" to the port walls, or would the faster moving air in the middle of the port keep the majority of the fuel away from the wall? I guess it depends on lots of different factors, for example, what would be the impact of turbulence on the homgenity of the incoming charge? Would a powerful vortex serve to "throw" the fuel onto the port walls? Also, injectors that have a particular spray pattern would only work at the exact distance, angle and alignment, and with aftermarket injectors, who knows these precise characteristics. This is looking more and more like a potential minefield!!

As a side note, I will be running a DTA S80 Pro with 5 amp outputs.

Thanks again for your help,

N.