Fuel injector spray pattern

[Mr Peepers]

I was disassembling an old turbo 1g head that threw a timing belt and noticed the intake side was clean where the injector had sprayed fuel. The rest of the intake port was black with carbon. So, I took some pictures

I've always heard not to polish the intake side to prevent pooling/puddling of fuel and leaving it rough to promote fuel atomization and good combustion. Whether this is true or not with fuel injected cars I still haven't seen proof, but I left my intake ports rough when I port matched/blended just in case. I've heard and seen pictures of people even cutting grooves into the bottom of the intake port to promote swirling and better fuel atomization. Maybe bigger injectors have a larger spray radius but still, this gives a good idea at where the fuel hits, and generally where you want to leave it rough/not polished to help you sleep better at night.

This is from a bone stock '91 Tsi with 90k miles. (450cc injectors)
I have more pics if anyone is interested

 

[SlowSpyder]

60 to 80 grit is good enough for intake ports. In a 4 valve head you want to promote tumble of air, promoting swirl is for 2 valve heads.

 

[DSMunknown]

I've always heard not to polish the intake side to prevent pooling/puddling of fuel and leaving it rough to promote fuel atomization and good combustion. Whether this is true or not with fuel injected cars I still haven't seen proof, but I left my intake ports rough when I port matched/blended just in case. I've heard and seen pictures of people even cutting grooves into the bottom of the intake port to promote swirling and better fuel atomization. Maybe bigger injectors have a larger spray radius but still, this gives a good idea at where the fuel hits, and generally where you want to leave it rough/not polished to help you sleep better at night.

That debate is still going on. The folks who are on the side of the corse walls (for the reason you stated) are up against the people who argue for getting the most air into the engine smoothly. (They also argue that an intake manifold with smooth walls will naturally allow for more air to flow into the head because of the lack (or decrease) in turbulence.

I have more pics if anyone is interested

We're always interested in more photos. You should know that by now.

 

[dsm-onster]

Personally, neither have I seen any evidence that fuel, or any matter injected, beads up against a surface smooth or not where there's such a heightened amount of airflow as charge racing through a head intake runner. Any surface that doesn't absorb the momentum (is as elastic as metal) will cause any amount of injected molecules to bounce.

Pool a sip of pepsi (or a discrete amount of beer) on a table top and blow on it. does it move? How fast? Does your piston have enough suction to draw harder and quicker than your lungs? Especially in closed quarters such as a head intake runner. I don't think said molecules will have long enough time to linger so as to puddle. If it bounces, no matter how slight, it is not contacting the runner surface and is moving towards the combustion chamber. If course, this will be debated.

I think the pics are great. It really does show where the fuel hits good w/ good functioning injectors. . . What style injector are you running?

 

[Mr Peepers]

I've been typing paragraphs and deleting them again, and I really don't know what to believe since they are all theories. If anyone has a link to some research I would love to see it, or even any personal experience.

These are the last pics worth showing. A note though, I'm sure the pattern changes when you go WOT and there is more airflow. Most of the time a car is cruising, so this is what the pictures most likely represent.

I don't know what style. Again, these are stock 450 injectors.

 

[Turbo Talon DL]

Im interested in seeing all the spray patterns of fuel injectors people on here commonly upgrade to. I have found a few on the net VIA Google search, but not as many as I would like. I have seen the FICs, and a couple other ones, but not enough of them to decide EXACTLY what I want. I did a search on the forum but didnt yeild anything either, so I decided to help other people become educated.

RC Engineering modded:
YouTube - RC 1300cc Modified 850cc RX7 Injectors

Stock injector spray pattern:
YouTube - DSM 450 Black Top Vs Blue Top Spray Pattern

FIC hooked it up with a nice educational DEMO:
YouTube - fuel injector

Not necssarily DSM injectors, but they demonstrate different styles and when you use too much fuel pressure.

 

[Grimis]

Turbo Talon DL, nice vid's

 

[spoonman]

I believe that the rougher walls on the heads intake ports are unneeded in fuel injection engines. The distance that the fuel travels combined with the vacuum at high RPM's should keep the fuel from ever pooling or beading on the walls of the port. In carbureted engines the fuel is pulled by vacuum at the top of the intake manifold and travels down through the intake and into the ports. With such a long distance the air/fuel mixture needs to have turbulence to keep the mixture atomized, but the carb. engine also has to make the mixture travel at least 11 inches for each individual intake and runner, while in fuel injected engines the mixture only travels 2 inches. Also if you look inside of a properly tuned carb engine's intake the start of the runners will have alot less deposits than at the end and in the intake port.

 

[Turbo Talon DL]

How about a look at these spray patterns INSIDE an intake manifold. Would anybody, particularly the Wisemen, know where to see something like this? There was a website that only said colleges and universities blah blah blah....some sort of doppler imaging hardware shows spray patterns inside an intake port with air moving through.

 

[SBR Joe]

The reason for not having the intake ports smooth is to prevent fuel from pooling. It helps keep the air/fuel mixture suspended.



Joe
SBR

 

[delta448]

I'm not an expert on head design or porting/polishing by any means, but I believe that the issue of fuel pooling is non-existant in a turbocharged engine operating at normal temps. The higher intake air temp of forced induction atomizes and holds the fuel pretty well.

From my understanding, the issue is only when the engine is cold started. The fuel falls out of suspension when it hits the lower pressure in the cylinder and loses it's momentum while the vapor is rolling all along the cold metal surfaces of the cylinder walls and piston, kinda like condensation on your beer bottle.

The intake runners are usually shaped and tapered so that they don't offer a place for fuel to build up even if there wasn't a buttload of air rushing through with increasing velocity per length. But pistons are often dished out or have valve reliefs that will hold fuel puddles. That's apparently why cold starting requires the incredibly rich mixtures it does, gasoline only burns once it turns back into a vapor. A lot of the cold-start gas is still burning after the exhaust valve opens.

The effects of a coarse surface on the intake side as much as I can speculate would only cause resistance to flow and a more turbulent intake charge. Some turbulence is probably good, most modern heads are designed with a small amount of turbulence inherent by the engineers on purpose to promote fuel economy and efficiency. However, too much turbulence (like if someone cut a spiral groove in the runner) could possibly dilute the charge near the plug and swirl-throw fuel toward the cylinder walls. -Again, let me say that this last paragraph is only speculation and is completely just my opinion. You are welcome to disagree.

 

[dsm-onster]

The effects of a coarse surface on the intake side as much as I can speculate would only cause resistance to flow and a more turbulent intake charge. Some turbulence is probably good, most modern heads are designed with a small amount of turbulence inherent by the engineers on purpose to promote fuel economy and efficiency. However, too much turbulence (like if someone cut a spiral groove in the runner) could possibly dilute the charge near the plug and swirl-throw fuel toward the cylinder walls. -Again, let me say that this last paragraph is only speculation and is completely just my opinion. You are welcome to disagree.

I think ... you are describing tumble. Which I agree, promotes atomization. The floor of the 1g ports look to do a better job than 2g ports by far. Tumble keeps the fuel in suspension longer before tuning to droplets. Droplets lead to detonation. High squish chambers (quick burn) are designed to limit the time a fuel/air charge looses fuel suspension and the drops ignite with their flame front colliding with the original, causing knock. High tumble keeps fuel in suspension longer. Port design, not just port wall surface ruffness, affects tumble and detontion characteristics.

 

[romeen]

In the third video that Turbo Talon DL linked to the Lucas injector (3rd from left) has more of a stream/narrow pattern as opposed to a mist. I thought that this is always bad. The guy says that he doesn't recommend it in a street car but that it works well in a turbo application.

Does anyone know why that is?

 

[Turbo Talon DL]

How about a look at these spray patterns INSIDE an intake manifold. Would anybody, particularly the Wisemen, know where to see something like this? There was a website that only said colleges and universities blah blah blah....some sort of doppler imaging hardware shows spray patterns inside an intake port with air moving through.

I like the replies and everything so far. It all sounds like it makes sense and no misinformation. I know that inside of an intake runner any spray pattern will be distorted. Some more than others probably. Even for how differently each car is modded im sure theres no 'one size fits all' for injectors (cost aside thats another factor). There has to be different reasons for all the spray patterns that exist and we need to see how they look distorted by the rush of incoming air. Phase doppler particle analysis is the name of the procedure.