NXRICKY

iTrader: (1)

This week not realy a tech tip, wanted to discuss fuel puddle-ing. This is just opinion something to think about.


Puddel-ing myth or fact.

What is puddle-ing?
Can it cause a backfire in my intake?
Why is this term used so often?

pud·dle P Pronunciation Key (p d l)
1.
a.A small pool of water, especially rainwater.
b.A small pool of a liquid.

Puddleing is a term used to described fuel collecting in an intake on the walls or in the floor of an intake.
Puddle-ing cannot make a car back fire. The fuel will not self ignite in this arena. And fuel cannot puddle in an intake.
The term is over used to describe a backfire. People will say “It is always the nitrous’ fault” when there is backfire while using nitrous. “It puddle” This thought process is simply because it is so violent when it does happen.
I have read the posts over the last few years about fuel collecting in an intake. OK
And the lean backfires. Ok

Question is “what lit the fuel in the runner”. What cause the flame to come into the intake side of things and light the fuel nitrous mixture in an intake? I believe it has to do the velocity. Airflow coming into cylinder must be decreased some how for the flame to be allowed into the intake track. This is why all nitrous companies tell you not to spray an engine below 3000 RPM’s. The nitrous injecting into your engine has a higher velocity then the actual engine cfm flow at that rpm. Air stalls or slows down just enough for the flame in the combustion chamber to come back up into your intake port and then you have a backfire. .
Also you will only be able to put X amount of nitrous and fuel into and engine. Being that it is an air pump the pump can only move so many cfm’s and a nitrous system can not pressurize the intake track. (non-boosted applications)

Damp areas are not going to light themselves; if there were any damp areas in an intake. Areas that are wet after an intake has been ran on car are from vapors that are hanging around once the car is turned off.

Air hushing into a cylinder helps push the unburned and burning media into the exhaust. If you ever started a car without a header or exhaust manifolds on; you have seen the flames. So as long as velocity is kept up no problems, this is a per cylinder way of looking at it.
Air travels though a 347cubic inch engine at __156__ mph at 6500 RPM with a 75mm throttle body. Now lets say from the backside of your throttle body to the exhaust port is 3 ft. It only takes air .0131 of a second to go from the throttle body to the exhaust port. So in no way can the fuel puddle in an intake. There is not enough time.

Note that these calculations make some assumptions like non-turbo, and airflow is equal to displacement, etc.

This is just my 2 cents on this matter.

Ricky

dug-e-fresh

I see it more as a cam timing/ignition timing thing. For the flame front to enter the intake the intake valves have to be open. Stock cams have overlap, aftermarket cams generally have more overlap (and more lift) and with the use of most programmable engine management systems, the end user can change the ignition parameters thus possibly igniting the mixture too soon (intake valves still open) causing the flame front to enter the intake.

Also to consider, the 4 stroke cycle. Exhaust is expelled via exhaust valves, piston is heading to TDC. Piston reaches TDC, exhaust valves begin to close, intake valves begin to open (overlap), exhaust valve fully closes. Then the piston reaches BDC and begins the compression stroke and the intake valves are closed/closing. Now sometime in the compression stroke is where ignition takes place (X degrees before TDC).

I imagine if someone was running too much advance, the intake valves could still be open when ignition occurs.... thus causing intake back-firing.

As for the puddling effect, I have read that getting fuel to pool (puddle) on the back side of the intake valve is common way in the racing world to push the injectors harder, essentially purposefully having the injector open while the valve is closed so when it does open theres more fuel available than if the injector waited to spray after the valve opens. Those precious milliseconds could make the difference in too lean or just right.

I am by no means an expert, but thats my thoughts based on what I know or think I know to be true.

def

Robert56

iTrader: (2)

A little input, lets say you have a pre-ign/ dentonation hot spot and when a cylinder opens it intake valve (intake stroke) it allready has a ignition source before power stroke and if puddling theres your fuel source and boom. Now, valve overlap can play/be problematic in this type of senario also because of un-burned fuel and hot spot/detonation.

Brains

iTrader: (7)

Another fun tidbit -- liquid gasoline isn't explosive ... Vaporized gasoline is ..

CAT3

iTrader: (9)

If this is an issue, I would think it would occur more so when spraying at low rpm where the intake charge is moving slower, the fuel not staying atomized as much as and laying against the sides of the intake and back wall. Although I dont want to prove any of these theories
The only mishap I have seen/heard of, is spraying nitrous in an engine not running and then upon cranking......pow goes the intake, which happened at a shop once.

NXRICKY

iTrader: (1)

During crank the is next to no velocity, and since the nitrous fuel mixture is just there and the first spark did light something in the cylinder but not enough air flow to get rid of it.... your right boooooommmm.....
Ricky

Stroker 1500

iTrader: (1)

I have another question.. Kinda related, how crucial is the nozzle placement on a wet system? can it be mounted bellow the throttle body or really close to it? Just something i have been wondering

NXRICKY

iTrader: (1)

Here is the skinny on nozzle placement... This applies to all cars and intake configurations..
You always want the nozzle as far as possible away from the throttle body this will also put the nozzle farthest from the first turn inside the intake... So if you put a Shark nozzle after the throttle body on an LS1 engine, there is a good chance that the nitrous and fuel mixture could miss the first runner in the intake. What this can do is to put the nitrous mixture into fewer cylinders giving you an unhappy engine.
Ricky

Robert56

iTrader: (2)

True story, but there's more, if you have puddling (fuel dropping) there is going to be vapors from evaporation and the intake charge flying by and correct me if I'm wrong, if you ignite the vapor then vapor burns to the puddled fuel. Listen to a wet car at the end of a run slight popping/backfire from extra fuel dropping to intake on deceleration. If you have timing issue or a hot spot you can get a hood removal.

white2001s10

iTrader: (4)

The only place that there is liquid gasoline without also gasoline vapor, is in the fuel lines, so this really isn't a relavant point.

In a running engine there is always gasoline vapor and free oxygen inside the intake manifold.

Wet systems will indeed create puddles of liquid fuel on the plenum floor of an LS1 intake manifold where it mixes from all the PCV oil that is already collected there. Then you basically get weedwacker fuel.
Letting off the throttle at the end of a pass creates a very high vacuum in the intake plenum. The good part about this is that the low pressure will greatly speed the evaporation of the weedwacker fuel on the plenum floor.
The down side of this low pressure is that it will pull exhaust flame up into the intake runner during the overlap period of the camshaft.

Just another reason why the typical wet system is not the way to go with an LS1.

white2001s10

iTrader: (4)

Fact, yes absolutely.

False. An extremely rich condition in the intake can indeed cause a backfire when the pressure in the intake drops. No it's not the nitrous' fault at all, but is completely a fuel problem caused by wet kits.

As I explained in my previous post, the extreme low pressure from closing the throttle at high RPM pulls flame up the runners during cam overlap.
There are also times after revving an engine up with hydraulic lifters that the exhaust valve can hang open a few degrees longer due to "pump up", until they once again reach their normal equalibrium.
Large overlap camshafts and lifter pump-up both increase the window for backfires in an intake manifold.
The backfire equation is then completely when an extremely rich air-fuel mix exists inside the intake manifold that will readily ignite.

You can simulate this backfire by disabling DFCO on any port injected EFI system. The backfires will be smaller due to the absence of the "wet kit".

For an LS1 with a small or stock cam, it is also possible for the engine to simply die at the end of a run because of the over-rich idle. People that shift to neutral at the end of the run have this happen often. It's annoying but better than the explosion

V6 Bird

iTrader: (15)

THats not always true because it can be from exhaust leaks too. So you cant say that it is from fuel puddling!

Mike

97LT1

iTrader: (3)

Explain about the exaust leak part.

5 Liter Eater

iTrader: (5)

I'm going to have to disagree with having the wet nozzle as far back from the TB as possible. I have always heard you want it as close to the TB as possible so the fual and hitrous does not separate as they like to repel each other. Granted putting the nozzle too close, say after the TB, could cause the mixture to bypass the front most runners. If it is too far from the intake the fuel will fall out of the mixture.

V6 Bird

iTrader: (15)

Let off the gas at a high RPM and Unburnt fuel in the collectors or whatever often times will ignite with the incoming air. No air for the fire to breathe no boom. Air tight seals wont ignite since fuel has no air to burn with it.

Mike

NXRICKY

iTrader: (1)

The fuel and nitrous with our nozzle can not seporate, Not enough time. I have first hand experience with getting a face full of the mixture. Did not even get my hair wet, but you could tell it was an extremly dangerous situation. Also again there just is not enough time even if they did split. Popping in the exhaust is 99.9% time caused by the mixture going rich and the unburned fuel that moved through the intake,combustion chamber got lit in the exhaust. Back to the velocity thing, and raw fuel can not burn. It was vaporized in the cumbustion chamber, and then ignited in the exhaust.
Ricky

Robert56

iTrader: (2)

I can agree with this. What I am saying is a wet N2O car running wet shot at the end of run will pop/backfire, whereas, the same car running n/a will not do this. Also, what your talking about is the left behind unburned fuel caused by radical cams/timing and does'nt normaly blow the hood. With the extra fuel in the intake on deceleration after run on wet kit (puddling), with what you say together, can and does sometimes blow the top of the motor.

Robert56

iTrader: (2)

This reply and your next one are very well said. I was trying to say this also, but you are a good tech writer and can get a point across well.

Stroker 1500

iTrader: (1)

This is the reason i asked about the placement.. I have seen quite a few people on here placing the nozzle in the tb or right at the tb. I thought that everything would atomize better and get a better spread once in the intake manifold if it was placed further back

NXRICKY

iTrader: (1)

You are correct...
Ricky