Why wet test?

[emarsh]

I just ordered the PTS instructions and as long as I'm going to build the bench was kicking around ideas on how to have it double as a wet bench.

Then a though came to me.

I don't understand exactly what the objectives are of doing a wet test. To see how it affects flow? To see if there are issues with fuel slicking out of the airstream and puddling?

This may seem like a dumb question to some, but what exactly are the goals of wet testing?

[49-1183904562]

Emarsh,

I would go back through this Topic and search from the beginning. Especially read what Chris (blaktopr) has done.

I think you will find in general it is about visualization, the media combined with the air may provide some alternate effect that is not recognized when just testing air flow effects (string on a stick, clay, pitot probe etc.)

Rick

[blaktopr]

Thanks Rick. Emarsh, the wetflow allows to to furthur "learn" about the air and air/fuel's characteristics (?) through a port and combustion chamber. There are no numbers involved, but another door to open into the quest for more information and understanding. Unfortunately, if you get hooked, you will find yourself staring at the formations of eddy currents and high/low pressure conditions while muddy water is being sucked out of a collapsed electrical trench. Good thing I'm the boss!:D

[emarsh]

Now you've got me thinking. I tend to kick ideas around like that myself. One idea that occurred to me is that it wouldn't be too hard to synchronize varied amounts of vacuum to the opening and closing of a valve but it would be very difficult to instrument. But if you just want to observe what's happening a digital video input would be all you need. You could even cut out every frame except those of interest creating a sort of digital "strobe". Interesting, but really this is something for another day, I guess.

[jfholm]

Food for thought. How much fuel is really introduced into the engine during one firing of the cylinder? What we have to consider is the air fuel ratio for the engine while it is running under acceleration.

Should be around 12.5 to 1. That is 12.5 parts air to 1 part fuel by weight. depending on the altitude and other conditions air weighs about .075 pounds per cubic foot at sea level. Now for my engine at 6500 rpm it needs around 780 cfm according to PipeMax. That calculates out to 58.5 pounds of air per minute. Now divide 58.5 pounds of air by 12.5 to get the weight of the fuel. That comes out to 4.68 lbs of fuel per minute for the whole engine.

Now let's look at per cylinder. Divide the 4.68 pounds of fuel by 8 since I have a V8 and you get .585 pounds of fuel per minute per cylinder. Now since a gallon of gasoline varies we will average it to 6.5 pounds per gallon for this discussion. So divide 6.5 by .585 to get the part of a gallon one cylinder uses per minute and that is a little over one eleventh of a gallon. Since we know that there are 128 oz in a gallon then one cylinder uses 11.52 oz. of fuel per minute.

Now how much fuel per firing. If my engine was turning 6500 rpm then it would fire 3250 times. So divide 11.52 oz. by 3250 and you get 0.0035446153846153846153846153846154 oz. of fuel per firing.

So I ask "How important is wet flow really?

John

[slracer]

John, If you don't think it is important, leave the fuel out the next time you race! :p -- Doug

[86rocco1]

It's probably next to impossible to accurately reproduce what the fuel does during the various engine cycles so in that regard, I think John's right about the importance of wet testing. However I think it can still be valuable as an aid to help visualize flow patterns especially if you're using a UV florescent dye.

[jfholm]

Ed,
I really do agree with you that we still need to see what is going on. I just wanted everybody to see how little amount of fuel we are dealing with.

Doug,
now speaking about minimum amounts of fuel. I bet you can run for a full year on what I use in one run

John

[slracer]

"now speaking about minimum amounts of fuel. I bet you can run for a full year on what I use in one run ."

My fuel bill is rather low, but 2 years ago, I had to add fuel to the tank the last day! The fuel truck owner has never laughed so hard!

Doug ???

[49-1183904562]

Doug,

Maybe that is the answer to your problem?

2 year old racing fuel! :p

Rick

[slracer]

Old racing fuel may be what killed my rototiller, but whatever is in the tank at the end of the race gets used elsewhere! (Even at $7/gal!) But I do have a great deal for anyone who wants some 110 octane parts cleaner! :p

Doug

[slracer]

As Ed said "However I think it can still be valuable as an aid to help visualize flow patterns especially if you're using a UV florescent dye."

If you are, you might be interested in one of these:



Not too bad a price to try things out! -- Doug

[49-1183904562]

Doug,

Great find as this UV power is what is needed to get good dye resolution. Here is a U-Tube link of what you can do with these LED's.



Rick

[jfholm]

WAY COOL! Doug I have been looking for one of those!!!

Thanks!

John

[86rocco1]

And have a selection of waterborne UV dyes, that I think should work very nicely for this application.

BTW, I email the people selling the flashlight Doug linked to to ask what wavelength that flash light operates at?