Foam Flow Tests

Over time we have obtained fuel cell foam from a number of sources.  We wound up with 5 distinctly different foams.  What we will call "Coarse", "Medium", "Fine", "Extra Fine" and "Yellow", which has a pore size similar to "Medium".  All of the foams claim a similar volume reduction of about 3%.  Here is a comparison:

     Extra Fine        Medium                  Fine                  Coarse                Yellow           

Visually, differences can be seen in the pore size, but also interesting is that the pore structures are also different.  The yellow foam has a wiry structure where the medium foam has perhaps more complete spheres.  The pore size itself is very similar, but the flow rates are different.  The purpose of this testing was to compare the different foams in terms of fuel flow resistance. 

The test apparatus consists of a 2.5 gallon "quick fill" fuel jug with the guts removed from the filler and a large hole cut into the bottom to form a large funnel.  A length of clear tube is clamped onto the cap.  The tube holds the samples to be tested and directs the outflow into a larger fuel jug.  A plug with a long handle is used as a quick full open valve to start each test


The tests entailed loading the tube with identically cut samples.  Filling the funnel to 1.5 gallons then pulling the plug and measuring the time taken for the fuel level to drop to the top of the sample.  Each test was repeated twice, with the results averaged The tests were performed with 12 inches of each foam.  We ended up with final resistance values equal to seconds added/(gallons*inches of foam).  Pretty specific to this setup, but good enough for comparisons

Times:             No Foam = 4 sec.    Coarse = 38    Med = 68    Fine = 55    XFine = 208    Yellow = 32

Resistance:     No Foam = 0.0   Coarse = 2.6   Medium = 4.2   Fine = 3.0   XFine = 15.0   Yellow = 2.2

The surprise was the medium foam being slower than all except the extra-fine and how much slower the extra-fine was than all the rest.  The flow rates are still way beyond the needs of the engines but may slow refueling.  Perhaps a hybrid kit with a coarse or yellow fueling ring is in order.  Between the foams there may be a tradeoff somewhere for different types of racing.