Why You Don’t Mess With Fuel Cell Foam

We’d been hearing rumors of penalties stemming from Kansas and everyone expected them to be announced Tuesday.  Since penalties usually have some scientific component, I was sort of hoping for some new material.  Tuesday came and went.  Nothing.  Wednesday, all heck broke loose as penalties were announced for the No 20 JGR car (engine issues) and the No 98 ThorSport truck.

The JGR issue isn’t that complicated — or interesting.  Someone screwed up and connecting rod that was too light got into an engine.  It’s beyond surprising that Toyota said that they don’t have the personnel to check all the engine parts – given that everyone knows that penalties for engine violations are huge, why would you risk something like this happening?  The penalty was pretty severe and NASCAR has to crack down.  I get taking away points, leveling fines and such — but the tradition of holding the crew chief responsible for the engine when the engine comes from a supplier who doesn’t let the team touch it is out-of-touch with the realities of NASCAR today.  That was a valid punishment when everything came from the team, but there is no reason Jason  Ratliff should be suspended over an issue that was entirely JGR.  I have no problems with the other penalties, but that one is pretty unfair in my opinion.

The more interesting — and less discussed — penalty is the ThorSport/Johnny Sauter one.  (It was a tough week for Wisconsin drivers).  The team was docked 25 points, which is pretty huge for the Truck Series and the crew chief fined $10,000.  (I realize that seems small when compared to the Sprint Cup Series penalties, but the Truck Series has correspondingly lower purses and salaries.)  Here’s the official NASCAR statement.

“The No. 98 truck was found to have violated Sections 12-1 (actions detrimental to stock car racing); 12-4K (if in the judgment of NASCAR Officials, race equipment that has been previously verified or previously approved and/or sealed by NASCAR for use in an event, pursuant to sub-section 8-6 and/or 8-12, has been altered, modified, repaired, or changed in any manner); 20B-16 (once a fuel cell or fuel cell components have been certified, modifications of any kind will not be permitted to the fuel cell or fuel cell components); and 20B-16.1B (standard black, safety foam with minimum free-standing height of eight (8) inches, acceptable to NASCAR Officials, and used as provided by an approved fuel cell manufacturer, must be used: Fuel cell safety foam modification.”

A fuel cell is slightly different than a fuel tank.  A fuel tank is pretty much an empty container, which leaves open the possibility of raging fires and/or explosions.  Fuel cells, which provide additional levels of safety, became standard after the death of Fireball Roberts from burns received during a car fire at Charlotte in 1964.

Engines_FuelCell_FuelSafeAs shown below, a fuel cell is a metal can (minimum thickness of 18 gage, which is 0.047″) fitted with a flexible bladder shaped to fit the can.  The bladder contains the fuel, but it’s not just a bag of fuel in a metal case.

The most important part of the fuel cell is the item labeled ‘1’ in the picture above – the safety foam baffling.  In the picture below, the black thing on the left is the bladder and the yellow stuff is the foam.  The foam is a cross between a nerf ball and the white styrofoam you use to make models of the solar system in elementary school.  That is to say that the foam is sort of coarse, like the white styrofoam, but it’s not rigid – it gives a little when you squish it.  It’s also gasoline resistant.


Foam is mostly air.  There are even special foams called aerogels, in which 99 percent of the volume of the foam is air.  (Those foams are fragile and would be destroyed by gasoline.)  The foam takes up a small volume of the fuel cell, so it doesn’t change the capacity of the fuel cell by very much; however, it plays two very important roles.

The function most people know is that the foam keeps fuel from sloshing around in the turns.  A full tank of fuel weights about  120 pounds.  When a car corners, everything that isn’t rigidly attached to the wheels feels a force to the right.  The grip you have depends on how much weight is pushing down on each tire.  When weight shifts to the right side of the car, you lose grip on the left side tires.  There’s only so much you can do to keep the body from rolling in the turns – you don’t need the gasoline moving to the right as well.

More importantly, the foam prevents explosions.   If you tossed a match into a container of gasoline (warning: do not attempt this at  or anywhere else), the explosion would happen before the match actually hit the gasoline.  When you have a cup of water, it looks like there is water in the bottom and air on top.  In reality, there are water molecules from the liquid escaping into the air (and water molecules from the air condensing back into the liquid) all the time.  When you microwave that water until it boils, you force more molecules from the liquid phase into the gas phase.  The hotter the water is, the more water molecules in the air immediately above the liquid water.

In order to smell something, the molecules from the thing you’re smelling have to make their way into your nose.  You don’t smell liquids – the molecules from the liquid vaporize and make their way into your nose.

Slide1Gasoline is volatile.  In fact, any liquid that you can smell is volatile, which simply means that the molecules can very easily move from liquid to vapor.  If you look at a traditional fuel tank that is only partially full, it isn’t a layer of gasoline and a layer of air.  It’s a layer of gasoline and a layer of gasoline vapor mixed with air.

When gasoline is purposely combusted in an engine, it has to be sprayed as a very fine mist.  The finer the mist, the more efficiently it combusts.  The top layer in the fuel tank – the gasoline vapor – is highly flammable.  A spark will combust the fuel vapor molecules nearest to it.  That combustion compresses the rest of the fuel vapor, leading to a chain reaction and an eventual explosion.

Foam in a fuel cell prevents a concentration of the fuel vapor plus air mixture, which significantly reduces the probability that the fuel cell will explode in case of a fire. Reducing the amount of foam in a fuel cell, either by not putting it in to the eight-inch mandated height, or by carving out hollows in the interior of the foam, creates a very highly flammable pocket of fuel vapor and a major safety hazard.

While manipulating the foam might give you an advantage in terms of being able to fit more fuel into the tank, it creates a major, major safety hazard by making the fuel cell more likely to explode in case of an accident.  While people talk about messing with the fuel being a major no-no, the big thing here is really the safety aspects.


1 Comment

  1. Tires, fuel, and engines are the “sacred cows” of NASCAR. My opinion is at odds with Larry McReynolds and Darrell Waltrip, two very knowledgeable, highly respected men. They say the appeal panel will not reduce fines, suspensions, etc. I’m thinking the public outcry may have some effect. To me its possible NASCAR is “firing one over the bow” to let everyone know, you don’t’ mess with engines, regardless of the logistics or who should have caught the illegal part. I’m confident TRD will pay all fines (then subrogate their European connecting rod supplier). I fully expect Jason’s suspension to be reduced. In summary, I believe Mike Helton and Robin Pemberton intend to put the fear of God in engine builders, crew chiefs, etc that should discourage any hijinks with engines, tires, or fuel.

1 Trackback / Pingback

  1. Fire: A Motorsports Safety Challenge - The Building Speed Blog

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.