Why You Don’t Mess With Fuel Cell Foam

 Explosions, Fines, Fuel Cells, Johnny Sauter, Kansas, Rules, ThorSport  1 Response »
Apr 262013
 

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.

http://i2.wp.com/www.fuelsafe.com/store/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/R/B/RB215_1_1.jpg?resize=410%2C274

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.

 

Is Tire Fall-Off the Way to Fix “Broken” Tracks?

 Atlanta Motor Speedway, Brandon Thomas, Bristol Motor Speedway, Bruton Smith, Dover International Speedway, John Probst, Josh Browne, Steve Letarte, Tires  5 Responses »
Apr 062012
 

There’s been an awful lot of talk recently about changing the layout at various track to make racing more exciting.  Bristol is the most-talked-about track, with Bruton Smith planning a $1M revamp of the track to take it back to the way it was before he changed it in 2007.

There are a number of factors that dictate how “exciting” racing is.  For example, the track width and how many “grooves” there are make a big difference in how easy it is to pass cars without “helping” them out of your way with your front bumper.  But last I looked, grip — the source of all speed — is dependent on the interaction of two things:  the tire and the track.  There’s a lot of talk about tracks, but not a lot of talk about tires.

Remember back a few years when tires were a topic of conversation every other week?  Tony Stewart lighting into Goodyear for the tires at Atlanta in 2008?  The Indy tire debacle that same year?  The 2005 Charlotte ‘levigation’ when they “smoothed” the track using a diamond grinder?  Tires aren’t much of a topic these days.  Goodyear’s done an amazing job amidst a slew of re-paving projects from Talladega and Daytona to Bristol and Michigan.

But have they done too good a job?  Some people have suggested that the tires stay in good shape for too long.  It’s possible to go multiple fuel runs without taking tires at many tracks.  If the tires wore faster, might that add an element to the racing that’s missing now by forcing crew chiefs to make tougher decisions about whether to take tires and drivers to take better care of their tires?  Harder tires don’t wear as fast as softer tires – but softer tires are more likely to fail by being worn down rapidly.  It’s a difficult balancing decision and the consequences for Goodyear if they’re not exactly right are significant in terms of how fans perceive the brand.  Take a look at the opinions below and tell me what you think.

Phoenix: Relay Race?

 Electronic Fuel Injection, Engines, Fuel Mileage, Mark Martin, Rodney Childers, Tony Stewart  1 Response »
Mar 062012
 

The race at Phoenix was the first non-restrictor-plate race.  A number of drivers experienced engine-related problems, leading some media outlets to start blowing the “EFI problems” horns as loudly as possible.  Mark Martin, the pole sitter, was an unfortunate casualties of a “flipped circuit breaker”.  One of the most interesting exchanges to me was a series of tweets and a radio interview with Mark Martin’s Crew Chief Rodney Childers (@rchilders55) in which Childers repeatedly said it not “an EFI problem”, the radio commentators persisted in saying that it was.

Here’s his verbatim tweets (and if you’re not following him on twitter, please do!)

Man I hate that!! We had a breaker POP on our ECU for the fuel injection about half way. Which makes it switch to a safety fuel map.

It popped about half way.. it didn’t affect the performance. Just the Mpg, which made us have to pit. But we are really happy..

That made our mileage go from 4.2 to 3.8… And no way we could have made it. Good job to mark and all the Aarons guys though.

The EFI deal isn’t really the issue.. probably a wiring issue that we have to figure out. We had the same deal happen in practice.

Each car has a relay box, which acts sort of like Mission Control.  I’ve said before that the ECU (Engine Control Unit) is the brain of the EFI system.  The ECU collects information from a number of sensors located in different places on the car that measure things like humidity, pressure, temperature, and air-fuel ratio.  The ECU makes decisions on what to do next based on the information it gets from the sensors, and it acts on those plans by sending messages to the rest of the car through the relay box.

What happens if one of the sensors stops working (or a wire breaks and the sensor, even though it works, can’t send information)?  If the ECU believed the data it was being given, it would have a rather warped view of reality and could start telling the car to do all types of goofy things, including some that could actually damage the engine beyond repair.

The EFI system is smart – smart enough to know when it is getting suspicious data.  Instead of acting on that data, a relay is triggered and the ECU changes over to an alternate engine map (what Childers called a ‘safety fuel map’).  The alternate map isn’t optimized for performance – it’s purpose is to allow you to keep running, but your performance won’t be as good as you would have with the information from the sensor and the optimized engine maps.   As an analogy:  You eat more efficiently when your eyes are open.  If someone blindfolded you, you could still eat, but it wouldn’t be as efficient (or clean) as with your eyes open.  This relay system protects the engine from the actions of a confused ECU.  You might not run as well, but you also might not destroy a whole engine.
The relays work on the basis of a voltage threshold.  They’re like an electron bouncer.   A relay has a maximum current or voltage it will tolerate.  Bob Pockrass reports these relays have limits at 5V and 100 mA.   If an electrical signal comes through with a higher voltage (or current, depending on the type of relay), the relay switches everything to an alternative circuit.  Unlike the circuit breakers in a house (which are normally on/off, in contrast to these, which are circuit 1/circuit 2), it’s very difficult to re-set the relays.  It’s not like there’s a switch that the driver or a crew member can reach down and flip back.  When they flip, you’re pretty much stuck with them for the rest of the race.
Teams will be looking for anything that might cause the relay to flip.  That could be a wire that vibrated loose, or an electrical spike (like, say, the spike you get when you turn a switch on or off perhaps…?)  I understand some teams are switching to boxes without relays – but then you take a chance that something gets out of whack and you blow up your engine entirely.  One of the real pains in the neck with a short or a transient spike is that they can be hard to reproduce.  You can do the same thing 10 times and the problem may only happen one time out of those ten.  Makes for some long nights for the engine shops.
Childers tweeted that the mileage dropped from 4.2 mpg to 3.8 mpg – that’s just about a 10% drop in efficiency.  Phoenix is a one mile track, which means that the change in fuel mileage cost them nine laps per tank of fuel.  When teams are scrapping for one-percent increases, a 10% decrease is just going to kill you.
Keep in mind that we’re in uncharted territory.  NASCAR teams are subjecting these systems to environments they haven’t seen before.  I expected a few problems like this at Phoenix and I expect a few more in Las Vegas.  Teams will figure out how to make their system withstand the high-vibration/high-temperature world under the hood of a race car and drivers will gradually learn which of their techniques still work with the new system and which ones they’re going to have to change.
And if you’re wondering exactly what an engine map is, I’ve got a video going up on Friday to explain it.

 

The Math of Fuel Mileage

 Engines, Fuel Mileage, Kansas, Pocono  6 Responses »
Jun 102011
 

The gas needed to do one lap at a one-mile track fits in this quart bottle

I guess when you have people feeding you all the numbers you need through your earpiece, you think they’re easy to come by.  That’s the only explanation I can figure out for the snarky comments by television commentators about crews not being “smart enough” to figure out how much gas to put in the car so that it doesn’t run out before the end of the race.  There have been a lot of fuel mileage races the last few weeks.  Pocono is traditionally also highly likely to be a fuel mileage race, so let’s clarify how easy (or hard) it is to not run out of fuel.

Average mileage under green is about 4 miles per gallon.  At a one-mile track, than means one lap (one mile) requires one quarter of a gallon, which is one quart.  A car running out of gas coming out of turn four is short by probably a cup of fuel.   On the one hand, it’s amazing that it takes a whole quart of gas to do one lap.  On the other hand, the fuel cell holds 18 or 19 gallons.  Let’s say they get 18.5 gallons in the fuel cell – that’s 74 quarts, so you’re talking being off by 1/74th of a tank, which is a pretty narrow margin of error.

For comparison, a passenger car getting 32 mpg would need only a half a cup of gas to do a lap at Phoenix.  Although much more fuel efficient, the television ratings would likely be much lower.

There are some other considerations.  Here are two that are hard to quantify:

  • The pickups on the fuel cell can’t pull all the gas out of the tank, no matter how much swerving the driver does.  There’s likely to be some fuel in the fuel cell that just doesn’t make it to the engine.  It is a small fraction of the fuel cell, but  if we’re talking about 8 ounces of fuel being the difference between making it and not, small amounts matter a lot.
  • The driver’s ability to save fuel varies, depending on the driver and if he’s racing hard or if he’s able to set his own pace.  If he’s racing hard with another driver, he’ll likely get less than the expected fuel mileage.  If he’s skilled (getting off the throttle earlier going into the corner and getting onto the throttle later coming out of the corner), he might save a lap or two or three worth of gas.  It’s the same principle as you and I not stomping on the gas or the brake to be more fuel efficient.  When the crew chief asks the driver how much gas he’s saved, the only thing the driver can do is guess.  The more experienced the driver, the better feel he is likely to have for how much gas he saved.

One of the biggest challenges for the crew chief is calculating the actual gas mileage.  Let’s say you or I are calculating the fuel mileage of our car.  We go to the gas station and fill up the car.   The next time we stop for gas, we figure out how many gallons it takes to fill the tank back up and how far we drove.  For example:

I fill up my tank.  300 miles later, I stop for gas again and find that I need 10 gallons to fill up the tank.  It took me 10 gallons to drive 300 miles, which means my gas mileage is 30 miles per gallon.

OK, that’s not perfectly accurate because what does “fill up” mean?  Some people top off the tank and others stop as soon as they sense it is close to full.  There’s some variation in the fuel pumps as to where the pump shuts off automatically.  300 miles on the expressway is different than 300 miles in town.  If you want a meaningful number that characterizes your own gas mileage, you need to measure it consistently over a period of time and use an average.  Of course, that’s not possible in NASCAR.

But at least you and I get a decent measurement of how much gas we put in the car.  NASCAR teams don’t get to measure how many gallons of fuel goes into the car: They get to measure how many pounds of fuel went into the car.

A NASCAR fuel can holds about 12 gallons of fuel.  Gas weighs about 6 lbs per gallon, so the full gas can holds 76 lbs of gas.  The can itself is about 20-25 lbs, so round numbers, 95-100 lbs total. (Thanks to the NASCAR Insiders for the numbers.  I am writing this from a neuroscience retreat and don’t have my notes handy.)

Before each pit stop, the team weighs each one of the gas cans.  Let’s say one of them weighs 96 lbs.  The car comes in to pit, they add fuel and then weigh each gas can again.  Let’s say that the can weighs 36 lbs after a stop.  The change in weight is 96 lbs – 36 lbs = 60 lbs.  At 6 lbs per gallon, you can infer that the can is missing 10 gallons.

Note that I very carefully said ‘the gas can is missing 10 gallons’ because we have no assurance that all 10 gallons went into the car.  You’ve seen gasoline spill out everywhere when the gasman pulls the dry break away from the fuel cell inlet.  That happens even more with the new dry breaks because they are a little trickier to put in place and pull out than the old gas cans were.

The crew chief looks down and makes a mental estimate of how much fuel is spilled, converts the masses from the cans into gallons and comes up with a number for how much fuel he thinks is in the car.  From that, he estimates how many laps they can run.  If you want to see a frustrated crew chief, look for the gas man with the raised eyebrows and the shrugging shoulders.  He thinks he got it full… but he’s not sure.  That’s actually sometimes worse than the one who knows he didn’t get it full.  Sometimes it’s better to know the answer, even if it’s bad, than to be unsure.  The scales in the pits have at least one decimal place, and my friend Josh (a member of the ex-Elliott crew chief club) suggests that the better teams have almost certainly moved to scales with two decimal places.

Do the decimal places really matter?  Turns out they do.  Sunoco provides NASCAR teams with the exact density of the gas on race day, and they provide it to two decimal places.  So instead of 6.00 lbs/gallon, they’ll tell you 5.94 or 6.06 lbs/gallon.  If you weigh 60 lbs of gas, that’s 1o gallons @6.00 lbs/gal vs. 10.6 gallons @6.06 lbs/gal.  Remember that on a one mile track, one lap requires 0.25 gallons.  That 0.6 gallons difference is more than two laps on a one-mile track.

One more thing that’s different this year.  Here’s your word to impress people with this week:  Hygroscopic (hi-grow-skop-ick).  It means very attractive to water.  Ethanol – and 15% of the NASCAR fuel is ethanol – is highly hygroscopic.  If you turn your back on ethanol for even a moment, you turn back and there it is sucking up water.  We use ethanol in the lab to clean things and we actually have to use acetone afterward to get rid of the water the ethanol leaves.

Two issues with hygroscopicity:  First, you’re getting water in the fuel and water isn’t combustible.  You put the same volume of liquid in the cylinder and you get less power because some of the molecules turn into steam instead of combusting.  So you need more rotations to get the same power and thus you’re using fuel at a different rate.

Second, water has a different density than the hydrocarbon fuel molecules (or the ethanol), so the amount of gas you’re getting in the car is different that what you think.   Density changes with temperature, so if you think about a race like Kansas, where it was really hot, or like Charlotte, when the temperature varied quite a bit from start to finish, you might experience meaningful changes in the density over the course of a race.  Even if you did all the calculations successfully, you might still be surprised because one of the inputs was off. Also, when the temperature rises, more water can be absorbed by the ethanol.  The water molecules hang out in the gas, pretending they belong there.  But when it cools down, the water can separate from the fuel, so it’s possible to have liquid in the tank, but not have a lot of fuel.  This is a tremendous unknown that the teams have no experience with and it may account for why there have been so many fuel mileage surprises.

A lot of factors go into correctly calculating fuel mileage.  I think if you really want to get it right, you’d want to use a model that involves calculus.  And I bet there are at least a couple teams doing that.  You can make little widgets for things like fuel consumption or gear ratios and rpm using something as simple as Excel.  I know NASCAR likes to portray itself as simple, but let’s give the folks sitting with all the computers up on the pit box their due.

A few misc notes:

  • Happy to hear that Chad Johnston is getting a shot at crew chief for the 56 team.  Chad was the engineer for Elliott Sadler’s team when I was following them around for the Physics of NASCAR book.  Chad is a talented guy who reminds me a little of Rodney Childers – not self-promoting, doesn’t talk when he doesn’t have anything to say, but when he has something to say, make sure you listen.
  • I wish the story about what happened to the Second Chance Motorsports Nationwide crew at Chicago got just a small fraction of the attention Richard Childress/Kyle Busch did.  It’s sad, but there are so many people trying to get into NASCAR that there will always be some people who will work for someone who doesn’t have a history of treating people right.
  • BTW – I’m tired of hearing about RC/KyBu… you can stop now.
  • Here are a couple neuroscience tidbits I learned this week.  Perhaps the most useful thing was that if you get eight hours of sleep, but it’s not continuous (think new moms), your reflexes and ability to think are comparable to someone seriously sleep deprived.  The least useful (but perhaps most interesting) piece of information was that rodents lack the ability to vomit.  If you want to test whether a drug induces nausea, you use ferrets because they barf pretty readily.  Moral of the story:  If you’re going out drinking, take the rat as your bar buddy and let the ferret be the designated driver.  (The second moral is that if you went into physics because you have a queasy stomach, watching that talk right before lunch was maybe not the best thing to do.)
  • Where have I been?  Well, the last year or so I’ve been dealing with some really, really serious medical issues and it’s been all I can do to get through the day.  Blogging was one of the many things in my life that just seemed to require too much energy to manage.  I’m starting to feel better now – sometimes I would go so far as to say “inspired” – so I’m hoping my comeback will keep.  Thanks to the many online buddies who have kept me in their thoughts and brightened my days.  You don’t know how much you have been appreciated.