Stock Car Science

Some drivers have stumbled out of their cars and asked reporters for a few moments to hydrate and catch their breath before giving interviews the last few weeks. At Pocono, Denny Hamlin and Dale Earnhardt, Jr., in particular, looked flushed and tired.

Drivers say the new car is too hot. The unleaded fuel does burn hotter. Kyle Petty mentioned that the exhaust was 40-50°F hotter, and John Darby conceded that this might translate to 10°F-20°F temperature rise in the car. But the unleaded fuel was used last year and heat in the car wasn’t an issue. In the new car, however, airflow underneath the car is decreased by the splitter, which lessens the under-car cooling (which is where the exhaust pipes are). In addition, the exhaust pipes are located in a different place than in the old car.

One obvious solution was advanced by Cup Series director John Darby, who suggested that some drivers are not availing themselves of existing driver cooling technologies. Hamlin admitted that his team was one of those; however, Greg Biffle didn’t have any complaints about the heat, even after his cooling device shut off during the Pocono race.

The disorientation, tiredness and flushing might be heat, but– as NASCAR has already recognized–it might also be a result of carbon monoxide.

Carbon monoxide (CO) is an odorless, colorless, invisible gas that prevents oxygen from being taken from your lungs to your brain, heart and anywhere else. Carbon monoxide is generated when combustion doesn’t go according to plan, which means furnaces, wood fires, portable generators and, yes, stock cars, can all produce CO.

The amount of CO in a typical passenger car’s exhaust is small (about 2%). The exhaust passes through a catalytic converter, where each CO molecule picks up an oxygen atom and is converted into a relatively harmless carbon dioxide (CO₂) molecule. Carbon dioxide isn’t poisonous, but it is a greenhouse gas.

Stock cars don’t have catalytic converters. Making a lot of engine power depends on getting the combustion reactants (gas and air) and products (exhaust) into and out of the engine quickly. A catalytic converter would slow the exhaust getting out of the engine and limit engine power. There are no catalytic converters (or mufflers, for that matter) on stock cars.

Carbon monoxide poisoning can be chronic or acute. Acute means a high dose in a short time (which can be deadly). Chronic means that effects build up from repeated small exposures, which is the main hazard to drivers. In 2002, driver Rick Mast retired because he had become so sensitive to carbon monoxide that he couldn’t bear to mow the lawn or ride in a convertible.

The symptoms of mild CO poisoning include confusion, failure to answer questions, and ignoring instructions. (Of course, that describes a couple of drivers on a good day.) The best indication is a change in the driver’s attitude over time, as Ray Evernham noted back in 1997 when he was Jeff Gordon’s crew chief.

“I can tell immediately, by the way Jeff answers me on the radio, when the carbon monoxide is getting to him,” says Evernham. “He becomes a smart-ass. When I started working with him, I thought he was a smart-ass. But the more I got to know him, and the more I learned about carbon monoxide, the more I realized what was happening. How many races are won or lost in the last 50 miles?”

The problem came to a head when the cars became more airtight to gain aerodynamic advantage. When Tony Stewart complained about how bad he felt at Martinsville in 2002, NASCAR and a number of teams (notably Hendrick Motorsports, Penske Racing, and Joe Gibbs Racing) developed catalysts to clean the driver’s air.

A catalyst is a material that makes a chemical reaction happen, but doesn’t take part in the reaction. The platinum in your car’s catalytic converter is a catalyst. CO doesn’t convert into CO₂ spontaneously: The platinum provides a little incentive for the CO to make the change. The problem is that the platinum has to be a few hundred degrees Fahrenheit to make this work.

The solution, which I detailed in The Physics of NASCAR, is a catalyst NASA originally developed to convert the carbon monoxide generated by space-based lasers back to carbon dioxide so it could be used again. Space is cold, which is why they needed to develop a special catalyst that would work at low temperatures. And if it will work in space, it ought to work just fine in a race car.

Small beads or honeycomb supports coated with the catalyst provide a large surface area and thus a high rate of converting CO to CO₂. Air is brought into the cockpit by NACA ducts and flows through the catalyst (and usually a battery-run air cooler), then is directed through a hose to the top of the driver’s helmet.

A car is a holistic system: Changing one thing can have ramifications in areas you might not expect. You might change running shoes and your hips start hurting. You don’t wear the shoes on your hips, but your hips are affected by different shoes.

The indication that there is more than one factor active is the lack of direct correlation between who was complaining and who wasn’t. Carl Edwards was fine, but Denny Hamlin wasn’t. Both have personal trainers who keep them in shape. Jeff Burton complained about a hot steering wheel, but not about feeling bad personally.

Where does carbon monoxide come into play? Heat can exacerbate the effect of CO. When you get hot, your heart beats faster and you need more oxygen. Even though there might be no more CO in the cockpit than before, the combination of the heat and the CO can have a disproportionate effect on the drivers. (See Walker, et al, Comparative Biochemistry and Physiology Part A, 128, 709 (2001).) Also, a driver is more likely to be exposed to CO when the car has body damage because a breach in the sheet metal can let more exhaust fumes into the cockpit. I seem to recall that, at Pocono, Denny Hamlin had some damage relatively early in the race and that might have exacerbated the issue. (I also recall that the very first COT races last year had some problems with CO that were attributed to using too-thin sheet metal in the exhaust system.)

There isn’t a simple way to make the drivers feel better in the car. Each car is set up slightly differently (different cooling devices, for example), and multiple effects make finding the cause much more complicated. The first step, before calling for NASCAR to change the car, is for individual teams to make sure they are doing everything they can to minimize the heat and the carbon monoxide the driver is exposed to.

Side note: If you didn’t check your CO and smoke alarms when we switched to daylight savings time, please take a moment and make sure they are functioning correctly. Race fans, remember to take all the appropriate safety precautions with generators when you’re camping out at the track. The June Speedway Illustrated has a story on disaster narrowly averted at the Short Track Nationals in Little Rock that everyone who uses a generator should read carefully.

UPDATE: ESPN reports that none of the drivers monitored for CO showed a ‘dangerous level’, and that the temperatures in the car vary depending on how much the teams do in terms of things like insulating the floorboards and the exhaust pipes. One can understand NASCAR’s frustration with drivers complaining about the new car being hot when their teams haven’t implemented even the simple things already in existence and known to mitigate the situation.