I ask because I read this story of a crash and fire at the Daytona 500, in which a car hit a truck that was circling the track and purportedly carrying 200 gallons of aviation kerosene.
WTF was a truck carrying this fuel (or any other fuel for that matter) on the track during the race? Yes, I know there was a caution, I just can’t figure out any rational reason why it would be done.
The truck was carrying a “jet dryer”- basically a big aero engine mounted on a truck and used to dry the track surface. There is a fuel cell on the truck to power the jet.
The truck had av gas. NASCAR up to 2008 used high octane leaded fuel in the top series. Environmental pressure led to the change to high octane unleaded.
In 2011, NASCAR began using E15 fuel, which contains ethanol. This fuel gave a horsepower boost with a decrease in fuel mileage.
I believe NASCARs run on a blend of gasoline and ethanol (alcohol). Jet fuel is actually far less flammable, being closer in composition to diesel.
Where does the horsepower boost come from?
Alcohol has much less energy per volume than gasoline. If you don’t change anything else, E15 will give you less horsepower and worse mileage.
Did they change something else to allow higher horsepower engines?
They didn’t have to. At the compression rations NASCAR engines naturally operate at E15 actually provides a slight power increase. See here (doesn’t give technical details though).
The jet fuel was in the truck to power the jet engine it was hauling to dry the track.
The jet dryer was hit by a race car under caution when the car had a mechanical breakdown
For images of a jet dryer and actualphotosof the incident
cough post 2 cough 
My understanding is that the engines can use the alcohol at a greater gal./min. rate.
Then the obvious answer is that they’ve changed something else. 
Alcohol has less energy per unit mass than gasoline, yes, but the stoichiometric air/fuel ratio is also much lower, so you can inject quite a bit more alcohol into a given mass of fresh air and still be able to burn it all.
In addition, alcohol has a much higher heat of vaporization than gasoline- nearly four times higher. Between that, and the larger quantities that are being injected (see previous paragraph), there’s a substantial cooling effect that you don’t get with gasoline, resulting in greater charge density. Cooler temps also mean you can run with higher compression ratios, more spark advance, or both, resulting in better engine efficiency without risking knock/detonation problems.
Anyone who missed the actual race incident last night can see video here. You can see kerosene pouring down the banked track by 0:15, and the fire starts getting pretty big within a minute or so; another minute, and the fire is REALLY big, and it takes the fire fighters a couple more minutes to get it under control.
Higher compression ratio.
A bit more detail:
The jet dryers use turbines originally made as helicopter engines and are used both for drying the track after rain, and to blow assorted debris off the track during caution periods. The latter usage has become more or less SOP for NASCAR in recent years. I believe three or four of the machines were on the track at the time of the incident.
Although pace speed is normally around 60-70 mph, a driver is allowed to speed up, at his or her discretion, to rejoin the field prior to a restart. In this case, Juan Pablo Montoya (#42) was accelerating to catch up to the field when something broke in the driveline of his car, locking one or both of the rear wheels and causing him to spin into the rear of the vehicle carrying the jet dryer, with the impact rupturing the jet engine’s fuel tank. There was an initial fireball at impact, which immediately went out; shortly thereafter, with fuel pouring down the track’s steep banking, something ignited the leaking fuel and a large fire erupted.
Apparently this was the first time this specific type of incident has occurred in NASCAR’s senior series, although there have been occasional cases of racers running into each other, the pace car or emergency vehicles during caution periods throughout the sport’s history.
NASCAR has a senior series? Do they drive around counterclockwise with their right blinker on?
Yes, the amount of fuel and air introduced into the combustion chamber is changed. That’s what the pedal on the right does. :dubious:
I think it would be by changing the timing of the engine instead of just using the gas pedal.
[nitpick]
Avgas and jet fuel are two different things. Avgas is gasoline used by piston-engine airplanes such as a Cessna Skyhawk or a Piper Cherokee. Jet fuel is used in jet engines and is closer to kerosene. Jet fuel is not as volatile as avgas.
[/nitpick]
The short news summaries of this event were very confusing, especially our local newscaster saying that “a car struck a safety truck that was carrying 200 gallons of jet fuel.”
A safety truck filled with jet fuel sounds kind of like a pillow filled with broken glass.
This is not to criticize, but to educate. What everyone saw running around in counter-clockwise circles last night at Daytona are not “NASACARS” (ain’t no such thing). I know it’s phonetically logical to refer to them as such, but they are “stock cars” and they compete under the auspices of NASCAR.
I feel better now that I’ve done my part.
