Top Fuel Dragster 6

[HydroScope]

Hi,

I recently discovered the world of drag racing and wondered why top fuel dragsters dont combine their nitromethane with nitrous? I understand that nitromethane is already a combination of methane ~ CH4 and nitrous ~ N2O that is a liquid ~ CH3NO2, but beleive it would still burn in nitous atmosphere, Am I correct?. Is it because nitromethane already develops a high enough power density no need for more? at limit of engine compents? or are these chemicals a bad combo for some reason?

 

[globi5]

^ I'm curious as well.

If you would know the exhaust pressure and the amount of fuel and air that is being consumed per second you could estimate it:

Downforce = Mass (of air and fuel)* Velocity / t (Impulse)

(Pressure = Density * Velocity^2/2)

Although pressure is probably so high that Bernoulli's law is not appropriate anymore. (Well, it certainly sounds like someone firing guns (=supersonic speed)).

 

[sbmar]

I found this information on a web site...........Could these numbers really be an accurate representation of a typical top fuel dragster engine?? If so, they are remakable..

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TOP FUEL DRAGSTERS INFO

One dragster's 500-inch Hemi makes more horsepower then the first 8 rows at Daytona. Under full throttle, a dragster engine consumes 1 1/2 gallons of nitro per second, the same rate of fuel consumption as a fully loaded 747, but with 4times the energy volume.

The supercharger takes more power to drive then a stock hemi makes.

Even with nearly 3000 CFM of air being rammed in by the supercharger on overdrive, the fuel mixture is compressed into nearly-solid form before ignition.

Cylinders run on the verge of hydraulic lock.

Dual magnetos apply 44 amps to each spark plug. This is the output of an arc welder in each cylinder.

At stoichiometric (exact) 1.7:1 air/fuel mixture (for nitro), the flame front of nitro methane measures 7050 degrees F.

Nitro methane burns yellow. The spectacular white flame seen above the stacks at night is raw burning hydrogen, dissociated from atmospheric water vapor by the searing exhaust gases.

Spark plug electrodes are totally consumed during a pass. After 1/2 way, the engine is dieseling from compression plus the glow of exhaust valves at1400 degrees F. The engine can only be shut down by cutting off it's fuel flow.

If spark momentarily fails early in the run, unburned nitro builds up in those cylinders and then explodes with a force that can blow cylinder heads off the block in pieces or blow the block in half.

Dragsters twist the crank (torsionally) so far (20 degrees in the big end of the track) that sometimes cam lobes are ground offset from front to rear to re-phase the valve timing somewhere closer to synchronization with the pistons.
To exceed 300mph in 4.5 seconds dragsters must accelerate at an average of over 4G's. But in reaching 200 mph well before 1/2 track, launch acceleration is closer to 8G's.

If all the equipment is paid off, the crew worked for free, and for once NOTHING BLOWS UP, each run costs $1000.00 per second.

Dragsters reach over 300 miles per hour before you have read this sentence. * Top Fuel Engines ONLY turn 540 revolutions from light to light!

The redline is actually quite high at 9500rpm.

To give you an idea of this acceleration, the current TF dragster elapsed time record is 4.477 seconds for the quarter mile. This means that you could be coming across the starting line in your average Lingenfelter powered "twin-turbo" Corvette at 200 mph (on a FLYING START) and the dragster would BEAT you to the finish line FROM A DEAD STOP in a quarter mile distance!

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Tony Athens

http://www.sbmar.com

 

[rmw]

Nitro; stuff not to be messed with.

http://www.nhra.com/50th/news/index.html?story=457

http://intox.org/databank/documents/chemical/nitromet/cie511.htm

The plant manager and maintenance manager were among those killed. Huge chunks of the plant equipment were blown off the plant property and into the town across the street. Buildings in Sterlington were literally blown down.

Treat with respect.

rmw

 

[JWaterstreet]

It's been quite a while since I've been in the pits, but years ago the prep guys for TF drags & funnies would dump an unknown liquid down the exhaust pipes right before powering up at the line.

Anyone know what the liquid is/was, and why? ( I always assumed it had to do with cooling)

Always was a hoot to see the stuff blown all over people too close when started up.....

 

[globi5]

1.5 gallon of nitro might be roughly 5kg.
So the total mass would be: Mass of nitro plus mass of air 1.7*(mass of nitro) which is equal to 13.5kg.

Downforce is apparently 9000N which would mean the velocity of the exhaust gases is roughly 670 m/s. (Which is about double the speed of sound.)
Based on the noise generated by these engines, it doesn't appear to be completely unreasonable.

Besides it's hard to believe that 8G's could be reached with a sticky rubber alone - so there must be some extra downforce.

 

[sbmar]

I'd like to know WHO turned the word "WEB" in my post above into a hyperlink completely unrelated to the topic and myself? This is the kind of stuff that is not kosher at all, and could certainly make many feel uncomfortable about posting here..........

Tony



Tony Athens

http://www.sbmar.com

 

[kenre]

The wing plays a large part in downforce, once there off the line and moving at speed.

The chassis is also designed to plant the tyres down on takeoff with controlled flexing. Apparantly they arch up in the middle.
The burnout before each run does 2 things, first it heats the tyres so there nice and sticky, and second it leaves a nice sticky layer of rubber on the track for more grip.

With acceleration from standstill to over 100MPH in less than a Second its a wonder they dont spin the earths orbit backwards.

If they wanted to burn more nitro easily, they would add some propylene oxide to the fuel... Only its banned!!!

Ken

 

[globi5]

Actually the fact that the chassis is lifted when the tires increase in diameter also generates an additional downforce initially.

Nevertheless the 2000 lbs. downforce from the exhaust pipes doesn't sound unreasonable to me.

 

[the3car]

Great topic..you guys are really riled up..thats cool.

On the topic of the nitrous..I was under the impression that the true reason nitrous helps develop more power was the cooling effect generates a higher O2 concentration in the charge, not the preceived chemical boost. All it does it help to pack more O2 into the chamber. For a TF motor, your already packing the cylinder with an enormous about of air, hence the lean condition problems.

I was told by a fueler engineer, that they fill the tank with 10 gallons, 7 of which are "dumped" during the burnout (only one Mag on, 2nd gets turned on after), and 3 to get down the track. Fuel pressures are in excess of 300psi, so the physics of having the front cylinders leaner than the rear cylinders sounds like a bunch of hooey.

The downforce question: How can the exhaust create downforce? It's directed UP, not down. The front of the wing is tipped DOWN, not up. The funny cars go almost as fast as the dragsters, for one reason only, FRONTAL AREA. So, I don't believe exhaust gases create downforce.

One last comment. The fuelers have sooo much power they don't know what to do with it. The real gains in speed, over the past 10 years have come from clutch management, not increased HP.

 

[rmw]

sbmar,

You need to red flag your own post, and note in the message section of the pop-up screen that you are red flagging your own post in order to ask a question about the linking of specific words, including the word "WEB" in your post to site management.

They should be able to send you a message to explain the site polices regarding this feature.

rmw

 

[patprimmer]

Ummm, in a rocket or jet, the exhaust points the opposite way to the thrust. That is kinda how they work. Action and reaction sorta thing.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[WilliamH]

"Action and reaction . . ."

I was waiting for you to catch that one Pat! This is an interesting thread. Keep it going guys.

Will

 

[Metalguy]

>"On the topic of the nitrous..I was under the impression that the true reason nitrous helps develop more power was the cooling effect generates a higher O2 concentration in the charge, not the preceived chemical boost. All it does it help to pack more O2 into the chamber. For a TF motor, your already packing the cylinder with an enormous about of air, hence the lean condition problems."<

Nitrous is N20-far more O than air has. The cooling effect helps but is minor. You can also increase HP a bunch with a simple oxygen/extra fuel addition (very little cooling effect), but detonation is a big problem if the spark isn't greatly retarded.

>"Fuel pressures are in excess of 300psi, so the physics of having the front cylinders leaner than the rear cylinders sounds like a bunch of hooey."<

300 psi *TO* the injectors doesn't mean anything to the fuel/air mass blasting thru the blower and into the ports. F/R fuel distribution WAS a problem back in the 1970's, but I'd bet it's all been compensated for now.

>"The funny cars go almost as fast as the dragsters, for one reason only, FRONTAL AREA."<

Wrong again, it's STREAMLINING.

 

[the3car]

Sorry guys but I have to clarify Metalguy's last comment.

Frontal Area is equivalent to streamlining. I think we are thinking the same thing. The more air you push @ 330mph, the more power it takes. Since the dragster's have less air to push, they go a tad bit faster. The funny cars have more total frontal area, thus the slight speed/et difference.

Thanks patprimmer...I wasn't thinking directional thrust, I guess I was focused on the wing. I still don't think there is an enormous benefit from the downward thrust @ take off, but it probably does provide some force. It's all about the clutches, hence the development of the multi-stage clutches.

 

[Metalguy]

Funnies are MORE streamlined than top fuelers. The funnies ET's are down a little compared with TF, but the MPH is pretty close. Gear both cars up and a funny will go faster in a half-mile.

 

[the3car]

Reduced frontal area is an important factor in the equation for speed. The smaller hole that you punch in the air, the less wake you will make in that air. Making a wake means stirring up the air, creating eddy currents and low pressure areas that induce drag, slowing the vehicle down. It is like dragging a parachute. Contrary to many people's views on drag, the bulk of the induced drag is not just pushing the air out of the way, it's filling the hole that you made in it. This is where I believe the next big development will be.

Improvements in boundary layer control, aiming vortices, and surface pressure control will raise the bar to new speed records. This will be particularly important to those of you who have been drooling over the .deciMach Prize.

Taken from:

http://www.recumbents.com/wisil/brunkalla/future-hpv.htm

 

[GregLocock]

So we've got 1.5 gallons per second of fuel, say 15 lb/s, and say twice as much air (I can't be bothered to work it out).

There are good reasons to believe that the exhaust velocity is less than the speed of sound, so taking that as the upper limit that gives a thrust of

F=delta(mv)/s

45/2.2*330 N

7 kN, or just under 2000 lbf.

However, I doubt the exhaust velocity is that high.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[turbocohen]

As the heated gasses expand upon leaving the pipes I can imagine there is quite a bit of force applied aside from exit velocity. From the initial burnout the exh temps are not as high as midway down the track so I would guess the down force runs between 500 pounds off the line and up to 1000 lbs through the mid run.

After about the first 1000-1500 feet of a run often the spark plugs are fried and the exhaust valves and surrounding surfaces are hot and the fuel ignited due to compression ignition aka dieseling... kinda like a cox airplane engine making 7500 horsepower. The exhaust valve acts like a glow plug mid pull and torches any remaining fuel.

So I think 500-1000 lbs downforce is probable. Thats my story and I'm stickin to it.

Happy new year yall, Turbo

 

[Metalguy]

TF engines use special plugs where the side electrode really comes in from the side--way up inside the threaded shell. The tiny gaps are set with a special tool that enters from the threads.

Not much to get real hot with them.

 

[turbocohen]

Metalguy, I am not a drag racer by any means but I spent some time in the pits a over a decade ago. Running one magneto all the time and the other part time cooked mag 1 plugs if I recall but it sounds like the tech has improved so I stand corrected, thank you.

Regards, T