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Top Fuel Dragster
6

Top Fuel Dragster

Top Fuel Dragster

(OP)
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?

RE: Top Fuel Dragster

Nimeth is a more efficiently metered as liquid.  Why add the weight of gas bottles?

RE: Top Fuel Dragster

(OP)
If you add the gas bottles to a octane burning dragster then you increase the amount of oxygen in the cylinder which far exceeds the loss in weight of gass bottle. wouldn't this happen again when burning nitromethane with Nitous atmosphere as oppossed to air in cylinder with nitromethane?

RE: Top Fuel Dragster

Nitro Methane and Nitrous Oxide both absorb a lot of heat from the charge. It gets to cold for the Nitromethane to evaporate on the compression stroke then with to much liquid at a very low temperature it is to hard to light the fire.

No fire equals no power

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.

RE: Top Fuel Dragster

Power density is clearly not the limiting factor.

There appear to be two limiting factors:

- Operating virtually all moving engine parts at the extreme left end of the S-N curve.  They appear to have the nitro dialed in well enough that any more would cause the engine to blow up before the car reaches the first timing light, and any less would cause the car to lose the round.  There's still a high probability of destroying at least one part during a run, so teardowns every quarter mile are standard practice.

- Coupling the engine torque to the pavement.  Absent computer controls (prohibited by the rules), the guy who tunes the clutch is probably the single most critical crew member ... aside from the one who rustles up the money.

Mike Halloran
Pembroke Pines, FL, USA

RE: Top Fuel Dragster

As nitro burns there is extra oxygen created, meaning a lean condition. So to counteract this more nitro is injected, vicious circle that ends up with the fuel still burning as it leaves the exhaust headers. This is why you can see flames clearly.  N20 is normally injected on engines to allow more fuel to be burnt, creating more power. Last thing a nitro engine needs.

Top Fuel engines are on the verge of hydraulic every compresssion stroke such is the huge quantity of fuel injected. Not unususal is for the car to wheel spin part way down the track, engine unloads, and cools enough that the fuel does not vapourise properly, leading to a hydraulic condition.

This is easily seen as a huge ball of flames as it happens,  the Conrods make a hasty exit out the side of the block.

Ken

RE: Top Fuel Dragster

>"Nitro Methane and Nitrous Oxide both absorb a lot of heat from the charge. It gets to cold for the Nitromethane to evaporate on the compression stroke then with to much liquid at a very low temperature it is to hard to light the fire."<

Nitro doesn't evaporate on the comp. stroke or any other one.  Evap. takes time, and there is just about none at 9,000 RPM.  

RE: Top Fuel Dragster

>"As nitro burns there is extra oxygen created, meaning a lean condition. So to counteract this more nitro is injected, vicious circle that ends up with the fuel still burning as it leaves the exhaust headers. This is why you can see flames clearly.  N20 is normally injected on engines to allow more fuel to be burnt, creating more power. Last thing a nitro engine needs."<

Nitro certainly can be too rich-there is no "vicious circle" involved.

RE: Top Fuel Dragster

Nitromethane does evaporate, just slowly compared to other fuels.

Pour some in a dish and leave it. It will evaporate.

Some, not all evaporates on the compression stroke. The higher the temperature, the more it will evaporate.

The higher the level of vapour, the easier it is to light.

Nitro methane burns slow, compared to petrol or methanol because it takes time to evaporate and burn during the power stroke. That is why nitromethane does not work well at very high rpm

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.

RE: Top Fuel Dragster

>"Nitro methane burns slow, compared to petrol or methanol because it takes time to evaporate and burn during the power stroke. That is why nitromethane does not work well at very high rpm"<

Yes, the rate of the flame front IS slower-that's why fuel engines use so much spark lead.  But 9,000+ RPM from 7+ liter 8 cyl. engines and 30,000+ from nitro-burning model engines is plenty fast.

RE: Top Fuel Dragster

If you ever sit in the traps on the top end of a drag strip and see a top fuel rail or funny car at 300+ mph, you will see large plumes of unburnt fuel coming out of the exhaust pipes.  This unburnt fuel performs more as a cooling agent than the cooling system.
Watch the pits too, the nitro in some cases adds up to 30% volume to the oil sump during a single run, due to washdown.
One of the biggest problems with a TF dragster is running lean, not rich.
Franz

eng-tips, by professional engineers for professional engineers
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RE: Top Fuel Dragster

"Watch the pits too, the nitro in some cases adds up to 30% volume to the oil sump during a single run, due to washdown.
One of the biggest problems with a TF dragster is running lean, not rich.
Franz"

All that nitro in the oil is what makes holed pistons so dangerous--like having napalm in your face.

Nitro plus 70 wt. Kendal=pea soup green!

RE: Top Fuel Dragster

I think F1 runs at 18,000 to 19,000 rpm. They run petrol not nitro.

The original question was why not run nitro and nitrous combo. One reason is that it gets so cold, it then stays to wet to ignite, even with the arc welder strength ignition systems used in top fuel.

Another possible problem is that a high load of nitro gets very close to hydraulic lock. Adding nitrous, then extra fuel to balance the nitrous will exacerbate the hydraulic lock problem

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.

RE: Top Fuel Dragster

If you ever sit in the traps on the top end of a drag strip and see a top fuel rail or funny car at 300+ mph, you will see large plumes of unburnt fuel coming out of the exhaust pipes.  This unburnt fuel performs more as a cooling agent than the cooling system.

I dont think the current top fuel engines use a cooling system anymore. Solid billet engines.

Ken

RE: Top Fuel Dragster

They are solid but overfueling is required to prevent immediate failure.  Lean on nimeth for 1 sec often turns precision parts into interesting artwork and lots of expensive little paper weights.

RE: Top Fuel Dragster

Things work advantageously the way they are. For one, Top Fuel engines are limited to 500 cu in, which is pretty small for that arena. Secondly, the amount of n/m they can use keeps getting cut back anyhow. And lastly, the 8 exhaust rockets can add as much as 2,000 pounds of downforce at take off.

RE: Top Fuel Dragster

wow  didnt realize it was that high

RE: Top Fuel Dragster

Also consider that the Fuelers are not looking for more power right now.  Tuning fuel delivery and clutch is the most important thing.  At 8,000 hp the guys are having a hard time NOT breaking the tires loose.  That's with a single speed trany.

This past year had many examples of fast guys going slow due to smoking tires 100 ft out of the box.

Could you add nitrous? Yes.  Is it needed? No.  Even if someone chose to do it -the touchy nature of nitro ( not enough = burn metal.....too much = lose power and chance hydraulicing the if the flame goes out.   If it's lean, add nitro....then find out for some reason it's even leaner!   Tough to tune.  Add in Nitrous and all that knowledge goes out the window.

Fuelers are limited to 3.20 gear and 8400 rpm mandated by a spec ignition system from MSD.  85% nitro max (except at Colorado - mile high - unlimited nitro percentage and unlimited blower overdrive) and limited blower over drive.  I can't see NHRA allowing it anyway.

RE: Top Fuel Dragster

Don't know how they're doing it today, but "way back" the fuel distribution was a bear to tune.  Engines didn't make great HP unless most of the fuel was injected ahead of the blower, not into each port.  But under all that accel. the heavy nitro would slam back against the rear of the blower, making the rear cyls. rich and the front lean (blam!).

Look at old movies of fuelers and funnies as they stage.  The fronts are running rich to try to compensate.

The "on top vs port split" got pretty important.

RE: Top Fuel Dragster

"And lastly, the 8 exhaust rockets can add as much as 2,000 pounds of downforce at take off."

Are you saying that there is significant down force from the exhaust gases? I doubt that it would be anywhere near 2,000 lbs.

Jonathan T. Schmidt
http://www.schmidtmotorworks.com

RE: Top Fuel Dragster

^ 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)).



RE: Top Fuel Dragster

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..

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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!
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


Tony Athens
http://www.sbmar.com

RE: Top Fuel Dragster

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.....

RE: Top Fuel Dragster

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.

 

RE: Top Fuel Dragster

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

RE: Top Fuel Dragster

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

RE: Top Fuel Dragster

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.

RE: Top Fuel Dragster

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.

RE: Top Fuel Dragster

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

RE: Top Fuel Dragster

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.

RE: Top Fuel Dragster

"Action and reaction . . ."

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

Will

RE: Top Fuel Dragster

>"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.

RE: Top Fuel Dragster

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.

RE: Top Fuel Dragster

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.

RE: Top Fuel Dragster

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

RE: Top Fuel Dragster

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.

RE: Top Fuel Dragster

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

RE: Top Fuel Dragster

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.

RE: Top Fuel Dragster

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

RE: Top Fuel Dragster

Greg you make a good point that the exhaust velocity cannot exceed sonic speed as the only way to reach supersonic speed is apparently by using a converging-diverging nozzles.
(I only read this as a fact but haven't read an explanation why this is so. So please post if anybody knows more about this.)
However the sonic speed of any gas is (among other factors)proportional to the squareroot of the temperature. Since the temperature in the exhaust gas is extremely high it can reach double the sonic speed of air (at 'normal' pressure and temperature) without exceeding the sonic speed limit of the exhaust gas.

Besides even if the velocity is lower, the pressure of the exhaust before leaving the pipes also adds to the downforce.
http://exploration.grc.nasa.gov/education/rocket/rockth.html
So if you combine the massflow and the pressure difference, 2000 lbs. doesn't sound unreasonable at all.

If you can increase the exhaust velocity by using converging diverging nozzle and if horsepower is less of an issue than tire friction (if the clutch is such a crucial element this only means that there's a lack of tire friction or downforce), why aren't there converging diverging nozzles mounted to the exhaust pipes? (Even if they increase backpressure and therefore reduce horsepower, they could significantly increase downforce).

RE: Top Fuel Dragster

This may not be "Top Fuel", but it is certainly "Top Diesel"..

The guys on this site  http://www.cumminsracing.com/     have taken the 5.9 L Cummins to level that I find hard to believe..

I know this engine well and knew was was tough, but I am now even more of a Cummins fan.............

Under 8 seconds, over 160 MPH,  and 100lbs of boost--all on bio-diesel.



Tony Athens
http://www.sbmar.com

RE: Top Fuel Dragster

Uh, if the exhaust pressure was really 2K lbs total as several posters have surmised, why wouldn't they all be pointing the pipes towards the rear of the car?

2K lbs of "jet thrust" surely would shave a few hundreds (or tenths) off the time, no?

Jeff

RE: Top Fuel Dragster

Uh, if the exhaust pressure was really 2K lbs total as several posters have surmised, why wouldn't they all be pointing the pipes towards the rear of the car?

2K lbs of "jet thrust" surely would shave a few hundreds (or tenths) off the time, no?


Jwaterstreet,

I see where your coming from, but forward thrust isnt where a top fuel is lacking, its tyre traction. More traction means more power can be applied to the tyres. Watch any jet verses car drag race, tyres always accelerate off the line faster than jets, Being a direct friction contact, compared to reaction/opposite reaction.

Ken

RE: Top Fuel Dragster

Also, of course, the downward thrust due to exhaust is high at low speed when the aero downforce is minimal, but when grip is most important.

But that was a good point.

Cheers

Greg Locock

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

RE: Top Fuel Dragster

I do think that the pipes lean back a few degrees from the vertical, so there would be some forward thrust as a result.

Norm

RE: Top Fuel Dragster

I guess the pipes should have movable deflectors, such that the downward thrust is 100% below 100 mph when the wing is not or less effective and 100% rearward thrust at top speed (the downforce and drag of the wing at 300 mph is almost 10 times higher than at 100 mph).

Since these car don't have gears or any kind of torque converters also indicates that they can't utilize the engine power at lower speeds (and confirms that there's a lack of tire friction).

RE: Top Fuel Dragster

The exhaust/rocket/downforce debate...

One thing people seem to have missed is that the speed of sound of hot exhaust gases is a whole lot higher than that of plain old cold air.  Remember the sqrt(gamma.R.T) formula?  How hot are the exhaust gasses of a dragster I wonder?  Even at a conservative 1200K that gives about 700 m/s.

RE: Top Fuel Dragster

One source suporting the claim of up to 2,000 pounds of downforce from exhaust was from tests done by Paul Van Valkenburgh and published in Race Car Engineering magazine.

RE: Top Fuel Dragster

Let me know if you think this would work, or if not please explain.

What about the idea of dropping the super-charger which I know consumes a Significant amount of hp, and instead having a small  
size, say 10 Liter tank of liquid O2 Regulated to the same PSI and flow rate that the super-charger adds to the engine. Also remember that normal air is only 21% O2 and that the tank is at 900psi and also the fact that liquid O2 expands 800 times in volume when vaporizing. You could even preheat it through the intake manifold or headers, you could regulate it to whatever atmosphere you needed at aprox. 21% 0f 3000 cfm. Any input. Could this work? Any benifit? 10 Liter tank only weighs about 65 pounds full. The engine would then be running on pure oxygen.

RE: Top Fuel Dragster

Quite a few metals are flammable in pure oxygen. This may be a problem with hot engine parts.

RE: Top Fuel Dragster

Peter Jensch. What you propose has been tried by at least one of the more adventurous souls on this board. You are basically building a bomb, or a rocket.

Your logic is fine, but the practicalities are lethal.

Cheers

Greg Locock

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

RE: Top Fuel Dragster

Pure O2 would produce lots of heat but the metal engine parts would not tolerate it and the risks are way too great for the driver.  Everything burns in the presence of O2

RE: Top Fuel Dragster

If I'm not mistaken, they're only allowed to use roots blower as superchargers (which aren't really designed to generate pressure ratios at that scale). If they were to use more efficient twin scroll superchargers, they could probably gain a significant amount of power as well.

RE: Top Fuel Dragster

Peter Jesch,
  read up on the Purdue University Charcoal Lighting Contest.

The record is something like three seconds to ignite 65 pounds of charcoal, by dumping LOX on it.  Not recommended.  The barbecue itself is also a consumable.

The actual Purdue site has been removed, but you can find stories about it.  The videos were most impressive.  Maybe there's an echo somewhere.

The important thing to remember is that with oxygen, any container you can put it in will serve nicely as fuel.  Industrial gas producers will provide sobering, if unspectacular, information.

Mike Halloran
Pembroke Pines, FL, USA

RE: Top Fuel Dragster

The whole point in limiting Top Fuel to a Roots blower (14:71 max I think) is because they are inefficient and they thereby limit the power to something like 6000 HP.

I believe they also limit OD ratio and the amount of nitro methane in the fuel to try to keep speeds down to a level that does not exceed their tyre ratings.

I am not fully up to date and not totally familiar with Top Fuel regs, but from anecdotal evidence, they seem a bit reluctant to also reduce wing substantially, and therefore reduce down force to a level where the tyres and chassis are relatively safe. I believe that they have had several fatalities in recent years due to chassis, and/or wing strut and/or tyre failures at the top end.

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.

RE: Top Fuel Dragster

Apparently they used to bombard spectators with blowers, because the mixture would pre-ignite before the intake valve closed. That's why they use straps to prevent this from happening.

If they had used more efficient superchargers (reduce the size of the engine instead), the temperature after the supercharger would have been lower and reduce the probability of pre-ignition before the intake valve closed.

Also if they used centrifugal superchargers they would have a more favourable torque curve. Less torque at low engine speeds and more torque at high engine speeds when more downforce is available. (The clutch could engage at a lower speed and generate less overall waste heat).

Or what's missing?

RE: Top Fuel Dragster

2
Implications that pure O2 will set the metal of the engine on fire are sensational.  When metered into the combustion chamber the O2 (whether dilute or concentrated) will always react first with whatever has the lower energy of activation.  At rich to stoichiometric ratios used for maximum power this will be the fuel and not the engine parts.  There may be lots of reasons why it won't work, but that difficulty isn't one.

RE: Top Fuel Dragster

A star for you DRWEBB. I was hoping someone would step in and define the chemistry in this discussion.

Will

RE: Top Fuel Dragster

Chemistry understood (sort of).  But is the mixture sufficiently homogeneous?  Mightn't a small but consistently lean region adjacent to something metallic develop a slightly different appetite?  

Norm

RE: Top Fuel Dragster

Lean mixture will oxidise engine parts, especially pistons even with atmospheric oxygen and normally aspirated.

With more air via supercharging, higher cylinder pressures via high compression and a lot of spark advance, even stoichiometric mixtures can burn holes. In high output engines A:F can be 10 to 15% rich, or even more on alcohol to prevent this.

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.

RE: Top Fuel Dragster

>>"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.<

Because of the twisted lobes in a Roots supercharger, more air is forced into the front cylinders. Crew chiefs used to compensate for this inherent dynamic by lowering the compresssion ratio in the front cylinders, leaving the middle four alone and raising the CR in the rear cylinders. This was accomplished with con rods about 0.070 shorter in the front than the rear. Some crew chiefs also tried to position air dams in the intake manifold to block air to the front cylinders in the hopes of creating equal distribution. A few years ago, Alan Johnson of the US Army team developed an intake manifold that positions the front of the supercharger over a central plenum. Called the setback supercharger, a longer drive snout is needed but there is more equal distribution to the cylinders. BTW, fuel pressure starts out at about 275psi at the start and increases to around 470psi at the end of the run.

RE: Top Fuel Dragster

Dr Webb,

Respectfully I disagree.  Admitting O2 in high doses is an experiment I have witnessed.  The engine/victim was a small industrial diesel that was used for a nox and particulate study with CNG and other fuels.  The piston and exhaust valve and seat were torched minutes after admitting O2.  The O2 sensor indicated stoich under load but the failure occurred while lean at part load.  Not a surprise.

RE: Top Fuel Dragster

Believe me I know Copressed Oxygen or Cryo-LOX are not things to goof off with. Think about it like this: If only 21% of the air you are shoving in to the engine actually is allowing the fuel to ignite, then what is all the other 79% doing? Well it does help keep from burning the valves and pistons but it also is using up prime real-esate through your ports and in the cylinders. I have built several liquid rocket engines and I know the the better I can control my mix and flows the better my engines will run. So why not loose the blower and pre-presurize the air you are gonna burn, before you even start the engine? If you don't want pure O2, how about 70%O2 and 20%Nitrogen, or whatever combination in between. I am no top fuel expert, I am just currious about what any of you think. I may be attemting this first with maybe a honda or something cheap that I can test my ideas on, without breaking the bank.

RE: Top Fuel Dragster

One more thing about the bomb aspect, to anyone concerned. The Saturn 5 rocket had alot more fuel and oxidizer onboard, thousands of dragsters worth at least. Yes they had their share of emergencies but, done right I realy think it would only be marginally more dangerous that top fuel is now.



Getting the mix to be homogeneous will be the key.



Gasoline = C8H18
100 octane gasoline is mostly C8H18
2(C8H18)+25(O2) => 18(H20) + 16(CO2)
A ratio of 25/2 = 12.5 Oxygen molecules per fuel molecule



Nitromethane is CH3NO2
4(CH3NO2) + 7(O2) => 6(H2O) + 4(CO2) + 4(NO2)
A ratio of 7/4 = 1.75

RE: Top Fuel Dragster

Top Fuel has strict rules regarding supercharging, as previously mentioned.

Using pure O2 as an oxidising agent would be considered as chemical supercharging and therefore in breach of the rules.

I think this point alone makes that argument redundant.

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RE: Top Fuel Dragster

Oxygen *enrichment* is something that can be done with relative safety.  Amazing what a tiny 1/8" rubber tube with only a few psi can do.  I used to run the carb. secondaries way rich, then slowly increase the oxygen psi until the HP came in.  Detonation is a big concern; the spark must be retarded as with nitrous.

Also ran a street Camaro with a big stainless fire ext. full of methanol in the trunk and pressurized with a small 12v tire inflator.  Sprayed the meth. down into the carb. and added the oxygen.  HP was amazing.  But I'd guess I only increased the oxygen level from 21% to maybe 24-5%--things happen in a hurry w/oxygen and even the much milder nitrous.

Running modified car engine on 100% oxygen and no air is NOT going to work, unless you're in the fireworks business-and it will happen in less than a second.

RE: Top Fuel Dragster

Being old as dirt and growing up in the early days of drag racing, I got to see and experience a lot of these things first hand both in dragsters and funny cars.
Exhaust....Garlits was one of the first to go from weedburners to zoomies and entered the 200 mph +. It was due to streamlining the air flow over the tires at first but today the down force is quite large and has been measured.
Adding nitrous to nitro is not allowed in competition. Not even to alcohol.... not that it hasn't been done.  It's not needed as noted in previous posts. There is still plenty of hp available when needed.
only 85% nito is allowed in TF and FC (last I heard) and blower OD is limited. I ran 60% OD on an 8-71 back in the mid 70's and it worked great for the launch but hurt the top end. It's still who gets there first that counts not how fast you run so it worked for us.
spark plugs... nitro cars burn the ends off by half track. yes they have recessed electrodes but the guts are toast quickly. The motor runs on the ragged edge of detonation all the time. We even burned the ends on alcohol, however 3-4 threads of heat is the preferred measurement. Alcohol likes to have spark all the time. In the old days there wasn't enough juice from the magneto to light the fuel that could be pumped so it was by-passed to the tank. It wasn't untill the dual mags and rare earth magnets that the fuel cars made leaps and bounds in speed and E.T. You don't ever want to grab todays mag and give it a twist. You will probably still have a good "buzz" on when you are talking to St.Peter. haha something like 40 amps or better.
fuel distribution...early on everyone noted differences in fuel burn patterns. Nobody really knew what caused it. Some leaned the front cyl, some richened them, some just ran the blower faster,put more fuel in it and advanced the mag...and paid the parts bills.  Lot's of things were tried before realtime testing took place.  Somebody came up with the "delta plate" which was a triangular opening plate under the blower to redirect the flow. Some ran it forward some ran it backward..some didn't run it at all.  Now the blowers come with it built in. Now some are moving the blower forward and backwards the rules are limiting it.
Racers will do about anything to gain an edge...including BS.ing. haha  don't ask how I know.
Drag racing today is very technical. Many teams employ engineers who do nothing but investigate how to go faster and quicker. It's come a long ways from blue jeans and grimy tee shirts of the old days....but it was sure fun back then.

RE: Top Fuel Dragster

Interesting thread. I'm an NHRA fan and a friend was the clutch guy for an alcohol funny car team (Steven Gasparrelli) while Randy Anderson was the crew chief. I got to learn a ton by hanging out in the pits with these guys.

There is massive thrust from the headers. There is empirical evidence for even casual observers by watching a fuel car make a pass. When you see a cylinder go out on one side of the car (exhaust plume goes white/cloudy), the resulting thrust differential will push the car towards the side with the dead cylinder. This happens quite often.

Beyond the rules banning the use of nitrous, as stated the engines make so much power that they can spin/smoke the tires at 300mph even with all the downforce so the focus is on traction instead of power. Typically, the fuel cars run less fuel at the beginning of the pass where traction is limited and build heat in the heads. Then the fuel is increased where the traction is better and the hotter heads help burn the increased fuel. That was a trick implemented by Bernstien's team to got him so many speed records at the time.

There have been a few turbocharged nitro dragsters but they have not been legalized by the sanctioning bodies.

RE: Top Fuel Dragster


I just stumbled accross this forum.  Interesting and very accurate. Nitrous has been used in the NHRA.  Don The Snake Prudome used it in his Funny Car and went 2 tenths faster than anyone before- blew up- and Nhra banned it.  Mickey Thompson built a funny car with compressed o2 cylinders alongside each frame rail and called it his bottle baby. Im not sure how it worked.  Other additives have been tried and some work well.  They are very caustic and unstable.  All are banned. Nitro is very trickey to get right.  We do lean our engine on the top end close to the 1.7 fuel to air ratio.  ( Gasoline  1 lb. gas to 15lbs. air--Nitro 1 lb. to 1.7 lbs. air)  This is where we burn pistons if we miss the corrected altitude/air density and load on the engine from nitro percentage, mag/ignition lead, prop selection, gearing and water density. The combinations are endless.  One last point the NHRA is retricted to 85% nitro and run a spec MSD Mag that limits RPM at 8400 by a rapid retard if it is reached.

http://dragboats.com/images/gallery/large/04_11_IHBA_6360_692.jpg
 

RE: Top Fuel Dragster

hey! new here, but i'd like to say i have 1st hand knowlage of the amount and force of the raw unburnt fuel exiting the pipes from a top fueler. picture if you will, three boys standing in direct line of fire from, Don "the snake" Prudomes ride. they load her up, and hit the starter motor on the blower and we are mezmerised... BAMM!
we caught the full force of them pipes smack in the face! it felt like a hammer to the face, with fumes... instantly blinded and slammed in the face, i did an immediate about face only to slam head first into a goose neck trailer directly behind me. almost broke my damn neck in the proccess. there are few things in this world that can truly drag your ass into existance like a face full of hot unburnt nitro!
ed

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