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?

 

[turbocohen]

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

 

[HydroScope]

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?

 

[patprimmer]

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.

 

[MikeHalloran]

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

 

[kenre]

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

 

[Metalguy]

>"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.

 

[Metalguy]

>"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.

 

[patprimmer]

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.

 

[Metalguy]

>"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.

 

[franzh]

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

 

[Metalguy]

"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!

 

[patprimmer]

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.

 

[kenre]

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

 

[turbocohen]

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.

 

[Fabrico]

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.

 

[turbocohen]

wow didnt realize it was that high

 

[Craighell]

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.

 

[Metalguy]

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.

 

[motorsportsdesign]

"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