Nitro engine injection and ignition parameters

[rocketgeek]

Hi everyone!!

I was looking for the injection/ignition parameters of a nitro engine that burns a 90/10 mixture of nitromethane and methanol

-Which kind of injectors are used and what's the pressure jump across them?

- What is the pressure in the chamber at the moment of combustion?

-Spark plug or glow plug?

-What is the energy and/or power absorbed by the spark/glow plug and how long does it stay on?

-Bonus question: how much spark energy does a 90/10 NM/methanol mixture required to ignite?

Thanks to everyone who will contribute

[Force]

Ouch, that was a lot to try to explain.
The ignition in a Nitro Top Fuel and Funny Car engine are done by dual MSD Pro Mag magnetos wich delivers 44 amperes current each to the 16 spark plugs and the timing advance is about 58-65 degrees before Top Dead Center as the Nitromethane burns slow, it still burns in the exhaust pipes thus the visible flames and very loud sound, the 16 spark plugs are burned up and melted by aproximately half track and the engine "diesels" down the track from the compression heat and the glowing red hot exhaust valves, the only way to stop the engine is to shut off the fuel delivery.
The fuel mixture is pumped by dual mechanical fuel pumps that can fill up a bathtub in a few seconds, the capacity of the pumps is around 100 US gallons per minute each, it's a constant flow fuel system with a system pressure around 500 psi where you regulate how much fuel the engine will get and burn (lean or rich) with how much fuel you return to the tank, and it's quite complex with a lot of valves, return lines and stuff, the fuel goes through a barrel valve and distribution blocks and is injected at three places in the engine through 42 or more nozzles, some of the fuel is injected under the injector hat on top of the supercharger and that fuel is mainly to cool and lubricate the supercharger, some of the fuel is injected under the supercharger in the intake manifold runners and the main part of the fuel delivered to the engine is injected through 2 nozzles in each of the intake ports in the heads right behind the intake valves and goes directly in to the cylinders.
As the engine has no water jackets it's also cooled by the large amount of fuel and they use about 15-20 US gallons of the Nitromethane/Methanol fuel mixture for one run.
Nitromethane carries two oxygen atoms in the molecule (CH3NO2) so a Nitro engine can burn about 7.6 times more fuel than a gasoline engine can because you get oxygen in with the fuel itself, so they push in as much fuel as it's possible to do without locking the cylinders hydraulicly, that will say very much but not as much so it fills up the whole cylinder, because you can compress gases but not liquids so you need to leave some room otherwise the heads will fly off, the engine block will split in half, kicking out the conecting rods through the block sides or the crank will exit through the oil pan...I have seen all of that happening.
A supercharged Nitro engine is calculated to produce 10 000-11 000 hp or more and over 7 500 ft-lbs of torque, the manifold pressure under the supercharger is around 55-75 psi and it takes about 800-1 000 hp just to drive the 14-71 supercharger at full pressure.
The cylinder pressure is about 1 160-1 450 psi and the exhaust gases from the engine produces 900-1 100 lbs of downforce through the individual zoomie headers at full throttle.
A fun thing is the the crank shaft in a Nitro engine at 8 000 rpm turns just around 500 revolutions from start to finish and a Top Fuel Dragster does 0-60 mph in 0.7-0.8 seconds and they go well over 60 mph at the first timing point at 60 feet.

You can read more here.

https://en.wikipedia.org/wiki/Top_Fuel

Here is a video on how much fuel a Nitro engine uses per cylinder, first at idle and then full throttle.

 

Edited June 25, 2021 by Force

[Bainford]

Nicely done, Force. I always enjoy reading minutia on nitro engines. My background is mechanical engineering, yet I never cease to be amazed at the mind bogglingly incredible numbers.

900-1100 lbs of down force from the zoomies! First time I heard this stat. Mind blowing. 
 

When I was a teen and really keen about understanding engine physics, I calculated the total number of revolutions for a top fuel run, and came up with a number similarly low to what quoted above. I was certain the answer was wrong, but couldn’t find a mistake in the math. Checked it several times, then the penny dropped… mind blown!

[Muncie]

Hakan, excellent summary, well done - lots of information and very concisely said.

[Straightliner59]

Hakan, excellent analysis! Look for anything you can find, online, from Tom Jobe, as well. I once read that some famous fuel guru explaining nitromethane said that it is more detonation than burn. To illustrate, he said you can pour some onto a steel bench top.  Throw matches at it, all day, and nothing will happen. He then advised against hitting it with a hammer.

[Force]

Thanks.
I have allways been facinated by Nitro engines since I experienced one the first time live in my life, it was a Swedish Nitro Funny Car called Ragnarök who was doing a burnout at a local car show back in 1977, and I have been hooked on Nitro cars ever since and need a shot of Nitro fumes and sound every year to feel complete.
That said I have learned a lot regarding Nitro engines over the years, allmost a bit nerdy, and I gladly pass on what I have learned to anyone who want's to know.
One thing one can say is allmost all you have learned about combustion engines can be thrown out when it comes to Nitro engines, the mechanical side is similar but the rest is a totally different ball game.

One thing about the powerful exhaust gases from a Nitro engine is that when a cylinder or two goes out (not igniting) on one side of the engine the car starts to drift towards that side as the exhaust gases from the four cylinders on the other side are so powerful that they push the car over and it often gets out of "the groove" and the driver has to lift.

From my screen name and avatar you might have guessed who my favourite driver is  and I have met the man himself 5-6 times both at his Yorba Linda shop, in Las Vegas at SEMA and at the Las Vegas and Pomona tracks, last time I met him was at the Yorba Linda shop and he came in to the  Race Station store and talked with us for a while, wrote some autographs and posed for some photos, so he's a neat guy.

Edited June 25, 2021 by Force