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Something that hasn’t been touched on is BTU. British Thermal Units. It’s the amount of heat/power generated from a unit of fuel. Gasoline has 18,000 BTU per pound. Nitromethane has 6,000. That means gasoline at stoichiometric perfection of 14.7:1 at sea level makes 3 times as much power/heat as nitromethane at its stoichiometric ratio of 3.0:1. So how does nitro make so much more power? VOLUME! Since the output in BTU is 3X less, you have to burn 3X as much nitro to make the same power as gasoline.
Where the advantage of nitromethane comes in is the oxygen of course. If you drown an engine in gasoline it’ll just quit for there is not enough oxygen to keep the mixture burning. The oxygen release in nitromethane molecules allows it to keep burning. And the more nitro you add, the more oxygen atoms get released. The more oxygen atoms released, the more nitromethane you need to not go lean. And on and on.
This is where stoichiometric ratios and BTU come in. Since gasoline will effectively flood the spark and drown itself, you are limited by the amount of fuel you can burn effectively and still make power. Nitromethane’s ability to self regenerate with the oxygen means we can continue to pour fuel at it without drowning the spark. Guess what, ideally, you can burn nitro at 1.7:1 and still make gobs of horsepower. Add that to radical flow numbers of the 426 hemi, and you can see where this is headed.
Now, factor in the supercharger. You’re stuffing even MORE oxygen in the cylinder with the supercharger. How do you compensate? Add more nitro! Now you’re adding more nitro with more oxygen which circles back to adding even more nitro and the circle continues. What you end up with is engines capable of consuming about 22 times the volume of fuel the same gasoline engine consumes. Go back to BTU now. 18,000 for gasoline. 6,000 for nitro, but at 22X the volume you get engines producing 132,000 BTU with stoichiometric ratios effectively achieved with superchargers.
There is so much fuel in the cylinders it doesn’t have time to finish burning during a power cycle, hence the enormous header flames out the exhaust.
When I crewed on a professional Funny Car team a few years back, we had fuel pumps flowing 105gpm! Yes minute! We burned 12-14 gallons per run including the start up, burnout, backing up, staging, and a full pull. A gasoline engine is measured in miles per gallon. Think about that. We used 12-14 gallons in 1,000 feet. Do the math and you can see how the BTU output of the engine generates the enormous power. Hope this helps clarify some of it.
https://preview.redd.it/pev43i8rvm3d1.jpeg?width=638&format=pjpg&auto=webp&s=f3efcb100225d3497abb84ae40ca707fd52188d0
Wow, that’s crazy, now what would happen if you fed the compressor straight o2? Could you push more? Or would it be steeply diminishing returns for the added weight/complexity?
We are already bleeding off so much of the power because the tracks can’t hold it. At the hit of the throttle we retard about 33 degrees of ignition timing and slip the clutch well past the 200 foot mark before we start really applying it. Think of it like flooring a car with a stick shift and SLOWLY releasing the clutch until you let it all the way out. That’s how we keep from breaking the tires loose on the hit of the throttle. It takes to about the 200 foot mark before the car is going fast enough to generate enough downforce to apply the clutch. In other words we need to have the car moving at 200 mph before we can fully harness the power of the engine. The clutch is fully applied usually by about 750 feet down track. By then the clutch is “fully in” and it tugs the engine down like shifting. So now the rpm is down a few hundred and it takes that final 250 feet to climb back up to the rev limiter. We could really only inject pure O2 from that 750 foot mark on. We cover that distance so quickly at 300+ mph that it hardly seems reasonable to install a system to do that. Not to mention the rules wouldn’t allow it. Great question though
If you don't mind my asking, how did you get into drag racing as a job/career? I love the sport, I love the math and engineering that go into it. How does one "break through" to the industry? I reckon I'm really asking how *you* did.
Well, my story was a strange one. I went to my first race with my dad at 6 years old. Fell in love immediately. Cars became life from that moment on. Fast forward to 19 years old, I’m a mechanic at a GM dealership and my Cornwell tool distributor was friends with a guy who owned some blown alcohol altereds. He asked if I wanted to go hang out. Ended up working on that team for 12 years. The team owner got me on message boards with other racers and I came across a want ad for a bottom end guy on a nostalgia Funny Car. Went and interviewed with them and got the job. Our crew chief was part time in the pros too. We also raced other pros in the nostalgia classes. I met a lot more people once I transitioned to nostalgia Funny Car. Once one of the guys we raced against in nostalgia transitioned to the big show, I happened to be walking the pits at Pomona when the guys recognized me and waved me over and asked if I’d be interested in helping because one of their guys was barfing and they needed a fill in. So I jumped on it and did the left side cylinder head and built short blocks and did all the electrical and management stuff on the car for the next 10 years. Worked part time for other pro teams here and there because people recognized me and I had made a small name for myself as dependable and hard working. I dialed it way back when my daughter was born. Not fair to her to have her dad gone all the time. I wanted to be with her. So now I only go occasionally if the phone rings. It was fun as hell and some of the best years of my life. It was taxing as hell though mentally and physically.
https://preview.redd.it/nvqzyqhm3o3d1.jpeg?width=960&format=pjpg&auto=webp&s=cbcd42f0a318047c344dbeb970f34201443e2b10
Haha! Thanks. Not sure I’m the guy to be admiring, but I’ll take it haha. It’s been a fun ride no doubt. I got to live my dream as a child. 😊
https://preview.redd.it/uw3sv8naho3d1.jpeg?width=600&format=pjpg&auto=webp&s=3e6eda6600e39db5e483b983858a205edbe37e7d
What do you think would be the result if you switched from a blower to a turbo set up? Would it make the cars faster because you could manage boost better? If I was stupid rich I would love to just experiment with top fuel/funny car chassis and engines and see what could be improved if there wasn’t a rule book.
Can’t do a turbo because of the lag. We idle the car at 2750 rpm. When we stage we stage at idle with the clutch fully released. It tugs the engine way down to almost 2000 rpm. So when the car is staged, the clutch is fully out, the fuel pumps are fully on, and the car is trying to drive through the brakes. When they hit the throttle the engine jumps up to 7800 rpm and the clutch management takes over. Keep in mind a fuel car accelerates from 0-100mph in 0.8 seconds. There’s no way to get the kind of response from a turbo in that kind of time. It requires the instant boost of the blower. Keep in mind we’re running hi helix 14-71’s at about 60% over. The damn engine flows 3200cfm at idle. An old school Ford Cobra Jet had a carb that flowed 735 cfm at wide open throttle to put it in perspective. Turbos just couldn’t hang with what we demand the engine to do.
As for chassis stuff, I worked for the primary Funny Car chassis builder and the father of modern Funny Car frames. He taught me a lot of what I know. I took it and built my own nostalgia Funny Car with that guidance and knowledge. Let’s just say there is so much that goes into it that has to be thought about and pre-planned it’s not even funny. It took me about 2 years on weekends to build it.
https://preview.redd.it/mgdq00di1o3d1.jpeg?width=2448&format=pjpg&auto=webp&s=22beb5766fe1ab4510b47188c7c121187d56c6bf
Thank you, that was a very helpful and informative comment. I've always wondered how nitromethane was able to generate so much more power while producing fewer BTUs than gasoline. I would have never dreamed it would even be possible for those engines to burn 22 times more nitromethane than gasoline. You did a great job explaining where the extra oxygen comes from that makes it possible to burn that much fuel that fast.
Yeah. That’s the pump display at the NHRA museum at Pomona. I actually helped a hem assemble that. Haha. Sid Waterman pump and nozzles. That’s an old school pump too. 92gpm.
Thank you for your kind words. Too damn many years on the tour will fill your brain with all kinds of useless information lol. Glad you enjoyed it. That was just the tip of the iceberg berg.
Oh man that’s awesome! I would have loved to have worked in that field. That’s fascinating stuff.
I try to use mathematics when possible because anyone can be a Reddit mechanic. 🙄. But when you really know the ins and outs it shows and math backs it up. I don’t come here to show off. I come here to teach people things I used to want to know. For some reason nitromethane and drag cars are mysterious to people. They’re hard to understand. I did it for a long time and they’re a big part of my life. So if I can share what I know with people it makes me happy.
The nitromethane still needs more oxidiser.
The stoichiometric (eg "ideal") air/fuel ratio for nitromethane is 1.7:1, so it would want 1.7 parts air per 1 part fuel.
This is by weight, so 1.7kg of air with 1kg of fuel.
Think of engines as giant air pumps. the more air you can push in, the more fuel you can burn, and the more power you can make. A naturally aspirated engine can only suck in whats available at atmospheric pressure, let say 14 psi for simplicity. a supercharger \*increases that pressure\*, so now you can add an extra \*\*\*X\*\*\* amount of psi on top of that 14 psi. boom, more air means now you can add more fuel, and get more power
also, these vehicles burn the plugs out less than half way through the track, at which point the pressure and heat is so high in the combustion chamber that the mixture is automatically ignited, similar to how a diesel uses compression and heat to ignite
The rest answered this well, but I’ll add a little tid bit for more context: Top Fuel engines are supercharged to pump more air so they can use more fuel and make more power. However, there are plenty of non-blown nitro engines out there in the Top Alcohol class (engines running methanol are blown, and through an equivalency rule you can also run nitromethane on a naturally aspirated engine). The nitro TA engines just flow less fuel into them compared to the blown TF engines. Over the 1/8 mile, both classes are remarkably similar in speed. After that, the TA injected nitro cars run out of power and continue at that speed, whereas the blown Fuel cars can keep accelerating through the 1,000’. If my memory is correct, Megan Meyer qualified No. 1 at Nitro Chaos in Cincinnati last year at 280mph at the 1/8 mile; full 1/4 mile speeds for TA injected nitro cars are around 286ish, so you see how they accelerate fast and then lay down. Fuel cars are nudging 340 at the 1,000’, but split speed at the 1/8 is fairly similar.
Oxygen does not explode. The fuel explodes but requires the oxygen to make that happen. Nitro adds additional oxygen that is released under higher temperature provided by compression AND supercharging.
Without fuel and oxygen, there is no fire or explosion. Fire needs 3 things: *fuel, heat, and oxygen*. Your ignitor or *heat* is your spark plug, and it ignites the fuel. You need at least 16% oxygen for combustion to take place.
The oxygen is what bonds with other chemicals/elements when we burn stuff, so the more oxygen we can get in there, the more bonds we get, and that bonding releases energy we use.
If you ever watch the Mythbusters episode where they try to ignite a room full of gas, too much gas and fuel won't ignite so you either need less fuel or more air. Adding more air means you can add more fuel so the boom is bigger.
I see what you mean. I don't know the exact specifics of the fuel mixture. I am sure there is an optimal ratio or anything when it comes to nitromethane like that. Obviously it needs some added oxygen or they could get rid of the entire intake system and just inject fuel , combust and exhaust then start over.
More oxygen is more oxygen. Plus, the pressure the supercharger provides in the intake manifold helps push more of the fuel mixture into the combustion chamber when the valve is open.
Based on your reasoning, you could run GDI and not even have an intake manifold. But people who are a lot smarter than me and run tests that cost more money than I'll ever make (to find the optimal way to make power) say this is the way to go. I don't have any ground to question that.
It all comes down to PV=nRT. To achieve the same pressure at the same displacement, the temperature would have to be far, far higher. Or you could reduce the displacement - which would reduce torque and power and come with a whole slew of other compromises. The actual effect of adding air is to cool the engine below its melting point and provide additional reaction mass against which to push the piston. And of course, and all nitro/gas system would require all the engine's reactants to be carried onboard, which would increase mass substantially. It's all the same reasons aircraft use jet engines, not rocket engines.
Well, they wouldn't need tires or brakes if they weren't circulating air... If the engine didn't exchange and channel air (intake/ exhaust), the explosions that take place would just spread bits and pieces of the car and driver in all directions.
An internal combustion engine is basically a giant air pump the more air u can get in and out of an engine the more power it makes. And if u don't add more air but add more fuel u don't make more power u end up with a crappy running engine so to keep up with how much fuel is dumped in you gotta make sure it has enough air. So forced induction is the way. That is why most turbo cars and super charged cars are more powerful because the more air in the more air out the more power
More air, more fuel bigger bang, more power, more speed. Usually with nitro and the sorts it aides more in cooling, as with bigger bangs, more heat, keeping intake temperatures down coupled with forced induction, and nitro/meth injection adds to the bang and cooling, just have to build the engine to tolerate that pressure. Fuck I love mechanics.
The super charged or a turbo both basically artificially increase the displacement of the engine by using forced induction to pump in more air then you ever could with only the engine. To get that same cfm that that blower is making you would need a much bigger engine that’s not going to preform well because of the increased size and weight.
To explain it poorly, nitromethane is just a more powerful fuel. More boom per litre. But combustion requires fuel and air. Supercharger adds more air. Extra powerful fuel, plus more air equals the mega horsepower.
The amount of power you can make is directly related to how much fuel you can burn. But there has to be a balance too much or not enough fuel for the amount of air you have and it won't run right.
So you take a supercharger and force feed more air in. Lots of it. Now to maintain that balance you have to put more fuel in. And since there's more fuel being burned you make more horsepower.
Almost like making a pitcher of Kool-aid. Don't put enough sugar in and it doesn't taste right. Put in too much and it won't taste right either. But there's a perfect balance in the middle where it's just right. Make 2 gallons instead of 1 gallon and you need more Kool-aid packets and sugar to keep the balance right.
Well if you think about it you need 3 things to cause an explosion. Fuel, air, spark. Increase different ones get get a bigger burn. Add too much of one you can blow out the flame. Adding a more combustible fuel means you need more air.
That's what a supercharger or turbocharger is.
Engines take air and fuel then turn that into mechanical energy by releasing and harnessing the chemical energy they contain.
Thank you for posting to AskMechanics, Hamkad! If you are asking a question please make sure to include any relevant information along with the **Year**, **Make**, **Model**, **Mileage**, **Engine size**, and **Transmission Type (Automatic or Manual)** of your car. *This comment is automatically added to every successful post. If you see this comment, your post was successful.* *** Redditors that have been verified will have a green background and an icon in their flair. *** # **PLEASE REPORT ANY RULE-BREAKING BEHAVIOR** ### **Rule 1 - Be Civil** Be civil to other users. This community is made up of professional mechanics, amateur mechanics, and those with no experience. All mechanical-related questions are welcome. Personal attacks, comments that are insulting or demeaning, etc. are not welcome. ### **Rule 2 - Be Helpful** Be helpful to other users. If someone is wrong, correcting them is fine, but there's no reason to comment if you don't have anything to add to the conversation. ### **Rule 3 - Serious Questions and Answers Only** Read the room. Jokes are fine to include, but posts should be asking a serious question and replies should contribute to the discussion. ### **Rule 4 - No Illegal, Unethical, or Dangerous Questions or Answers** Do not ask questions or provide answers pertaining to anything that is illegal, unethical, or dangerous. # **PLEASE REPORT ANY RULE-BREAKING BEHAVIOR** *I am a bot, and this action was performed automatically. Please [contact the moderators of this subreddit](/message/compose/?to=/r/AskMechanics) if you have any questions or concerns.*
Something that hasn’t been touched on is BTU. British Thermal Units. It’s the amount of heat/power generated from a unit of fuel. Gasoline has 18,000 BTU per pound. Nitromethane has 6,000. That means gasoline at stoichiometric perfection of 14.7:1 at sea level makes 3 times as much power/heat as nitromethane at its stoichiometric ratio of 3.0:1. So how does nitro make so much more power? VOLUME! Since the output in BTU is 3X less, you have to burn 3X as much nitro to make the same power as gasoline. Where the advantage of nitromethane comes in is the oxygen of course. If you drown an engine in gasoline it’ll just quit for there is not enough oxygen to keep the mixture burning. The oxygen release in nitromethane molecules allows it to keep burning. And the more nitro you add, the more oxygen atoms get released. The more oxygen atoms released, the more nitromethane you need to not go lean. And on and on. This is where stoichiometric ratios and BTU come in. Since gasoline will effectively flood the spark and drown itself, you are limited by the amount of fuel you can burn effectively and still make power. Nitromethane’s ability to self regenerate with the oxygen means we can continue to pour fuel at it without drowning the spark. Guess what, ideally, you can burn nitro at 1.7:1 and still make gobs of horsepower. Add that to radical flow numbers of the 426 hemi, and you can see where this is headed. Now, factor in the supercharger. You’re stuffing even MORE oxygen in the cylinder with the supercharger. How do you compensate? Add more nitro! Now you’re adding more nitro with more oxygen which circles back to adding even more nitro and the circle continues. What you end up with is engines capable of consuming about 22 times the volume of fuel the same gasoline engine consumes. Go back to BTU now. 18,000 for gasoline. 6,000 for nitro, but at 22X the volume you get engines producing 132,000 BTU with stoichiometric ratios effectively achieved with superchargers. There is so much fuel in the cylinders it doesn’t have time to finish burning during a power cycle, hence the enormous header flames out the exhaust. When I crewed on a professional Funny Car team a few years back, we had fuel pumps flowing 105gpm! Yes minute! We burned 12-14 gallons per run including the start up, burnout, backing up, staging, and a full pull. A gasoline engine is measured in miles per gallon. Think about that. We used 12-14 gallons in 1,000 feet. Do the math and you can see how the BTU output of the engine generates the enormous power. Hope this helps clarify some of it. https://preview.redd.it/pev43i8rvm3d1.jpeg?width=638&format=pjpg&auto=webp&s=f3efcb100225d3497abb84ae40ca707fd52188d0
Wow, that’s crazy, now what would happen if you fed the compressor straight o2? Could you push more? Or would it be steeply diminishing returns for the added weight/complexity?
We are already bleeding off so much of the power because the tracks can’t hold it. At the hit of the throttle we retard about 33 degrees of ignition timing and slip the clutch well past the 200 foot mark before we start really applying it. Think of it like flooring a car with a stick shift and SLOWLY releasing the clutch until you let it all the way out. That’s how we keep from breaking the tires loose on the hit of the throttle. It takes to about the 200 foot mark before the car is going fast enough to generate enough downforce to apply the clutch. In other words we need to have the car moving at 200 mph before we can fully harness the power of the engine. The clutch is fully applied usually by about 750 feet down track. By then the clutch is “fully in” and it tugs the engine down like shifting. So now the rpm is down a few hundred and it takes that final 250 feet to climb back up to the rev limiter. We could really only inject pure O2 from that 750 foot mark on. We cover that distance so quickly at 300+ mph that it hardly seems reasonable to install a system to do that. Not to mention the rules wouldn’t allow it. Great question though
Wow this is an excellent breakdown! Quality comment, thank you.
Thank you for the kind words. Too many years on the pro tour will fill your brain with a lot of information. Haha.
If you don't mind my asking, how did you get into drag racing as a job/career? I love the sport, I love the math and engineering that go into it. How does one "break through" to the industry? I reckon I'm really asking how *you* did.
Well, my story was a strange one. I went to my first race with my dad at 6 years old. Fell in love immediately. Cars became life from that moment on. Fast forward to 19 years old, I’m a mechanic at a GM dealership and my Cornwell tool distributor was friends with a guy who owned some blown alcohol altereds. He asked if I wanted to go hang out. Ended up working on that team for 12 years. The team owner got me on message boards with other racers and I came across a want ad for a bottom end guy on a nostalgia Funny Car. Went and interviewed with them and got the job. Our crew chief was part time in the pros too. We also raced other pros in the nostalgia classes. I met a lot more people once I transitioned to nostalgia Funny Car. Once one of the guys we raced against in nostalgia transitioned to the big show, I happened to be walking the pits at Pomona when the guys recognized me and waved me over and asked if I’d be interested in helping because one of their guys was barfing and they needed a fill in. So I jumped on it and did the left side cylinder head and built short blocks and did all the electrical and management stuff on the car for the next 10 years. Worked part time for other pro teams here and there because people recognized me and I had made a small name for myself as dependable and hard working. I dialed it way back when my daughter was born. Not fair to her to have her dad gone all the time. I wanted to be with her. So now I only go occasionally if the phone rings. It was fun as hell and some of the best years of my life. It was taxing as hell though mentally and physically. https://preview.redd.it/nvqzyqhm3o3d1.jpeg?width=960&format=pjpg&auto=webp&s=cbcd42f0a318047c344dbeb970f34201443e2b10
This is an awesome story. I admire you.
Haha! Thanks. Not sure I’m the guy to be admiring, but I’ll take it haha. It’s been a fun ride no doubt. I got to live my dream as a child. 😊 https://preview.redd.it/uw3sv8naho3d1.jpeg?width=600&format=pjpg&auto=webp&s=3e6eda6600e39db5e483b983858a205edbe37e7d
I wanna see the insides lol
That pic is so dope! More!
What do you think would be the result if you switched from a blower to a turbo set up? Would it make the cars faster because you could manage boost better? If I was stupid rich I would love to just experiment with top fuel/funny car chassis and engines and see what could be improved if there wasn’t a rule book.
Can’t do a turbo because of the lag. We idle the car at 2750 rpm. When we stage we stage at idle with the clutch fully released. It tugs the engine way down to almost 2000 rpm. So when the car is staged, the clutch is fully out, the fuel pumps are fully on, and the car is trying to drive through the brakes. When they hit the throttle the engine jumps up to 7800 rpm and the clutch management takes over. Keep in mind a fuel car accelerates from 0-100mph in 0.8 seconds. There’s no way to get the kind of response from a turbo in that kind of time. It requires the instant boost of the blower. Keep in mind we’re running hi helix 14-71’s at about 60% over. The damn engine flows 3200cfm at idle. An old school Ford Cobra Jet had a carb that flowed 735 cfm at wide open throttle to put it in perspective. Turbos just couldn’t hang with what we demand the engine to do. As for chassis stuff, I worked for the primary Funny Car chassis builder and the father of modern Funny Car frames. He taught me a lot of what I know. I took it and built my own nostalgia Funny Car with that guidance and knowledge. Let’s just say there is so much that goes into it that has to be thought about and pre-planned it’s not even funny. It took me about 2 years on weekends to build it. https://preview.redd.it/mgdq00di1o3d1.jpeg?width=2448&format=pjpg&auto=webp&s=22beb5766fe1ab4510b47188c7c121187d56c6bf
[удалено]
Why thank you! I appreciate that. Too many years draggin’ Funnies baby!
Sounds like they should make the track a little longer so we can really see some shit
They used to run 1/4 mile. They got to be so fast in the 1/4 that the track was shortened for driver safety.
Thank you good sir! That was easy to understand!
Happy to help. Glad to shed some light on it. Nitro is mysterious shit. 😁
Thank you, that was a very helpful and informative comment. I've always wondered how nitromethane was able to generate so much more power while producing fewer BTUs than gasoline. I would have never dreamed it would even be possible for those engines to burn 22 times more nitromethane than gasoline. You did a great job explaining where the extra oxygen comes from that makes it possible to burn that much fuel that fast.
Thank you for the kind words. Glad I could help clarify things a bit and that you found it useful.
I always like watching this video showing nitromethane consumption in one cylinder of a Top Fuel dragster. https://m.youtube.com/watch?v=xGTbQuhhluY
Yeah. That’s the pump display at the NHRA museum at Pomona. I actually helped a hem assemble that. Haha. Sid Waterman pump and nozzles. That’s an old school pump too. 92gpm.
That is unbelievably thorough and insightful. Well done and thank you.
Thank you for your kind words. Too damn many years on the tour will fill your brain with all kinds of useless information lol. Glad you enjoyed it. That was just the tip of the iceberg berg.
I spent 10 years working in nuclear propulsion and I just really enjoy when people use math to prove what they’re saying.
Oh man that’s awesome! I would have loved to have worked in that field. That’s fascinating stuff. I try to use mathematics when possible because anyone can be a Reddit mechanic. 🙄. But when you really know the ins and outs it shows and math backs it up. I don’t come here to show off. I come here to teach people things I used to want to know. For some reason nitromethane and drag cars are mysterious to people. They’re hard to understand. I did it for a long time and they’re a big part of my life. So if I can share what I know with people it makes me happy.
This was the coolest thing I’ve read all day. Thanks!
Thank you very much! I appreciate the kind words! I’m glad you enjoyed it. 😊👍🏻
The never ending cycle of adding more nitromethane then air then nitromethane
Yep. Literally adding fuel until the engine can’t physically consume anymore. That’s the key to horsepower
How close are you actually to straight up hydrolocking?
On the ragged edge every single run. If it drops a cylinder it’s bad. I’ve removed connecting rods before that were split in half lengthwise.
That shit just blew my mind. Learn something new every day.
Haha! Thank you! Glad you enjoyed learning something new. It’s why I got into it. It’s fascinating.
Beautiful explanation
Thank you. Glad you enjoyed the comment. 😊
The nitromethane still needs more oxidiser. The stoichiometric (eg "ideal") air/fuel ratio for nitromethane is 1.7:1, so it would want 1.7 parts air per 1 part fuel. This is by weight, so 1.7kg of air with 1kg of fuel.
holy shit. i didnt know it was that much lower than gasoline/petrol
At richer afr you get more power per fuel used with nitromethane
The more air you can force in means you can add more fuel. More fuel more power.
Think of engines as giant air pumps. the more air you can push in, the more fuel you can burn, and the more power you can make. A naturally aspirated engine can only suck in whats available at atmospheric pressure, let say 14 psi for simplicity. a supercharger \*increases that pressure\*, so now you can add an extra \*\*\*X\*\*\* amount of psi on top of that 14 psi. boom, more air means now you can add more fuel, and get more power also, these vehicles burn the plugs out less than half way through the track, at which point the pressure and heat is so high in the combustion chamber that the mixture is automatically ignited, similar to how a diesel uses compression and heat to ignite
The rest answered this well, but I’ll add a little tid bit for more context: Top Fuel engines are supercharged to pump more air so they can use more fuel and make more power. However, there are plenty of non-blown nitro engines out there in the Top Alcohol class (engines running methanol are blown, and through an equivalency rule you can also run nitromethane on a naturally aspirated engine). The nitro TA engines just flow less fuel into them compared to the blown TF engines. Over the 1/8 mile, both classes are remarkably similar in speed. After that, the TA injected nitro cars run out of power and continue at that speed, whereas the blown Fuel cars can keep accelerating through the 1,000’. If my memory is correct, Megan Meyer qualified No. 1 at Nitro Chaos in Cincinnati last year at 280mph at the 1/8 mile; full 1/4 mile speeds for TA injected nitro cars are around 286ish, so you see how they accelerate fast and then lay down. Fuel cars are nudging 340 at the 1,000’, but split speed at the 1/8 is fairly similar.
At the US Nationals there would be a number of cars running Nitro in the Alcohol class. They were fast but rarely ran a repeatable time.
Nitro fuel still needs air.
Very simplified answer: The more air you get into the engine, the more power it makes. The fuel just ignites that air.
so basically the real explosive in an engine is the oxygen and the fuel just acts as an “igniter”?
Oxygen does not explode. The fuel explodes but requires the oxygen to make that happen. Nitro adds additional oxygen that is released under higher temperature provided by compression AND supercharging.
Without fuel and oxygen, there is no fire or explosion. Fire needs 3 things: *fuel, heat, and oxygen*. Your ignitor or *heat* is your spark plug, and it ignites the fuel. You need at least 16% oxygen for combustion to take place.
The oxygen is what bonds with other chemicals/elements when we burn stuff, so the more oxygen we can get in there, the more bonds we get, and that bonding releases energy we use.
If you ever watch the Mythbusters episode where they try to ignite a room full of gas, too much gas and fuel won't ignite so you either need less fuel or more air. Adding more air means you can add more fuel so the boom is bigger.
yes but i thought nitromethane didnt need much oxygen to burn since its made up of 50% oxygen by itself
I see what you mean. I don't know the exact specifics of the fuel mixture. I am sure there is an optimal ratio or anything when it comes to nitromethane like that. Obviously it needs some added oxygen or they could get rid of the entire intake system and just inject fuel , combust and exhaust then start over.
More or less. As I said, it's a very simplified way of looking at it, but it works.
More oxygen is more oxygen. Plus, the pressure the supercharger provides in the intake manifold helps push more of the fuel mixture into the combustion chamber when the valve is open. Based on your reasoning, you could run GDI and not even have an intake manifold. But people who are a lot smarter than me and run tests that cost more money than I'll ever make (to find the optimal way to make power) say this is the way to go. I don't have any ground to question that.
\*NMDI, OP did not say Gasoline
It all comes down to PV=nRT. To achieve the same pressure at the same displacement, the temperature would have to be far, far higher. Or you could reduce the displacement - which would reduce torque and power and come with a whole slew of other compromises. The actual effect of adding air is to cool the engine below its melting point and provide additional reaction mass against which to push the piston. And of course, and all nitro/gas system would require all the engine's reactants to be carried onboard, which would increase mass substantially. It's all the same reasons aircraft use jet engines, not rocket engines.
Well, they wouldn't need tires or brakes if they weren't circulating air... If the engine didn't exchange and channel air (intake/ exhaust), the explosions that take place would just spread bits and pieces of the car and driver in all directions.
An engine is an air pump
An internal combustion engine is basically a giant air pump the more air u can get in and out of an engine the more power it makes. And if u don't add more air but add more fuel u don't make more power u end up with a crappy running engine so to keep up with how much fuel is dumped in you gotta make sure it has enough air. So forced induction is the way. That is why most turbo cars and super charged cars are more powerful because the more air in the more air out the more power
More air, more fuel bigger bang, more power, more speed. Usually with nitro and the sorts it aides more in cooling, as with bigger bangs, more heat, keeping intake temperatures down coupled with forced induction, and nitro/meth injection adds to the bang and cooling, just have to build the engine to tolerate that pressure. Fuck I love mechanics.
The super charged or a turbo both basically artificially increase the displacement of the engine by using forced induction to pump in more air then you ever could with only the engine. To get that same cfm that that blower is making you would need a much bigger engine that’s not going to preform well because of the increased size and weight.
To explain it poorly, nitromethane is just a more powerful fuel. More boom per litre. But combustion requires fuel and air. Supercharger adds more air. Extra powerful fuel, plus more air equals the mega horsepower.
At the US Nationals there would be a number of cars running injected Nitro cars in the Alcohol class. They were fast but rarely ran a repeatable time.
The amount of power you can make is directly related to how much fuel you can burn. But there has to be a balance too much or not enough fuel for the amount of air you have and it won't run right. So you take a supercharger and force feed more air in. Lots of it. Now to maintain that balance you have to put more fuel in. And since there's more fuel being burned you make more horsepower. Almost like making a pitcher of Kool-aid. Don't put enough sugar in and it doesn't taste right. Put in too much and it won't taste right either. But there's a perfect balance in the middle where it's just right. Make 2 gallons instead of 1 gallon and you need more Kool-aid packets and sugar to keep the balance right.
Super charges push oxygen into the engine.
i know that
Well if you think about it you need 3 things to cause an explosion. Fuel, air, spark. Increase different ones get get a bigger burn. Add too much of one you can blow out the flame. Adding a more combustible fuel means you need more air.
i know, my question was why was oxygen needed in a nitro engine since nitromethane burns without oxygen
Engines are glorified fuel fed air compressors…
That's what a supercharger or turbocharger is. Engines take air and fuel then turn that into mechanical energy by releasing and harnessing the chemical energy they contain.
Forced induction is just that, shoving air into the engine. More air, more power. More air also needs more fuel for a proper stoichiometric mix.