23 replies to this topic

[wingsbgone]

Quick top of the head thought/calculation: Does a 3.0l 4-stroke engine (current F1), running at 18k rpm require (very) roughly 27,000 liters of air/minute (450 l/sec)?? I'm estimating one 3.0l intake displacement every 2 rotations.
That seems like quite a bit of airflow, especially if the vehicle is not moving. Maybe the airboxes should have warnings analogous to the intakes of jet aircraft?
Just a thought.....

[AdamLarnachJr]

182ci X 18000rpm = 3276000/3456 = around 950cfm.

This is a relatively simple way of doing it, but thats the "equational" airflow required.

[wingsbgone]

Thanks. I guess the metric/english units made thing more dramatic in my mind. The 950 cfm number is on par with my high-school era V-8 carb. Don't recall any fears of getting sucked into the engine with that!

But, still, 450 liters/seconds SOUNDS impressive.....

[AdamLarnachJr]

Yeahp... there is a guy up in the Pro Mod ranks who runs an 850ci V8 that spins up to 7500rpm. It needs 1800cfm just to get up to speed. This is just the minimum, Im sure with the F1 engines IR intake, each port is probably consuming 200+cfm, so multiply that by 20, its about 4000cfm?

Cya

[wingsbgone]

850 ci V-8:eek: That's one big mutha!

What does "IR" refer to regarding the intakes of an F1 engine?

And being terribly simple-minded, any guess as to the intake cfm of a powerful vaccuum cleaner (eg. an industrial "shopvac"). Just trying to get a mental image of the intake requirements (and effect on surroundings) of these amazing engines.

My next thought are then the exhaust gases, but that's for another thread.....

Ciao.

[Yelnats]

AdamLarnachJr;...... 182ci X 18000rpm = 3276000/3456 = around 950cfm.

But a 4 stroke only sucks air every second revolution so shouldn't this result be divuded by two? And with input resonance boosting cylinder filling by up to 20% perhaps we should increase this a bit just in case.

Damn it, isn't anything about F1 simple?

[Engineguy]

Originally posted by Yelnats
AdamLarnachJr;...... 182ci X 18000rpm = 3276000/3456 = around 950cfm.

But a 4 stroke only sucks air every second revolution so shouldn't this result be divuded by two? And with input resonance boosting cylinder filling by up to 20% perhaps we should increase this a bit just in case.

He snuck that division by 2 in there when he divided by 3456... a cubic foot contains 1728 cubic inches.... so his calculation is valid.

[AdamLarnachJr]

Oops.. I mean 805ci.. either way thats a big crank:)

Thats just a theorectical CFM, and its the only basis that I could start off of because I dont have any F1 cylinder head flow charts:)
But like I said, the Individual Runners (IR) have to be able to support the volume of each intake port, and that is probably around 200cfm, since there are 2 intake ports per cylinder, that comes out to 20 intake ports... 20 X 200 = 4000cfm.

[jdowns]

Originally posted by Yelnats
AdamLarnachJr;...... 182ci X 18000rpm = 3276000/3456 = around 950cfm.

But a 4 stroke only sucks air every second revolution so shouldn't this result be divuded by two? And with input resonance boosting cylinder filling by up to 20% perhaps we should increase this a bit just in case.

Damn it, isn't anything about F1 simple?

Just to complicate things further, @18,000rpm you'd be down many percent on efficiency... Up 20%, down xx%...

Anyone care to make a guess at the area of the air intake? 4"x5"=20 sq inches? 950 cfm through 20 sq inches = 6840 feet/minute (air flow speed), = ~78 mph. Not quite jet engine intake speed ;)

[desmo]

From what little I was able to find on the net, intake velocities for stationary gas turbines are in the region of 110-130m/s or 246-291mph. So indeed!

[jdowns]

wingsbgone,
you have to remember that there are 1,000 litres per cubic meter, so they're only sucking in less than 1/2 a cubic meter per second. Imagine a cubic area of space 1m to a side (imagine a box waist heigh and 'square'), then halv that - that's what they're sucking in per second.

Other useless ways of thinking of it:
448 l/s = .544kg/s = 1.2 lb/s

To accelerate .544 kg/s up to the car's speed of 350mph (Hockenheim?) would take 6.6 kw or 8.8 hp. (caveat before I get flamed: lots of 'ifs-butts-maybes' in there, heating, cooling, turbulance, drag from the collector to catch that much air, etc... This is just the 'useless trivia' dept ;) )

Of course, you get more than that back by directing the exhaust backwards (you'd need to know the additional mass of fuel added to the air, and the velocity of the exhaust gasses).

Also, the cfm rating of carbureters (sp?) is the flow per minute at a 'standard' pressure drop - it doesn't directly relate to the maximum air flow through it when on an engine. There's also a different pressure used for 2 barrel vs 4 barrel (ie. a 350cfm 2 barrel carby will not allow the same amount of air flow through it on a particular engine as a 350cfm 4-barrel - they're just given the same number by different testing systems, they could be very different in the real world). You could get thousands of cubic feet per minute out of a 800cfm RATED carby if you put enough of a pressure drop across it. Putting a smaller carby than optimum will restrict flow through into an engine, but not to the cfm rating of the carby - but by some percentage, not to a fixed limit.

Don't know for a fact how much air goes through a vacuum cleaner, but a 750watt (ie. 1 hp) running at 25% efficiency (my electrical engineering lecturer said that vacuum cleaners often made the best heaters ;) ) would impart about 200 joules/second to the air. With a 1" radius nozle you get ~118 grams/second ( 0.26 lb/s) and 58.2 m/s (130mph).

Again, so many unknowns that the figures could be way out, but I'm procrastenating (should be working ), so there you have it. God, I'm bored, need a life, got the flu, gonna get sued if I don't get this work done....

[blkirk]

The flow rates people have been quoting here may not sound like much, but they can still have significant effects.

Back a few years ago, one of the car magazines for the masses (Car and Driver?) had it's 25th anniversary. To celebrate, they decided to build a completely over-the-top car. In keeping with the 25th anniversary theme, they wanted a car that had been in production as long as they had been around. Their options (American only, of course ) were the Corvette and Thunderbird. That decision only took a few seconds and they soon had a Corvette on its way to John Lingenfelter along with a large stack of cash.

I can't remember what exactly he did to the car, but it was definitely the fastest 'Vette he'd ever made. There in a great picture in the article of Lingenfelter standing next to the car, hand on the LR fender, with the tires . At any rate, the magazine folks got quite a surprise when they stood on the gas. The engine sucked down air so fast that the pressure drop in the intake piping was enough to collapse it. Apparently Lingenfelter hadn't tested the engine with all of the bits attached.

[jdowns]

Man, that must have sucked!

[Janzen]

Great calculations,

I know a friend who does some amateur racing cars in his garage he has got one of those setups that takes the exhaust outside, the only thing was that when he was running the bigger engines at revs he got a underpressure in the garage so the doors would get stuck, thats what he told me. I would think reading your calculations that a smaller garage it would be possible.

[AdamLarnachJr]

Could you suffocate yourself that way? I mean if the engine sucked all the available air, it would start to die down and you might get dizzy.

[Croaky]

I just read a book about U-boats in WW2. Apparently someone invented a "snorkel" so they could run the diesel engines while submerged. Trouble was, if a wave broke over the snorkel it would seal for a second or two and the diesels would start sucking air from the cabin. They had all sorts of trouble with the sudden dramatic drop in pressure, enough to burst eardrums if the sailors were unlucky. Yuck!

[jdowns]

Adam,
I guess it'd a fight between the humans and the engine, both after oxygen - first one to die loses ;)

In reality, you'd always have air leaks in a garage. The rate of air flow would eventually reach equilibrium. The air pressure in the garage would undoubtedly be down a few psi from the outside, but I think it'd need to be down a _lot_ for it to bother people. It's mostly the percent of O2, which, as your engine's sucking air into the garage at a rate of knots, wouldn't be a problem.

I vagely remember that the air on top of Mt Everest was less than 1/4 the pressure at sea level, but people have climbed it without oxygen. 3/4 of an atmosphoere difference between outside and in, on a 4 meter high, by 20 meter long wall (80 sq metres) would be the eqivalent of laying the wall on it's side, and puttin 620 tonne(!) of weight on it. I think the walls would cave in (or the roof collapse, windows break) long before you were in trouble. And that's only if you could seal your garage up that well, and if your engine would still work at 1/4 atm, etc.... I think you'd be OK, but your ear drums could be at risk.

Fun to try though ;) Got any aprentices who know that there are no left handed hammers, or checkered paint, or already know what's a piecost - get 'em to seal the garage up real tight, pipe the exhaust outside, and see if you can suck their ear wax out Tell 'em you need to test how the car would run in a city with a high elevation.

Jordan.

[Ursus]

Croaky, I've been told a similar story. A workmate of my dad's was a cook on a submarine. (In the 50's or 60's) His main problems with waves splashing over the snorkel was that all the calmly simmering pots would suddenly start to boil like mad when the pressure dropped.

[palmas]

Originally posted by Ursus
Croaky, I've been told a similar story. A workmate of my dad's was a cook on a submarine. (In the 50's or 60's) His main problems with waves splashing over the snorkel was that all the calmly simmering pots would suddenly start to boil like mad when the pressure dropped.

Some pressure drop! to reduce boiling temperature to 90ºC, pressure would be 0,715 at ( or kgf/cm2)

[jdowns]

Palmas,
I thought about that, but I think I worked out another explanation (this is a guess):

For the pots to be simmering, they would need to be at (or near) 100 degrees. The energy lost by the water boiling off simply has to equal the energy in (by the hot plate or flame) to keep the water at 100 degrees (say 400 Joules/second - the same as four 100 Watt light bulbs). If the pressure drops so that (for instance) the boiling point drops by only 1/10th of a degree, then the water would suddenly have to lose a ton of energy (10 litres of water would need to lose 4,000 KJ in a hurry! = 10,000 seconds worth of energy at the old rate). So it would boil furiously for a while, then return to simmering (at the new 99.9 degree boiling temperature). Then, when the pressure was restored, it would stop simmering for a whilte until the temp rose, then start again. I don't think it would take a huge drop in pressure to create some furious boiling, but I could be wrong.

Don't know what the hell I'm doing posting this on an F1 BB - Oh, yeah, that's right, I'm procrastenating...

[Ursus]

I'm not guaranteeing that the story is the truth, the whole truth and nothing but the truth. We all know what happens to stories when we try to impress our friends.;)

[jdowns]

I beleieve it, it make sense. A minor drop in pressure would cause things to boil furiously. Also, not exactly the kind of thing that'd be easy to think up.

I'm sure none of my friends exaggerate or make up stories ;)

[Croaky]

I certainly believe it. Apparently if you try to boil an egg up Mount Everest, it takes ages and ages because the lower pressure makes a real difference to the boiling point of water. So if you live in a submarine or up Mount Everest it's probably best just to microwave everything

[Melbourne Park]

It also would have buggered up the temperature when the pressure was restored, after all that energy loss ... no wonder the cook was not happy ...