Exhaust Blown Floor - Forward Exhaust Exit

[xpensive]

When you don't even know the proper values for input data for such an analysis, it becomes obvious that you are just using one of those standard programmes which my kids sometimes tries to use at work without my knowledge.

Ta-da, but what is this world coming to?

[ringo]

You know, i think i told you this before, but you don't have any manners.

You have issues or some kind of complex, go take it out on your "young whipper snapper" co workers.

Telling me what i know... impudent.

[volarchico]

Woah...I thought we were getting somewhere for awhile when ringo, shelly, et al were discussing. The equations were nice, the discussion was informative. Now, I'm not sure what exactly happened. Seems personal though.

[shelly]

@ringo: the gurney is there on every 2011 car, including hrt. Most of them have it not-slotted.
Agree with you that exhaust pipes are samller than marekk's estimate.

Bernoulli is not of any help in this case, it is not a point of "faster below, slower above".

I think first we have to set a rough estimate of exit condition, then see waht happens to a injection of hot gas in that condition in a free ambient: does the con open up abruptly? does it keep a closed dimension for a while then burst?

why is temperature beneficial? we all agree on the fact that speed is an advantage , but how can be the gas being hot converted in some downforce gain? just by the fact that its density is lower?

those are very general questions and I think that we can find answers to them, which would help us in understanding 2011 designs

[godlameroso]

I don't think any disrespect is implied, but back to the matter at hand, perhaps I'm nit-picking. I highly doubt even f1 exhaust gets to 800c at the exhaust outlet(the combustion event is around 900c iirc), maybe briefly during overrun. Exhaust pulses slow down a lot as they make their way, I've helped tune some pretty fast street cars and their egt's were usually around 700f before the o2 sensor. Its probably different for f1 though, are you allowed to ceramic coat the exhaust manifolds? If there is no real insulation in the headers then the exhaust is going to give up a nice chunk of energy through radiation this is probably by design, all things being equal slowed flow means lower pressure(which is good at the header level because it aids cylinder scavenging). Exhausts don't glow as much as headers, anyway most of you probably know good exhaust means a compromise between the path of least resistance and maintaining speed, that means there is pressure changes that occur to the pulses as they make their way out just from the way they are routed.

As an aside I think it's good that people chime in when someone is wrong as it allows more precise information and discussion.

I also think that to try to debunk someone is counter productive to effectively sharing ideas, I don't like debunkers if it were up to I'd place them all in de bunkers, for life.

[machin]

slowed flow means lower pressure(which is good at the header level because it aids cylinder scavenging

low flow velocity near the exhaust valves means low momentum... and that is bad for cylinder scavenging... Bigger isn't always better....

[marekk]

why is temperature beneficial? we all agree on the fact that speed is an advantage , but how can be the gas being hot converted in some downforce gain? just by the fact that its density is lower?

I think we should talk a little about thermodynamics of this solution.
After combustion there is some energy added to exhaust gases. At pipes exit we see kinetic energy of flow (Ek=m*v^2/2) and internal energy of gases (temperature).
Even if we take ringo's numbers (220m/s, 850 degree), only roughly 4% of added energy is converted to kinetic energy, the rest being stored as gas internal energy.

There are many possible ways to use some of that energy (about 600-700kW for F1 engine) to do usable work.

One can for example try to get a volume of hot gases under the floor, and as gases cool down, they'll decrease volume (almost 4 times going from 1150K to 300K), working like a pump, sucking and speeding up surrounding air, decreasing dynamic pressure (downforce), increasing mass flow to diffuser.
I'm not telling we can use 100% or even 20% of that energy to create downforce - but every 1% gives you quite significant gain.

[godlameroso]

slowed flow means lower pressure(which is good at the header level because it aids cylinder scavenging

low flow velocity near the exhaust valves means low momentum... and that is bad for cylinder scavenging... Bigger isn't always better....

Indeed, the pressure gets lowered as the temperature radiates out of the headers, and as the pulses enter the collector. I know that gas coming out the exhaust ports is very very hot and very very fast, not sure if it's super-sonic or not.


In a turbo car you actually want to speed up the flow going into the turbine as much as possible. We often use try to use the shortest manifold we can, and insulate it, truth be told designing manifolds for turbo cars is much more straight forward than atmospheric ones. Personally I would go with a very simplistic design, as short as possible, ceramic coated for insulation and not worry too much about optimizing for firing order or that sort of thing. Like with all engineering it's a compromise between overall power, and response, I'll take the response over power any day especially as there isn't much to gain in turbo cars from overly intricate manifold design. In an atmospheric engine all these things affect torque production, because atmospheric engines...blow at making torque as opposed to charged engines.

[ringo]

I don't think any disrespect is implied, but back to the matter at hand, perhaps I'm nit-picking. I highly doubt even f1 exhaust gets to 800c at the exhaust outlet(the combustion event is around 900c iirc), maybe briefly during overrun. Exhaust pulses slow down a lot as they make their way, I've helped tune some pretty fast street cars and their egt's were usually around 700f before the o2 sensor. Its probably different for f1 though, are you allowed to ceramic coat the exhaust manifolds? If there is no real insulation in the headers then the exhaust is going to give up a nice chunk of energy through radiation this is probably by design, all things being equal slowed flow means lower pressure(which is good at the header level because it aids cylinder scavenging). Exhausts don't glow as much as headers, anyway most of you probably know good exhaust means a compromise between the path of least resistance and maintaining speed, that means there is pressure changes that occur to the pulses as they make their way out just from the way they are routed.

As an aside I think it's good that people chime in when someone is wrong as it allows more precise information and discussion.

I also think that to try to debunk someone is counter productive to effectively sharing ideas, I don't like debunkers if it were up to I'd place them all in de bunkers, for life.

I think the difference with the production race car and the F1 is probably the compression ratio and the stroke; ie if you are comparing naturally aspirated cars.
Higher compression leads to higher pre and post combustion temperatures.
A shorter stroke also means reduced time for the engine block to absorb heat.

850 is modest i think. It may not be the exact temperature coming out the ends of the pipe, because we don't know the pipe length and the type of insulation being used.
but this is probably more credible if the exhaust temperature is critical to the discussion.

http://www.f1network.net/main/s491/st112411.htm
this is for the BMW P86/7 2007 V8 engine

- The exhaust reaches a temperature of up to 950 °C, while the air temperature in the pneumatic system rises to 250 °C.

[Raptor22]

You think this is a talent show case!!?

The exhuast is around 850, and if someone ask me how i get it then i'll say. No sense in show and tell if it doesn't add to the discussion.

ok since it's a show and tell.




simply little excel file and it's pretty accurate, basic thermodynamics theory.
This was for the 2013 engine thread, it's good for both turbo and non turbo calculation.

What have you contributed Mr. Xpensinve engineer? You're suppose to be expensiive, why all the cheap talk?

Your heating value and density are way out.
47MJ/kg and 750Kg/m^3 should be Heating value and density respectively.

[ringo]

Yes, but it's all changeable.
Notice how weak the engine is at 721hp, plus this is indicated power, so brake horsepower is even lower if we take away friction power.
Friction power is experimental, that's an unknown. So this engine is not really great, and is purely down to the fuel and compression ratio.
Volumetric efficiency is also experimental.

I have to use a flame temperature program to calculate the combustion temperature T3.
The temp in asterisk is from the program. The theoretical is from a rule of thumb calculation which gets inaccurate over certain pressures.
The flame temp program is more accurate, but requires data on the fuel.

One thing though, it's best to use lower heating values in fuel. The higher heating value has certain considerations.

[marekk]

@ringo:
what should this adiabatic pressure/flame temp mean ? No heat transfer to cooling fluid/radiators/oil ?
Do you make calculations for real engine, or adiabatic one ?

[ringo]

Adiabatic and constant volume combustion. Referring to just the combustion, combustion is instantaneous so it is considered adiabatic.
So i guess at that point it happens too quickly to consider heat transfer to the cooling flow.
Heat transfer to cooling is probably reserved for the power stroke and exhaust. You may need to know the engine geometry and thermal properties. It can be modeled but it sounds like something a serious engine simulator would do.
So this is an adiabatic engine. Anything outside of that is a lot of experimentation and correlation.

But to stay on topic, i think 850C is modest. BMW was reported in an article at over 900C. flame temps can probably be higher than theoretical since there are all kinds of oxygenators used in the fuel.

[shelly]

Proposal: let us accept a 950° C exhaust temperature at the beginning of the pipe, just for carrying on some ball park estimate.

After that, I think we have to try to set ranges for pressure and density, and then estimate how much energy is lost along the pipe, so estimate output temperature.

If we had a high enough res pic of the thermotapes attached on r31 seen from above, we could estiamte expected range of temperature in that zone outside

[marekk]

Adiabatic and constant volume combustion. Referring to just the combustion, combustion is instantaneous so it is considered adiabatic.
So i guess at that point it happens too quickly to consider heat transfer to the cooling flow.
Heat transfer to cooling is probably reserved for the power stroke and exhaust. You may need to know the engine geometry and thermal properties. It can be modeled but it sounds like something a serious engine simulator would do.
So this is an adiabatic engine. Anything outside of that is a lot of experimentation and correlation.

Real world is complex. Thats true.
But it means, you miss about 35% of fuel's energy in your calculations (which is in real world delivered to cooling system). Exhaust temp will be much lower, and on pipe's exit even more so, as you calculated 896 degree at 4 bar, and there is just very slightly over 1 bar.