Exhaust Blown Floor - Forward Exhaust Exit

[marekk]

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

i'm afraid it's way to complex and beyond our skills to build numerical models for that.
We can only estimate total (kinetic + thermal) energy of gases at about 270kW per pipe (at max power output of the engine).
We can investigate further how much is lost in pipe (probably not to much due to insulation), how much finds it's way under floor, how much heat gets radiated and transfered to tarmac and floor (temp delta along car's floor), how much is volume decrease from this temp delta, how much pressure decrease results from that ...
Realy way to complex either, so we can have only an idea how it works, but nothing close to real numbers. Sorry.

[shelly]

Found here:

http://www.jsme.or.jp/esd/COMODIA-Procs ... 5_P449.pdf

an old intersting artivcle with some images, which could be relevant to our discussion, even if experiments are carried out on a 1 cylinder engine at 1500rpm

[shelly]

Realy way to complex either, so we can have only an idea how it works, but nothing close to real numbers. Sorry.

I think you misunderstood my post: I think, like you that we can only have an ideaof how it works, has we can not model it. No need to be sorry, just let's try to find some shared ideas.

[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.

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.

Where did you get that 1 bar value from?

It depends on where you are taking that measurement and where the exhaust to atmosphere is.
If it was just over 1 bar, a turbo charger would not work on any engine. Turbos work on pressure difference.
so the pressure directly from the exhaust port is not 1 bar.
This pressure is representative right as exhaust stroke starts.

Explain also why BMW v8 exhaust is 950 degrees.
Is their engine burning 3 times hotter?


This lemans, and we know diesels burn cooler.
http://www.caranddriver.com/features/07 ... our-column

Although a number of suppliers make such devices, Audi and Peugeot turned to a newcomer for the particulate filters on their racing engines. Dow Automotive has created a filter that, at a glance, looks much like the bundle of tiny ceramic soda straws used in conventional traps. But the passages in Dow's filter are extremely porous, and every other one is blocked, causing the exhaust gas to flow through the walls of the passages as it exits the filter.

Apparently, this technology produces a combination of filter size, weight, and back pressure that works well for racing. And Dow brags that the 2007 filters are 40 percent smaller and 13 pounds lighter than last year's model. Each of the two filters on the Audi looked to be about eight inches wide and long by four inches high. Clogging with soot is not a problem at Le Mans, as the cars run with an exhaust temperature of 1600 or more degrees. Every time the driver backs off the throttle, the particulate traps regenerate vigorously.

What's the deal? what's so controversial about exhaust being 950 degreesC, i don't get the disbelief?
These are race cars moving under full load.

[shelly]

Agree with you ringo that temperatures are very high (1000°C maybe) at the exit of the cylinder; also I think from the picture of ferrari uncovered that this year team have worked in oredr to insulate more the exhausts and limit temperature loss along the pipe via radiation.

Let's tackle the whole problem from a more integral point of view: we all agree on the mass flow rate value, and I think we all agree on the energy content of exhausts being in the range of 600kW.
So we can step beyond peak temperature value discussion and go on: we have total enthalpy and from that we can make reasonable hypotesis on exahust temperature, knowing they are subsonic.

[marekk]

Where did you get that 1 bar value from?

atmospheric pressure.

If it was just over 1 bar, a turbo charger would not work on any engine. Turbos work on pressure difference.
so the pressure directly from the exhaust port is not 1 bar.
This pressure is representative right as exhaust stroke starts.

1 Bar at pipe's exit - please read a little bit more carefully.

As the exhaust stroke starts, there is just 1 bar inside - exhaust valves open long befor BDC.

You have to decide - exhaust pressure or speed. You cant have both at the same time in subsonic flow.

Explain also why BMW v8 exhaust is 950 degrees.
Is their engine burning 3 times hotter?

It's temp of exhaust on exhaust port. And not 3 times hotter - it needs to have just +33% energy.

This lemans, and we know diesels burn cooler.

Actually flame temp of diesel is slightly higher than for light fuel.

[shelly]

This lemans, and we know diesels burn cooler.

Actually flame temp of diesel is slightly higher than for light fuel.

I think biggest difference comes from le mans engine being turbo, thus with higher temp-pressures

[ringo]

Where did you get that 1 bar value from?

atmospheric pressure.

If it was just over 1 bar, a turbo charger would not work on any engine. Turbos work on pressure difference.
so the pressure directly from the exhaust port is not 1 bar.
This pressure is representative right as exhaust stroke starts.

1 Bar at pipe's exit - please read a little bit more carefully.

As the exhaust stroke starts, there is just 1 bar inside - exhaust valves open long befor BDC.

You have to decide - exhaust pressure or speed. You cant have both at the same time in subsonic flow.

Explain also why BMW v8 exhaust is 950 degrees.
Is their engine burning 3 times hotter?

It's temp of exhaust on exhaust port. And not 3 times hotter - it needs to have just +33% energy.

This lemans, and we know diesels burn cooler.

Actually flame temp of diesel is slightly higher than for light fuel.

It seems your aim is to counteract me at every stage.

Diesels have lower temperature, the combustion is constant pressure while gasoline is at constant volume.

Your throwing the kitchen sink at me and you don't know the theory behind your opinions.

the exhuast stroke does not begin at 1 bar.

look at point 4, point 1 is atmospheric:

i should have let you continue in ignorance, but that would be bad for the forum.

[ringo]

This lemans, and we know diesels burn cooler.

Actually flame temp of diesel is slightly higher than for light fuel.

I think biggest difference comes from le mans engine being turbo, thus with higher temp-pressures

he is incorrect.

[marekk]

It seems your aim is to counteract me at every stage.

Diesels have lower temperature, the combustion is constant pressure while gasoline is at constant volume.

Your throwing the kitchen sink at me and you don't know the theory behind your opinions.

the exhuast stroke does not begin at 1 bar.

look at point 4, point 1 is atmospheric:

i should have let you continue in ignorance, but that would be bad for the forum.

If you ask me, i start to slightly doubt your fluid dynamics degree, ringo

1. Diesel flame temp

Adiabatic flame temperature (constant pressure) of common gases/Materials
Fuel Oxidizer Tad (°C) Tad (°F)
Kerosine air 2093 [3] 3801
Light fuel oil air 2104 [3] 3820

2. real engine (please stop to post incomplete otto cycle pictures from wikipedia, we are trying to talk about real world).


And belive me, i know the theory behind my opinions quite well.

[ringo]

i don't have a degree in fluid dynamics.
Just plain old mechanical engineering.

but you know you are wrong right?

a turbo chager would not work under marek's laws.

That cycle that you posted is still not at 1 bar at point 4.
That's the real thing, but why should i post that if you can't follow it. where does the exhaust stroke begin ?

can you explain why it looks like that?


You are wrong man. Just accept it. Both on the exhaust temp front and the cylinder pressure.

I find it amazing how a simple blog or website can convince a whole forum, but yet maths cannot.
If i found a website that says the temperature is -50C, that would be enough to validate any position.
It's a good thing i found one that says the temp is 950 degrees C for the F1 V8.
You can't dispute that, for it came from le internets!!

[ringo]

this is to your detriment because as soon as the exhaust valves open the gases begin to go to the exhaust, if it's before bdc all the better. So using this very same graph, it seems to be about 60 or 75 psi above atmospheric. which is about 4 bar gauge or 5.

[marekk]

@ringo:
My last attempt.
We are talking about pressure, temp and speed at PIPE'S EXIT.
If you are interested, real pressure at exhaust port looks like that:


If you have well designed exhaust, average pressure at pipe's end is just slightly above ambient.
Let's go further with our topic.

[Raptor22]

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.

Where did you get that 1 bar value from?

It depends on where you are taking that measurement and where the exhaust to atmosphere is.
If it was just over 1 bar, a turbo charger would not work on any engine. Turbos work on pressure difference.
so the pressure directly from the exhaust port is not 1 bar.
This pressure is representative right as exhaust stroke starts.

Explain also why BMW v8 exhaust is 950 degrees.
Is their engine burning 3 times hotter?


This lemans, and we know diesels burn cooler.
http://www.caranddriver.com/features/07 ... our-column

Although a number of suppliers make such devices, Audi and Peugeot turned to a newcomer for the particulate filters on their racing engines. Dow Automotive has created a filter that, at a glance, looks much like the bundle of tiny ceramic soda straws used in conventional traps. But the passages in Dow's filter are extremely porous, and every other one is blocked, causing the exhaust gas to flow through the walls of the passages as it exits the filter.

Apparently, this technology produces a combination of filter size, weight, and back pressure that works well for racing. And Dow brags that the 2007 filters are 40 percent smaller and 13 pounds lighter than last year's model. Each of the two filters on the Audi looked to be about eight inches wide and long by four inches high. Clogging with soot is not a problem at Le Mans, as the cars run with an exhaust temperature of 1600 or more degrees. Every time the driver backs off the throttle, the particulate traps regenerate vigorously.

What's the deal? what's so controversial about exhaust being 950 degreesC, i don't get the disbelief?
These are race cars moving under full load.

1600 degrees fahrenheit = 872 degrees celcius and diesel burn a heck of a lot hotter than petrol/gasoline engines. Diesel burns faster more of an explosion than petrols deflagration.

F1 fuel is more alkylate based so it dioes burn very quickly but its heating value is lower than normal gasoline which derives is higher heatng value from the aromatics fraction. F1 engines require a higher flame speed not necessariya higher heating value.

Also "all sorts of oxygenators"?HUH??
The only oxygenate used is Ethanol. TAME and MTBE or ETBE are not allowed due to environmetal concerns

[PlatinumZealot]

[youtube]http://www.youtube.com/watch?v=B0Pnvgc2_gA[/youtube]