Exhaust flow and temperature?

[xpensive]

With all the aerodynamacists frequenzing this forum, I was wondering if anyone could quantify the volumetric flow, exit-speed and temperature of the exhausts from an F1 engine on full song?

[Jersey Tom]

You should be able to get the volumetric flow within "close enough" if you know the engine displacement and RPM...

[xpensive]

Interesting, please enlighten me?

[kilcoo316]

You should be able to get the volumetric flow within "close enough" if you know the engine displacement and RPM...

Indeed - with one assumption.


The volume flow in will be approx dependant on engine displacement and RPM.

0.0024*18000/60 ~ 0.72 m^3 per second

The massflow can then be obtained from this by multiplying by atmospheric air density.

0.72*1.225 ~ 0.882 kg/s

The volume flow out will depend on local density, which is dependant on the air temperature at the exhaust exit point.

(anyone any idea of the temp?)

Vol(out) = 0.882/density

where:

density ~ 101325/(287*temp)

(I'm assuming the exhaust exit is subsonic)

The exhaust exit velocity can then be quickly be calculated from the exhaust exit area.

Vol/Area = Velocity

[xpensive]

A very good start, thanks both of you, but what I think is missing here is the exhaust-gas temperature, while I also wonder what has happened to the burned fuel (volume-wise) along the way?

One small thing though kilcoo, did you take into account that it is a four-stroke engine in your flow-calculation?

[kilcoo316]

A very good start, thanks both of you, but what I think is missing here is the exhaust-gas temperature, while I also wonder what has happened to the burned fuel (volume-wise) along the way?

The fuel would represent a very small percentage of the overall volume flow, we're already making approximations that would be bigger than it.

One small thing though kilcoo, did you take into account that it is a four-stroke engine in your flow-calculation?

Nope - sorry, my bad.

Should be (0.0024/4)*(18000/60)= 0.18m^3/sec

[rjsa]

Pretty hot, empirically evaluated.

[youtube]http://www.youtube.com/watch?v=7iXTDjOiIBk[/youtube]

EDIT: It might be running rich for the afterburning show, but I´ve seen bright pipes like this more than once.

[rjsa]

http://en.wikipedia.org/wiki/Color_temperature

I'd say from 2000K to 3000k, from the light of the color emitted. This is a night scene, so the cmera must be making the color look hotter than it really is. Pretty hot anyway.

[Scotracer]

I would guess that exhaust gas temperatures were around 1000C.

The exit velocity of the gases can't exceed Mach 1 at the local condition so you've got your peak gas velocity...

[Belatti]

I would guess that exhaust gas temperatures were around 1000C.

Good guess!

[alexbarwell]

Scotracer, is there a point I'm missing as I can't immediately think why the exhaust velocity can't exceed mach 1. Granted the shockwave might not help, but there are already a number of shockwaves developed.
Anyhow the volumetric rate will be proportional to engine speed.

[xpensive]

For kilcoo:
What you have calculated is little more than the theoretical volumetric flow of intake-air at a 100% filling-ratio.

What is interesting here is how big will the volumetric flow of 1000+ C exhaust-gas be after burning fuel and the air's oxygene to carbondioxide and whatever, when mass-flow of fuel is 50g per second?

[riff_raff]

xpensive,

The exhaust gas local velocity and temperature varies widely depending upon where you measure it in the exhaust tract. The max velocity and temperature will occur in the flow area between the exhaust valve and seat just as the exhaust valve opens. The velocity and temperature quickly drop as the gas flow expands into header primary tube volume, but being a compressible fluid, the pressure will also rise.

The acoustic pressure wave front produced by the valve opening event then progresses down the header pipe at the sonic velocity conditions created by the local conditions. When the wave front hits the increased cross section of the collector, a reverse wave front heads back down the header pipe in the opposite direction.

As for temperatures, the blue flame color you see would indicate near-stoichiometric combustion conditions at the exhaust outlet (likely due to over-scavenging of the intake charge and excess fuel in the exhaust flow). Stoichiometric combustion means adiabatic flame temps around 2800K at constant volume.

[xpensive]

Most interesting riff_raff, but I don't think it really answers my initial question, see top.

[kilcoo316]

For kilcoo:
What you have calculated is little more than the theoretical volumetric flow of intake-air at a 100% filling-ratio.

Thats all I've supplied numbers for.

The formulae are there for the rest as soon as an exit static temperature and exit area are known.


I don't know the exit area or temperature - if anyone does....



Oh, and the teams spend the extortionate amount of money to ensure they get damn near 100% fill (if not a touch over with smart design).

What is interesting here is how big will the volumetric flow of 1000+ C exhaust-gas be after burning fuel and the air's oxygene to carbondioxide and whatever, when mass-flow of fuel is 50g per second?

The fuel is irrelevant - the density of air at 288 degK is 1.225 kg/m^3, as temperature increases, this will tend to reduce further. Meanwhile the density of fuel is 800 kg/m^3 (or thereabouts).


When we do calculations on aircraft engines, you may include the fuel mass (as its mass, not volume your measuring) - but even then its only a >1% difference or so.