afterburners

[Steven]

hi people,

this idea just crossed my mind and wanted to hear your thoughts about this.

You are probably aware that the Concorde (an airplane ) uses afterburners on the engines to give extra power on takeoff especially. This increases power to 107%.

Now I was wondering... couldn't that be a good idea for race cars? I don't know much detail of the afterburners, but I know it's an ignition system that burns remnants of the fuel exhaust gasses.
Are there maybe any series that use this kind of technique to improve performance? I suppose also that it is forbidden in F1, or hihgly unusable there (why then?)

[Monstrobolaxa]

The after burner is only used during aceleration....in a F1 car you have to acelerate out of the corners....so probably it would be an advantage to use an afterburner...but...the after burner is a cast of pot-combustion reheating (correct me if I'm wrong)....

This powerful thrust comes from a normal jet engine with the addition of a post-combustion system. The aim of post-combustion is to reheat the exhaust gases from the engine to increases thrust by 27%. (from concorde-jet.com)

My question is....wouldn't a system like this require a big quantity of enery to reheat the exhaust gases?
Another importante thing is from where do you ger the energy for this system? Not from the battery or alternator of the car....cause a F1 car is already running with it's battery close to the limit....a F1 car during a pit-stpo has the engine pre-set to a minimum of 3000 to 5000 rpm...to mantian the battery at a safe level....below this level the engine won't recieve the energy necessary to stay on...and will stall.

So an energy souce is needed....well you could rev the engine a little higher....but it could cause some reliability problems....and the engine might not have enough rpms to produce the amouts of energy necessary....

you could try another form of energy.....well...but this wouldd bring extra weight...to the car...which would change the cofg and would....alter the veicle dynamics.....so the real question is....would it be such a big advantage that it's worth using?

And don't forget aircrafts only turn on the aftrburner after the engine has been stabelized at the 95% thrust....(the maximum allowed in civic aircrafts.....over 95% only in case of emergency).....so.....I really don't think after burners in F1 are that much of an advantage.....

I could also talk about the influence of the very hot air...the would come from the exhausts......but this post is already pretty long....

Monstrobolaxa

[Steven]

The big advantage of an afterburner is that you can significantly increase the thrust of the engine without adding much weight or complexity to the engine. An afterburner is nothing but a set of fuel injectors, a tube and flame holder that the fuel burns in, and an adjustable nozzle. A jet engine with an afterburner needs an adjustable nozzle so that it can work both with the afterburners on and off.

The disadvantage of an afterburner is that it uses a lot of fuel for the power it generates. Therefore most planes use afterburners sparingly. For example, a military jet would use its afterburners when taking off from the short runway on an aircraft carrier, or during a high-speed maneuver in a dogfight.

Well I looked this up, and can conclude some main things:
- What you said about weight seems rather trivial.
- One problem we can wonder about is how much O² is left in the exhaust? It may be less than in a jet (fighter) engine.
- However I don't really know how te explain this, all afterburners apparently need a veriable width of exhaust at the ends. An afterburner heats exhaust air even further, therefore increasing thrust. I think thereby that veriable exhausts are forbidden in F1
- Afterburners are apparently designed to give thrust by pushing gasses out. That is actually not really what F1 needs. We need rotation power for the wheels. Thrust would be however quite interesting, as the car is pushed forward without demanding acceleration grip from the tyres.
BUT... since turbines (and therefore I think also thrustpower) is forbidden

would be nice though, seeing the back of the car glowing red when accellerating from slow corners

[KeithYoung]

dont get me wrong I am no engine guy, but this theory may help if there were a little affect of the afterburner idea, it would help suck the exhaust out of the engine. I dont know alot about valve timing, but i am sure this would change it. Another thing, is the thrust would need to be very small as I am sure the exhaust of an F1 car cannot support a ton of thrust. correct me if i am wrong, but afterburners greatly increase aircrafts lbs/min, and obviously a big goal in F1 is fuel economy, less fuel=lighter car, the less fuel u consume, the less you need to pump back in during pit stop.

[Monstrobolaxa]

Yup that is true...thinking a little bit more....probably the after burner gets its energy from burning some more fuel......cause turning on the after burner in the concorde increases the fuel comsumption in 25000lbs/hour.....yes 25 thousand...an hour....(I did an paper for my flight mecanics classe about the concorde)!

Well what you said Keith....is quite true it might help with the exhaust "evacuation".....but you can also get better suction from changing the exhaust pipes geometry......

And about what Tomba said....well it's true that an airplane is pushed....by the air that comes from the engine....so in our case......why don't we build something like a turbo compressor.....we afterburn the exhaust gases.....make them turn some kind of wheel that is conected to the car wheel!!!!in this case we would have 2 "engines" pushing the car.....a compsution one and a exhaust one!!! LOLOL

But returning to keith....we have to worry about fuel consumption....on the Concorde the afterburner is used for about 30 seconds during aceleration.....not only to save fuel but also to reduce noise....

[Reca]

The problem is exactly the lack of O2. A jet engine, by design, burns a lot less air than the total entering in the intake, the (total air)/fuel ratio is typically over 50 while the stoichometric (help me with spelling please, Word don’t knows that word...) is just 14, less than 1/3 of the air entering the intake actually enters in the combustion chambers. This means that there’s still a lot of “fresh” air to be burned behind the turbine stages and that’s exactly what the afterburner does, more fuel is injected and burned after the turbine stages. Another advantage is that there’s no more the temp limitation (1300-1400 K) imposed by the turbine itself, so the fuel used is more than the amount previously used in the “standard” combustion chambers (hence the impressive fuel consumption).
On the contrary in a piston engine all the air entering in the intake enters in the combustion chamber, the piston engine is designed to burn all the air.

Tomba : you’ll understand the variable nozzle exit area from this relationship :
mass flow [kg/s] = Nozzle Area [m2] * gas density [kg/m3] * gas velocity [m/s].
With the afterburner also if the velocity of the airflow increases, the density of the exhaust gasses decreases a lot (as I said the temp is lot higher) so the product (density * velocity) as a whole becomes lower. Furthermore the mass flow is a bit (few %) higher because of the added fuel, the ratio mass flow / (density * velocity) increases and so the required area of the nozzle has to be larger.

[TD]

well I for one would sure hate to be the car behind the "after-burner" car in front coming out of a corner

The heat in the cockpit is bad enough during normal races, let alone being BLASTED by fire

[Monstrobolaxa]

F1 BBQ!

[TD]

well maybe "Par for Course"

sometimes one wonders how many "SAUSAGES" there are in F1

hehehehehehehehehehehehehehehehehehehehehehehe