Renault R31

[Holm86]

ignoring the facts of waves and acoustic phenomena and their ability to get more than a 100% filling I fail to see those exhaust gas speeds at the exit.

So it´s 2.4litre engines -we can say each bank is 1.2litres swept volume. a four stroke engine fires and exhausts gas only every second revolution so that is reducing exhaust volume to .6l per rev ....times 16000 revs and we arrive at 9600 l/min...or 160l/sec or 16000cm³/s ...we got an exit area of say 80mm by 40mm and arrive at average 40m/s exit speed for 16K revs...
of course you have consider the vehicle ground speed

where do I go wrong?

You also need to consider that the air comming out of the cylinders is alot hotter and has expanded. That should increase the velocity right?

[PhillipM]

^Expansion of the exhaust gases due to heat...the bit that makes the engine go around

[Pierce89]

Allison about blown floor:
http://www.lotusrenaultgp.com/5751-Blow ... ml?lang=en

On average, in the corners, the speed of the exhaust gasses is around 6 times the speed of the car. If this high speed gas can be directed at the underside of the floor, then as far as the part of the floor that is in contact with the exhaust is concerned, it will produce downforce just as if it was going 6 times as fast.

So Renault seem much more concerned with the impact that the FEE has on the leading edge of the floor and it's suction peak than the course of the airflow towards the diffuser or not.

Also an indicator that the exhaust gas velocity is around 1000mph.

I personally believe this article discredits the people who said the Renault exhaust gas wasn't going under the floor.

[Pierce89]

The air skirts are not as effective at low speeds.

This article somewhat discredits your airskirts
http://www.lotusrenaultgp.com/5751-Blow ... ml?lang=en

[Byronrhys]

All I can say is they took a big hit and James Allison is looking really bad, he himself was touting they wouldn't be affected and look how big they were, Terrible development on the car also, were around 3rd at the seasons start now they are around 6th.

[BreezyRacer]

All I can say is they took a big hit and James Allison is looking really bad, he himself was touting they wouldn't be affected and look how big they were, Terrible development on the car also, were around 3rd at the seasons start now they are around 6th.

Yes, I've been disappointed in the steady march towards to back of the grid as the season goes on. Historically Renault have been steadily improving pace thru the season. Last year they knew what every little change was worth. This year it's like they've lost the handle on aero development. Typically they come out before every race saying they've found the problem and and now they are moving in the right direction .. slow corners favor the front blowing exhaust, then slow corners hamper the front blowing exhaust, etc.

I really think the aero department is lost in the woods, precisely because they are alone in being the only team to build the car around the front blowing exhaust. It's just much easier to get off track when you're the only team taking a particular approach. Just look at how McLaren and Ferrari got back on pace after copying the Newey diffuser layout. Renault don't have the luxury of copying ..

[PlatinumZealot]

The air skirts are not as effective at low speeds.

This article somewhat discredits your airskirts
http://www.lotusrenaultgp.com/5751-Blow ... ml?lang=en

Why? Please tell me. There is nothing in the article that discredits the skirts because the exhaust does go under the floor... nobody denies that - He just didn't say where. There is visual, recorded evidence of the air skirts as well as CFD estimations. So, you have to try again!

“In the same way as an aeroplane generates lift as air passes over the curved surfaces of its wings, so does an F1 car create downforce by using similar shapes mounted upside down. The faster the air passes over its downforce generating surfaces, the more downforce it will create.

One of the most important parts of the car for generating downforce is the floor. Its curved edges and ramped rear surface account for around 40% of the downforce of the whole car. F1 designers spend a lot of time tweaking the detail design of the shape of the floor to extract the last drop of available performance.

On average, in the corners, the speed of the exhaust gasses is around 6 times the speed of the car. If this high speed gas can be directed at the underside of the floor, then as far as the part of the floor that is in contact with the exhaust is concerned, it will produce downforce just as if it was going 6 times as fast. The extra downforce that is produced is substantial and can improve the laptime of the car by around 1sec/lap. “

This is nothing new, It applies to ALL F1 cars and it's obvious he is not giving away any details.

[marcush.]

maybe a too consevative Bob Bell would have been a good rock in the stormy sea now....
Formula 1 seems to be hyped up by the benefit of quick evolution and ever shorter lead times to introduction of new parts.
As I said many times before...how can you be sure of the benefits of changes before maximising on what you got? I fully underwrite to change as long as you have areas that lag condsiderable or you are unable to dial the car into a useful working window....but that constant evolution of the front wing bits is making not a big impression on me apart from the dramatic looks of course.

[ringo]

Allison about blown floor:
http://www.lotusrenaultgp.com/5751-Blow ... ml?lang=en

On average, in the corners, the speed of the exhaust gasses is around 6 times the speed of the car. If this high speed gas can be directed at the underside of the floor, then as far as the part of the floor that is in contact with the exhaust is concerned, it will produce downforce just as if it was going 6 times as fast.

So Renault seem much more concerned with the impact that the FEE has on the leading edge of the floor and it's suction peak than the course of the airflow towards the diffuser or not.

Also an indicator that the exhaust gas velocity is around 1000mph.

I personally believe this article discredits the people who said the Renault exhaust gas wasn't going under the floor.

On the contrary. The floor exist all over.
It discredits the diffuser people.
The exhuast comes into contack with the front parts of the floor and flow coming from the splitter.
That is the only place where the speeds are 6 times the speed of the car.
At the diffuser the speed is greatly reduced.
So this reinforces everything that was said in the front exhuast thread.

On average, in the corners, the speed of the exhaust gasses is around 6 times the speed of the car. If this high speed gas can be directed at the underside of the floor, then as far as the part of the floor that is in contact with the exhaust is concerned, it will produce downforce just as if it was going 6 times as fast. The extra downforce that is produced is substantial and can improve the laptime of the car by around 1sec/lap. “

These speeds only exist at the pipe exit, no where else, as the gases lose energy as they move down along the car. So in contact must mean in front of the car.



parts in contact with the exhuast? Here they are.
6 times the speed of the car would make this simple and stubby airfoil shaped edge of the floor behave like it was 36 times bigger in area.

Also the speed calculation that i was touting all allong and no one believed it.
220m/s was my conservative estimate and it's basic thermodynamics.
Divide that by 6, 36.6m/s or 131 kph. hmm seems close enough for a low speedturn.
Let's take it to the FEE thread, cause this is very relevant to that thread.

[marcush.]

ignoring the facts of waves and acoustic phenomena and their ability to get more than a 100% filling I fail to see those exhaust gas speeds at the exit.

So it´s 2.4litre engines -we can say each bank is 1.2litres swept volume. a four stroke engine fires and exhausts gas only every second revolution so that is reducing exhaust volume to .6l per rev ....times 16000 revs and we arrive at 9600 l/min...or 160l/sec or 16000cm³/s ...we got an exit area of say 80mm by 40mm and arrive at average 40m/s exit speed for 16K revs...
of course you have consider the vehicle ground speed

where do I go wrong?

You also need to consider that the air comming out of the cylinders is alot hotter and has expanded. That should increase the velocity right?

But the claim was not all are doing hot blowing ,right ? and as air is quite a bad
heat conductor I don´t think that will give you much in terms of volume change ...

add to it fuel mass vapourising it and igniting the mixture is sure a different story..but that was not my point.

[ringo]

The air will still be very hot relatively.
It's more temperature change, and density change.

just reposting a sample calculation:

2.4 lt engine
exhaust stroke every 2 cycles, at 9,000 cylces per minute is, 150 exhausts per second.
for half the car it's 1.2kg per side. so it's 150 x 1.2 kg 180 l/s

which is .18m3 x 1.2kg/m3 = 0.216kg/s using density at ambient!
mass flow does not change, se we use ambient to find mass and we stick with the mass from now on.

at 850 degrees density is 0.31kg/m3 which is not ambient!
for a diameter of 2.5 inch, area = 0.00316 m2
using our known and constant mass, not density!

velocity = mass flow/density (at 850C!) x area = 0.216 / 0.31 x 0.00316 = 220m/s

This is hot blowing, but just change the exhuast temp to what you think it is and the pipe area. Density charts can help of use of gas laws.
But either ways its very fast becuase the mass flow has to be the same while coupled with very low density.

[marcush.]

The air will still be very hot relatively.
It's more temperature change, and density change.

just reposting a sample calculation:

2.4 lt engine
exhaust stroke every 2 cycles, at 9,000 cylces per minute is, 150 exhausts per second.
for half the car it's 1.2kg per side. so it's 150 x 1.2 kg 180 l/s

which is .18m3 x 1.2kg/m3 = 0.216kg/s using density at ambient!
mass flow does not change, se we use ambient to find mass and we stick with the mass from now on.

at 850 degrees density is 0.31kg/m3 which is not ambient!
for a diameter of 2.5 inch, area = 0.00316 m2
using our known and constant mass, not density!

velocity = mass flow/density (at 850C!) x area = 0.216 / 0.31 x 0.00316 = 220m/s

This is hot blowing, but just change the exhuast temp to what you think it is and the pipe area. Density charts can help of use of gas laws.
But either ways its very fast becuase the mass flow has to be the same while coupled with very low density.

No question you will not have 850°C when rushing air through the engine.Just think about how long the single air molecule will travel inside the engine that´s roughly 2000mm from the air intake to the exhaust tailpipe opening ....it will definitely not rise from say 40 to 800....when cold blowing?

[ringo]

That is a question for the teams.
Is cold blowing really zero combustion, or low fuel combustion?

Were Renault hot blowing?

By the sounds of their exhuast we could say yes.

They have no parts coming in direct contact with the diffuser like the rear blowers so overheating the floor isn't a risk.

However if they themselves say 6 times the car's speed, then they must be reffering to full throttle in the straights and on corner exits. The gas has to be around 1000 degrees to attain those speeds.

[mep]

Some little notes:

2.4 lt engine
exhaust stroke every 2 cycles, at 9,000 cylces per minute is, 150 exhausts per second.
for half the car it's 1.2kg (I think there is a typo, shouldn't this be liters?) per side. so it's 150 x 1.2 kg 180 l/s

which is .18m3 x 1.2kg/m3 = 0.216kg/s using density at ambient!
mass flow does not change, se we use ambient to find mass and we stick with the mass from now on.

at 850 degrees density is 0.31kg/m3 which is not ambient!
(The value of 0,31kg/m3 is still for ambient pressure of 1,013bar. When the pressure in the pipe is higher the density will also be higher resulting is reduced speed.)
for a diameter of 2.5 inch, area = 0.00316 m2
using our known and constant mass, not density!

velocity = mass flow/density (at 850C!) x area = 0.216 / 0.31 x 0.00316 = 220m/s

All in all I agree with your calculation.

No question you will not have 850°C when rushing air through the engine.Just think about how long the single air molecule will travel inside the engine that´s roughly 2000mm from the air intake to the exhaust tailpipe opening ....it will definitely not rise from say 40 to 800....when cold blowing?

I don't think the reason for the air getting hot is because it flows trough hot pipes. As you say the system is round about 2m long and when we consider a speed of 200m/s its trough the system in 0,01seconds. The cause for the heating up must be the compression it experiences in the cylinder.

We should be able to calculate this by using thermodynamics?
The problem is just that a engine is a quite stupid pump because it compresses and decompresses the air before it pumps it out. If we consider the same process (isentrope compression) for this we would end up on the same point in the p-v diagram because there is no heat added by combustion. In this case marcush would be right and the temperature would not rise any considerably amount. We might have to use an isentrope compression and a isotherm expansion. The exhaust of the air will possible not require a lot of pressure so I think this can be neglected. The air will be heated up during compression but can't give back the heat to the cylinder walls during the short time of expansion.
What do you guys think about it?
We should give this its own topic and exercise it trough.

[Lorenzo_Bandini]

http://en.espnf1.com/greatbritain/motor ... 53842.html

Renault Sport has had to reduce the performance of its engines to ensure they are reliable under the exhaust regulations for the British Grand Prix.

When Renault team boss Eric Boullier was asked if he had any reliability concerns ahead of the race, he said: "We have some."

He added: "We know that the margin is very, very close to where we don't want to be."