I could very well be wrong, but my interpretation was they keep the throttle open and cut out fuel (maybe not entirely) and spark, with the engine kept spinning by the car momentum. Not sure how risky that would be in terms of stalling, but im probably missing something anyways.
well ,the question is what they do with their spark .I always thought they had retarded ignition and it sounds like that.This is surely not helping exhaust valve temperature .
Putting fuel through the engine without igniting it with the sparkplug will result in what? cooling of the valves ? When these are glowing the fuel will ignite there and surely that will not cool anything .You can use fuel for cooling in an overly rich condition but when the engine is not fired by the sparkplugs the fuel you are injecting will not simply evaporate ,the engine parts a re just too hot as soon as your mixture is combustible it will ignite ..fuel has a very low flame point so.....how much could or should you put in to have cooling effects and not causing an uncontrolled fire?
We have seen flame throwers in overrun in sportscar racing (remember the Panoz or the BMW M3 GTO?)so it´s not really new but is that actually cooling the engine?
And once again I point out you wouldn't get the flamethrower effect (the gas wouldn't ignite without a spark) if it wasn't oxygenated,,,This BS that they run the same fuel you can get at the pumps is just that ...BS.
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Sir Stirling Moss
There was a thread on what fuel is used with some info from Shell. It was a little dated but the rules a more restrict now than then if anything.
I was surprised by the very low levels of alcohol, the most common form of oxygenate in street gas. I assumed this might be a weight concern. I believe the current rule require constituents similar to pumped/street gas. Is MTB still used in Europe?
Not many other ways to bring oxygen to the party if you have pump gas restrictions.
@marcush: Cooling the engine by throwing fuel without ignite it is a common technique. My brother explained me that years ago. I was young so I don't remember everything, I just send him a message to have more details...
Basically, fresh fuel is injected but not ignite to cool the engine parts. Then it is waisted onto the exhaust and burns here (1200° is kinda hot).
The possibility of unburnt fuel in the exhaust is in my view not present as we would see con´siderable black clouds coming from the exhaust.
I cannot imagine the fuel getting just vapourized in the exhaust after cooling the valves and not starting to burn ....
Why black clouds? are you thinking an overly rich mixture burning? As i understand it it's never igniting, without the necessary pressure and spark, i'm not sure that the exhaust is hot enough to light up the mixture?
The other thing is, i'm not 100% sure they need any gas injected there, though it probably helps. A regular street injected engine cools best while on overrun, so even in the older engines you basically keep the spark going but no fuel gets added, however you don't need an open throttle for that to happen so that's the bit i'm not too sure about.
I also didn't understand why black clouds?
Auto-ignition temperature of fuel is about 300°C and formula one exhaust temperature is more than 1000°C. So all the gas should burn when hitting the exhaust pipe.
My brother thinks it is plausible that the weird sound come from here. He also said that it can increase engine performance when reopening throttle because it already has some fuel inside the cylinder and it keeps some activities inside the exhausts.
It also should be very well designed because they can have some problems with pressure returning back (not sure on how translate that, in french: retour de pression) to the back of exhaust vavle.
Some more details about the cooling technique: you can use fuel only, air only or fuel/air mixture. Fuel only is very effective but very costly as air only is less effective but free.
The plug doesn't spark (otherwise it is useless) and engine cannot stall because it is drived by the wheels.
What is required of the engine's exhaust for the best blown diffuser performance? Are the heat levels important?
Assume the engine must stay engage for KERS, the brakes could just make it to the end of the race and the fuel tank size was set before the use of exhaust overrun.
my understanding of a COLD blown exhaust was that even out of the throttle the inlet and exhaust valve would open and close allowing gasses (effectivly AIR) to pass throught the trumpets..engine..exhaust. But both valves remain open, so at best only the operating faces would be cooled.
A HOT blown exhaust is where they lock the exhaust outlets open and just open the inlets, inject fuel and retard the ignition to just past top dead center to allow as much of the firing cycle to vent out the exhaust. Then when back on the throttle the exhaust valves regain there natural movement to allow torque to be produced from the engine. But maps can alos be created to ignite selected cyinders just BEFORE ttc to decrease engine speeds as fast as possiable.
From what i know the "extreme" measures are now that a certain team...no names...is able to tune the engine mapping to generate a certain amount of hot exhaust gas in certain cylinders per different engine map.
Example...china, Tight 1st sector high downforce, engine map 1 (example) Overrun on all 8 pistons.
Sector 3 long straight with very tight hairpin at the end, maximum power on the exit so go to map 2, overun only on 4 pistons, 2 each side.
Think about of this (and they may well be, only time will tell) engine maps could be mixed in with the diff settings and be able to generate differing amounts of DF on either side of the car out off the trottle to help turn in and save fuel that would be wasted (TWISE, from the engine and excess DF)
I don't understand most of what you just wrote, but let me say that there's no variable lift or timing in the valves, so as long as the engine is turning the valves will do what they always do.
1) Say we switch the clutch paddles into engine map paddles after the start of the race. Then the driver could change maps for every turn. Now... to optimize performance do we change the engine map before or after the gear selection? I assume the engine map has sequential steps?
Do you really think the drivers are up to this task?
2) Assume the engine must stay engage for KERS, the brakes could just make it to the end of the race and the fuel tank size was set before the use of exhaust overrun. These are all valid assumptions.
With modern exhaust valve alloys, like Inconel 718, combined with the small diameter of exhaust valves on a current F1 engine, no supplemental cooling should be necessary. If a team is intentionally injecting fuel during overrun, it's probably for some other purpose, such as to create more exhaust flow energy for assisting aero performance.
"Q: How do you make a small fortune in racing?
A: Start with a large one!"
Over a year ago, maybe more, it had been 'reported' that Mclaren had engine mapping paddlles next to shift paddles, effectively changing mappings on the fly during each gear change. not sure whether that was true or not
