Ferrari Power Unit Hardware & Software

[godlameroso]

I understand where you're coming from, because you're absolutely right from a conventional engine perspective. These engines are a different beast altogether, the rules force you to think from a different point of view. The limitations of normal engines are of little consequence when you consider the level of sophistication involved with these power units. They run on a completely different wavelength, here the key term is more heat = more power, everything else be damned, it just has to hold together for 4,000km then it can incinerate itself for all they care.

If you think about it, detonation is really the best way to get maximum power, detonation is so powerful that it can send a piston straight through the head, crack the block in half and take the body work with it.



Imagine if the engine could harness that power

[gruntguru]

All I am saying is that inter-cooling is text-book way of increasing the efficiency an engine. You just can't argue this because it is fundamental thermodynamics. You are lowering your average heat rejection temperature buy doing this, and you are also reducing the irrevesibilities int he gas on the way to reaching your final peak pressure. It is text-book stuff. That is why the manufacturers go through so much trouble of getting their inter-cooling right.

Inter cooling is a textbook way of reducing the power requirement of compressors. Cooling the compressed gas will increase its density (reduce its volume) if pressure is held constant, or reduce its pressure (if volume is held constant).

Inter cooling is NOT a textbook way of increasing the efficiency of an IC engine. Please don't bet your life on this. I have never met you but I am sure your life is worth more than this.

Heat rejection should be at the lowest possible temperature - after the working fluid has been expanded to recover as much work as possible. Removing heat after doing compression work on the gas, is throwing away internal energy that could potentially be recovered later n the cycle.

[gruntguru]

I understand where you're coming from, because you're absolutely right from a conventional engine perspective. These engines are a different beast altogether, the rules force you to think from a different point of view. The limitations of normal engines are of little consequence when you consider the level of sophistication involved with these power units. They run on a completely different wavelength, here the key term is more heat = more power, everything else be damned, it just has to hold together for 4,000km then it can incinerate itself for all they care.

If you think about it, detonation is really the best way to get maximum power, detonation is so powerful that it can send a piston straight through the head, crack the block in half and take the body work with it. Imagine if the engine could harness that power

Detonation is a very inefficient operating mode. Even if you built an engine strong enough to withstand heavy detonation, it would not be efficient. The detonation shock wave destroys the boundary layer at the chamber wall and accelerated heat transfer out of the working fluid and into the metal. This what melts piston lands and destroys engines, but it also wastes a lot of energy.

[sosic2121]

Detonation is a very inefficient operating mode. Even if you built an engine strong enough to withstand heavy detonation, it would not be efficient. The detonation shock wave destroys the boundary layer at the chamber wall and accelerated heat transfer out of the working fluid and into the metal. This what melts piston lands and destroys engines, but it also wastes a lot of energy.

Is detonation operating mode of diesel engine? if not, what's the difference?
tnx

[gruntguru]

Definitely not.

A Diesel (normally) burns the fuel at a slower rate than it is put into the engine (fuel combusts as it is mixed with the air).

A Diesel engine often "knocks" at the beginning of combustion because some fuel is injected and mixes with air before ignition occurs. At this point all the fuel injected prior to ignition will burn almost simultaneously - the same as a detonating SI engine - see below.

A spark ignition engine (normally) burns the pre-mixed air-fuel at the rate the flame travels through it. Think of a trail of gunpowder lit at one end.

A SI engine (detonating) burns the air fuel as fast as a pressure wave can travel across the air-fuel mix. This detonation usually follows a period of normal combustion so not all the mix is "detonated". The severity of "knock" depends on what percentage burns normally and how much remains to be detonated.

[godlameroso]

Given that these engines run rather lean, there could be some advantage to having some knock. I think teams are experimenting with knock to increase power. The regulations kind of encourage that kind of reasoning allowing up to 5 sparks per 4 stroke cycle on each cylinder.

[rscsr]

Cooling the charge increase efficiency.
There are two compression stages in these engines. The compressor and then the piston. Cooling the charge increases the isentropic efficiency of these components. The teams now that a cooler charge gives more horsepower. It is only a matter of limiting returns.

No.
Read my previous two posts.
1. Aftercooling reduces the work done by a compressor (by moving the operating point to a lower pressure or flow) but it does not improve the isentropic efficiency.
2. These engines have two stages of expansion. Heat removed from the charge is heat energy that is no longer available for expansion and conversion to work (power).

I just checked it by using a standard Otto process and one with a isothermal compression instead of the first isentropic compression and gruntguru seems to be correct in the first point.
The modified version (intercooled) shows a lower efficiency than the standard version. At stochiometric mixture I get 66.1% vs. 63.4% and the gap widens a bit with a higher AFR (AFR=20 --> 62.3%).

And it even makes sense, since heat energy has a higher exergy content at higher temperatures. But of course you are limited by the temperature your parts are able to withstand, so intercooling is usually necessary.

[PlatinumZealot]

His first point is correct - no dispute there.

I know where he is getting at. Removing heat from the intake stream seems counterproductive to improving efficiency doesn't it? I would agree too. But depending on the type of engine and what the engine is used for it makes sense to intercool. I'm at work so I have no material in-front of me.

[Brian Coat]

I believe GG's right on both points, when purely considering the *direct* thermodynamic effect.

And in the context of overall cycle performance (with a knock limit), the loss of heat (and aero!) to the intercooler is a worthwhile trade.

[NL_Fer]

I wouldn't be surprised if the engineers are exploring the bounderies between engine knock and hcci,,since they are related to eachother.

[wuzak]

All I am saying is that inter-cooling is text-book way of increasing the efficiency an engine. You just can't argue this because it is fundamental thermodynamics. You are lowering your average heat rejection temperature buy doing this, and you are also reducing the irrevesibilities int he gas on the way to reaching your final peak pressure. It is text-book stuff. That is why the manufacturers go through so much trouble of getting their inter-cooling right.

I think people get confused between power and efficiency.

If you get more power it doesn't necessarily mean you got it through efficiency.

Using the intercooler to lower temperatures allows more air (by mass) to be stuffed inside the cylinder allowing more fuel to be burned, often in a very rich mixture. Thus more power is, indeed produced, but you've also used more fuel to gain that power so there is no gain in efficiency.

[rscsr]

His first point is correct - no dispute there.

I know where he is getting at. Removing heat from the intake stream seems counterproductive to improving efficiency doesn't it? I would agree too. But depending on the type of engine and what the engine is used for it makes sense to intercool. I'm at work so I have no material in-front of me.

The obvious answer is, that you can "reinvest" your lower temperature in CR. Especially if you are more limited by your combustion temperature, since it is only dependent on you compression end temperature (and of course the added heat and the gas you use). But you also increase the pressure after the compression and combustion, so it is a trade off what limits your performance.
I checked for the modified Otto cycle from above and if you increase the CR from 15 to 19 you have the same efficiency with obviously lower temperatures and higher pressures.

[NL_Fer]

So by lowering intake temperature, CR can be increased and in that more energy can be converted in mechanical energy.

Only problem is since fuel is limited, turbo pressure cannot be increased beyond the maximum AFR. So CR has to be embedded in the cilinder design and this makes intercooling/boost/compression ratio linked together in design.

[godlameroso]

Well to get a stochiometric burn you'd only need about 3.5 bar, but if the rumors are true Ferrari and Mercedes are running 4.5 bar. So whatever they're doing with combustion let's them run much leaner, if the rumors are true.

[NL_Fer]

Yeah, that is the Jet Ignition. The multiple flames jets ignite several points in the otherwise slow burning lean mixture, to speed up the process. And probably knock is no issue anymore.

Thinking about this. The extra air is also heated/expanded, would this help in driving the Turbo/Mgu-H?