Ferrari Power Unit Hardware & Software

[NL_Fer]

Fuel is limited at 100kg/h, more efficiency = more power.

@Wuzak: What you are saying, a higher intake temp (and higher pressure to compensate for less air density) just leads to higher cilinder pressure (more crank power, more blowdown) and higher exhaust temps. As long as the pistons, exhaust valves and turbine can cope with it.

And the key to this is prevent knocking on other ways, instead of the ussual low intake temp and spark retard?

Although spark retard could increase blowdown and mgu-h recovery.

This engine really blows my mind sometimes.

[wuzak]

Fuel is limited at 100kg/h, more efficiency = more power.

@Wuzak: What you are saying, a higher intake temp (and higher pressure to compensate for less air density) just leads to higher cilinder pressure (more crank power, more blowdown) and higher exhaust temps. As long as the pistons, exhaust valves and turbine can cope with it.

Yes.

TE = (T1-T2)/T1

Where T1 is the combustion temperature and T2 is the exhaust temperature.

T2 is limited by how much you can expand the gas to extract its energy and the ambient temperature. So you want to make T1 as high as possible.

[wuzak]

You are watching only one side of the medal (efficiency) and forgetting about the other (power). They come togheter.

I am not.

Power and efficiency are interlinked. The better the efficiency the higher the power.

In old style turbo engines the limit was how much air you could stuff into the engine and thus how much fuel you could put in. By cooling the inlet charge the air has more mass per unit volume, more air can be pushed into the cylinder and you can add more fuel.

That is not possible with the current engines because, as it has been pointed out, the engines are fuel limited.

Cooling the inlet charge will put more air mass into the cylinder, but you can't add more fuel, as you are at the maximum.

[mattia.bobbo]

You are watching only one side of the medal (efficiency) and forgetting about the other (power). They come togheter.

I am not.

Power and efficiency are interlinked. The better the efficiency the higher the power.

In old style turbo engines the limit was how much air you could stuff into the engine and thus how much fuel you could put in. By cooling the inlet charge the air has more mass per unit volume, more air can be pushed into the cylinder and you can add more fuel.

That is not possible with the current engines because, as it has been pointed out, the engines are fuel limited.

Cooling the inlet charge will put more air mass into the cylinder, but you can't add more fuel, as you are at the maximum.

So cooling the charge is the simplest way you have to improve power and efficiency, both now and in the old turbo era. You just cannot say: the higher the inlet temp, the higher is the efficiency, because this is a pure theoretical assumption. In real world you have to stay within the limit of knocking and other thousand limits.

[wuzak]

So cooling the charge is the simplest way you have to improve power and efficiency, both now and in the old turbo era. You just cannot say: the higher the inlet temp, the higher is the efficiency, because this is a pure theoretical assumption. In real world you have to stay within the limit of knocking and other thousand limits.

Cooling the charge doesn't necessarily give you more efficiency even if you get more power.

If cooling the charge improved efficiency always then they would be endeavouring to lower the air as close to possible to ambient. I'm quite sure they are not.

The limit on how high the inlet temperature can be is the knocking limit. But that also depends on compression ratio.

But yes, if they can run inlet temperatures higher without getting knocking or other issues as it will give more power for a given amount of fuel (ie efficiency) and will allow them to run smaller coolers which is a benefit to the car's aerodynamics.

[NL_Fer]

But, the higher combustion and exhaust temps would lead to more heat expelled from the turbohousing and engine cooling radiators. So the heat is still leaving the back of the car, only from another source.

The lower intake temp, would make air denser and less pressure needed for the same amount of air. This lowers energy used during compression stroke.

Just... mindblowing concept.. even two years after introduction of these engines.

[gruntguru]

So cooling the charge is the simplest way you have to improve power and efficiency, both now and in the old turbo era. You just cannot say: the higher the inlet temp, the higher is the efficiency, because this is a pure theoretical assumption. In real world you have to stay within the limit of knocking and other thousand limits.

No.
The amount of fuel you can add is limited to 100 kg/hr. Adding more air (whether by increasing revs, VE, MAP or charge density) simply makes the mixture leaner, it doesn't increase the power.

In a pure thermodynamic sense, reducing CAT (charge air temperature) will decrease efficiency and therefore decrease power. The reason is mainly due to reduction in energy of the working fluid available for expansion, both in the cylinder and in the turbine. For example, turbine power increases 18% when you increase the exhaust temperature from 800*C to 1000*C.

Another reason is slower flame speed and reduced rate of heat release. Heat released nearer to TDC can be used more effectively during the expansion stroke. This is less important for engines using TJI which seems to permit combustion rates and pressure rise rate close to the limit the engine can tolerate.

Of course increasing CAT has at least two major downsides - detonation and combustion chamber/exhaust temperatures. So at least some intercooling is required - to maintain the optimum CAT to balance the above conflicting requirements.

[gruntguru]

But, the higher combustion and exhaust temps would lead to more heat expelled from the turbohousing and engine cooling radiators. So the heat is still leaving the back of the car, only from another source.

The lower intake temp, would make air denser and less pressure needed for the same amount of air. This lowers energy used during compression stroke.

Most of the energy used during the compression stroke is returned during the expansion stroke anyway - there is no compression disadvantage in running higher boost.

The compressor work is increased (very slightly) but this is recovered (plus interest) as extra turbine work.

Did you know that nearly all of the compressor work goes into heating the air and only a very small portion goes into the pressure increase?

[wuzak]

A simplistic way to look at it is that for every MJ of energy you transfer out through the intercooler another MJ has to be added with fuel to have the same power.

[PlatinumZealot]

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.

[gruntguru]

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).

[trinidefender]

Regarding knock, it has been rumoured that all or most PU's run with some level of knock in some engine modes. These are not road car engines, they don't have to last 100's of thousands of kilometres.

Frankly it wouldn't surprise me if that is one of the key points of Mercs qualifying mode. An over designed ICE that can run much higher levels of knock safely for longer periods of time.

[PlatinumZealot]

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 remember this part quite clearly in my mind from school days. The cooler a gas is the closer it follows the isentropic compression curve. This the MAIN reason why inter-cooling is applied. Inter-cooling does not lower pressure or flow as you say. I assure you. I could bet my life on it.

[trinidefender]

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 remember this part quite clearly in my mind from school days. The cooler a gas is the closer it follows the isentropic compression curve. This the MAIN reason why inter-cooling is applied. Inter-cooling does not lower pressure or flow as you say. I assure you. I could bet my life on it.

As you reduce the temperature of a gas in a in a fixed volume the pressure will decrease.

I have actually seen a tuning shop that built a turbocharger setup , for testing intercoolers, in a road car with pressure sensors pre and post intercooler result in a pressure drop post-intercooler as a result in temperature drop. The pressure drop was larger than just as a result of the intercooler as well. Take that for what you will.

[PlatinumZealot]

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.