F1 engine design and model

[davidm2m]

Hello,

I'm using AVL Boost software to design a F1 V6 1.6 liters engine.

My initial goal was to develope 670 HP just using a combustion engine compression ratio of 10, boost pression of 2.8 bar absolute, at 10500 rpm.

My AVL Boost model is https://drive.google.com/file/d/0B-OgN_ ... sp=sharing

The first simulation developed 550 HP, without friction and tune-up.

Questions:
1- Higher or lower power goal?
2- Highest boost pressure, higher or lower?
3- A/F Ratio limits?
4- Friction Model to use?

Thank you in advance

[matt21]

IMO it is depending on what you´re BSFC is actually.
I would try to go to around 13.000 rpm with the according boost.

[davidm2m]

Because of fuel consumption restrictions, BSFC depends on how much boost is achived at 10500 rpm (at this point the engine must burn all fuel to achieve maximum power as soon as possible) without destroying the engine:

- More boost means lower BSFC and more power
- Both BSFC and power remain constant at higher revs and the boost decreases smoothly (same air to maximum fuel consumption)
- Engine runs as lean as possible because that improves cycle efficiency

I would like to know the value of lambda that produces the best performance without compromising the stability of the combustion so I can calculate the maximum boost.

[Wayne DR]

From what I have read (and learned from Grunt Guru), boost should be in the order or 3.3-3.5 Bar Absolute, and AFR (Lambda) of 1.4 for best BSFC. Maximum Volumetric Efficiency should probably also be around 10,500 RPM.

From simple math, using the maximum fuel flow (0.0278 kg/s at 10500RPM and adopting the above lambda value), we get a target mass air flow of 571.7 g/s above 10,500 RPM. This could be managed by either dropping boost pressure, or simply designing the engine so Volumetric Efficiency limits mass air flow into the cylinder. Inlet manifold pressure could be in excess of target boost pressure, removing the constraint to control boost for engine safety (not sure how this would work in practice).

I have heard numbers in the order of 46 MJ/kg for fuel energy and "over 40%" for thermal efficiency (both may be slightly overstated), and again using simple math to calculate power output from max fuel flow, thermal efficiency and fuel energy we get:
Thermal Efficiency 36% and Fuel Energy 42MJ/kg, gives power output of 560hp (conservative).
Thermal Efficiency 38% and Fuel Energy 44MJ/kg, gives power output of 620hp.
Thermal Efficiency 40% and Fuel Energy 42MJ/kg, gives power output of 620hp.
Thermal Efficiency 42.5% and Fuel Energy 46MJ/kg, gives power output of 725hp (extreme, but not unlikely).

There are SO many variables to consider, and if overly conservative values are chosen, you will fall short of the target, for example:
How does your model deal with the excess power from the turbine, not used by the compressor (say around 80-90hp at 10,500RPM)?
What efficiency have you assumed for the turbine and compressor?
Have you assumed a stratified or homogeneous charge? This will impact the heat carry over to the cylinder walls.
etc...

[davidm2m]

From what I have read (and learned from Grunt Guru), boost should be in the order or 3.3-3.5 Bar Absolute, and AFR (Lambda) of 1.4 for best BSFC. Maximum Volumetric Efficiency should probably also be around 10,500 RPM.

I guess that boost level will get to those levels, but an AFR of 1.4 seems difficult as the combustion will be hardly stable according to some books I have read.
If you recalculate the engine for such data (in a Excel sheet made for those engine preliminar calculations), in order to achieve the necesary air flow to burn all the fuel you will need a boost pressure of 4 bar absolute, in the 80's a 4,5 bar absolute boost pressure was reached but with an AFR of about 0.9-0.8, which reduce the knock probability, so we would have to check if the aforementioned AFR of 1.4 is possible.

From simple math, using the maximum fuel flow (0.0278 kg/s at 10500RPM and adopting the above lambda value), we get a target mass air flow of 571.7 g/s above 10,500 RPM. This could be managed by either dropping boost pressure, or simply designing the engine so Volumetric Efficiency limits mass air flow into the cylinder. Inlet manifold pressure could be in excess of target boost pressure, removing the constraint to control boost for engine safety (not sure how this would work in practice).

I have heard numbers in the order of 46 MJ/kg for fuel energy and "over 40%" for thermal efficiency (both may be slightly overstated), and again using simple math to calculate power output from max fuel flow, thermal efficiency and fuel energy we get:
Thermal Efficiency 36% and Fuel Energy 42MJ/kg, gives power output of 560hp (conservative).
Thermal Efficiency 38% and Fuel Energy 44MJ/kg, gives power output of 620hp.
Thermal Efficiency 40% and Fuel Energy 42MJ/kg, gives power output of 620hp.
Thermal Efficiency 42.5% and Fuel Energy 46MJ/kg, gives power output of 725hp (extreme, but not unlikely).

I obtain the same results for those calculations, but with some HP of difference. But for doing so, it would smarter to increase the compression ratio in the cylinder mantaining the boost level lower and an AFR of 1.1-1.2, which ensures an adecuate combustion as well as a lower knock probability.

- compression ratio 13, fuel energy of 44MJ/kg (42 MJ/Kg is for diesel, not for gasoline), boost pressure 3.1 bar absolute, AFR 1.12, thermal efficiency 44% resulting 740 HP (only thermal engine, if we sum the MGU-K 900 HP aproximately)

Comment: to calculate the termic efficience I use correlations taken from the compression and afr. data.
That is "the optimum" for me but it seems difficult to reach a compress relation in the cylinder without knock.

There are SO many variables to consider, and if overly conservative values are chosen, you will fall short of the target, for example:
How does your model deal with the excess power from the turbine, not used by the compressor (say around 80-90hp at 10,500RPM)?
What efficiency have you assumed for the turbine and compressor?
Have you assumed a stratified or homogeneous charge? This will impact the heat carry over to the cylinder walls.
etc...

For the moment I am working with AFR 1, it has to grow but I don't know until what point. In the model it is used a system that calculets the wastegate to guarantee a constant boost pressure at 10500rpm. Turbine and compressor efficiency is 85%, but in the future it will be used a comercial compressor map and turbine to aproximate better to the real behaviours and simulate different revolutions. The load using a AFR 1 is homogeneous.

The inital simulation from which I obtained the data was just to verifythemodel and from it I have to try to get little by litte to where I want to go.

[gruntguru]

Are you recovering the surplus turbine energy?
Turbine and compressor efficiencies used?
Intake manifold air temperature?
Turbine inlet pressure/Manifold Absolute Pressure?
Volumetric efficiency?
Trapping ratio?

670 hp sounds like a good starting point.
A/F should be 1.1 - 1.5 (lambda). Boost pressure will need to vary in line with A/F. May need up to 3.5.

Once you get to 670, it would be interesting to try bypassing some air from compressor discharge, through a heat exchanger using turbine exit exhaust to heat the air then add the hot air to the turbine inlet.

[davidm2m]

Are you recovering the surplus turbine energy?

At the moment, I'm only modeling the thermal engine, ERS will be modeled after tunning-up thermal engine.

Turbine and compressor efficiencies used?

Turbine and compressor efficiencies are both of 85%, but they will be changed for turbine and compressor's maps of any manufacturer.

Intake manifold air temperature?

I don't know intake manifold temperature, but at intecooler's output has 40ºC, because of intercooler was designed to a temperature differential of 15ºC.

Turbine inlet pressure/Manifold Absolute Pressure?

In my previous calculation with standard air cycle, the pressure before opening the exhaust valve was 14 bar absolute.

Volumetric efficiency?

Volumetric efficiency is calculated by the program when it determines the model, but I couldn't watch it

Trapping ratio?

Can you explain what do you mean?

670 hp sounds like a good starting point.
A/F should be 1.1 - 1.5 (lambda). Boost pressure will need to vary in line with A/F. May need up to 3.5.

Compression ratio, A/F ratio and boost pressure are limited by knock.
- A/F ratio should guarantee the stability of combustion. In my opinion A/F ratios over 1.2 hinder the stability of the combustion, further knock problems can be appear.
- Boost pressure should guarantee that all fuel is burned at the desired A/F ratio, from 10500 RPM boost gently decrease because no more air is needed to burn all gasonline, limited by regulations.
- Raise compression ratio is interesting to increase combustion efficiency. In my opinion here is another problem, known maximum compression ratio that the fuel resists without knock problems with desired A/F ratio and boost pressure.

Once you get to 670, it would be interesting to try bypassing some air from compressor discharge, through a heat exchanger using turbine exit exhaust to heat the air then add the hot air to the turbine inlet.

As a anti-lag system?