0.32 Discussion Thread

I might have found a curious thing about the thermal simulation of combustion engines:

(Tested in safe mode)

It seems that Superchargers - counterintuitively - add more thermal stress to an engine than a turbocharger of identical wheel power output:

On an otherwise identical vehicle with the same V6 Engine after 10 miles of driving with a sustained engine power output of 466 bhp:

The supercharged engine reads the following thermal data:

Coolant: 192 °F
Oil: 238 °F
Block: 197 °F
Cylinder Wall: 220 °F
Exhaust Manifold: 913 °F




The turbocharged engine reads the following thermal data:

Coolant: 191 °F
Oil: 233 °F
Block: 194 °F
Cylinder Wall: 207 °F
Exhaust Manifold: 799 °F



Video of the test:



This seems odd.

Both engines spin at almost 6000 RPM and produce 466 bhp of engine power output. This means that both engines take in the same amount of air and fuel and burn it inside the cylinder. The pistons depress with the same force in the combustion stroke for both engines as indicated by the identical flywheel torque.

So we are burning the same amount of fuel and air on both engines... so total thermal output of the engine should the same. Burning 1 liter of fuel always creates the same amount of heat energy so the same amount of waste heat has to be removed from both engines. We are just looking at the engine here, no auxilary systems.

We induct air and fuel worth 466 bhp and we spin at 6000 RPM, so both waste heat from burning fuel and waste heat from friction should be identical.

So if we would assume a scenario where both turbo and supercharger are driven by an external power source and that the exhaust has the same backpressure, then thermal load on the engine should be identical.

We have heat generated by combustion which is identical because we output the same torque and power and we have the heat generated by friction which is also identical, because both identical engines spin at almost 6000 RPM.

So any difference in thermal stress on the engine, has to come from the supercharger or the turbo charger, please correct me if I am wrong.

Both Super and Turbocharger add more air to the engine, increasing torque and power. The super charger however is driven directly by the engine, sapping away power. So less of the supercharged engines power reaches the wheels of the car.
And indeed the supercharged cars needs to stay at wide open throttle to maintain 183 mph of speed while the turbocharged one can decrease throttle (and is capable of going faster than 183 mph) There is certainly a loss of power on the supercharged car... but it seems to happen after the combustion and as such, heat output on both engines should be identical.

But it isnt.

And even more curious, it isnt the glowing hot engine oil cooled turbocharger that increases thermal stress on the engine.... no... it is the comparable cold supercharger that drives up the temperature of the engine. A supercharger that in theory should have its own independent lubrication system and operates at far lower temperatures than the engine oil cooled turbocharger.

So why is the oil temp of the supercharged engine hotter than the one of the turbocharged engine? Remember, we burn the same amount of fuel and air at the same RPM.... so by all means, the waste heat output of the actual engine operation should be identical. There is not more combustion heat nor is there more friction... so why is the oil temperature higher?

If anything has a right to drive up the oil temperature, it should be the turbocharger. Spinning at 10000s of revolutions per minute and half of it being placed right into the exhaust stream where conditions are quite literally hell on earth. With the exception of some modern engines, the only thing keeping a turbocharger cool, is the engine oil pumped through it. This of course heats up the oil and would explain a higher oil temperature.


Could it be, that there is an issue in the code that treats superchargers as turbochargers and vice versa at least as far as engine thermals are concerned?




Some other notes:

• Thermals have some oddities in them in general:
  - Exhaust manifold is always cooler than Turbocharger temperature which is odd, because it comes before the turbo and as such should be hotter.
  - Exhaust manifold temperature seems pretty cold compared to real life values. It is a bit hard to find information on this but from my knowledge it is something like this:
  Diesel @ idle: 200 - 250 °C
  Diesel @ wide open throtte: 550 - 650 °C
  Petrol @ idle: 450 - 600 °C
  Petrol @ wide open throttle: 1000 °C
  Turbocharged Petrol @ wide open throttle: 1050 - 1200 °C (this is BTW why classical petrol turbo engines guzzle fuel like mad, to avoid this temperature from melting the catalytic converter additional fuel has to be added to decrease exhaust temperature which will significantly increase consumption and ruin emissions because the mixture is way to rich for the converter to handle. Hence many modern petrol turbo engines water cool the turbocharger to avoid the need to enrich the mixture which will avoid that significant fuel consumption by keeping both turbo and following that the converter at a safe operating temperature. Sometimes both exhaust manifold and turbo charger are water cooled.
  
  
• The way the turbochargers operates in games, makes it perfectly possible to have a stationary turbo even though the engine is at significant load. For example turbocharged cars above a certain power level, may operate at such low engine loads to maintain speed, that the ingame turbo spins down all the way to zero. This is probably not very realistic but I understand may be a limitation of how the system works ingame.
  
  
• A bit more explanation about different values in the forced induction debug app and how different types of superchargers work, would be nice.

 

This is because the game apparently does not simulate the existence of an intercooler/air to water cooler/interchiller in superchargers in general

 

floating charging station bug.

 

The second problem I’m having too if not everyone is Problaby having this issue hope the devs will fix this issue soon!

 

what does vulkan change?
i dont see any differences

 

allows for further graphical improvements and better performance. also it's used for the Linux build.