Formula for power given volumetric flow and pressure

[oldcorollas]

Agreed 100% about its better to have more boost less compression, but in this case due to the outlet temps getting hot upwards of .8 bar (1.8PR)...
I figured if you pop the compression up nothing huge i.e. 8.5:1 - 9.5~10:1 the torque of the motor should go up considerably but still be able to handle a bit of boost..
Plenty of torque throughout the rev range it wouldn't need to be running 17psi..
I dunno just the way I see it...

how do you figure the torque will go up considerably? how much?

not NEED to run 17psi?? but he WANTS to run 17psi....

[Radar]

I'd assume torque goes up with compression? No clue how much by though...?
Indeed you want what ya want, cant argue with that.
But what if you could get 200kw all the time without having to run 17psi? Whats the point of running 17psi... *As I wrote that I just realized exactly why: What happens when you want more power, the compression will already be to high and wont allow for more boost*
Eh maybe just low compression 17psi E85 and water injection?

[oldcorollas]

how about you redo the calc to see what combinations of boost and rpm will give 200kw.. adn then think through from there to how to achieve that?

maybe just low compression 17psi E85 and water injection?

but people already run 20-25psi on 98 (turbo) with stock 4AG's....??
why run less boost AND less compression AND a fuel that allows more of both?

you are confusing me.. again

[Radar]

I'm confusing myself again SCRAP my last few posts
Leave it to the experts

[oldcorollas]

no experts here, otherwise there would be no discussion

[RonRob]

Twinscrew compressors are far more efficient and run cooler then our sc12 and 14. On both the sc12 and 14 I have recorded 350f+ on the outlet using thermocouplers. Overspinning a smaller twinscrew netted me 188kw at the wheels with an outlet temp of 250f on a 85f degree day. The real beauty was after running 21 psi on this less then 1 liter twinscrew, the 250f temp at the outlet dropped to 100f degrees in less then 8 seconds.

Ron

[oldcorollas]

Ron, do you find the case of the SC heats up much? or most of the heating is occuring in the manifold itself, or piping post-SC?

[V-Na]

Thanks for the replies kids !


oldcorollas, sorry but i dont understand how i use than formula to calculate power from the volumetric flow ? I have seen that calc before but i dont think it helps me.

What i need is a relationship between power and airflow, or if you take the pressure out of the equation the mass flow rate.


Basically what i am saying is if i want say 200 kw at the wheels MAX then you need a given mass of air to make that power with a given mass of fuel at the given A/F ratio.

Obviously there are losses heat / driveline etc but these are all generic factors(more or less) i just want to get into the ballpark.

An old school example of what i am getting at is with old carbies. They were /are rated at a certain CFM Cubic Feet per Minute of air, and the old school guys knew (all things being equal) you whack on a given size carby, get the AF mixtures right and you will end up with "X" HP.

So thats essentially what i am after how much air do i need to make 200 kw at the wheels (say)

The comparable property between engines is mass flow rate. However you can calculate this from volumetric flow rate, pressure AND temperature:

mass flow rate = volumetric flow rate * pressure / (gas constant * temperature)

To calculate the power produced at this air mass flow rate:

power = air mass flow rate * heating value of the fuel * thermal efficiency / air fuel ratio

Or by substituting and rearranging:

volumetric flow rate = power * gas constant * temperature * air fuel ratio / (pressure * heating value of the fuel * thermal efficiency)

So in your case assume at the inlet:

power = 200,000 W

gas constant = 287 J/(kg*K) [for air]

temperature = 300 K

air fuel ratio = 14.7 [stoichiometric]

pressure = 101,000 Pa

heating value of the fuel = 42,500,000 J/kg [LHV for gasoline]

thermal efficiency = 0.35 [approximate]

volumetric flow rate = 200000 * 287 * 300 * 14.7 / (101000 * 42500000 * 0.35)

= 0.169 m^3/s

= 10.1 m^3/min

[RonRob]

Ron, do you find the case of the SC heats up much? or most of the heating is occuring in the manifold itself, or piping post-SC?

My readings where done at both the outlet of the blower and intercooler. Twinscrew case stays cooler then the 12 and 14. At 14 psi the stock blowers push 160 at best to the wheels while at the same boost level the twinscrew netted 212whp with stock intercooler, afm, and injectors.

Ron

[nick.parker]

Series supercharging requires a bigger supercharger to pump into a smaller supercharger

I'm not advocating this is a good idea....series supercharging just requires the first pump to be displacing more than the second pump. The same size charger (the first one) spinning faster, would have higher losses related to turbulence and heat generation, , however, you might be able to offset that a bit by using a lower pressure ratio across the first charger. You'd need to appreciate the combined losses in order to determine if there was any net gain doing this.

[nick.parker]

Hey Gun,
What's your email? I have a very simple spreadsheet I can share with you for calculating engine HP. Basically the CRUDE AS way to work it out is ROUGH ENGINE HP = the number of milligrams of AIR your engine consumes PER SECOND. Its crude but close enough. All simple physics posted in this thread should allow you to work that out easy enough. Of course you need to subtract a bit for taking into account the drive of the charger, to get the USEFUL engine output available to your gearbox!!!

[GUN METAL]

Nick freaking Parker..................HOW THE HELL ARE YOU ????!!!!!

mate glad to see you here and hope you are well, your name came up in conversation only recently and it was a pure fluke i saw your reply here i havent been near this thread for ages.

thanks for your feed back

thanks to you other guys as well will have to do some more reading.

i really havent done any more research on this as the SC12 is still going strong and kicking Lotus exige arse

but thats niot going to stop me trying to improve the trusty 4A and of course the adub !