Flow calculations, wow

[KeltonDSMer]

Tonight after realizing what ignorant bullshit got that last thead closed, I decided to so some carefull calculations. They back up my theory about a stroker motor here at 5500 ft having smilar performance characteristics as a 2.0 at lea level; both being at the same pressure ratio. Considering a 2psi pressure drop in the IC in both cases, 16 psi here is almost exactly the same pressure ratio as 20psi at sea level, (2.5 and 2.496 respectively). Cosidering a post IC temp of 130 degrees, the density, (Di), of the air going into the motor up here would be 7.55E-5 lb/cubic inch. The manifold air on the sea level motor would be at a density of 9.19E-5 lb/cubic inch.

After calculating the flow rates of each motor thorugh out the rev range, I was pretty suprised. At any given RPM above 3500, both motors were within 1 or 2 lbs/min of airflow!

The reason I think this is a big deal is that our turbos here have to be pushed to extreme pressure ratios to flow the amount of air our sea level buddies do regularly.

I used the following formulas, please tell me if I could make something more accurate: flow=(Di*displacement in CI*RPM)/(2*V.E.)
Di=(boost+atmos.)/(53.3*12*Post IC temp in absolute temperature)
I also took off a couple lbs/min off each flow number because any air filter causes a pressure drop in the intake pipe. This gave me a somewhat corrected mass flow from the origional number.

If anyones curious, I'll post my numbers later; otherwize I just want to hear people's thoughts. Thanks.

[hotrod]

I need a little clarification on your formula. I'm not sure what the terms 53.3*12 are for in your density calculation?


I expected your density forumula to be of the form:

(MAP/ATMabsPress * ATMabsTemp/MAT ) * ATMdensity = Manifold Air Density

To place that in common terms
MAP = Manifold absolute pressure would equal (manifold boost + local atm pressure)
ATMabsPress = the local atmospheric pressure
ATMabsTemp = 459+intake air temp
MAT = Manifold absolute temprerature which would equal ( 459+IC discharge temp)
ATMdensity = the local density of the Atmosphere, at the Intake air temp and local atmospheric pressure.

Most of what your trying to figure out is explained in great detail in a book called.
"Turbochargers" by HP books, ISBN 0-89586-135-6 . Pick up a copy and it will answer most of your questions and give you worked out examples of the process of turbocharger calculations.

The other "bible" for turbocharger calculation is "Maximum Boost" by Corky Bell ISBN 0-8376-0160-6, a very good book in general but I have some problems with his obvious bias against water injection systems, and the assertion that they are a crutch for a poorly designed system.

Larry

[DlandryTSI]

Side note: I cleaned up that other thread....

--Dave

[v413nc3]

I also agree with your view of water injection systems. Even a properly designed system can benefit from water or propane injection.

[KeltonDSMer]

Sorry I haven't replied for a while, I have been in Greely for a Western States Orchestra, (I play the double bass). In my equations, R=the constant from the ideal gas law, PV=nRT which just happens to be 53.3. The 12 is to maintain the inch units in the equation because to do my other calculations, my Di had to be in lb/cubic inch.

I don't know how water injection works, could someone elaborate on this? I do know a guy named Todd that I see at Bandi all the time who uses propane as the added fuel to his nitrous system. He claims the combo to add 200hp and 300 lb/ft; those numbers seem way too optimistic but he does have the fastest viper in CO and it is an old RT-10 so he must be doing something right. The insanely large gauging of the propane and nitrous lines from the trunk don't tell a different story either. Think this is bullshit? I saw him run a 12.4 w/o nitrous and he miss-shifted into 2nd gear. I don't understand why the let him keep coming back because he frequently goes deep into the 11's w/o a rollcage.... If anyone knows who I'm talking about, approach him and ask him about his nitrous/popane injection.

I like the idea of propane injection epecially the lowered intake and burn temp. of the mixture, but is it really worth driving around w/ a propane tank in your trunk?

[KeltonDSMer]

Does anyone know how much lower of a heat propane burns at compared to petrol?

[hotrod]

The actual heat of combustion of Propane is very similar to gasoline as they are both simple hydrocarbon fuels.

It is much much colder prior to ignition due to its phase change as it expands from a liquid to a gas though, so has much higher charge density.

I'll look around and see if I can turn up a number when I get the chance.

Larry